DJO April - June vol 32 No 4 07072022

DJO Vol. 32, No. 4, April-June 2022

Table 1: Pre-operative data- Both eyes

Eye BCVA Manifest WTW ACD Keratometry ECD CCT Angles Axial Length
refraction (mm) (mm) (D) (Cells/ mm2) (micron) (ASOCT) (mm)
OD 6/18 3.15
N6P -20DS ADD+2.5DS 11.2 OPTICAL 2396 573 Nasal-370 28.75
3.34 K1-43.05 Temporal-40
2884
OS 6/9 N6 -9.0DS 11.2 @147 553 Nasal-440 26.63
3.0DC K2-44.35 Temporal-58
@110 ADD
+2.5DS @57
MANUAL

K1-43.3
@129.1
K2-44.5
@50.9

OPTICAL
K1-41.98

@109
MANUAL

K1-42.3
@163.5
[email protected]

Figure 2: Pre-operative posterior segment image- fundus image of right eye Surgical Procedure

astigmatism in the left eye. Pre-operative refractive data was After maximum possible mydriasis using a combination
collected using various instruments and documented. (Table of topical medications, and peribulbar block, 2 side ports
1) were made to provide for IPCL positioning spatula. Self-
sealing clear corneal tunnel of size 3mm was created at
After giving consideration to a variety of surgical options, the 180-degree axis temporally. Anterior chamber was formed
patient elected for the placement of implantable lens in his with ophthalmic viscosurgical device (OVD), and an
right eye with a piggyback technique. A-scan was performed attempt was made to release the posterior synechiae with
using an ultrasound biometer on pseudophakic mode and iris repositor. However, it was noted that the stability of the
confirmed on optical biometer. Keratometry using both previous IOL was getting disturbed hence synechiae were
optical biometer and baush and lomb keratometer was done. left as it is. The IPCL was loaded onto the cartridge, which
The size (length) of the implanted IPCL was determined was lubricated with OVD and injected into the anterior
based on the patient’s white-to-white (WTW) measured chamber. The haptics of IPCL were then carefully dialled in
by digital calipers and anterior chamber depth (ACD) on between iris and IOL plane into the sulcus. Rotation of IPCL
optical biometry. The pre-operative biometry data was sent to achieve 0-180 degree placement was attempted, but it was
to the manufacturer and the IPCL power from the modified not possible due to posterior synechiae. Since the IPCL had
vertex formula was calculated with target emmetropia. The only spherical power, it was rotated until it was found to
Implantable Lens power of the right eye was -21.50 D with be stable closest to the horizontal axis. Patency of peripheral
length 12.0 mm and an optical diameter of 6.6 mm. iridotomy was confirmed. The viscoelastic material was
removed by irrigation and aspiration. Air bubble was
injected into AC. Edges of the clear corneal tunnel incision
and side ports were hydrated. Antibiotic drop was instilled
in the conjunctival cul-de-sac and the eye was patched for 24
hours. Postoperative steroid and antibiotic drops were given
for 4 times a day initially and tapered as required.

Follow-up

On postoperative day 1, patient’s uncorrected visual acuity
(UCVA) in his right eye was hand movements close to face.
The slit-lamp examination of right eye showed a secured
temporal corneal wound, quiet anterior chamber with 60%
air bubble and IPCL in the sulcus with PCIOL in situ. His
postoperative IOP was constant with all angles open. At
1-week follow-up, patient reported subjective improvement
in his vision with UCVA finger counting 3metres. The slit-
lamp examination was notable for well apposed healed
temporal wound, quiet anterior chamber, and visualization
of the IPCL in the sulcus anterior to his PCIOL with space
present between the two implants.

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DJO Vol. 32, No. 4, April-June 2022

At 3 weeks, patient did not report any new visual complaints. Sachdev and Singh et al.10 in 2019 compared retrospectively
Absorption of air bubble and resolution of postoperative implantation of two types of posterior chamber phakic
inflammation lead to gradual improvement in vision with intraocular lenses: Visian Implantable Collamer Lens and
UCVA of right eye 6/12(20/40) and BCVA 6/9 (20/30) N6 with Implantable Phakic Contact lens in 322 eyes with myopia
manifest refraction of +2.0dc@ 30 add +2.5ds. Intraocular and myopic astigmatism and found similar efficacy and
pressure was 16mmHg on non-contact tonometry and IPCL safety profile in both the groups.
in situ. The patient is under further monthly follow-up to
monitor for visual acuity, intraocular pressure and any long- The results from the patient presented in this report are
term complications. After ensuring safe outcome of right similar to those previously reported, as he had improved
eye, similar procedure will be planned for left eye. BCVA. This off-label technique offers an alternative to
standard methods of treating pseudophakic myopia. IPCL,
Discussion which is implanted in our patient, is made from reinforced
hybrid hydrophilic acrylic material with six haptic pads
Amongst the various treatment options available for for better stability in the ciliary sulcus. Its availability over
pseudophakic anisometropia as seen in our patient, wide range of power for ametropia correction, long term
spectacles are an inconvenient approach as due to effectiveness and economical affordability are some of its
anisometropia, binocular refractive balancing may be advantages.
required that prevents achieving emmetropia. Contact
lenses are the best available non-surgical treatment option. Conclusion
However, they have potential risks of allergy, intolerance to
contact lens, infections, difficulty in insertion and removal Pseudophakic myopia can be safely treated by placing
besides being of no interest to our patient(6). IOL exchange implantable phakic contact lens by piggyback technique
is a feasible option but in cases of longstanding treated after ensuring regular postoperative follow-up to monitor
congenital cataract such as our patient, adherence of lens for visual acuity, intraocular pressure and inflammation.
to the capsular bag is usually present, which may lead to
potential complications such as capsular tear, vitreous loss, References
retinal detachment, PCIOL dislocation and excessive tissue
handling thereby causing postoperative inflammation. 1. Holladay JT (1999): How to prevent refractive surprise.
RevOphthalmol 6:97–98, 10: 1.
Corneal refractive surgeries such as photorefractive
keratectomy (PRK) and LASIK can be used to correct/ lower 2. David A, Hal K, Derek T, Naval S & Daniel E (2002):
the amount of refractive error when the corneal thickness is Refractive change in pediatric pseudophakia: 6-year follow-up. J
in the safe range, but complications such as haze, corneal Cataract Refract Surg 28: 810–815.
scarring, flap associated complications and regression may
be seen . In case of high refractive error, such procedures 3. Schempf T, Jung H, C: Off-Label Use of Phakic Intraocular Lens
require ablation of too much tissue, hence unable to maintain with a “Piggyback” Technique. Case Rep Ophthalmol 2018;9:465-
adequate residual corneal thickness.5 In such cases, the 472. doi: 10.1159/000494712
posterior chamber implantable lens provides an alternative
approach. 4. Venter JA, Oberholster A, Schallhorn SC, Pelouskova M. Piggyback
intraocular lens implantation to correct pseudophakic refractive
Myopic shift following primary IOL implantation in children error after segmental multifocal intraocular lens implantation. J
is a common refractive concern as reported by David et al.7 Refract Surg. 2014;30:234–9.
showing a mean myopic shift of 4.60 D over an average of
5.8 years postoperatively in children who are operated at the 5. Jin GJ, Merkley KH, Crandall AS, Jones YJ. Laser in situ
age of 2 or 3 years. Such refractive shift was also observed in keratomileusis versus lens-based surgery for correcting residual
our patient. refractive error after cataract surgery. J Cataract Refract Surg.
2008;34:562–9.
Our case illustrates the off-label ‘piggyback’ use of
intraocular phakic contact lens in pseudophakic myopic 6. Eissa, S. A. (2016). Management of pseudophakic myopic
patient to achieve emmetropic surgical refractive goal. The anisometropic amblyopia with piggyback Visian®implantable
principle of piggybacking is to use two or more IOLs in the collamer lens. Acta Ophthalmologica, 95(2), 188–193. doi:10.1111/
posterior chamber of the same eye. aos.13203

The first reported use of phakic intraocular lens in 7. David A, Hal K, Derek T, Naval S & Daniel E (2002):
pseudophakic eyes was performed in 2010 by Kojima et al.8, Refractive change in pediatric pseudophakia: 6-year follow- up. J
where piggyback insertion of a toric IOL to correct residual Cataract Refract Surg 28: 810–815
refractive error was done in 8 pseudophakic eyes of 5 adult
patients and was found effective with predictable results. 8. Kojima T, Horai R, Hara S, Nakamura H, Nakamura T, Satoh
Hsuan et al.9 in 2002 reported six pseudophakic adult Y, et al. Correction of residual refractive error in pseudophakic
patients with anisometropia ranging from 2.00 to 7.9D who eyes with the use of a secondary piggyback toric Implantable
underwent Implantable Collamer Lens insertion showing Collamer Lens. Journal of refractive surgery (Thorofare, NJ: 1995)
diminution in anisometropia to asymptomatic levels with an 2010;26((10)):766-9.
average reduction of 3.15D.
9. Hsuan JD, Caesar RH, Rosen PH, Rosen ES, Gore CL. Correction of
pseudophakic anisometropia with the Staar Collamer implantable
contact lens. Journal of Cataract & Refractive Surgery. 2002
Jan 1;28(1):44-9.

10. Sachdev GS, Singh S, Ramamurthy S, Rajpal N, Dandapani
R. Comparative analysis of clinical outcomes between two
types of posterior chamber phakic intraocular lenses for
correction of myopia and myopic astigmatism. Indian journal of
ophthalmology. 2019 Jul;67(7):1061.

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DJO Vol. 32, No. 4, April-June 2022

Cite This Article as: Kanchita Pandey, Devika Joshi, Shrikant
Dinkar Joshi. Management of Pseudophakic Myopia Using
Implantable Phakic Contact Lens with A ‘Piggy Back’ Technique
Delhi J Ophthalmol 2022 32 (4) 48-51
Acknowledgments: Nil
Conflict of interest: None declared
Source of Funding: None
Date of Submission 07 Sep 2021
Date of Acceptance: 05 May 2022

Address for correspondence
Kanchita Pandey, DNB, Resident

Department of Ophthalmology,
Deenanath Mangeshkar Hospital and
Research Center, Erandwane, Pune,
Maharashtra, India India.
Email: [email protected]

E-ISSN: 2454-2784  P-ISSN: 0972-0200 51 Quick Response Code

Delhi Journal of Ophthalmology

DJO Vol. 32, No. 4, April-June 2022

Case Report

Cornea Verticillata With Toxic Optic Neuropathy: A Case Report

Anurag Kumar Kashyap, Archana Yadav, Deepak Mishra, Tanmay Srivastav, Kirti Verma, Prashant Bhushan

Regional Institute of Ophthalmology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India.

Corneal verticillata presents with whorl like brown deposits in corneal epithelium. They rarely result in reduced vision. The most
important potential side effect of anti-tubercular drugs is optic neuritis and can result in corneal verticillate. We report a case
of young male with chief complaint of diminution of vision in both eyes undergoing anti-tubercular treatment for pulmonary
Abstract tuberculosis with corneal verticillata in both eyes. His visual acuity was 3/60 in both eyes with normal fundus findings. This
patient had toxic optic neuropathy due to linezolid. Linezolid and clofazimine were discontinued and rapid improvement of visual
acuity was seen. Keywords: Corneal verticillata, toxic optic neuropathy, linezolid and clofazimine.

Delhi J Ophthalmol 2022; 32; 52-55; Doi http://dx.doi.org/10.7869/djo.768

Keywords: Corneal Verticillata, Toxic Optic Neuropathy, Linezolid And Clofazimine

Introduction centrocecal scotoma, and reduced color vision. Toxic optic

Cornea verticillata, or vortex keratopathy, manifests as neuropathy [TON] manifests as a painless, progressive,

a clockwise whorl-like pattern of golden-b­ rown or grey bilateral and symmetrical diminution of vision with variable

deposits in the inferior interpalpebral portion of the cornea. disc pallor. Variety of toxins can damage optic nerve and can

A variety of medications bind with the cellular lipids of the cause TON.Antitubercular drugs such as ethambutol and

basal epithelial layer of the cornea because of their cationic isoniazid and antibiotics such as linezolid are among the
and amphiphilic properties. Ocular medications deposit many causes of toxic optic neuropathy.14,15

within the cornea as a result of their concentration within the Case Report
tear film, limbal vasculature, or aqueous humor or because
of their chemical properties i.e., specific affinity to corneal A 20-year-old male patient presented to a tertiary eye centre
tissue. Certain drugs deposit in a characteristic pattern and with a chief complaint of painless progressive diminution
in particular corneal layer. It is unusual for these deposits of vision in both eyes from past 1 month. There was history
to result in reduced vision. Cessation of the drug often of an ongoing anti-tubercular treatment for pulmonary
eliminates the symptoms and resolves the drug deposits.1,2 tuberculosis.

Cornea verticillata presents as a characteristic whorl like He was apparently asymptomatic 17 months back when he
corneal deposits and it rarely results in diminuition of developed moderate to high grade fever with chest pain.
vision. Eye medications bind with the cellular lipids of the He was diagnosed with pulmonary tuberculosis and was
basal epithelial layer of the cornea because of their cationic given four drug regimen anti-tubercular treatment. From
and amphiphilic properties and gets deposited in particular past 6 months he has received treatment for extremely drug
corneal layer. Stopping the drug usually resolves the drug resistant tuberculosis with following drugs bedaquiline
deposits.1,2 (400mg), linezolid (600mg), clofazimine (100mg), cycloserine
(750mg), pyrazinamide (1750mg), ethionamide (750mg),
Toxic optic neuropathy (TON) is a group of medical pyridoxamine (100mg). He also complained of skin
disorders characterized by visual impairment due to optic hyperpigmentation throughout the body. Darkening of
nerve damage by a toxin. The condition often presents hand and foot (figure 1A and 1B) was present which was not
as a painless, progressive, bilateral, symmetrical visual present earlier as per the patient. There was no significant
decline with variable optic nerve head pallor.2,3 This can be personal or family history.
characterized by papillomacular bundle damage, central or

Figure 1: (1A) and (1B) represent darkening of hand and foot

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DJO Vol. 32, No. 4, April-June 2022

On examination visual acuity was 3/60 in both eyes which intraocular pressure was 16mmHg in both eyes and visual
improved to 6/60 with pinhole in both eyes. His pupils field analysis showed central visual field defects in both
were circular and sluggish in response to light. Color vision eyes. Lens and fundus examination (figure 3A and 3B) were
assessment using Ishihara color plates revealed red green within normal limits. His visual field analysis (figure 4A and
dyschromatopsia. Slit lamp examination showed reddish 4B) showed central visual field defects in both eyes and OCT
brown corneal deposits in whorl like pattern involving RNFL showed thinning in superior quadrant in both eyes.
central to paracentral area at the level of the basal epithelium Based on above examination findings we diagnosed this
in both eyes. Using higher magnification (16x) reddish brown case as corneal verticillata with toxic optic neuropathy in the
pigmentation was well appreciated (figure 2A and 2B). His form of retrobulbar optic neuritis in both eyes.

Figure 2: (2A) and (2B) represent slit lamp picture of corneal verticillata in both eyes.
Figure 3: (3A) and (3B) represent normal fundus findings in both eyes.

Figure 3: (3A) and (3B) represent normal fundus findings in both eyes.

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DJO Vol. 32, No. 4, April-June 2022

In consultation with pulmonologist, he was advised to Conclusion
stop tablet linezolid for 1 week and tablet clofazimine for 5
days. Tablet linezolid was restarted in lower dose (½ tablet Pulmonologists must advise for a complete ophthalmological
for 3days/week for 2 weeks then ½ tablet daily) and tablet examination before starting anti-tubercular treatment.
clofazimine was restarted in full dose after 1 week and 5 days Patients should be counselled for potential side effects of
respectively. At 2 months of follow up visit his visual acuity the treatment and the importance of regular eye check-ups
was 6/6 in both eyes and color vision was restored to normal during the course of treatment.
though the corneal verticillata was still visible faintly.
References
Discussion
1. Weisenthal WR, Daly KM, Freitas D, Feder SR, Orlin ES, Tu YE,
Corneal verticillata is characterized by whorl-like corneal Van Meter SW, Verdier DD. Basic and Clinical Science Course,
epithelial deposits. It is unusual for these deposits to result in Section 8. American Academy of Ophthalmology; 2018-2019. p.
reduced vision, but if there is reduced vision the possibility of 111-132.
optic neuropathy among other causes should be considered.
The deposits typically resolve with discontinuation of the 2. R.K. Barot, V. Viswanath, M.S. Pattiwar, R.G. Torsekar
responsible drugs. 3. Crystalline deposition in the cornea and conjunctiva secondary

Our patient had diminution of vision with BCVA 6/36 in to long-term clofazimine therapy in a leprosy patient
both eyes with whorl like brown pigment deposits in corneal 4. Indian J Ophthalmol, 59 (4) (2011), pp. 328-329
epithelium of both eyes with normal fundus findings in both 5. Lessell S. Nutritional deficiency and toxic optic neuropathies.
eyes. We attribute clofazimine to be the cause of corneal
verticillate in our patient. Clofazimine produces pink to In: Albert DM, Jakobiec FA, editors. Principles and Practice
brownish skin pigmentation in 75-100% of patients within of Ophthalmology. 2nd ed. Philadelphia: W.B. Saunders
a few weeks, as well as similar discoloration of most bodily Company;2000. p. 4169-76.
fluids and secretions. These discolorations are reversible but 6. Phillips PH. Toxic and deficiency optic neuropathies. In: Miller
may take months to years to disappear.4 NR, Newman NJ, editors. Biousse V, Kerrison JB, associate
editors. Walsh and Hoyt’s Clinical Neuro-ophthalmology. 6th
Toxic optic neuropathies are characterized by painless, ed. Baltimore, Maryland: Lippincott Williams and Wilkins; 2005.
bilaterally symmetric diminution of vision due to optic nerve p. 455-6.
damage causing central or centrocecal scotoma. Linezolid 7. Gladwin M, Trattler B (2014) Clinical Microbiology Made
is a protein synthesis inhibitor and prevents formation Ridiculously Simple (3Edn). Med Master Publication, Miami FL,
of ribosome complex and binds to 23S ribosomal RNA of USA.
50S subunit. Linezolid is an effective treatment against 8. Javaheri M, Khurana RN, O’hearn TM, Lai MM, Sadun AA.
infections caused by multidrug-resistant Gram-positive Linezolid–induced optic neuropathy: A mitochondrial disorder?
bacteria. Linezolid is one of the core drug according to WHO Br J Ophthalmol 2007;91:111‑5.
criteria for treatment of multidrug resistant mycobacterium 9. Agrawal R, Addison P, Saihan Z, Pefkianaki M, Pavesio C. Optic
tuberculosis. Linezolid acts by inhibiting protein synthesis neuropathy secondary to Linezolid for multidrug-resistant
by binding to 23S rRNA and stopping ribosomal complex mycobacterial spinal tuberculosis. Ocul Immunol Inflamm.
formation.Various drugs can cause TON and result in central 2015. February; 23(1): 90–92. 10.3109/09273948.2013.874447
or centrocecal scotoma.Various case reports established 10. Karuppannasamy D, Raghuram A, Sundar D. Linezolid-induced
optic and peripheral neuropathy in linezolid treated patients optic neuropathy. Indian J Ophthalmol. 2014. April; 62(4): 497–
for more than 28 days.5,6,7 Ethambutol toxicity has been 500. 10.4103/0301-4738.118451
identified as dose‑related, with a reported incidence of 18% 11. Citron KM, Thomas GO. Ocular toxicity from ethambutol.
in patients receiving >35 mg/kg/day, 5-6% with 25 mg/kg/ Thorax 1986;41:737‑9.
day, and <1% with 15 mg/kg/day of ethambutol, for more 12. Leibold JE. The ocular toxicity of ethambutol and its relation to
than two months.6,7 dose. Ann N Y Acad Sci 1966;135:904‑9.
13. Rucker JC, Hamilton SR, Bardenstein D, Isada CM, Lee MS.
Ethambutol induced toxic optic neuropathy was less likely Linezolid-associated toxic optic neuropathy. Neurology. 2006.
in our patient because he did not have any vision related February 28;66(4):595–598.
complaint for the initial 11 month of treatment and it was 14. Saijo T, Hayashi K, Yamada H, Wakakura M. Linezolid-induced
only after he had received linezolid (600mg/day) for 6 optic neuropathy. Am J Ophthalmol. 2005. June; 139(6):1114–
months, visual decline occurred. We attribute toxic optic 1116.
neuropathy to linezolid in this patient because visual
improvement started after discontinuation of linezolid.
Other than stopping the drug, no specific treatment is
available for the optic neuropathy caused by the responsible
drug. It is imperative to know the importance of monitoring
visual function in patients on long‑term linezolid therapy
because early recognition of toxicity and discontinuation of
drug results in complete visual recovery.

E-ISSN: 2454-2784  P-ISSN: 0972-0200 54 Delhi Journal of Ophthalmology

DJO Vol. 32, No. 4, April-June 2022

Cite This Article as: Anurag Kumar Kashyap, Archana
Yadav, Deepak Mishra, Tanmay Srivastav, Kirti Verma,
Prashant Bhushan. Cornea Verticillata with Toxic Optic
Neuropathy: A Case Report (India) Delhi J Ophthalmol 2022;
32 (4): 52 - 55.

Acknowledgments: Nil

Conflict of interest: None declared

Source of Funding: None

Date of Submission: 01 Mar 2022
Date of Acceptance: 05 May 2022

Address for correspondence
Anurag Kumar Kashyap, MS,

Senior Resident

Regional Institute of Ophthalmology,
Institute of Medical Sciences, Banaras
Hindu University, Varanasi, India
E-mail: [email protected]

E-ISSN: 2454-2784  P-ISSN: 0972-0200 55 Quick Response Code

Delhi Journal of Ophthalmology

DJO Vol. 32, No. 4, April-June 2022

Case Report

Bilateral Herpes Simplex Keratitis Associated with
Dengue Fever

Ravi Kaur Sandhu, Pawan Prasher

Department of Ophthalmology, Sri Guru Ram Das Institute of Medical Sciences and Research, Vallah, Amritsar, Punjab, India.

We report a unique case of a 45-year-old female who presented with complaints of diminution of vision, redness,

watering, photophobia and foreign body sensation in both eyes along with haemorrhagic crusts involving periocular skin

on both sides. She had recently been diagnosed and treated for dengue fever. There was also history of administration

of Covid vaccine 1 month back. There was no history of any other chronic systemic illness. Ocular examination showed

Abstract congestion of conjunctiva, haziness of corneas and diminished corneal sensations in both eyes. Fluorescein stain
revealed characteristic dendrites of herpes simplex keratitis in both eyes. Prompt and aggressive treatment for the

ocular and skin lesions was started. She responded well to the treatment and recovered completely as observed on

subsequent follow ups. Our case highlights the need for physicians or ophthalmologists treating patients with dengue

fever to be aware of these complications.



Delhi J Ophthalmol 2022; 32; 56-58 Doi http://dx.doi.org/10.7869/djo769.
Keywords: Herpes Simplex Virus, Keratitis, Bilateral, Dengue Fever

Introduction On presentation in eye clinic, the best corrected visual
acuity (BCVA) was 6/18 in right eye and 6/18P in left eye.
Dengue is a highly endemic vector borne viral disease Intraocular pressure was 13 mm of Hg in right eye and 11
occurring mostly in tropical and sub-tropical areas. It is mm of Hg in left eye. There were multiple erythematous,
caused by the 4 serotypes of Dengue virus and is transmitted crusting skin lesions present in the periocular and maxillary
within humans through female Aedes mosquitoes. Dengue area on both sides (Figure 1). On slit lamp examination
disease varies from mild fever to severe conditions of dengue conjunctiva showed congestion in both eyes. Corneas of
haemorrhagic fever and dengue shock syndrome which may both eyes showed irregular epithelium with mild loss
be fatal.1 of transparency. Fluorescein staining revealed a 7-8 mm
horizontal, linear dendrite with characteristic branching
Dengue fever may rarely be associated with ophthalmic and terminal buds overlying the pupillary area in right eye
complications. Various complications reported in literature and two vertically placed dendrites measuring 2 mm and
include macular oedema with blot haemorrhages, cotton 4 mm involving nasal and temporal part of the cornea in
wool spots, retinal vasculitis, exudative retinal detachment, the left eye (Figure 2). The corneal sensations in both eyes
anterior uveitis, corneal ulceration and subconjunctival were diminished. Examination of anterior chamber, lens and
haemorrhage.2-4 fundus was unremarkable in both eyes. On dermatological
consultation, she was reported to have multiple skin lesions
Herpes simplex virus (HSV) keratitis is a rarely reported characterized by cystic erosions with surrounding erythema
complication associated with dengue fever. Richardson superimposed with haemorrhagic crusts over some lesions
et al. reported 6 cases of herpes keratitis among 20,000 on both eyelids and maxillary area, consistent with lesions
cases of dengue clearly showing its rarity.1 To the best of characteristic of herpes simplex.
our knowledge, bilateral HSV keratitis in association with Laboratory investigations of the patient revealed that she
dengue fever has not been previously reported. Herein, we was positive for dengue NS1 antigen and erythrocyte
present a unique case of bilateral HSV keratitis along with sedimentation rate was raised at 100 mm/hr. X-ray chest
bilateral periocular skin lesions associated with dengue showed mild pleural effusion involving left lung more
fever.
Figure 1:On external examination, multiple periocular cystic lesions with
Case Report haemorrhagic crusts and surrounding erythema seen around both eyes 1879

A 45-year-old female presented with complaints of
diminution of vision, photophobia, irritation, foreign body
sensation and redness in both eyes for last 7 days. It was
associated with appearance of skin lesions in ocular adnexal
area bilaterally 3 days after the onset of diminution of vision.
The patient had been diagnosed with dengue fever 10 days
back and was under treatment from a physician. She also
reported to have been recently administered covid vaccine
(Covishield) – first dose taken 2 months back and second
dose 1 month back with no complications in the intervening
period. There was no history of diabetes mellitus,
hypertension, tuberculosis, epilepsy, atopy, malignancy or
any other chronic illness.

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DJO Vol. 32, No. 4, April-June 2022

Figure 2: Slit lamp pictures showing irregular and hazy corneas on torch light deviation induced by dengue infection. All of the 6 cases
examination in right eye (2a) and left eye (2b). Fluorescein staining revealed of HSV keratitis among 20,000 cases of dengue reported by
branchingepithelialdendriteswithterminalbudsinrighteye(2c)andlefteye(2d) Richardason et al. had unilateral involvement.1 In contrast,
our patient presented with bilateral HSV keratitis along with
than the right. Other investigations such as Complete periocular skin eruptions. The exact cause of this presentation
Blood Counts, Viral markers (HIV, HBsAg and HCV), Anti- could not be ascertained; however, we speculate it to be as
Nuclear Antibody and Montoux test were within normal a result of complex interplay of multiple factors including
limits. Laboratory investigation for Herpes virus was not dengue infection, likely reactivation of herpes infection and
available and a clinical diagnosis of bilateral Herpes simplex recently administered covid vaccine.
keratitis along with periocular skin eruptions was made, and
the patient was prescribed oral tablet acyclovir 400 mg five Our patient reported administration of second dose of
times a day for two weeks, tablet cefadroxil 500 mg twice Covishield vaccine 1 month back. There have been a few
daily for 1 week and tablet levocetirizine 5 mg twice daily reports of unilateral HSV keratitis after administration
for 1 week along with ointment mometasone-nadifloxacin of covid vaccine;7,8 however, to the best of our knowledge
(0.1%) twice daily for skin lesions by the dermatologist. there has been no report of bilateral HSV keratitis. There are
Ocular treatment included ganciclovir eye ointment (0.15%) also reports of development of herpes zoster ophthalmicus
five times a day, moxifloxacin (0.5%) eye drops three times post covid vaccines, however our patient has corneal
a day and homatropine (2%) eye drops twice daily in both lesions characteristic of HSV keratitis and her skin lesions
eyes. The patient responded well to the treatment and there were consistent with those of herpes simplex.9,10 Also, the
was gradual resolution of symptoms and recovery of vision. keratitis in the current case occurred one month after the
At follow up visit of 2 weeks the skin lesions had resolved administration of covishield vaccine, so a direct causal
with no residual scarring. Slit lamp examination showed relationship is difficult to establish. However, an additive
clear corneas with negative fluorescein staining and BCVA immune deviation effect along with subsequent dengue
of 6/6 in both eyes. Rest of the ocular examination was infection acting as trigger for fulminant HSV lesions cannot
unremarkable. be ruled out and may be investigated in future studies. Our
patient responded well to treatment with no residual skin
Discussion or ocular sequelae. Bilateral HSV keratitis has been reported
to be associated with higher proportion of subsequent
Bilateral HSV keratitis is a relatively uncommon entity complications including progressive ocular inflammation
which has been reported to be associated with underlying and corneal opacities, however, most of these patients had
conditions of atopy and other immune deviations, and chronic underlying conditions like atopy or other immune
results in higher proportions of subsequent complications.5,6 deviations.6 Our patient did not have any of these underlying
Souza PM et al. reported 7 patients with bilateral keratitis conditions and is likely to have developed it as a result of
out of 544 patients with herpes simplex eye disease; out acute dengue virus infection. Also, prompt diagnosis and
of which 5 patients had systemic atopy and 2 patients had treatment for both ophthalmic and dermatological lesions
ocular rosacea.5 Welhismus et al. reported 30 bilateral cases might have been a factor in good clinical outcome in the
in a population of 1000 patients with corneal involvement current case.
and found that patients with bilateral HSV keratitis were
younger and had systemic atopy as compared to those with In conclusion, we report a rare case of bilateral HSV
unilateral disease.6 Our patient reported no such history of keratitis associated with bilateral periocular skin herpetic
atopy, rosacea or any chronic systemic illness and likely lesions following dengue fever and administration of covid
developed manifestations of HSV keratitis due to immune vaccine. Any physician or ophthalmologist treating a patient
diagnosed with dengue fever should be aware of these
complications. Prompt diagnosis and timely intervention
helps in preventing any drastic visual complication.

References

1. Richardson S. Keratitis as a complication of dengue fever.
Southern Medical Journal 1927;20:32-36.

2. Chan DP, Teoh SC, Tan CS, et al. Eye Institute Dengue –
Related Ophthalmic Complications Workgroup. Ophthalmic
complications of dengue. Emerg Infect Dis. 2006;12:285-289.

3. Kapoor HK, Bhai S, John M, Xavier J. Ocular Manifestations of
dengue fever in an East Indian epidemic. Can J Ophthalmol.
2006;41:741-746.

4. Mehta S. Ocular lesions in severe dengue hemorrhagic fever
(DHF). J Assoc Physicians India. 2005;53:656-657.

5. Souza PM, Holland EJ, Huang AJ. Bilateral herpetic
keratoconjunctivitis. Ophthalmology. 2003;110:493-496.

6. Wilhelmus KR, Falcon MG, Jones BR. Bilateral herpetic keratitis.
Br J Ophthalmol. 1981;65:385-387.

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DJO Vol. 32, No. 4, April-June 2022

7. Li S, Jia X, YuF, Wang Q, Zhang T, Yuan J. Herpetic Keratitis Cite This Article as: Ravi Kaur Sandhu, Pawan Prasher.
Preceded by COVID-19 Vaccination. Vaccines.2021;9:1394. Bilateral Herpes Simplex Keratitis Associated with Dengue
Fever. Delhi J Ophthalmol 2022; 32 (4) 56-58.
8. Song MY, Koh KM, Hwang KY, Kwon YA, Kim KY. Relapsed Acknowledgments: Nil
disciform stromal herpetic keratitis following mRNA COVID-19 Conflict of interest: Nil
vaccination. Korean J Ophthalmol.2021 Nov 26. Epub Ahead of Source of Funding: None
Print. Date of Submission: 29 Jan 2022
Date of Acceptance: 16 May 2022
9. Thimmanagari K, Veeraballi S, Roach D, Al Omour B, Slim
J. Ipsilateral Zoster ophthalmicus post COVID-19 Vaccine in Address for correspondence
Healthy Young Adults. Cureus. 2021;13. e16725. Pawan Prasher, MS

10. Park E, Mays C, Konda S, Leffler C. Herpes Zoster Ophthalmicus Department of Ophthalmology,
Following Covid-19 Vaccination: A Case Report. Journal of Sri Guru Ram Das Institute of Medical
Infectious Diseases & Case Reports. 2021;143:2. Sciences and Research,
Vallah, Amritsar, Punjab, India.
Email: [email protected]

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DJO Vol. 32, No. 4, April-June 2022

Case Report

A Unique Case of Conjuctival Choristoma Masquerading As
Nasal Pterygium
Mukta Sharma, Shruti Anand

Department of Ophthalmology, Dr. Radhakrishnan Govt. Medical College Hamirpur, (RKGMC) Himachal Pradesh, India.

Abstract Being at the distinctive position of covering the eye ball, conjunctiva is frequently involved in array of local and systemic
disorders. Tumors of cornea and conjunctiva often present the ophthalmologist with a difficult diagnostic and therapeutic
challenge Histopathology findings force us to revisit our diagnosis.With this background we present our distinctive case of
conjunctival cyst which extended to the cornea and gave the appearance of a pterygium Choristoma which masqueraded
itself as inflamed pterygium makes it one of the very rare cases to be reported. It is suggested that dermoid choristoma
should be included in the differential diagnosis of lower eyelid masses.

Delhi J Ophthalmol 2022; 32; 59-60; Doi http://dx.doi.org/10.7869/djo.770

Keywords: Conjunctival Dermoid ; Choristoma ; Pterygium

Introduction when the report of histopathology arrives, forcing us to

The outermost covering of the globe is universally labelled as re-think our strategies to manage such patients. With this
conjunctiva. It is a mucous membrane similar to the mucous
membrane elsewhere in the body, containing blood vessels, background we present our distinctive case of conjunctival
nerves and lymphatic channels supplying the anterior
segment of the eye. Apart from the nutritive function, it cyst which extended to the cornea and gave the appearance
also contributes to the formation of tear film through the
microscopic goblet cells which produce mucin. Being at the of a pterygium.1 Case Report
distinctive position of covering the eye ball, it is frequently
involved in array of local and systemic disorders. These A seventy five year old man presented to our department
vary from conjunctivitis and innocuous pingulecula and
Bitot spot’s at the one end to precarious Kaposi’s sarcoma with chief complaints of diminution of vision in left eye for
and malignant melanoma at the other end. Very often we
come across very innocent looking lesions in which we are the past one year , associated with redness and watering for
very sure of the diagnosis relying on our clinical acumen
and experience. Our overconfidence is often shattered the past six months. There was no history of associated pain,

itching or burning sensation from the left eye. No relief was

obtained despite prescription of multiple eye drops (details

not available)

On examination distance vision 6/60 right eye, corrected to
6/24. Counting finger counting close to face left eye. Slit lamp
biomicroscopy revealed nuclear cataract grade II along with
cortical cataract was right eye. Left eye revealed multiple
epithelial, sub-epithelial and stromal corneal opacities.
Nasal pterygium seen in left eye extended to a cystic growth
in forniceal conjunctiva. Mass was translucent, oval, about
4 mm in diameter and freely mobile from the underlying
structures (Figure1).

Pterygium was excised completely leaving underlying sclera
bare and translucent cyst in inferior fornix was excised
(Figure.2).

Figure 1: Photograph of anterior segment of left eye showing pterygium Figure 2: Post operative photogaraph showing bare sclera and excision of
along with whitish cyst like growth in palpebral conjunctiva cyst like growth

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Figure 3: Histopathology picture of the lesion showing stratified squamous Conjunctival choristomas in palpebral conjunctiva are
epithelium along with lacrimal galnd and hair follicles very rare growths. Epibulbar choristomas are common
in children, 5 with only 15 cases been reported so far.
Histopathology revealed hyperplastic stratified squamous They commonly present as small translucent swelling
epithelium with attached sebaceous glands, hair follicles and resembling the retention cyst. Treatment includes surgical
lacrimal gland suggestive of conjuctival choristoma. (Figure 3) excision when symptomatic or causing cosmetic concern.
Recurrences or malignant transformation have not been
Discussion reported.6 Dermoid cyst presenting as a chronically red eye
has been documented.7 The fact that our case of choristoma
Tumors of cornea and conjunctiva often present a diagnostic manifested at older age of seventy- four , and masquerading
challenge. Tumors of ocular surface are classified according as inflamed pterygium makes it a rare presentation
to the cell type they originate from including epithelium,
melanocytes, lymphocytes, vascular epithelium and References
mesenchymal cells. Conjunctiva has squamous cuboidal
cells that cover a rich connective tissue composed of delicate 1. Dagher MH, Colby K. Tumors of cornea and conjunctiva.
substantia propria with abundant blood vessels, lymphatic Albert Jakobiec’s Principles and Practice of Ophthalmology.
channels and nerve endings. The lamellar arrangement Philadelphia, PA] : Saunders Elsevier, 2008, Volume 1.Chapter
of the corneal stroma and the condensation of the outer 58:pg 790..
layer into bowman’s layer protect the cornea from deep
invasion by many tumors that arise in conjunctiva.2 A 2. Shields CL, Shields JA. Tumors of the conjunctiva and cornea.
choristoma is a congenital tumor like growth that contains Indian J Ophthalmol.Dec.2019;67(12):1930-48.
displaced epithelial cells and other dermis like elements not
normally indigenous to the site they are found. Four types of 3. Mallik KK. Pathology of ocular dermoid. Indian J Ophthalmol.
choristoma are recognised: Simple, Dermoids, Dermolipoma 1957;5 :60-3.
and complex choristomas. Dermoids are universally defined
as normal tissue in abnormal location. It implies that in case 4. Mansour AM, Barber JC, Reinecke R.Ocular choristomas. Surv
of conjunctiva, stratified squamous epithelium along with Ophthalmol.1989;33:339-58.
hair follicles and sweat glands. If however, special tissue
elements like those of cartilage or lacrimal glands are present 5. Ojha PR, Deshpande AH, Gargade CB. Epipalpebral conjunctival
then it is classified under choristomas. The most common chondroid choristoma: Interesting developmental anomaly
episcleral choristoma is dermoid. Conjunctival dermoids presenting in an adult. Indian J Ophthalmol. 2017;65(7):613-4.
are well well circumscribed, smooth, elevated white, round
to oval most commonly present at inferotemporal limbus. 6. Herdiana TR, Takahashi Y,Valencia MRP. Epibulbar osseous
On HPE keratinized epithelium, hair, sebaceous and sweat choristomawithin a dermolipoma. Case report and literature
glands, smooth muscles, cartilage etc .Complex choristoma review.. Orbit 2019;38:407-11.
shows presence of bone, cartilage, lacrimal gland , hair
follicles etc.3 It differs from hamartoma which is an excessive 7. Martinez LM, Cohen KL. Conjunctival dermoid cyst
proliferation of normal tissue at the normal site. Choristomas seen on examination as a chronically red eye. Arch
may occur in association with ocular coloboma, Goldenhar Ophthalmol.1998;116(8):1109-11.
syndrome or epidermal nevus syndrome. The differential
diagnosis should include chalazion, dermoid, dermolipoma, Cite This Article as: Mukta Sharma, Shruti Anand. A
pyogenic granuloma and papilloma.4
Unique Case Of Conjuctival Choristoma Masquerading
As Nasal Pterygium. 2022; Vol 32, No (4): 59 - 60.

Acknowledgments: Nil

Conflict of interest: None declared

Source of Funding: None

Date of Submission: 15 Aug 2021
Date of Acceptance: 20 May 2022

Address for correspondence

Mukta Sharma, MS

Senior Resident

Department of Ophthalmology,
Dr. Radhakrishnan Govt. Medical
College Hamirpur, (RKGMC)
Himachal Pradesh, India.
Email: [email protected]

Quick Response Code

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Abstract Case Report

Central Retinal Artery Occlusion Secondary
To High Altitude Exposure

Diviyanshu Nadda1, Jyoti Sheoran2, Saurabh Sachar3, Anurag Narula4

1Department of Ophthalmology, Command Hospital Chandimandir, Panchkula, Haryana, India.
2Department of Ophthalmolgy, Military Hospital Dehradun, Uttarakhand, India.

3Department of Radiodiagnosis, Consultant in Shri Mahant Indiresh Hospital Dehradun, Uttarakhand, India.
4Department of Ophthalmology, Consultant, VMMC and Safdarjung Hospital, New Delhi, India.

CRAO can be considered as an ocular analogue of stroke or an ocular equivalent of acute myocardial infarction. We present a
case report of a 32-years-old serving soldier posted at high altitude area with no premorbidities who presented with symptoms
of sudden painless loss of vision in the left eye (LE). Best-corrected visual acuity in the LE was PL+ with PR inaccurate . A relative
afferent pupillary defect grade IV was observed in the LE. Ocular fundus examination of LE was suggestive of central retinal artery
occlusion. Systemic evaluation revealed Steno occlusive disease of bilateral carotids L>R. Haematological investigations revealed
increased haemoglobin. Raised haemoglobin due to long stay in high altitude area is tantamount to a sustained inflammatory
state that results in endothelial dysfunction by causing hypercoagulable state culminating in small calibre vessel blockage.

Delhi J Ophthalmol 2022; 32; 61-65; Doi http://dx.doi.org/10.7869/djo.771
Keywords: CRAO, Altitudinal Exposure, Retinal Vasculature

Introduction 2. Transient NA-CRAO is most often caused by a migrating
embolus, and sometime by a transient marked fall of
Central retinal artery occlusion (CRAO) was first described perfusion pressure in CRAO10 or high rise of intraocular
by von Graefes in 1859.1 It is analogous to an acute stroke pressure.
of the eye and is an ophthalmic emergency. The incidence
is estimated to be 1 in 100 000 people and accounts for 1 in 3. Arteritic CRAO is due to thrombosis of the common
10 000 ophthalmological outpatient visits.2 A prospective trunk of the posterior ciliary artery and CRA arising from
study of 260 eyes with CRAO showed that people suffer the ophthalmic artery11 caused by giant cell arteritis, not
profound monocular visual loss, with 80% of patients of CRA per se.
having a visual acuity (VA) of 20/400 or worse.3 This
reduction in vision increases the fall risk and thus results in Carotid artery disease can produce CRAO by the
increased dependency, and in worst-case scenarios leads to following three mechanisms
institutional care.4 CRAO signifies end-organ ischaemia and
often the underlying atherosclerotic disease. It is the same 1. Embolism, which is by far the most common cause of
underlying atherosclerotic risk factors that in turn place an CRAO12
individual at risk of future cerebral stroke and ischaemic
heart disease. 2. A significant stenosis (about 70% or more) or
complete occlusion of the internal carotid artery, by
Although analogous to a cerebral stroke, there is currently markedly reducing the ocular blood flow, can result in
no guideline-endorsed evidence for treatment. Current development of CRAO.12 In a study >80% stenosis of the
options for therapy include the so-called ‘standard' internal carotid artery was seen in 18% of CRAO cases.13
therapies, such as sublingual isosorbide dinitrate, systemic
pentoxifylline or inhalation of a carbogen, hyperbaric 3. A study on atherosclerotic monkeys showed that
oxygen, ocular massage, globe compression, intravenous serotonin, a powerful vasoconstrictor, released by
acetazolamide and mannitol, anterior chamber paracentesis, platelet aggregation on atherosclerotic plaques in the
and methylprednisolone. None of these therapies have been carotid artery, produces a transient spasm, which can
shown to be better than placebo.5 There has been recent cause transient, complete occlusion, or impaired blood
interest in the use of tissue plasminogen activator (tPA) with flow in the CRA14
two recent randomized controlled trials on the treatment of
acute CRAO.6,7 Case Report

Causes of CRAO A 32 years-old-male serving soldier, posted at 18000 feet
initially reported with sudden, acute, painless loss of vision
1. Classical Non Arteritic CRAO (NA-CRAO) is most in right eye since last 24 hours. There was no headache,
common due to permanent occlusion of the CRA, caused vomiting, convulsion or any neurological deficit. He had no
by an impacted embolus at the narrowest part of the precommorbidities.
CRA, where it enters the sheath of the optic nerve8 (not
at the lamina cribrosa, as is often erroneously described). On general examination, he was conscious, oriented, afebrile
The emboli originate from plaques in the carotid artery with pulse rate of 110/ min, blood pressure of 130/70 mmHg.
or the heart rarely, CRAO is due to vasculitis, chronic His peripheral pulsations were well felt, no carotid bruit was
systemic autoimmune diseases, or thrombophilia.9 heard. He had all deep tendon reflexes brisk on examination.
Rest of the general examination was unremarkable. He had
no addiction. Other personal history was insignificant. He
had no history of any medications or drugs. His family
history was insignificant.

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On ophthalmological examination Figure 1: Fundus photography of the left eye showing the presence of a pale
optic disc, diffuse arterial narrowing, a mild ‘cherry-red spot’ macula and
The best-corrected visual acuity (BCVA) was 20/20 in the right
eye and light perception, projection of rays was inaccurate peripheral areas of retinal pigmented epithelium hyperpigmentation.
in the left eye. Right eye ophthalmologic examination was
unremarkable, while the left eye showed a relative afferent Figure 2: Fluorescein angiography of the left eye, showing a delayed arrival
pupillary defect gd IV. Dilated fundus ophthalmoscopy of the dye in the eye 43 s after the injection , peripheral areas of capillary
revealed the presence of severe arterial narrowing, retinal
whitening in the macular region with loss of the physiological nonperfusion, arterial narrowing, CRAO, central retinal artery occlusion.
macular reflex. Cherry red spot, peripheral areas of retinal
pigment epithelium hyperpigmentation was seen (Figure 1).
Optical coherence tomography (OCT) showed normal vitreo
macular interface ,increased and distorted foveal contour
with increased CMT, normal IS-OS junction and normal
RPE choroid interface, (Figures 3). CRAO was suspected.
Fluorescein angiography (FA) performed, confirmed the
diagnosis of CRAO revealing severe delay in the filling of
the retinal arteries and a delayed arteriovenous transit time,
areas of peripheral capillary nonperfusion, arteriovenous
anastomoses, and cherry red spot (Figure 2)

Systemic Examination

Lab tests: CBC showed raised HB of 19g/dl(13-18), MCV
102fl(76-96), MCH 34.8pg(27-32), RDW-CV 15.6%(11.5-
14.5). LFT, RFT, Lipid profile, RBS were within normal
limits. ANA, ds DNA, and Anti phospholipid antibodies
workup was negative & other autoimmune markers were
also negative with an ESR of 20 mmhg at 1 hour. Also his
ANCA panel was negative, including both myeloperoxidase
and perinuclear antibodies. Coagulation profile including
Protein C, Protein S and antithrombin III were normal.

ECHO showed EF of 65%, no vegetative growth, clot, PAH.
Normal LV function.

CT Cerebral angiography (Figure 4,5) showed calcified
plaques bilateral ICA with 30% stenosis on the right and 50%
stenosis on the left.

Carotid doppler study showed steno-occlusive disease
bilateral carotids(L>R). In right carotid a hypoechoic plaque

Figure 3: OCT scan of left eye shows thickening of retinal layers and distortion of foveal contour.

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Figure 4: Cerebral CT Angiography shows a hypoechoic plaque causing 50% Figure 5: Cerebral CT Angiography shows a hypoechoic plaque causing 50%
occlusion of R CCA occlusion of L CCA

Figure 6: 3D Recon of Cerebral CT Angio showing stenosis of R ICA. Figure 7: 3D Recon of Cerebral CT Angio showing stenosis of L ICA.

causing 50% occlusion of lumen of CCA and extending till Discussion
ICA. In left carotid there was a hypoechoic plaque causing
50-69% occlusion of lumen in left CCA, bulb and extending Currently, there are only a few reports on retinal artery
into left ICA. On colour doppler imaging and spectral occlusion secondary to high-altitude exposure. A case of
waveform evaluation there was increase in velocity in post central retinal artery occlusion secondary to bilateral buried
stenotic segments. The spectral waveform was normal. optic nerve drusen at high altitude was reported in 1995,15
while another case of central retinal artery occlusion caused
Management by the expansion of intraocular gas during mountain travel
at high altitude was reported in 2002.16 A recent report has
Medical review was done. Patient was started on anti- shown that cilioretinal artery occlusion and related central
coagulants, anti platelets, statins. retinal vein occlusion occurred as a complication following
high-altitude exposure.17 It has been speculated that the

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DJO Vol. 32, No. 4, April-June 2022

reason for a few reports of retinal artery occlusion secondary Abbrevations
to high-altitude exposure might be that some clinicians do
not suspect retinal vascular occlusion, thus do not inquire CRAO : Central Retinal Artery Occlusion
the patient’s travel history or consider high altitude as a risk PL : Perception of Light
factor. Possible reasons for retinal artery occlusion secondary PR : Projection of light
to high-altitude exposure may be related to hematocrit, CRA : Central Retinal Artery
hemoglobin concentration, and blood viscosity that were all CMT : Central macular thickness
increased in the hematologic examination of high-altitude IS-OS : Inner space-outer space junction
climbers, which indicated the higher coagulative activity,
as the present case shown.18 The patient was in a state of References
hypercoagulability. The atmospheric pressure decreases
along with the increase of the altitude, after which the retinal 1. Graefe A. Ueber Embolie der Arteria centralis retinae als
arteries and veins tend to dilate. Retinal vascular occlusion Ursache plötzlicher Erblindung. Albrecht von Graefes Archiv
in patients with circulatory impairment has been shown to für Ophthalmologie. 1859;5(1):136-157.
be triggered by reactive vasoconstriction, which may occur
during the descent.19 Furthermore, hypoxia has an important 2. Rumelt S, Dorenboim Y, Rehany U. Aggressive systematic
role in the development of retinal artery occlusion. Hypobaric treatment for central retinal artery occlusion. American Journal
hypoxia caused thrombosis, which further decreased the of Ophthalmology. 1999;128(6):733-738.
oxygen transport capacity.
3. Hayreh S, Zimmerman M. Central Retinal Artery Occlusion:
There has been a great interest and controversy in its Visual Outcome. American Journal of Ophthalmology.
management ever since CRAO has been known. As with 2005;140(3):376.e1-376.e.
most instances of ischemia, the colloquialism “time is vision”
may apply here as well. Best outcomes likely result when 4. Vu H, Keeffe J, Taylor H. Vu, H.T., Keeffe, J.E., McCarty, C.A.
applied within the first eight hours from the onset of visual and Taylor, H.R. (2005) Impact of Unilateral and Bilateral Vision
impairment.21 Usually, one or a combination of the following Loss on Quality of Life. British Journal of Ophthalmology, 89,
conventional modes of treatments have been advocated in 360-363.
acute CRAO and have claimed success.
5. Fraser S, Adams W. Interventions for acute non-arteritic central
These include retinal artery occlusion. Cochrane Database of Systematic
Reviews. 2009;.
(i) ocular massage, in an effort to dislodge the embolus in
the CRA; 6. Feltgen N, Neubauer A, Jurklies B, Schmoor C, Schmidt D,
Wanke J et al. Multicenter study of the European Assessment
(ii) a reduction of IOP by paracentesis, massage of the Group for Lysis in the Eye (EAGLE) for the treatment of
eyeball, administration of acetazolamide, and so on to central retinal artery occlusion: design issues and implications.
improve blood flow; EAGLE Study report no. 1. Graefe's Archive for Clinical and
Experimental Ophthalmology. 2005;244(8):950-956.
(iii) vasodilation of the CRA;
(iv) inhalations of 95% oxygen and 5% carbon dioxide; 7. Chen C, Lee A, Campbell B, Lee T, Paine M, Fraser C et al.
(v) rebreathing of expired CO2 in a bag; and Efficacy of Intravenous Tissue-Type Plasminogen Activator in
(vi) retrobulbar vasodilators. Central Retinal Artery Occlusion. Stroke. 2011;42(8):2229-2234.

Except for ocular massage, which occasionally dislodges 8. Schumacher M, Schmidt D, Jurklies B, Gall C, Wanke I, Schmoor
the embolus, there is no evidence that the rest show any C, et al Central retinal artery occlusion: Local intra-arterial
significant benefit.22 fibrinolysis versus conservative treatment, a multicenter
randomized trial Ophthalmology. 2010;117:1367–75.
Conclusion
9. Hayreh S. Ocular vascular occlusive disorders: Natural history
Prompt recognition of CRAO symptoms should be followed of visual outcome. Progress in Retinal and Eye Research.
by a detailed neurologic and vascular evaluation for 2014;41:125.
concurrent stroke and carotid artery stenosis or occlusion in
patients who are working, or travelled to high altitude. These 10. Hayreh S, Zimmerman M. Central Retinal Artery Occlusion:
patients are also at risk for ischemic events after treatment Visual Outcome. American Journal of Ophthalmology.
as prolonged stay in high altitude areas is tantamount to 2005;140(3):376.e1-376.e.
a sustained inflammatory state that results in endothelial
dysfunction by causing hypercoagulable state. This case 11. Hayreh S. Anterior ischaemic optic neuropathy. II. Fundus on
highlights the high risk to these patients, which requires ophthalmoscopy and fluorescein angiography. British Journal of
intensive workup and admission from the emergency room Ophthalmology. 1974;58(12):964-980.
and promt treatment, both ocular and systemic.
12. Hayreh SS, Podhajsky PA, Zimmerman MB. Retinal artery
occlusion: Associated systemic and ophthalmic abnormalities
Ophthalmology. 2009;116:1928–36.

13. Central retinal artery occlusion. Indian Journal of
Ophthalmology. 2018;66(12):1684.

14. Hayreh S. Serotonin-Induced Constriction of Ocular Arteries
in Atherosclerotic Monkeys. Archives of Ophthalmology.
1997;115(2):220.

15. Newsom R, Trew D, Leonard T. Bilateral buried optic nerve
drusen presenting with central retinal artery occlusion at high
altitude. Eye. 1995;9(6):806-808.

16. Fang I, Huang J. Central retinal artery occlusion caused by
expansion of intraocular gas at high altitude. American Journal
of Ophthalmology. 2002;134(4):603-605.

17. Gokce G, Metin S, Erdem U, Sobaci G, Durukan A, Cagatay H
et al. Late Hyperbaric Oxygen Treatment of Cilioretinal Artery
Occlusion With Nonischemic Central Retinal Vein Occlusion
Secondary to High Altitude. High Altitude Medicine & Biology.
2014;15(1):84-88.

18. Bhende MP, Karpe AP, Pal BP. High altitude retinopathy. Indian

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DJO Vol. 32, No. 4, April-June 2022

J Ophthalmol. 2013;61(4):176–7. Cite This Article as: Diviyanshu Nadda, Jyoti Sheoran,
19. Willmann G, Fischer M, Schommer K, Bärtsch P, Gekeler F, Saurabh Sachar, Anurag Narula. Central Retinal Artery
Occlusion Secondary To High Altitude Exposure. Delhi Journal
Schatz A. Missing correlation of retinal vessel diameter with of Ophthalmology.2022; Vol 32, No (4): 61 - 65.
high‐altitude headache. Annals of Clinical and Translational Acknowledgments: Nil
Neurology. 2014;1(1):59-63. Conflict of interest: None declared
20. Barthelmes D, Bosch M, Merz T, Petrig B, Truffer F, Bloch K et Source of Funding: None
al. Delayed Appearance of High Altitude Retinal Hemorrhages. Date of Submission: 16 Jan 2022
PLoS ONE. 2011;6(2):e11532. Date of Acceptance: 04 Jun 2022
21. Hadanny A, Maliar A, Fishlev G, Bechor Y, Bergan J, Friedman
M et al. Reversibility of retinal ischemia due to central retinal Address for correspondence
artery occlusion by hyperbaric oxygen. Clinical Ophthalmology. Jyoti Sheoran, MS, Ophthalmology
2016;Volume 11:115-125.
22. Hayreh S. Acute retinal arterial occlusive disorders. Progress in Department of Ophthalmolgy,
Retinal and Eye Research. 2011;30(5):359-394. Military Hospital Dehradun,
Uttarakhand, India.
Email : [email protected]

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DJO Vol. 32, No. 4, April-June 2022

Pictorial CME

A Rare Case of Cilia Incarnata Externum

Divya Ramraika, Bithi Chowdhury, Anurag Anand

Department of Ophthalmology, Hindu Rao Hospital, New Delhi, India.

Cilia incarnata externum is the term used to describe an eyelash that burrows under the skin to the surface. The
Abstract patient presents due to the appearance of bump. It is asymptomatic and usually requires no treatment but as the

patient had cosmetic blemish, a small incision is usually given over the bump and after which cilia is epilated.

Delhi J Ophthalmol 2021; 32; 66; Doi http://dx.doi.org/10.7869/djo.772

Keywords: Cilia Incarnata Externum, Normal Root Of Cilia

A 17-year-old boy presented to outpatient department with Cilia incarnata is the misdirection of eyelashes whereby they
complaint of appearance of bump in his right eye upper grow under the skin through the surface ‘or’ posteriorly
lid. Patient has no other symptoms/ history of any trauma. to the conjunctival surface instead of emerging normally
Examination revealed a misdirected eye lash running from the eyelid margin. The lash root is normal in both the
underneath the skin from the lid margin of the upper right conditions.1 The lash grows in the path of least resistance.

eyelid. Hair was running vertically underneath the skin Cilia incarnata is caused in adults by mechanical misdirection
(Figure 1,2). Vision was 6/6 and there were no symptoms of either the lash follicles ‘or’ the lashes themselves as a
and any other abnormal findings. Hence, we concluded with result of some abnormal lid condition.2-5 Previously most of
the diagnosis of cilia incarnata externum. After anesthetizing the cases reported were of both females and males.6
we had just incised the skin over the bump and cilia was
epilated. References

1. Patel BC, Malhotra R. Cilia Incarnata. [Updated 2021 Jul 26]. In :
Stat Pearls [Internet]. Treasure Island (FL): Stat Pearls Publishing
;2021 Jan

2. Bloch FJ. Minor anomalies in position of the eyelashes. Arch
Ophthalmol. 1947;37:772-4.

3. Agarwala HS. Cilium inversum. Am J Ophthalmol. 1963;55:48-9.
4. Herzog H. Pathologie der Cilien, Z Augenheilkd 1904;12:256.
5. Belfort R, Ostler HB. Cilia incarnata. Br J Ophthalmol

1976;60:5946.
6. Ayachit S, Helaiwa KA, et al. Cilium Incarnatum Externum and

its management- A rare presentation. Health Sci J. 2022;16(2):914

Figure 1: External image depicting root of origin of cilia incarnata externum Cite This Article as: Divya Ramraika, Bithi Chowdhury,
shown by black arrow above right eye Anurag Anand. A Rare Case of Cilia Incarnata Externum.
Delhi Journal of Ophthalmology.2022; Vol 32, No (4): 66.

Acknowledgments: None

Conflict of interest: None

Source of Funding: None

Date of Submission: 26 Dec 2021
Date of Acceptance: 05 May 2022

Address for correspondence

Divya Ramraika, DOMS, DNB,

Senior Resident

Department Of Ophthalmology,
Hindu Rao Hospital, New Delhi, India.
Email : [email protected]

Figure 2: External image depicting bump over right upper eyelid as shown Quick Response Code
by black arrow
Delhi Journal of Ophthalmology
E-ISSN: 2454-2784  P-ISSN: 0972-0200 66

DJO Vol. 32, No. 4, April-June 2022

Omnibus Humanus (Masters, Change Makers, Out of Box Thoughts)

Medicine Through A Humanistic Lens

Upreet Dhaliwal

Delhi J Ophthalmol 2022;32; 67-68; Doi http://dx.doi.org/10.7869/djo773

SIn our country, even now, children are encouraged to choose one field from among the Humanities, the Arts, and the Sciences
for further study after class Xth Those who choose the Sciences are thereafter denied formal access to the Humanities or the
Arts. It is as though the latter disciplines are too frivolous for somebody trying to become a doctor or a nurse or an engineer.
This is an unfortunate assumption, given that the ‘non-science’ disciplines hone observation skills, critical thinking, clinical
reasoning, curiosity, reflection and creativity. They encourage an exploration of phenomena that influence human behavior,
including one’s own. These disciplines allow a deeper understanding of the social issues that impact health. Importantly,
they highlight the uniqueness of individuals who are products of their own diverse abilities and singular experiences.1-5 Such
‘non-science’ learning is extremely important for people who hope to look after the health and ameliorate the suffering of
other human beings.

Healthcare practitioners are already adept at listening to patients’ stories. So often, a cup of tea placed on the doctor’s desk
gets cold as they listen with rapt attention to the patient narrate details of their illness. However, this ‘medical’ listening
uncovers only part of the truth. This is because the doctor is trying to zero in on a medical diagnosis from helpful clues
in the patient’s history. Those aspects of the narrative that don’t directly contribute to the final diagnosis are relegated to
the background. On the other hand, if we use ‘narrative’ listening, ask the kind of questions that encourage our patients to
divulge the whole truth, and listen holistically, we might be able to heal the human being in addition.6 An anecdote might
illustrate this better. A middle-aged woman presented with a congenital jaw-winking ptosis and asked if it could be fixed.
Though we were surprised that she wanted it corrected after having lived with it for more than half a century, we told her it
was definitely correctible, and the work-up for surgery began. Some of us, who wanted to know more about the circumstances
surrounding the belated request for surgery, decided to ask more ‘why’ questions instead of the ‘what’ and‘when’ as is usual
during a history taking endeavor. In response to the ‘why’, the woman divulged after some hesitation that her son had
recently got married and his new bride took great pleasure in taunting her about her ‘witchy’ winking eye.

Even without knowing the background human story we would have striven for the best possible surgical outcome for the
lady; however, now we had a stronger motivation. Not just the eyelid, we also wanted to ‘fix’ the apparent lack of respect
that the mother-in-law received. Post-surgery, when the younger woman visited to inquire after her mother-in-law’s health,
we made it a point to praise our patient‘s courage and cooperation in glowing terms in front of the visitor. We might have
imagined it, but it seemed as though our patient - who had appeared anxious about the visit - sat up straighter and the frown
lines on her forehead eased somewhat. The daughter-in-law’s face, we noticed, softened, and she jumped off her bedside
stool to fluff up the pillows so that her mother-in-law could be made more comfortable. This anecdote shows how narrative
history-taking can create multiple strands of connectedness between patient and physician. Connection is important for the
establishment of a successful doctor-patient relationship.7,8

This human story highlights the socio-cultural influences on health and illness. Story-telling, as also poetry, history, cultural
studies, and disability studies are useful tools from the humanities. Being alert to these possibilities is a prerequisite to
providing compassionate and equitable, patient-centered healthcare. For example, giving a child a good pair of glasses
may relieve their headache. However, knowing that the child dropped out of school due to this, and then following up with
the parents as to whether the child did indeed get readmitted to school, has an even greater impact on the child’s future. As
is said – ‘a good doctor treats the disease, but a great doctor treats the person!’

The Humanities have made their way into the new competency-based curriculum rolled out by the National Medical
Commission,9 and it is up to us to learn to use these powerful, versatile tools so as to train our learners to ask the right
questions. Unless we pose the questions through a medical as well as a humanistic lens, how do we unravel what it is that
makes a disease much harder for one patient but easier for another to manage? Is there a drunken or an abusive or disabled

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DJO Vol. 32, No. 4, April-June 2022

family member in the picture but one who is kept out of the physician’s view from embarrassment or a fear of stigma? Is it
child abuse or ignorance or economics at play or does patriarchy have a role when a girl child presents with a melted cornea
due to vitamin A deficiency? The Humanities teach us to ask the why questions and to delve below the surface for a more
complete version of the truth so that the right solutions - holistic solutions - can be found.

Through the use of poetry, patient-narratives and theatre in teaching-learning exercises, real dialogue can potentially take
place. Conversations can be generated between those who are powerless (patients and caregivers) and those in power
(physicians, for example). These techniques can give a voice to those who are usually unheard or underserved, and the
vulnerable.5

Exposure to poetry, storytelling, the visual arts, different forms of theatre and media, and other Humanities tools like history,
cultural studies, disability studies, sociology, philosophy, language, geography and economics can improve the caregiving
skills of healthcare practitioners. As one explores this fascinating field, one may discover that medicine and the humanities
are not parallel roads that never intersect, but are complementary to each other and intersect all the time in surprising and
useful ways.

References:

1. Prince G, Osipov R, Mazzella AJ, Chelminski PR. Linking the Humanities with Clinical Reasoning: Proposing an Integrative Conceptual
Model for a Graduate Medical Education Humanities Curriculum. Acad Med. 2022 Apr 5. doi: 10.1097/ACM.0000000000004683.

2. Singh S, Khan AM, Dhaliwal U, Singh N. Using the health humanities to impart disability competencies to undergraduate medical students.
Disabil Health J. 2022;15(1):101218. doi: 10.1016/j.dhjo.2021.101218. Epub 2021 Oct 1.

3. Shapiro J, Rucker L. Can poetry make better doctors? Teaching the humanities and arts to medical students and residents at the University of
California, Irvine, College of Medicine. Acad Med. 2003;78(10):953-7. doi: 10.1097/00001888-200310000-00002.

4. Dhaliwal U, Singh S, Singh N. Reflective student narratives: honing professionalism and empathy. Indian J Med Ethics. 2018;3(1):9-15. doi:
10.20529/IJME.2017.069. Epub 2017 Jul 18.

5. Singh S, Barua P, Dhaliwal U, Singh N. Harnessing the medical humanities for experiential learning. Indian J Med Ethics. 2017;2(3):147-152.
doi: 10.20529/IJME.2017.050.

6. Charon R. Narrative medicine: caring for the sick is a work of art. JAAPA. 2013;26(12):8. doi: 10.1097/01.JAA.0000437751.53994.94.
7. Ghosh AK, Joshi S. Enhancing Physician's Toolkit: Integrating Storytelling in Medical Practice. J Assoc Physicians India. 2021;69(7):11-12.
8. Hill MB. It's Not You, It's Me: Learning to Navigate the Patient-Physician Relationship. Ann Fam Med. 2021;19(3):271-273. doi: 10.1370afm.2644.
9. Medical Council of India. Competency Based Undergraduate Curriculum for the Indian Medical Graduate. 2019; 1–64. Available from: https://

www.nmc.org.in/wp-content/uploads/2020/01/FOUNDATION-COURSE-MBBS-17.07.2019.pdf.

Dr Upreet Dhaliwal

MBBS, MS (Ophthalmology) CMCL-FAIMER 2015

Former Director-Professor of Ophthalmology
and founding member, Health Humanities
Group, University College of Medical Sciences,
University of Delhi India.

E-ISSN: 2454-2784  P-ISSN: 0972-0200 68 DOI : http://dx.doi.org/10.7869/djo.
Delhi Journal of Ophthalmology

DJO Vol. 32, No. 4, April-June 2022

Theme Section

Demystifying Intraocular Lens Power Calculation

Nirupama Kasturi1, Arup Chakrabarti2

1Department of Ophthalmology, Jawaharlal Institute of Postgraduate Medical Education & Research (JIPMER) Pondicherry, Tamil Nadu, India.

2Cataract and Glaucoma services, Chakrabarti Eye Care Centre, Trivandrum, Kerala, India.

Cataract surgery has advanced from a mere replacement of the cloudy lens to a refractive-cataract surgery due to
the advancements in diagnostic and surgical instrumentation and techniques. The availability of premium intraocular
lenses provides patients the opportunity to regain excellent vision and be less dependent on spectacles. In order to
Abstract attain the desired postoperative refraction or target emmetropia following cataract surgery, accurate biometry and
appropriate intraocular lens power formula selection are required, along with safe and precise surgery. This article
reviews the salient features and recent advances in biometry and intraocular lens power calculations.

Delhi J Ophthalmol 2022; 32; 69-76; Doi http://dx.doi.org/10.7869/djo.774

Keywords: Biometry, Intraocular Lens Power Calculation, Formulas

Introduction Neglecting their effects can lead to a significant postoperative
overcorrection or undercorrection, especially in eyes with
The quest for accurate intraocular lens (IOL) power corneal abnormalities. Before performing keratometry,
calculation has existed ever since Sir Harold Ridley it is important to treat any dry eye or meibomian gland
implanted the first IOL in 1949.1 The postoperative refraction disease. Also, discontinue contact lens wear 1 week for soft
was highly myopic due to the higher refractive index of and 4 weeks prior for rigid gas permeable lenses to prevent
the IOL as compared to the crystalline lens. In the present keratometry errors due to corneal warpage.5
day, with high patient expectations, even a prediction
error of 0.5 D can make the patient unhappy, especially In Manual keratometry, the central cornea is assumed to be
with multifocal and toric implants. Intraocular lens power a perfect sphere and acts as a spherical convex mirror. From
calculation has met with several developments over the the size of the reflected image formed by the anterior surface
years in the form of better instrumentation and the use of of the cornea (3-3.2mm zone), the radius of curvature is
more precise mathematical formulae that have significantly determined, which is then converted to power in diopter or
improved surgical outcomes. The major components of IOL mm. Eg. Bausch & Lomb Keratometer.6 It requires a highly
power calculation are precise biometry, appropriate use of skilled technician and is operator-dependent, affecting
formulae, and understanding patient expectations. If the measurement accuracy. It is preferred in patients with poor
calculations are not performed accurately, then patients may fixation, distorted mires, highly toric cornea, and a dry
be left with a significant refractive error post-operatively. ocular surface where automated keratometry is not possible.
Automated Keratometers provide the K readings at the central
(I). Ocular Biometry 3mm of the cornea in the steepest and flattest meridians. The
optical biometers have included auto-keratometers enabling
The refractive power of the human eye depends on the measurements of K readings and axial length from a single
power of the cornea (Keratometry-K), the refractive index instrument. The IOL Master (Carl Zeiss Meditec) and
of the lens, the position of the lens (Effective lens position Lenstar LS900 (Haag Streit) have incorporated automated
-ELP), and the length of the eye (Axial length-AL) [Figure keratometers that calculate K readings by analyzing reference
1]. Accurate assessment of these variables is essential in
achieving optimal postoperative refractive results. The
modern-day IOL power prediction errors are due to
keratometry (22%), axial length measurement (36%), and
post-op anterior chamber depth (ACD) estimation (42%).2

Keratometry (K) Figure 1: Diagramatic representation of variables used for IOL power
calculation
The central corneal power is an important factor, and
an error of one dioptre can translate to a 0.9 D error in
IOL power. The average adult keratometry (K) reading is
43.0 - 44.0 D, with barely a dioptre difference between the
two eyes. It can be determined using various instruments
like the manual or auto-keratometers or keratometers
incorporated in optical biometers and corneal topography/
tomography-based keratometry. The standard keratometry
relies purely on measurements of the anterior corneal
surface and extrapolates it by assuming a constant ratio
between the anterior and posterior corneal radii (Gullstrand
ratio) to obtain the total corneal power and astigmatism.3,4
However, the posterior curvature and corneal thickness
also contribute to the total refractive power of the cornea.

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points on the anterior cornea. The IOL Master makes six The echoes received back into the probe from each of these
measurements at 3mm of the central cornea, and the Lenstar interfaces are converted by the biometer to spikes arising
performs 16 central corneal readings—eight at 1.7mm and from the baseline. The axial length is measured as the product
eight at 2.3 mm radius.7 There is no interoperator difference of the time taken by the sound to travel from one interface
in its measurement accuracy. The T-cone topography add to another at a given velocity. Other measurements obtained
on to Lenstar LS 900 provides placido topography with 11 are the anterior chamber depth (ACD), Lens thickness (LT),
placido rings on the central 6 mm of anterior corneal surface and vitreous chamber depth (VCD). Two types of A-scan
which evaluates keratometry measurements of the cornea ultrasound biometry currently in use are the Contact
through the position of 32 projected light reflections in 2.3 applanation Ultrasound and Immersion Ultrasound.
mm (outer) and 1.65 mm (inner) rings. For each measuring
point, the equivalent of an ideal sphere is calculated. Bench Contact Applanation Biometry
tests in addition to evaluation of real eye data showed that
K-readings calculated from the topography image and the This technique requires placing an ultrasound probe on the
Lenstar’s standard dual zone keratometry are equivalent. central cornea. Errors in measurement almost invariably
The newer version of IOL Master 700 uses telecentric result from the probe indenting the cornea and shallowing
keratometry at 18 points, with constant spot distance the anterior chamber. Since the compression error is
irrespective of device-to-eye distance, which makes it easier variable, it cannot be compensated for by a constant. IOL
to use and more precise. It also measures the anterior and power calculations using these measurements will lead to
posterior corneal power separately to generate the total an overestimation of the IOL power, which is amplified
keratometry (T K value), which translates accurately into the in shorter eyes. (Error due to 1mm corneal compression-
true corneal power.8 Average eye: 2.5D, Long eye: 1.75D, Short eye: 3.75D). The
patient must lie flat on a couch and fixate on their thumb
Corneal Topography is highly recommended in post- held directly above the eyeball. The eyelids are held apart
refractive surgery eyes, toric IOL, and patients with gently with a wire speculum. The probe should gently be
keratometry readings < 40 D or > 46D. The cornea is mapped brought in contact with the moist cornea.
in detail, giving the simulated keratometry (SimK) within
the central 3 mm optical zone. The topographic axis is Immersion A-scan biometry requires placing a saline-filled
more valuable than the topographic cylinder and becomes scleral shell (Ossoinig or Prager) between the probe and the
extremely useful when planning a toric intraocular lens.9 eye. Since the probe does not exert direct pressure on the
cornea, compression of the anterior chamber is avoided. A
Corneal Tomography includes the Oculus Pentacam, which mean shortening of 0.25–0.33mm has been reported between
images the anterior segment of the eye using a rotating applanation and immersion AL measurements, which can
Scheimpflug camera and provides a tomographic analysis translate into an error of IOL power by approximately 1 D. In
of the corneal front and back surfaces as well as the central general, immersion biometry is more accurate than contact
corneal thickness. It can generate a “True Net Power” applanation biometry in several studies.11
map of the cornea and measure the power of the post-
refractive-surgery cornea within ±0.55D at the central 4.5 Limitations of ultrasound methods include poor image
mm. The ‘‘Holladay EKR Detail Report’’ which generates resolution due to the use of a relatively long, low-resolution
the equivalent keratometry reading (EKR) was developed of 0.03 mm for a 10 MHz probe. The fovea is not located
to calculate the total corneal power specifically for patients accurately, and variations in retinal thickness surrounding the
who have undergone corneal refractive surgery. It takes fovea contribute to inconsistency in the final measurement.
measurements at 1-mm intervals in the central cornea from Incorrect assumptions regarding sound velocity can lead to
1 mm up to 7 mm. The 4.5-mm corneal zone, as the actual errors.
zone, is also measured. The Anterior segment OCT can also
be used to measure both the anterior and posterior corneal Tips for accurate measurement of axial length (using
power separately and generates the corneal power without applanation):
using the Gullstrand ratio.10 The ultrasound machine must be calibrated and set
for the correct velocity setting (e.g., cataract, aphakia,
Axial Length (Al) pseudophakia). The probe must be perpendicular, and the
echoes from the cornea, anterior lens, posterior lens, and
The AL is the most important factor in IOL calculation. A retina should produce good amplitude spikes. The retinal
1-mm error in AL measurement results in a refractive error of spike should be a sharp straight line with no humps or
approximately 2.5 D in an average eye. It can be measured by steps on its ascending edge. If the alignment of the A-scan is
Ultrasound methods or Optical biometry. It should be noted along the optic nerve instead of the fovea (recognized by an
that optical and acoustic ALs are not equivalent because absent scleral spike), the axial length will be underestimated.
the retinal pigment epithelium (RPE) is the endpoint of the Excessive indentation – corneal compression (indicated by
optical measurements, and the internal limiting membrane reduced ACD and AL but normal VCD) commonly causes
(ILM) is the endpoint of the ultrasonic measurements. errors. Average the 5–10 most consistent results giving the
lowest standard deviation (ideally < 0.06 mm).
Ultrasound methods: A parallel sound beam is emitted from
the probe tip at approximately 10 MHz, which echoes back Optical biometry is a highly accurate non-invasive
into the probe tip as the sound beam strikes each interface. automated method for measuring the anatomical details

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of the eye. In 1999, the first automated optical biometry the anterior surface (vertex) of the cornea to the effective
device became available for clinical use – IOL Master 500 principal plane of the lens in the visual axis.15
(Carl Zeiss Meditec, Jena, Germany). Because of its ease of
use, non-contact technique, accuracy, and reproducibility, The ELP needs to be estimated mathematically before the
optical biometry is now considered the current gold implantation of IOL, and a 0.25 mm change in ELP can alter
standard of IOL power calculation in clinical practice and is the IOL power by 0.5D. It is the only variable that cannot be
an indispensable tool for preoperative evaluation of cataract measured directly and has to be estimated using other eye
patients. However, ultrasound biometry may be helpful dimensions measured. This factor was historically referred
in media opacities like corneal leucoma, dense cataracts, to as the anterior chamber depth (ACD) because the optic of
or vitreous hemorrhage. The newer optical biometry all IOLs in the early era was positioned in front of the iris, in
devices provide several biometric measurements, namely the anterior chamber. This value is required for all formulae,
AL, keratometry (K), anterior chamber depth (ACD), lens and it is incorporated into the lens constant along with lens
thickness (LT), central corneal thickness (CCT), and pupil geometry, placement, and refractive index, which is different
size (PS), and white‑to‑white distance (WTW). The currently for different IOLs [Figure 2]. The A constant is specific to
available optical biometers are based on one of the following each IOL style is used for regression formulas, Surgeon
technologies: 12,13,14 factor (SF) in Holladay 1, personalized ACD in Hoffer Q,
a0,a1,a2 constants in Haigis, lens factor in Barett Universal 2,
(1) Partial coherence interferometry (PCI): and C constant in Olsen formula. The manufacturer supplies
Zeiss IOL master 500, Galilei G6, and Nidek AL scan the nominal lens constant based on its design and material,
(2) Optical low‑coherence reflectometry (OLCR): which the surgeon can refine for more accurate results.16,17
Haag Streit Lenstar LS900, Topcon Aladdin
(3) Swept‑source optical coherence tomography (SS‑OCT): The concept of personalization was first introduced by
Retzlaff using A constant to refine the formula with data from
Zeiss IOL master 700, Argos-Movu, OA-2000 by Tomey, a single user in ultrasound biometry. It is recommended that
Anterion by Heidelberg engineering each surgeon conducts at least 20-30 uneventful cases with
the specific IOL model of interest. The eyes should all contain
Anterior Chamber Depth And Effective Lens Position the same lens style by the same manufacturer implanted
And Lens Constants by the same surgeon. Eyes with postoperative surprises or
visual acuity worse than 6/12 should be excluded. Specific
When the human lens is replaced with an IOL, the optical IOL formula is selected and determine the starting point
situation becomes a two-lens system (cornea and IOL) of the associated lens constant. Post-op manifest refraction
projecting an image at the fovea. The distance between 6 weeks after surgery is noted. IOL formula can be
the two lenses (Effective Lens Position, or ELP) affects personalized by adding the mean error to the lens constant.
the refraction, as does the distance between the two-lens
system and the macula. ELP is defined as the distance from

Figure 2: Role of ELP and lens constant in IOL power calculation and how it varies with lens design [Adapted from Fig.2&3, Devgan U. Ocular surgery news 2012].

Table 1: Holladay concept of nine-types of eyes

Anterior segment size vs. Axial length

Large AS Megalocornea + axial hyperopia (0%) Megalocornea (2%) Large eye, Buphthalmos, Megalocornea + axial myopia (10%)

Normal AS Axial hyperopia (80%) Normal (96%) Axial myopia (90%)

Small AS Small eye nanophthalmos (20%) Microcornea (2%) Microcornea +axial myopia (0%)

Short AL Normal AL Long AL

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Table 2: List of formulae used in the present day along with the principle, variables, and lens constant used

IOL Formula Principle Preoperative Measurable Variable used for ELP Lens Constant

Holladay I Vergence Variables estimation Surgeon factor (SF)
SRK/T Vergence A-constant
Vergence AL, K AL, K pACD
Hoffer Q Vergence a0, a1, a2
Haigis Vergence AL, K AL, K ACD

Holladay II Vergence AL, K AL, K Lens factor (LF)
Vergence SRK/T ULIB A constant
Barett Universal II Ray Tracing AL,K,ACD Pre-op ACD, AL
EVO C-constant
Olsen AL, K, HWTW, Refraction K, Pre-op ACD, LT, age,
Okulix
(previous), ACD, LT, Age refraction
PhacoOptics
AL, K, ACD, WTW*, LT

AL, K, ACD, LT, WTW

AL, K, ACD, LT AL,K,Pre-op ACD,LT, age,
refraction

Hill RBF, Super Ladas, Artificial Intelligence (AI) AL, K, ACD, WTW*, LT* A-constant
Clarke neural network AL, K, ACD, LT, CCT

Kane

Intra-op aberrometry Modified refractive ASE, AL, K, WTW Specific surgeon factor
ORA SYSTEM vergence/AI

The personalized lens constant can then be generated by (II). Iol Formulae
the back-calculation method using the stable postoperative
manifest refraction and the preoperative measurements Various IOL calculation formulae have evolved through
(e.g., AL, K, ACD, HWTW, LT, etc.) with the selected several generations and are reclassified based on the method
formula. The personalization process can be repeated when or principle used19
more cases, including more anatomically non-average eyes,
are available, targeting a standard error of the mean of less 1. Theoretical
than ±0.25 D. Optimisation of IOL constants is made with 2. Regression
pooled data from many users in Zeiss IOL master, available 3. Vergence
in the User group for Laser Interference Biometry (ULIB) 4. Ray tracing and artificial intelligence
database.18 Manufacturer-recommended lens constants,
either calculated theoretically or optimized clinically with Theoretical formulae were based on mathematical and
the data from a group of surgeons, are a starting point for geometric principles revolving around the optics of the eye
individual surgeons. Lens Constant personalization is a using theoretical constants. They used a fixed power based
critically important step for each surgeon to further improve on the patient’s refraction and optics of the eye. Fyodorov
their patients’ refractive outcomes [Figure 3]. published the first IOL power formula in 1967.20

Regression formulae were of the 2nd generation and arrived
at by looking at the postoperative outcomes and working
backward using regression analysis to arrive at the desired
IOL power. Retzlaff, Sanders, and Kraff each developed a
regression formula based on an analysis of their previous
surgical cases. This work was amalgamated in 1980 to yield
the SRK I and II formula.21

Vergence formulae include third, and fourth-generation
formulae that incorporate both theoretical (geometric
optics) and regression formulae. They are used to accurately
estimate the effective lens position (ELP) and are further
subclassified by the number of biometry variables used to
predict this ELP. The two-variable formulas, such as the
Holladay 1, Hoffer Q, and SRK/T employ axial length and

Figure 3: Graph showing improvement in post-operative refractive outcomes •Formula •Modification
with optimisation of the lens constant. [Adapted from Fig.9, Olsen T. Acta •Holladay 1 •0.829XAL+4.27
•0.928XAL+1.56
Ophthalmol Scand. 2007;85:472-85]. •Haigis •0.854XAL+3.72
•SRK-T •0.853XAL+3.58
•Hoffer Q

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corneal curvature; the three-variable Haigis formula also crystalline lens. It is defined as a ratio of the distance between
uses anterior chamber depth, and the latest five variable the center of IOL (post-op) and the preoperative anterior
version Barrett universal 2 includes lens thickness and lens capsule to the preoperative crystalline lens thickness.
corneal diameter. 22,23,24 The Holladay 2 utilizes 7 variables C= (ACDpost + TIOL/2- ACDpre)/LTpre. The prediction
which include age and refraction.25 (Table 1) Holladay et al. of IOL position with the C-constant is used in Olsen’s ray
studied the variables correlation between AL and the size tracing-assisted IOL power calculation.3
of the anterior segment and determined the predictors of
ELP. Horizontal WTW measurements emerged as the next Artificial Intelligence-Based Formula
most important variable after AL and K. It was also proved
that there is almost no correlation in 80–90% of the eyes and The Hill RBF, Clarke neural network, Super Ladas, Kane
developed the concept of nine types of eyes–not just three formula use regression based on a huge database and AI-
(short, medium, or long).26 based complex statistical models whose accuracy may be
limited by the type of data.
These results led to the formulation of the Holladay 2 Hill‑RBF (radial basis activation function) is an advanced,
formula, an easy‑to‑use program in which 7 variables (AL, K, self-validating method for IOL power selection. It was
ACD, LT, WTW, age of the patient, and previous refraction) launched in 2016. It is purely “data-driven,” independent
are inserted for calculation of ELP and appropriate IOL of ELP, and has no data bias. RBF method uses artificial
power. The Barrett Suite is a combination of five formulas: intelligence-driven pattern recognition and sophisticated
i) Barrett Universal II for non-toric IOL calculation with data interpolation. RBF algorithms are used globally in a
Keratometry (K) values. ii) Barrett Toric for toric IOL variety of technologies such as facial recognition software
calculation with Keratometry (K) values. iii) Barrett True K and thumbprint security scanners.31 A special feature is that
for non-toric IOL calculation for post Laser Vision Correction it is the only IOL power calculation formula that provides
cases (LASIK, LASEK, PRK) and RK with Keratometry (K) the user the reliability of the result; that is, the software can
values. iv) Barrett TK Universal II for non-toric calculation tell whether the result is correct or whether it is incorrect
with Total Keratometry (TK) values. v) Barrett TK Toric for and outside the ability of the calculator. Hill-RBF has been
toric calculation with Total Keratometry (TK) values which optimized for biometry data from LenstarLS900 optical
is available online at apacrs.com and also incorporated in biometer and a particular IOL (Alcon SN60WF biconvex
the IOL master 700. Barrett RX formula is available online IOL). The latest version 3 has an expanded database for
to calculate the IOL power for piggyback lenses and IOL calculations in the range of +6 to +30D for biconvex IOLs and
exchange. from -5 to +5D for meniscus IOLs.
Most of the newer generation formulae give accurate results
The Kane formula is a combination formula that uses in average-sized eyes, but the results are varied in short and
theoretical optics with both regression and artificial long axial length eyes32 (Figure 4).
intelligence components to refine the predictions further. It
uses the AL, K, ACD, LT, central corneal thickness (CCT), Figure 4: Graph showing Prediction errors using various IOL calculation
and biological sex to make its predictions.27 formulas across different IOL powers [Adapted from Fig. 5, Melles RB et al.

The emmetropia verifying optical (EVO) formula is also Ophthalmology. 2018;125(2):169-178]
a newer, thick-lens, vergence-based formula that considers
the eye's optical dimensions and different IOL geometries. (III).Special Circumstances
It estimates ELP based on the fact that there is a specific
axial length and ELP to achieve emmetropia for specific 1. Long eyes
corneal power.28 In a retrospective study, the formula The presence of a posterior staphyloma can lead to difficulty
showed a lower prediction error compared to Holladay 1, in the identification of fovea, and a paraxial erroneously
Haigis, Hoffer Q, SRK/T, and the Hill-RBF 2.0 but was less longer axial length may be obtained with ultrasound
accurate than the Kane, Olsen, and Barrett formulas.27 The biometry. The addition of the A-scan measurement of
performance of the EVO suffered in the short and long axial
length eyes, indicating the emmetropization concept may
break down at the extremes of the axial lengths.

Ray tracing. Similar to the theoret¬ical versions above in
their dependence on ELP, methods like the Olsen formula
use individual rays that refract light on all surfaces of the
lens and cornea. It calculates the postoperative lens position
as a fraction of the crystalline lens thickness and the ACD.
This approach allows accurate calculation of the lens position
independent of the corneal status of the eye. It also takes
the corneal and IOL higher-order aberrations into account,
thus improving accuracy.29 The concept of the C-constant
was developed by Dr.Olson as a method to predict ELP
from the preoperative dimension and position of the natural

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DJO Vol. 32, No. 4, April-June 2022

anterior chamber depth and lens thickness to the B-scan power. A small or decentered optical zone of treatment is
measurement of vitreous depth may give a more accurate more likely to induce this type of error when compared to a
measurement of the axial length. This is overcome by the large 6 mm treatment zone. The normal relationship between
use of a fixation target in optical biometers if the patient’s the anterior and posterior cornea is lost as the anterior
vision is fairly good and more accurate with IOL master 700, corneal radius alone is flattened. This alters the Gullstrand
which directly visualizes the fovea on OCT image during ratio and leads to errors in corneal power estimation
measurement. Optimizing the A-constant shifts the power when the anterior corneal power alone is measured. The
prediction curve and optimizes the formula to operate well standard methods of measuring corneal power cause the
over a wide range of axial lengths. The third-generation power to be underestimated in myopia and overestimated
formulas overestimated the axial length leading to hyperopic in hyperopia. Tomographic devices that measure central K
refractive surprise. Wang Koch suggested modification of anterior and posterior surface powers are more accurate, like
the AXL to offset this error as follows.33 the Pentacam, Lenstar, or IOL master 700 and Galilei G6.36
SRK/T uses K reading to alter ELP. Due to myopic Lasik,
Newer formulae like Kane, Olsen, Barrett Universal 2, and the formula will erroneously assume a shorter ACD and an
Hill RBF can be used without any modification giving more anterior ELP in eyes with a flat cornea. The resultant IOL
accurate values in longer eyes. The percentage of eyes within will be underpowered for that eye and result in a hyperopic
a prediction error of ±0.5D using the top-performing formula postoperative error. To avoid the ELP-related IOL prediction
ranged from 57 to 86.5%.27 The surgeon can aim for residual error, Aramberri proposed the double K method, where the
myopic refraction to avoid a hyperopic refractive surprise. pre-refractive surgery corneal power is used to estimate the
Also, myopic patients are accustomed to using near vision, ELP and the post-refractive surgery corneal power is used
and if they are corrected to Plano, their ability to see near to calculate the IOL power. Formulas that do not use K to
objects will be lost. alter ELP like Haigis-L or Shammas do a better calculation.
Haigis L uses measured ACD for post Lasik eyes and can
2. Short eyes give 70% of eyes within 0.5D. When only the anterior corneal
Short eyes requiring higher dioptric IOLs tend to have higher measurement is known, the Barrett’s True K formula gives
prediction errors compared to long eyes ranging from 43- good results as it utilizes a predicted corneal power using a
83.2% for ±0.5D.27 Optical biometry with advanced formulae theoretical model known as the predicted posterior corneal
like Kane, Olsen, Haigis, Holladay, 2 Barett universal II, astigmatism (PCA) method.37
or Hill RBF is preferred over ultrasound biometry as the
estimation of ELP is more accurate in these. Many surgeons Online calculators
prefer Hoffer Q for IOL power estimation in short axial
length eyes. It is preferable to use multiple formulas to obtain The Iolcalc.ascrs.org has the post-refractive surgery IOL
concordance in the readings and also explain the risk of a calculator. This was the gold standard until recently. The
refractive myopic surprise post-operatively. Piggyback IOLs calculator accepts pre-refractive surgery data and post-
may be better than large powered single IOL in reducing the refractive surgery data from various sources. Multiple
spherical aberration.34 formulas, including Shammas PL or Barrett True K formula,
give a suggested set of IOL powers. If the calculations do
3. Post-refractive surgery eyes not agree, extreme values are disregarded, and the median
A pre-operative topography to assess the extent, depth, value is selected. In post-refractive surgery eyes requiring
regularity, and centration of the ablation, along with a careful a toric IOL, intra-operative aberrometry helps the surgeon
fundus exam with a +90D lens, indirect ophthalmoscopy, confirm IOL powers by neutralizing refractive astigmatism
and OCT of the macula to assess its structure and possible with high accuracy.38,39 Other clinical pearls include aiming
function is needed. Eyes that have undergone refractive for residual myopia, operating on the non-dominant eye
surgery will have to be evaluated for dry eyes, epithelial first, and refining the dominant eye's calculation based on
basement membrane dystrophy (EBMD) changes, irregular the outcome. Avoid using multifocal IOL as it can exaggerate
and decentered ablation, and irregular and thickened corneal the optical aberrations in post-refractive surgery eyes.
epithelium.35
4. Post silicone oil-filled globe
Post Radial keratotomy Gain must be increased to visualize the echospikes. The
average sound velocity used for routine axial length
The Gullstrand ratio is not altered as both the anterior and measurement is 1550 m/sec, while the sound velocities in
silicone oil-filled eyes are 980 m/sec (low viscosity-1300 cSt)
posterior corneal radii are flattened. Eyes with fewer cuts and 1040 m/sec (high viscosity-5000 cSt).

and a larger optical zone can be treated like a regular eyes If one uses the typical default velocity setting in the A-scan
machine, the axial length obtained will be erroneously long,
with predictable results. With multiple cuts, the cornea's and IOL power is underestimated by 2-3 D. In the velocity
conversion method, the true AL may be calculated by
structural integrity is lost, leading to a progressive anterior determining the ACD, LT, and corrected VCD separately.
Corrected VCD = velocity of silicone oil/ velocity in vitreous
corneal flattening and hyperopic drift. It is better to aim for X calculated vitreous length. A conversion factor of 0.71

postoperative -0.75 to -1.00 D myopia to compensate for

this.24 Post-PRK, LASIK, and SMILE

The major cause of the error is the fact that most keratometers

measure at the paracentral 3 mm zone of the cornea, which

often misses the central flatter ablated zone of effective corneal

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DJO Vol. 32, No. 4, April-June 2022

corrects the apparent increase in AL induced by silicone oil References
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3. Olsen T. Calculation of intraocular lens power: a review. Acta
5. Aphakic and pseudophakic eyes Ophthalmol Scand. 2007;85:472-85.
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The pseudophakic mode is selected in the biometers, in 6. Garg A. Mastering the techniques of intraocular lens power
which the calculation compensates for the change in velocity calculations. 2nd edition, Jaypee:2009.
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The intraoperative wavefront aberrometry can be used 8. Sharma, Ajay; Batra, Akanksha, Assessment of precision of
to measure and analyze the refractive power of the eye. astigmatism measurements taken by a swept-source optical
The ORA (optiwave refractive analysis) SYSTEM by coherence tomography biometer - IOLMaster 700, Indian Journal
Alcon captures a total ocular refraction measurement that of Ophthalmology.2021;69:1760-5.
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as well as post-myopic PRK/LASIK and long and short lens selection in cataract surgery. Curr Opin Ophthalmol.
eye measurements to provide guidance for adjustments of 2018;29:323-27.
lens selection and placement for all eye types and refine the
toric IOL axis.41 The ORA Analyz OR database can identify 10. Omoto MK, Torii H, Masui S, Ayaki M, Tsubota K, Negishi K.
outliers mid-procedure to help surgeons hit refractive targets Ocular biometry and refractive outcomes using two swept-
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it verifies IOL power constants against manufacturer segmental or equivalent refractive indices. Sci Rep. 2019;9:6557.
recommendations with global outcomes data to calculate
optimized global and surgeon-specific lens constants. 11. Ademola-Popoola DS, Nzeh DA, Saka SE, Olokoba LB,
Obajolowo TS. Comparison of ocular biometry measurements
Frontiers to be conquered include achieving greater accuracy by applanation and immersion A-scan techniques. J Curr
in measuring total corneal power and ELP prediction, Ophthalmol. 2016;27:110-114.
adopting a true optical path length, and availability of IOLs
in smaller dioptric increments (e.g., 0.25 D) to facilitate more 12. Nazm N, Chakrabarti A. Update on optical biometry and
precise targeting. intraocular lens power calculation. TNOA J Ophthalmic Sci
Res2017;55:196‑210.
Conclusion
13. Savini G, Taroni L, Hoffer KJ. Recent developments in intraocular
The accuracy of IOL biometry can be improved by lens power calculation methods-update 2020. Ann Transl Med.
implementing a single calibrated biometer, repeating and 2020;8:1553.
verifying measurements by a second instrument or formula
when necessary, using the IOL Master or immersion biometry 14. Devgan U. Refining the A-constant yields more accurate
rather than a contact applanation technique, using one of the refractive results after cataract surgery. Ocular surgery news.
newer IOL power calculation formulas, and personalizing Aug 2012.
the lens constants for each formula, tracking the refractive
outcomes, and optimizing the surgical technique by making 15. Gatinel D, Debellemanière G, Saad A, Dubois M, Rampat R.
the capsulorhexis round, centered and overlapping the Determining the Theoretical Effective Lens Position of Thick
lens optic edge can all help to optimize the postoperative Intraocular Lenses for Machine Learning-Based IOL Power
outcomes. Understanding the advantages and limitations of Calculation and Simulation. Transl Vis Sci Technol. 2021;10:27.
the current technology and following these guidelines makes
it possible to consistently achieve highly accurate results. 16. J. T. Holladay. Standardizing constants for ultrasonic biometry,
keratometry, and intraocular lens power calculations. J Cataract
Refract Surg, vol. 23, pp. 1356-1370, 1997.

17. Langenbucher A, Szentmáry N, Cayless A, Müller M, Eppig
T, Schröder S, Fabian E. IOL Formula Constants: Strategies
for Optimization and Defining Standards for Presenting Data.
Ophthalmic Res. 2021;64:1055-1067.

18. ULIB, “User Group for Laser Interference Biometry,” [Online].
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2022].

19. Wang L, Koch DD, Hill W, Abulafia A. Pursuing perfection in
intraocular lens calculations: III. Criteria for analyzing outcomes.
J Cataract Refract Surg. 2017;43:999-1002.

20. Fyodorov SN, Kolinko Al. Estimation of optical power of
intraocular lens. Vesin Oftalmnol 1967; 80: 27-31.

21. Menezo JL, Chaques V, Harto M. The SRK regression formula
in calculating the dioptric power of intraocular lenses. Br J
Ophthalmol. 1984;68:235-7.

22. K. J. Hoffer. The Hoffer Q formula: A comparison of theoretic
and regression formulas. J Cataract Refract Surg, vol. 19, pp. 700-
712, 1993.

23. J. T. Holladay, “International Intraocular lens & Implant Registry
2003,” J Cataract Refract Surg, vol. 29, pp. 176-197, 2003.

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24. W. Hill, “doctor-hill.com”.Available: https://doctor-hill.com/iol- 27 04 2019].
power-calculations/. [Accessed 27 04 2022]. 39. W. Hill, “doctor-hill.com,” [Online]. Available: https://www.

25. G. D. Barrett. An improved universal theoretical formula for doctor-hill.com/physicians/docs/Haigis-instructions.pdf.
intraocular lens power prediction. J Cataract Refract Surg, vol. [Accessed 04 2019].
19, pp. 713-720, 1993. 40. Murray DC, Potamitis T, Good P, Kirkby GR, Benson MT.
Biometry of the silicone oil-filled eye. Eye (Lond). 1999;13:31924.
26. Holladay JT, Gills JP, Leidlein J, Cherchio M. Achieving 41. Spekreijse LS, Bauer NJC, van den Biggelaar FJHM, Simons RWP,
emmetropia in extremely short eyes with two piggyback posterior Veldhuizen CA, Berendschot TTJM, Nuijts RMMA. Predictive
chamber intraocular lenses. Ophthalmology 1996;103:1118-23. accuracy of the Optiwave Refractive Analysis intraoperative
aberrometry device for a new monofocal IOL. J Cataract Refract
27. Kane JX, Chang DF. Intraocular Lens Power Formulas, Biometry, Surg. 2021;48:542–8.
and Intraoperative Aberrometry: A Review. Ophthalmology.
2021;128:94-114. Cite This Article as: Nirupama Kasturi, Arup Chakrabarti.
Demystifying Intraocular Lens Power Calculation. Delhi
28. Chung J, Bu JJ, Afshari NA. Advancements in intraocular Journal of Ophthalmology.2022; Vol 32, No (4): 69- 76.
lens power calculation formulas. Curr Opin Ophthalmol.
2022;33:3540. Acknowledgments: Nil

29. Melles RB, Kane JX, Olsen T, Chang WJ. Update on Intraocular Conflict of interest: None declared
Lens Calculation Formulas. Ophthalmology. 2019;126:1334-
1335. Source of Funding: None

30. T. Olsen and P. Hoffmann, “C constant: New concept for ray Date of Submission: 02 May 2022
tracing-assisted intraocular lens power calculation,” J Cataract Date of Acceptance: 13 May 2022
Refract Surg, vol. 40, pp. 764-773, 2014.
Address for correspondence
31. Hill-RBF Calculator Version 2.0,” [Online]. Available: https://
rbfcalculator.com/lens-constants.html. [Accessed 29 04 2019]. Nirupama Kasturi, MS

32. Chung J, Bu JJ, Afshari NA. Advancements in intraocular lens Additional Professor & Head - Ophthalmology
power calculation formulas. Curr Opin Ophthalmol. 2022 Jan
1;33(1):35-40. Department of Ophthalmology,
Jawaharlal Institute of Postgraduate
33. Wang L, Koch DD. Modified axial length adjustment formulas in Medical Education & Research
long eyes. J Cataract Refract Surg. 2018;44:1396-1397. (JIPMER) Pondicherry,
Tamil Nadu, India.
34. Hoffman RS, Vasavada AR, Allen QB, Snyder ME, Devgan U, Email : [email protected]
Braga-Mele R, et al. Cataract surgery in the small eye. J Cataract
Refract Surg 2015;41:2565-75.

35. Piggyback IOL Intraocular Lens Power Calculations Primary
Polypseudophakia Eye Cataract Surgery Eyes; doctor-hill.com

36. Li Wang, MD, Ph.D., Warren E. Hill, MD, Douglas D. Koch, MD
Evaluation of intraocular lens power prediction methods using
the American Society of Cataract and Refractive Surgeons Post-
Keratorefractive Intraocular Lens Power Calculator; J Cataract
Refract Surg 2010; 36:1466–1473

37. Maya C. Shammas, H. John Shammas Post-LASIK IOL Power
Calculations: Where Are We in 2012: Curr Ophthalmol Rep
(2013) 1:39–44

38. J. T. Holladay, “Holladay IOL Consultant Software & Surgical
Outcome Assessment_The optics we all need to know,” [Online].
Available: http:// www.hicsoap.com/handouts.php. [Accessed

E-ISSN: 2454-2784  P-ISSN: 0972-0200 76 Quick Response Code
Delhi Journal of Ophthalmology

DJO Vol. 32, No. 4, April-June 2022

Abstract Theme section

Classification of Intraocular Lenses

Vaibhav Nagpal

Guru Nanak Eye Centre, Maulana Azad Medical college & assoc. Hospitals New Delhi, India.
This article aims at providing a synopsis of intraocular lenses which are being used in the present practice. The types
have been classified based on structure, sites of fixation, optic and haptic material, Focality and also asphericity. The
article also emphasizes the IOLs which have special functions and are used in uncommon situations. Future designs and
newer concepts are being introduced every year owing to the advancements in our field.

Delhi J Ophthalmol 2022; 32; 77-82; Doi http://dx.doi.org/10.7869/djo.775
Keywords: Intraocular Lenses, PMMA, Anterior Chamber IOL, Posterior Chamber IOL.

Introduction A special mention about the most important change in the
newer anterior chamber IOLs which significantly reduced
The history of replacing the cataractous lens with an the complications with older designs was the change in the
intraocular lens to eliminate the “first complication of cataract haptic design. The haptic of the Multiflex was distinctive in
surgery” i.e., Aphakia dates back to Casanova(1750s).1-3 its structure that it allowed flexion in the same plane as the
haptics avoiding anterior movement of the optic.
The first successful IOL implantation was done by Sir
Harold Ridley on November 29, 1949. The Inspiration stems Classification Of Types Of Intraocular Lenses
from a simple question by a medical student about replacing
the lens after removal. Sir Harold Ridley’s sharp observation 1) Types based on IOL construction
helped him choose the inert material when he noticed no • Single piece design: The whole lens has been
deleterious effects from stationary particles of PMMA in the constructed from the same material (Figure 1).
eyes of Royal Air Force pilots who sustained injuries from • Multi-piece design: The haptics and the optic are made
shattered spitfire during World War.2 up of different materials.

IOLs were invented to treat the refractive error following Optics Edges
cataract surgery. However, they are now being used to
provide the patient with additional features and better • Round-edged IOLs
visual quality. In this article, an overview of the types of • Square-edged IOLs
Various studies have shown that a square posterior optic
intraocular lenses is provided. edge is associated with better results in preventing posterior
capsule opacification (PCO). It can be attributed to many
Evolution of Intraocular Lenses mechanisms

Following generations4 of IOLs have been invented since 1) Mechanically preventing migration (Figure 2)
then and the development is still going on. 2) Contact inhibition of migrating lens epithelial
3) Higher pressure over posterior capsule with square edge
Generation 1: Sir Ridley posterior chamber IOL
Generation 2: Early anterior chamber lens Maximal prevention of PCO can be achieved when the
Generation 3: Iris-supported lenses square edge is present for the whole circumference of the
Generation 4: Modern anterior chamber IOLs optic. Single piece designs in which the junction has an even
Generation 5: Rigid posterior chamber lenses transition the square edge effect is lost and may lead to the
Generation 6: Foldable IOLs starting of PCO.5
Generation 7: Multifocal IOLs
Generation 8: Accommodative IOLS

Not only the posterior edge but the design of the sidewall

of the optic edge is important. Unpolished or “textured”

sidewalls had lower rates of glare compared to the smooth

ones.5 Optic-haptic junction

Angulation between the optic and the haptic is responsible

for the stability of the IOL and also to prevent complications.

Posterior angulation increases the contact between the lens

and capsule hence preventing PCO formation. When an

IOL is placed in the ciliary sulcus this angulation provides

sufficient space between the lens and iris preventing

rubbing.5

Figure 1: Alcon AcrySof Multi-piece (left) Single piece (right) A. Single piece IOL with 0° angle: Smooth transition at
junction and PCO can start at these junctions.

B. Single piece with step-vaulted design: The haptic is
shifted anteriorly from the plane of the optic which

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DJO Vol. 32, No. 4, April-June 2022

Figure 2: Square edge blocking the migration of lens epithelial cells(left) compared to the round edge(right) Image courtesy: Findl, Oliver.
“Intraocular Lens Materials and Design.”

allows the optic to have a 360° square edge and hence and have fewer complications and are cosmetically more
prevents PCO formation. accepted.
C. 3-piece lenses: Angulation of up to 10° provides sufficient
pupillary clearance and adhesion to the posterior • Posterior Chamber
capsule.5
Capsular bag: Ideal site of fixation for posterior chamber
2) Types based on site of Fixation IOLs. Prevents PCO formation, tilting, decentration and
IOLs can be placed in the anterior or posterior chamber uveal tissue rubbing. Minimal magnification and safer in
depending upon the status of the capsular bag. children and young adults.
• Anterior Chamber
Ciliary sulcus: IOL is placed in this position when the
Angle: These IOLs are placed in an eye which has a healthy integrity of the posterior capsule is compromised but the
iris and adequately deep chamber but lacks an intact capsule. residual capsular support is enough to support the lens. To
The most widely used ACIOL is the Kelman Multiflex prevent uveitis-glaucoma-hyphema syndrome angulated
design (Figure 3). This newer design is better in terms of IOLs preferably a 3-piece IOL with sufficient iris clearance
fewer chances of complications like secondary glaucoma, should be used. A posterior optic capture can also be
pseudophakic bullous keratopathy, and cystoid macular performed if a central and adequately sized rhexis is present
oedema compared to older designs. The size of the lens is which ensures centration and avoids rubbing over the iris.5
selected by adding 1mm to the white-to-white distance.5
Iris: Rigid one-piece PMMA lenses. These are fixated on the
iris stroma with claws. An example is the Artisan aphakic
lens (Ophtec, Netherlands)(Figure 4). Iris enclavation is
done with the help of a special instrument.

Figure 4: Artisan iris-claw ACIOL (Image by Ophtec BV)

Figure 3: Schematic of the Kelman Multiflex III ACIOL (Image by Alcon 3) Types based on IOL Material
Laboratories,Inc.)
Optic material
There are two types:
Pre-pupillary iris-claw lenses: These IOLs are associated 1) Rigid IOLs
with more corneal complications and are less commonly Since the Ridley era, PMMA is the commonest material used
used for the manufacturing of IOLs. It is rigid, chemically inert
Retro-pupillary iris-claw lenses: Fixated behind the iris and has a higher refractive index (1.49) which helps to make
thinner and lighter lenses. The material has excellent optical
properties and laser resistance. Since it’s a rigid lens larger
incisions are required.6

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DJO Vol. 32, No. 4, April-June 2022

2) Foldable IOLs Following are the FDA approved aspheric IOLs:
a. Silicone IOLs • TechnisZ9000 (Advanced Medical Optics)
The material is hydrophobic. It has a lower refractive index Negative SA value of 0.27 um with an anterior prolate surface
and thus the IOLs are thicker. These IOLs are difficult to • AcrySof IQ
handle with poor control during implantation. The risk of Negative SA value of 0.20 um with a posterior prolate surface
silicone oil adhesion is high6. However, the chance of PCO • Sofport AO
formation is low. SA value of zero which does not contribute to any pre-
existing HOA and has both anterior and posterior prolate
b. Hydrogel IOLSs surface
The material swells in water. Made up of polyhydroxyethl 5) Premium IOLs
methacrylate and has a water content of about 18%. A. Multifocal IOLs
The optics of multifocal IOLs are designed to focus on
c. Acrylic IOLs distance as well as near. The technology works on the brain’s
i. Hydrophilic ability to select the clearest image presented to it.
It is a mixture of hydroxyethylmethacrylate and a There are two types:
hydrophilic acrylic monomer. 18-26% water content with a
contact angle of lower than 50°. Easy handling but the risk of Refractive optics multifocal IOLs
PCO formation is higher.
The refractive IOLs have annular zones of different powers
ii. Hydrophobic which provide the focus for far and near. They provide a
Copolymers of acrylate and methacrylate. Minimal water better intermediate and distant vision while the near vision
absorption and contact angle of >70° with a higher refractive may not be sufficient. These IOLs are pupil-dependent,
index of 1.44-1.556 ensuring thinner IOLs. It has good sensitive to minimal decentration, intolerant to change in
resistance to YAG laser and has significantly lower chances angle kappa, higher rates of glare and halos and also provide
of PCO formation compared to other IOL materials low contrast sensitivity.9
Refractive IOLs are available in two styles:
3) Rollable IOLs
1) Two-zone lenses: Central near vision segment and
IOLs are implanted in Microincision Cataract surgery peripheral distance vision segment

(MICS) through a ≤ 2mm incision. The term ‘Phaconit’ means 2) Annulus type: Central distant vision surrounded by
near vision, surrounded by distant vision ring (Figure
phacoemulsification (phaco) with a needle (N) opening via 5).

an incision (I) and with the phaco tip (T). This concept of Examples:
• Array multifocal IOL (AMO)
surgery through 0.9mm incision was publicised by Dr Amar • ReZoom multifocal IOL (AMO)
• PREZIOL (Care Group)
Agarwal.7
Diffractive optics multifocal IOLs
Examples:
These lenses are based on the principle of diffraction which
• Acri.Smart™ lens states that each point of a wavefront can function as its source
of secondary wavelets9, When diffractive microstructures
• Ultrachoice 1.0 rollable thin lens are placed in concentric zones with decreasing distance
as they move towards the centre, a Fresnel zone plate is
• Slimflex lens Haptic material5
Figure 5: Annulus refractive IOL (Image from Lane, Stephen, Mike Morris, Lee
Materials which are being used for the production of the T. Nordan, Mark Packer, Nicholas Tarantino and R. Bruce Wallace. “Multifocal

haptics of 3-piece lenses are: intraocular lenses.” Ophthalmology clinics of North America 19 1 (2006))

a. PMMA
b. Polypropylene (Prolene)
c. Polyamide
d. Polyvinylidene fluoride (PVDF)
e. Polyethersulfone (PES)

4) ASPHERIC IOLs8
Spherical aberration (SA) is one of the higher-order
aberrations (HOA), however, it affects the quality of the
vision the most. When the peripheral rays of light focus in
front of the central rays, it is called positive SA and if behind
the central rays, it is negative SA. The normal SA value of
the cornea is positive which does not change much with the
ageing process. The SA value of the young crystalline lens
is negative which balances the corneal spherical aberration.

With the ageing process, there is a shift of negative SA value
in the crystalline lens to positive. When we implant an IOL
with positive SA the total SA increases which decrease the
contrast sensitivity8.With the advances in technology, there
is the availability of Aspheric IOLs which balance the SA of
the cornea and give better optical quality, especially in low
light and low contrast situations.

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DJO Vol. 32, No. 4, April-June 2022

produced which can produce optic foci (Figure 6).9 chromatic aberration
The IOLs have an aspheric anterior surface and posterior
Diffractive IOLs lose 18% of light and divide the remaining achromatic diffractive surface. Example:
light into two foci, 41% for distance and 41% for near. These
IOLs provide excellent distance and near vision but an • TECNIS Symfony (AMO)(Figure 8)
acceptable intermediate vision. • AcrySof IQ Vivity
Apodization solves the problem of poor intermediate vision EDOF lenses improve the distance, intermediate and near
to some extent. The apodised IOLs have a gradual decrease vision. EDOF lenses also preserve contrast sensitivity10.
in diffractive step from centre to periphery that creates a EDOF lenses provide excellent distance and intermediate
smooth transition of light between the focal points which vision but are less efficient for near vision when compared
increases the quality of intermediate vision. to Trifocals.

Example: iDIFF plus and AcriDIFF

Figure 6: Diffractive IOL principle (Image from Voskresenskaya A, Pozdeyeva Figure 8: Tecnis Symfony IOL
N, Pashtaev N, Batkov Y, Treushnicov V, Cherednik V. Initial results of trifocal
diffractive IOL implantation. Graefes Arch Clin Exp Ophthalmol. 2010 B. Accommodative IOLS
Accommodative IOLs have been developed based on
Sep;248(9):1299-306) Helmholtz's theory of accommodation. The theory states
that with contraction of ciliary muscle there is zonular
Diffractive IOLs are less pupil-dependent and can tolerate laxity which allows the lens to increase its anteroposterior
angle kappa and decentration. These IOLs have more chances diameter hence increasing the dioptric power.
of producing glares and halos and the main disadvantage is
the loss of light due to scattering. The following approaches are being used to restore
Examples: accommodation:
A. Change in axial position
• Tecnis Multifocal IOLs (AMO) a. Single optic
• Acrysof IQ ReSTOR (Alcon) The basic mechanism behind these IOLs is the forward
• Panoptix (Alcon)(Figure 7) movement of the optic and variation of radius of curvature
of the anterior surface.11
Extended Depth of Focus (EDOF) IOLs Example:

EDOF lenses create a single elongated focal point to enhance i. Crystalens HD (B&L) (Figure 9)
the depth of focus. Two technologies are used:
1) Diffractive optical design
2) Achromatic technology reduces the eye’s natural

Figure 7: Panoptix IOL (Image from Kohnen T. First implantation of a Figure 9: Crystalens IOL (Image from Alió JL, Plaza-Puche AB, Montalban R,
diffractive quadrafocal (trifocal) intraocular lens. J Cataract Refract Surg. 2015 Javaloy J. Visual outcomes with a single-optic accommodating intraocular lens
and a low-addition-power rotational asymmetric multifocal intraocular lens. J
Oct;41(10):2330-2)
Cataract Refract Surg. 2012 )

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DJO Vol. 32, No. 4, April-June 2022

ii. Tetraflex Multifocal toric Multifocal toric
iii. 1CU AcrySof Toric IOL AcrySof IQ ReSTOR
b. Dual Optic Hoya iSert Toric 351 Tecnis Symfony Toric
The anterior component has a high plus power and the
posterior component has a minus power to make the eye Staar Toric IOL EnVista toric IOL
emmetropic. Two components are connected by a bridge AMO Tecnis Toric IOL
with spring action11. The IOL is not available commercially.
Example: Synchrony (Visiogen Inc.)(Figure 10). rotate off-axis. When AcrySof toric rotates by 3°, 10% of
the correction effect is reduced. The full effect is lost when
Figure 10: Synchrony IOL (Image from Dick HB. Accommodative intraocular IOL rotates by 30°.
lenses: current status. Curr Opin Ophthalmol. 2005 Feb;16(1):8-26
6) Special function IOLs
B. Change in shape or curvature
a. FluidVision13 A) Aniridia IOLs
The Haptic and interior of the optic are filled with silicone Aniridia is the absence of iris tissue. It can be congenital or
oil. It is designed in such a way that while accommodating traumatic. Associated cataract and weak zonules are present
the silicone oil migrates from the haptic into the optic and in 50-85% of patients with congenital aniridia. Aniridia IOLs
the anteroposterior diameter of the optic increases which are available for scleral fixation, ciliary sulcus placement and
increases the dioptric power. also endocapsular insertion in patients who have a normal
b. NuLens12 capsule.
PMMA haptics and PMMA reference plane with a small
chamber that contains solid silicone oil with a posterior The lens has a central clear zone which corrects the refractive
piston. When the piston is pressed the silicone gel bulges. error and a peripheral opaque zone which reduces the entry
The IOL is not available commercially. of light and acts as an iris diaphragm. This diaphragm
C. Change in refractive index or power reduces glare and photophobia which is troublesome to
a. Lumina patients with aniridia.15
The IOL has two optical elements and both have a U-shaped
elastic loop with a spring action which is connected to the B) Implantable miniature telescope IOLs
optic via a non-elastic element. When the ciliary muscle » Implanted in the posterior chamber
contracts the optics move in the opposite direction and the » Developed by VisionCare Ophthalmic Technologies
optical power of the lens increases.
C. Toric IOLS (California)
Toric IOLs are astigmatism correcting IOLs and are indicated » Microlenses magnify objects in the central visual field
in patients with ≥ 1.0D of regular astigmatism. Standard toric » Indicated in patients with Age-related macular
lenses are available in cylinder powers of 1.5D to 6D.14 They
are available as monofocal and multifocal lenses. degeneration
» For the calculation of IOL power, standard websites of
C) Piggyback IOLs
various companies are available. In patients with nonophthalmic eyes, IOLs with very high
» Preoperative marking of the axis, central rhexis and powers are required which is not possible in a single IOL due
to the thickness and reduced image quality due to spherical
thorough removal of OVD is very essential. aberration. To combat this issue the concept of piggyback
» The correction effect of toric IOLs decreases when they IOL was introduced.

One IOL is placed in the capsular bag and the second IOL is
placed in the ciliary sulcus. Complications:

• Interlenticular opacification
• Unpredictable IOL position

Other special IOLs are Smart yellow IOLs and Blue blocking
IOLs.

7) Phakic IOLs
In patients with high ametropia, the corneal refractive
surgery has reduced safety, predictability and efficacy.
Phakic IOLs provide us with predictable results and superior
visual outcome and also preserves the cornea.

Phakic IOLs are indicated in moderate to high myopia, high
hypermetropia and high astigmatism16. Three varieties of
Phakic IOLs are available based on the site of fixation:

I. Angle supported lenses
•AcrySof Cachet – single-piece foldable, soft hydrophobic
acrylic phakic IOL.
•Kelman duet – The duet consists of a separate PMMA

E-ISSN: 2454-2784  P-ISSN: 0972-0200 81 Delhi Journal of Ophthalmology

DJO Vol. 32, No. 4, April-June 2022

tripod haptic which is implanted first and the foldable optic 7) Agarwal A, Agarwal S. Rollable IOL enhances cataract surgery
is inserted after that which is fixed to the haptic with the help through 0.9mm incision. Ocular Surgery News Europe Asia
of a Sinskey hook. Pacific Edition. Jan 02, 2002
These lenses have a higher risk of pupillary ovalisation,
endothelial cell loss and elevation of IOP. 8) Khanna A, Dhiman R, Khanna R, Rathore YR, Arun SRole
of Asphericity in Choice of IOLs for Cataract Surgery.DJO
II. Iris-fixated lenses 2015;25:185-189
• Artisan iris-claw (Ophtec)
• Verisyse (AMO) 9) Alio JL, Plaza-Puche AB, Férnandez-Buenaga R, Pikkel J,
The lens is fixated on the mid-peripheral iris which renders Maldonado M. Multifocal intraocular lenses: An overview. Surv
it immobile during pupillary movements. Ophthalmol. 2017 Sep-Oct;62(5):611-634
It is associated with pigment dispersion, endothelial
loss, glaucoma, iris atrophy, dislocation and also cataract 10) Nivean M, Nivean PD, Reddy JK, Ramamoorthy K, Madhivanan
formation. N, Rajan M, Sengupta S. Performance of a New-Generation
Extended Depth of Focus Intraocular Lens-A Prospective
III. Posterior chamber lenses Comparative Study. Asia Pac J Ophthalmol (Phila). 2019 Jul-
• PRL (IOLTech/CIBA Vision) Aug;8(4):285-289
• ICL (Implantable collamer lens- STAAR Surgical Co.)
These are associated with lower rates of complications with 11) Sheppard AL, Bashir A, Wolffsohn JS, Davies LN.
excellent visual outcomes. Accommodating intraocular lenses: a review of design
concepts, usage and assessment methods. Clin Exp Optom. 2010
8) Future IOL designs Nov;93(6):441-52.
A. Injectable gel IOLs
Femtosecond assisted cataract surgery allows us to remove 12) Alió JL, Ben-nun J, Rodríguez-Prats JL, Plaza AB. Visual and
the cataract through a small incision and allows us to inject accommodative outcomes 1 year after implantation of an
the IOL in the gel form. This research began in 1986 at accommodating intraocular lens based on a new concept. J
the Bascom Palmer Eye Institute. The technology has the Cataract Refract Surg. 2009;35(10):1671–1678.
possibility of restoring accommodation.
13) Kohl JC, Werner L, Ford JR, Cole SC, Vasavada SA, Gardiner
B. Light adjusted IOLs GL, Noristani R, Mamalis N. Long-term uveal and capsular
A Noble-prize-winning technology allows us to change the biocompatibility of a new accommodating intraocular lens. J
refractive power of the lens after implantation. The lens Cataract Refract Surg. 2014;40(12):2113–2119.
has been developed by Roy freeman of RxSight. The IOL
is made up of special macromers. When these macromers 14) Khan MI, Ch’ng SW, Muhtaseb M. The use of toric intraocular
are exposed to the light of a specific wavelength they get lens to correct astigmatism at the time of cataract surgery. Oman
photopolymerised. J Ophthalmol. 2015;8:38–43

Myopia, Hypermetropia and even astigmatism can be 15) Weissbart SB, Ayres BD. Management of aniridia and iris defects:
treated with these lenses. An update on iris prosthesis options. Curr Opin Ophthalmol.
Once the adjustment is done the entire lens is irradiated to 2016;27:244–249
polymerize and fix the remaining macromers.
16) Guell, J.L., et al., Five-year follow-up of 399 phakic Artisan-
C. Intraocular pressure sensor implanted with IOL Verisyse implantation for myopia, hyperopia, and/or
High-tech innovation which is implanted during cataract astigmatism. Ophthalmology, 2008. 115(6): p. 1002-12.
surgery. It is a microelectronic sensor that measures
intraocular pressure.17 17) Dick HB, Gerste RD. Future Intraocular Lens Technologies.
Example: Ophthalmology. 2021 Nov;128(11):e206-e213
Eyemate ( Implandata Ophthalmics Products GmbH)
Cite This Article as: Vaibhav Nagpal . Types of
References intraocular lenses Delhi J Ophthalmol 2022; 32 (4): 77 - 82.

1) Taieb A. DesMemoires di Casanova á l'operation di Ridley. Arch Acknowledgments: Nil
Ophtalmol (Paris)1955;15:501-503.
Conflict of interest: None declared
2) Münchow W. Zur Geschichte der intraokularen Korrektur der
Aphakie. Klin Monatsbl Augen-heilkd1964;145:771-777. Source of Funding: None

3) Ascher KW. Prosthetophakia two hundred years ago. Am J Date of Submission: 14 June 2022
Ophthalmol 1965;59:445-446. Date of Acceptance: 20 June 2022

4) Apple DJ, Ram J, Foster A, Peng Q. Evolution of cataract surgery Address for correspondence
and Intraocular Lenses (IOLs) IOL quality Surv Ophthalmol.
2000;45(Suppl 1):S53–69 VaibhavNagpal

5) Werner L. Intraocular Lenses: Overview of Designs, Materials, MS, DNB, FICO MRCSEd,
and Pathophysiologic Features. Ophthalmology. 2021 Senior Resident
Nov;128(11):e74-e93
Ophthalmology, Guru Nanak Eye Centre,
6) Čanović, Samir, Suzana Konjevoda, Ana Didović Pavičić and New Delhi, India.
Robert Stanić. “Intraocular Lens (IOL) Materials.” (2019). E-mail: [email protected]

Quick Response Code

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DJO Vol. 32, No. 4, April-June 2022

Theme section

Prisms in Ophthalmology

Abstract Himshikha Aggarwal

Guru Nanak Eye Centre, Maulana Azad Medical college & assoc. Hospitals New Delhi, India.

With their numerous diagnostic and therapeutic applications, prisms are an indispensable part of ophthalmology. Prisms have
been used as reflectors in various ophthalmic instruments, while their other properties have made them an essential tool in the
diagnosis and management of strabismus. Hence, an in-depth knowledge of their correct use is crucial for all ophthalmologists.
This article aims to summarise the various types of prisms, their optics, and their applications in ophthalmology.

Delhi J Ophthalmol 2022; 32; 83-87; Doi http://dx.doi.org/10.7869/djo776.

Keywords: Prisms, Optics, Uses Of Prisms, Strabismus, Fresnel Prisms

A prism is a portion of a refracting medium bordered by two
plane surfaces inclined at a finite angle. Prisms have been
used in ophthalmology for many years for diagnostic and
therapeutic purposes, as well as a part of many ophthalmic
instruments, and hence form an indispensable part of
ophthalmology.

Parts of a Prism Figure 2: Optics of a prism

Prism, a transparent solid triangular refracting medium, has
two parts – an apex and a base. The finite angle at which
the two surfaces of the prism are inclined is known as its
refracting angle (α) or apical angle. A line bisecting this
angle is the axis of the prism and the opposite surface is
called its base (Figure 1). Orientation of prism is indicated
by the position of its base e.g. base-in, base-out, base-up,
base-down.

Figure 1: Parts of a Prism Figure 3: A straight line drawn on a paper appears displaced towards the
apex of the prism
Optics of Prism
1. Refractive index of the material used to make the prism
Light passing through a prism is deviated as per Snell’s law, 2. Refracting angle (α) of the prism
such that a ray of light deviates towards the prism’s base 3. Angle of incidence of the light ray
(Figure 2). Hence, the image formed by a prism is virtual,
erect and displaced towards its apex (Figure 3). The net This angle of deviation is least when the angle of incidence
change in the direction of the light ray is called the angle of equals the angle of emergence, and is known as angle of
deviation which depends on: minimum deviation, while it is greatest when the ray strikes
one face of the prism at normal incidence. Thus, the power
of a prism can be specified in two positions: the position of
minimum deviation and the Prentice position. In the Prentice
position the surface of prism is at 90 degrees to the ray of
light such that all deviation takes place at the other surface.
Since the angle of deviation in this position is more than
the angle of minimum deviation, the power of any prism in
the Prentice position is greater than its power in position of
minimum deviation.1

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Power of a prism is often donated in prism diopters, wherein Figure 5: Fresnel Prism
one prism dioptre (PD) is defined as the prism power which (Image source: Redrawn from Duane TD, ed. Clinical Ophthalmology.
produces an apparent linear displacement of 1cm of an
object situated 1m from the prism. Hagerstown, MD: Harper & Row; 1976: vol 1, chap 52, fig 52-2)

Types Of Ophthalmic Prisms

Ophthalmic prisms can be made up of either glass or
plastic. Glass prisms have a higher refractive index and
therefore deflect light more than plastic prisms. The Prentice
position power in which prisms are held with their back
perpendicular to the line of sight is normally specified
for glass prisms while power in the position of minimum
deviation is used for plastic prisms (Figure 4). In practice,
plastic prisms are usually held in the frontal plane position
with their back surface parallel to the face as this is near
enough to the position of minimum deviation.

Figure 6: Loose prisms

Figure 4: Positioning of prisms Figure 7: Prism bars with vertical and horizontal prisms

Fresnel prism consists of a plastic sheet of parallel tiny effective power of such a stack will be significantly different
prisms of identical refracting angles (Figure 5). It is based from the sum of powers of individual prisms. In such cases,
on the principle, that the power of an optical system is prisms can be split between the two eyes (Figure 9) but even
unaffected by changes in the thickness of the system elements then, measurement is slightly different from the sum of the
or their separation. Thus, the overall prismatic effect is same powers of the two prisms. (Table 1) gives the combined effect
as that of a single large prism with the added advantage of different pairs of prisms held in front of the two eyes.4
of the lighter weight of these sheets which can be easily On the other hand, a vertical and a horizontal prism can be
stuck on patient’s glasses. Moreover, these Fresnel prisms stacked in front of each other as their planes of refraction
are more acceptable cosmetically as they are affixed to the
concave surface of the spectacle lens, and they allow much
larger prismatic corrections (up to 40 PD).2 However, these
are not without problems, some of which are - decreased
visual acuity, especially towards the base which may induce
an abnormal head posture, decrease in contrast sensitivity
and chromatic aberrations.3 Majority of these problems can
be mitigated by closely matching the refractive index of the
spectacle lens material and the prism.

For diagnostic purposes, loose prisms (Figure 6), prism bars
(Figure 7), trial set prisms (Figure 8), or Fresnel prisms can
be used. Prisms in the trial set range from ½ PD to 12 PD,
loose prisms range from 5 PD to 60 PD while prism bars
range from 1 PD to 40 PD. Fresnel prisms range from 1 PD
to 40 PD.

When deviation exceeds the largest amount of prism
available, stacking of prisms over one another is not
recommended because light entering the second and
subsequent prisms is not at the correct incident angle, thus the

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Figure 8: Prisms in trial set • Direct ophthalmoscope
• Indirect ophthalmoscope
• Operating microscope
• Slit lamp microscope
• Goldmann applanation tonometer
• Stereoscopes
• Pachymeter
• Keratometer
• Haidinger brushes
• Exophthalmometer
• Pupillometer

Prisms in Strabismus

Another important application of prisms is in the field
of strabismus. Various tests have been described for the
diagnosis and measurement of squint to aid in correct
surgical planning. Some of the tests have been discussed
here briefly.

1) Prism Alternate Cover test

The prism alternate cover test is the gold standard to measure

the angle of deviation on near or distance fixation and in

any gaze position. Prisms of increasing strength are placed

in front of one eye with the apex pointed in the direction

of deviation (that is base-in prism for exotropia, base-out

prism for esotropia, base-up prism for hypotropia and base-

Figure 9: Splitting of prism between two eyes when deviation exceeds the down prism for hypertropia). The alternate cover test is
largest amount of prism available performed continuously as stronger prisms are introduced,
the amplitude of refixation movement should gradually
are perpendicular and therefore independent of one another. decrease as the strength of prism approaches the extent of

For therapeutic purposes, prisms can either be worn deviation (Figure 10). The end point is reached when no
temporarily in the form of clip-on spectacle prism for trial movement is seen. The strength of the prism at this position
wear or they can be worn permanently by incorporation of gives the angle of deviation.

prism into patient’s spectacles by either grounding them into 2) Krimsky Test
a spectacle lens or decentring the spherical lenses already In this test prism is placed in front of the deviating eye (with
present. The prismatic effect of spherical lenses is given by its apex towards the deviation) to correct the deviation of the
the Prentice rule which states that the prismatic power of a corneal light reflex. The strabismus measurement is equal to
lens at any point on its surface is equal to the distance from the amount of prism necessary to centre the corneal light
its optical centre in centimetres times the power of the lens reflex on the pupil of the deviating eye.
in diopters.

Clinical Applications Of Prisms 3) Modified Krimsky Test
This test is similar to Krimsky test, with the only difference
Prisms in ophthalmic instruments that here the prism is placed in front of the fixating eye to
centre the corneal light reflex on the pupil of the deviating
Prisms are commonly used in ophthalmic instruments as eye. The advantage of this technique is better visualisation
reflectors of light. The common instruments in which prisms of the light reflex in the deviating eye as it is not covered by
are used are as follows: the prism.

• Synaptophore

Table 1: Deviation in prism diopters for the addition of two prisms (glass or plastic) with one prism held in front of each eye.

Left eye prism (labeled Right eye prism (labeled value in prism diopters)

value in prism diopters) 10 12 14 16 18 20 25 30 35 40 45 50

10 20 22 24 26 29 31 36 41 47 52 58 63
12 22 24 26 29 31 33 38 44 49 55 60 66
14 24 26 29 31 33 35 40 46 52 57 63 69
16 26 29 31 33 35 37 43 48 54 60 66 72
18 29 31 33 35 37 39 45 51 57 63 69 75
20 31 33 35 37 39 42 47 53 59 65 71 78
25 36 38 40 43 45 47 53 59 66 72 79 86
30 41 44 46 48 51 53 59 66 73 80 87 94
35 47 49 52 54 57 59 66 73 80 87 95 103
40 52 55 57 60 63 65 72 80 87 95 104 113
45 58 60 63 66 69 71 79 87 95 104 113 123
50 63 66 69 72 75 78 86 94 103 113 123 133

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Figure 10: Prism alternate cover test Figure 11: 4 PD base-out test in left microtropia with central suppression
scotoma. (A) No movement of either eye (B) Both eyes move to the left but
4) 4 Prism-Diopter Base-Out Test there is absence of re-fixation. (Image source: Bowling, B. (2015). Kanski’s
This test is used to distinguish normal bifoveal fixation
from foveal suppression/central suppression scotoma in clinical ophthalmology (8th ed.). W B Saunders, chapter 18, fig. 18.27.)
microtropia. Herein, a 4 PD base-out prism (as microtropia
is commonly esotropic) is placed in front of one eye which Apart from these diagnostic uses, prisms are also used in the
results in the deviation of image away from the fovea treatment of many conditions as discussed below.
temporally. In case of normal bifoveal fixation a corrective
movement is noted in both eyes in the direction of the prism 7) Prisms To Relieve Diplopia
apex followed by an opposite fusional re-fixation movement Prisms are used to relieve diplopia and increase the field of
by the fellow eye not under prism. binocular single vision in patients with incomitant strabismus
like acquired third, fourth or sixth cranial nerve palsies as
In the presence of microtropia, 4 PD base-out prism is well as in acute acquired comitant esotropia, decompensated
placed in front of the eye with suspected central suppression heterophoria and convergence insufficiency. These prisms
scotoma. As the image is moved temporally it falls within also stimulate the unaffected antagonistic muscle in paralytic
the central suppression scotoma and hence, no movement is strabismus, thereby preventing its secondary contracture.8
observed in either eye. The prism is then moved to the other
eye which adducts to maintain fixation and as per Hering’s 8) Orthoptic Exercises
law, movement is also observed in the eye with central Orthoptic exercises have been an established part of therapy
suppression scotoma, but no fusional refixation movement for heterophoria, intermittent strabismus, convergence
is observed in this eye as now the second image falls within insufficiency and accommodative problems for many years.
the central suppression scotoma. (Figure 11) Adverse prisms, that is, prisms with their base towards
direction of deviation are prescribed for giving exercise to
5) Simultaneous Prism Cover Test weak muscles.9
A prism of approximate power (as estimated by Hirschberg
test) is placed in front of the deviating eye while an occluder 9) Prisms In Treatment Of Phorias And Tropias
is simultaneously placed over the fixing eye. The power Prisms are more commonly used for the treatment of
of prism is increased till there is no refixation movement heterophorias than tropias. They can be used both for
observed behind the prism.5 esophoria as well as exophoria with their apex pointing
towards direction of deviation. An accurate cycloplegic
6) Prism Adaptation Test refraction followed by prescription of appropriate glasses
Introduced by Jampolsky, this test is performed should be done first and then the minimum power of prism
preoperatively in acquired esotropia as well as intermittent that eliminates symptoms should be prescribed.
exotropia to determine the maximum angle of strabismus
and fusional potential. Herein, a prism is introduced in front 10) Prisms For Abnormal Head Posture
of the deviating eye (with apex towards the deviation) so Patients with nystagmus often adopt an anomalous head
as to first correct the deviation. The prisms maybe required posture to place their eyes in null position. Prisms which
to be used for longer periods varying from few hours to place eyes in such position can be prescribed to these
days. While some patients show no further movement
others might eat-up the prism with re-establishment of the
deviation. In such cases the prism power is increased till the
deviation is stable and the amount of surgery is augmented
in accordance with the amount of increased prism adapted
angle.6,7

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DJO Vol. 32, No. 4, April-June 2022

patients to abolish anomalous head posture. A trial of prisms Cite This Article as: Himshikha Aggarwal. Prisms in
can be given before surgery or in cases where surgery is Ophthalmology. Delhi J Ophthalmol 2022; 32 (4): 83 - 87.
contraindicated. Acknowledgments: Nil
Conflict of interest: None declared
Patients with head or neck positioning problems, such Source of Funding: None
as patients with severe ankylosing spondylitis, may also Date of Submission: 29 Apr 2022
benefit from prisms. In patients with an orthopedic chin- Date of Acceptance: 18 May 2022
down posture, for example, bilateral equal-power, base-up
yoked prisms can allow for improvement in straight-ahead Address for correspondence
vision and thereby facilitate mobility. Himshikha Aggarwal, MS,

Prisms As Low Vision Aids Senior Resident

Prisms can be tried in patients with hemianopia or tubular Guru Nanak Eye Centre,
vision due to advanced glaucoma or retinitis pigmentosa. New Delhi, India.
Prisms are used to reorient the visual field such that images E-mail: [email protected]
from the area of visual field defect are brought to areas where
vision is intact. Prisms have also been used for redirection of Quick Response Code
incoming images towards the preferred retinal loci (PRLs)
for restitution of potential visual acuity (PVA) in low vision Delhi Journal of Ophthalmology
cases with age-related macular degeneration.10

Prisms In Patients with Hemispatial Neglect

Recent studies have shown that yoked prisms which move
both visual fields to the opposite side improve function in
patients with hemispatial neglect. The mechanism for this
improvement is believed to be that, in order to compensate
for the shifted binocular visual field, the patient must remap
his or her sensorimotor coordinates, and this has been shown
to improve function on the neglected side.11

References

1. Elkington AR, Frank HJ, Greaney MJ. Clinical Optics. 3rd
edition. Oxford: Blackwell; 1984, Ch4 Prisms.

2. Flanders M, Sarkis N. Fresnel membrane prisms: clinical
experience. Can J Ophthalmol. 1999;34(6):335-40.

3. Véronneau-Troutman S. Fresnel prisms and their effects on
visual acuity and binocularity. Trans Am Ophthalmol Soc.
1978;76:610-53.

4. Thompson JT, Guyton DL. Ophthalmic prisms. Measurement
errors and how to minimize them. Ophthalmology. 1983
Mar;90(3):204-10.

5. Deacon MA, Gibson F. Strabismus measurements using the
alternating and simultaneous prism cover tests: a comparative
study. J Pediatr Ophthalmol Strabismus. 2001;38(5):267-72.

6. Takada R, Matsumoto F, Wakayama A, Numata T, Tanabe F,
Abe K et al. Efficacies of preoperative prism adaptation test
and monocular occlusion for detecting the maximum angle
of deviation in intermittent exotropia. BMC Ophthalmol.
2021;21(1):304.

7. Akbari MR, Mehrabi Bahar MR, Mirmohammadsadeghi A,
Bayat R, Masoumi A. Short prism adaptation test in patients
with acquired nonaccommodative esotropia; clinical findings
and surgical outcome. J AAPOS. 2018;22(5):352-355.

8. Tamhankar MA, Luo S, Kwong B, Pistilli M. Benefits and side
effects of prisms in the management of diplopia in adults: a
prospective study. J AAPOS. 2021;25(2):85.e1-85.e6.

9. Horwood A, Toor S. Clinical test responses to different orthoptic
exercise regimes in typical young adults. Ophthalmic Physiol
Opt. 2014 Mar;34(2):250-62.

10. Markowitz SN, Teplitsky JE, Taheri-Shirazi M. Restitution of
potential visual acuity in low vision patients with the use of
yoke prisms. J Optom. 2021;14(4):342-345.

11. Keane S, Turner C, Sherrington C, Beard JR. Use of fresnel prism
glasses to treat stroke patients with hemispatial neglect. Arch
Phys Med Rehabil. 2006;87(12):1668-72.

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Theme section

Electrophysiology In Vision

Aakanksha Raghuvanshi, Paromita Dutta

Guru Nanak Eye Centre, Maulana Azad Medical college & assoc. Hospitals New Delhi, India.

Electrophysiological tests in ophthalmology acts as an important clinical tool in evaluation, diagnosis and management of
ophthalmic and neurological disorders. They give us information about functional integrity of the visual system and assess the
disorders affecting visual pathway, retina, optic nerve and higher visual processing centres. Along with advanced imaging it
Abstract gives an additional information of various ocular diseases. There are different types of electrophysiological tests which include
electroretinography (ERG), electro oculography (EOG) and visual evoked potential (VEP). This article highlights various tests and
test procedures in brief, their clinical implications and also recent advances in this field so that it can provide an aid in day-to-day
ophthalmic clinical practice.

Delhi J Ophthalmol 2022; 32; 88-96; Doi http://dx.doi.org/10.7869/djo.777

Keywords: Electrophysiology, ERG, EOG, VEP, Neurophthalmology

Introduction Full-Feld Electroretinogram

A highly ordered neural structure in retina originates from This electrical response is recorded in a dilated, dark-adapted
the photoreceptors and exits the eye through the ganglion eye using various corneal electrodes. 20 minutes of dark
cell axons.1-3 ERG and EOG represent the function of adaptation is required before dark adapted ERG recording
different retinal layers and post-retinal visual pathway is and 10 minutes of light adaptation before light adapted ERG.
represented by VEP. A simplified schematic diagram shows Dark-adaptation test should be performed under dim red
different retinal layers along with the electrophysiological light. 5 min of extra dark adaptation should be allowed after
test that best represents their functional integrity.( figure 1) insertion of contact lens electrodes. Low strength flashes
followed by stronger flashes should be presented to avoid
Electro Retinogram partial light adaptation from strong flashes. The patient
should be steady as ocular movements may produce large
The ERG is an electrical response of the retina to light electrical artifacts, may change electrode position or may
stimulus which is useful in determining the clinical status cause blockage of light by the eyelids/electrode.
of the retina. It is recorded by using a thin fiber electrode
which is kept in contact with cornea or an electrode that is Types of Recording Electrodes
embedded within a corneal contact lens. These electrodes
allow the electrical activity generated by the retina to be • Burian-Allen (BA): it has stainless steel ring surrounding
recorded at the corneal surface. ERG underwent various a polymethylmethacrylate (PMMA) contact-lens core. It
modifications in past. The ERG gives information about has a lid speculum that minimizes eye blink/closure. BA
inherited and acquired retinal disorders, monitor disease lenses are reusable and are available in various sizes.
progression and detect retinal toxicity due to various drugs
or retained intraocular foreign bodies. • Dawson-Trick-Litzkow (DTL): these have conductive
silver/nylon thread, are disposable and more comfortable
for the patients.

• Jet: disposable plastic lens with a gold-plated peripheral
circumference.(figure 2)

• Skin Electrode: the electrode is placed on skin over the
infraorbital ridge near lower eyelid.

• Mylar Electrode, cotton wick and Hawlina-Konec
Electrode (not in common)

Figure 1: Schematic diagram showing retinal layers labelled according to Figure 2: Jet electrode. Source: Guru Nanak Eye Centre
ocular diseases that affect specific retinal layers. Various electrophysiological
test indicated- Retinal Pigment Epithelium (RPE)function (Electro oculogram), Delhi Journal of Ophthalmology
photoreceptor to bipolar, horizontal and amacrine cell function (full-field
ERG), ganglion cell function (pattern ERG) and retino-cortical pathway

function (Visual Evoked Potential).

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Placement Of Electrodes(Figure 3) cells. Although c-wave is generated by the retinal pigment
epithelium but is a reflection of the interactions between the
• Recording electrodes: in contact with cornea, bulbar RPE and photoreceptors6 and so depends on the integrity
conjunctiva, or skin below lower eyelid after topical of the photoreceptors. Photopic responses can be isolated
anesthesia. under light adapted conditions using a stimulus wavelength
more than 680 nm or 30 Hz flicker, while scotopic response
• Reference on ipsilateral lateral canthus and ground is isolated by dark-adaptation for 45 min followed by a
electrode on forehead. single flash stimulus or 10 Hz flicker.7 Rods cannot follow
a flicker stimulus faster than 20 Hz, whereas cones can
The scotopic measurements target rod-pathway function, follow 30–50 Hz stimulus as they have faster recovery time.8
whereas photopic measurements target cone pathway So, a 30 Hz stimulus with high background illumination
function. isolates maximum rods and allows cone function to be
The three major components of the ERG waveform are the recorded.4 As number of rods are more than cones, photopic
a-wave, b-wave, and c-wave. The a-wave is the first corneal- conditions produces small b-wave amplitudes with short
negative wave, followed by corneal-positive b-wave and latency, whereas scotopic conditions produce larger b-wave
last corneal-negative c-wave.4 The amplitude of the a-wave amplitude with longer latency.9
is measured from baseline, whereas the larger b-wave
is measured from peak to peak. Implicit time is the time The International Society for Clinical Electrophysiology of
between stimulus onset and maximum amplitude. Rods and
cones in the outer photoreceptor layer generate the a-wave, Vision (ISCEV) has introduced standards for various forms
whereas the b-wave is produced by bipolar and muller
of ERG recordings which were most recently updated in
Figure 3: Electrode Placement in ERG. Source: Guru Nanak Eye Centre.
2015. Indications

ERG is a useful in diagnosis of conditions like congenital

stationary night blindness, congenital achromatopsia,

retinitis pigmentosa, cone–rod dystrophies, cancer-

associated retinopathy, melanoma-associated retinopathy

and toxic retinopathies but not for localized pathologies.10-12

In most retinal disorders, there is significant reduction in ERG

amplitude and also implicit time.4 In retinitis pigmentosa,

early disease affects the rods, thus produce reduced scotopic

waves5 and in severe RP, all ERGs are extinguished and both

scotopic and photopic b-wave implicit times are prolonged.5

Cone-rod dystrophy appears to involve only cones early

in the disease, later the ERGs usually show attenuated rod

physiology. ERG changes in cone-rod dystrophies are shown

in (figure 4a,b) Completely extinguished ERGs can also

occur in Leber’s congenital amaurosis, retinal aplasia, total

Figure 4: (a) Advanced stage scotopic ERG of cone-rod dystrophy showing flat waves in right eye and decreased amplitude and prolonged latency. Source:
Gurunanak Eye Center.

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Figure 4: (b) advanced stage photopic ERG of cone-rod dystrophy having flat waves in right eye and decreased amplitude and prolonged latency in left eye.
Source: Gurunanak Eye Center

Figure 5a: ERG showing patient having incomplete CRAO in the right eye. ERG pattern of CRAO eye (right eye) and the fellow uninvolved eye (left eye). There is
slight decrease in b-wave amplitude of CRAO eye compared to normal eye in the dark-adapted 3.0 ERG. Also, PhNR amplitude is depressed in eye with CRAO

compared to normal eye. Source: Correlation of electroretinography components with visual function and prognosis of central retinal artery occlusion18

Figure 5b: ERG of patient having subtotal CRAO in the right eye and normal fellow eye having decreased b-wave amplitude in both dark-adapted and light-
adapted responses. Also PhNR amplitudes decreased considerably in the subtotal CRAO, compared to the fellow uninvolved eye.

Figure 5c: ERG of patient diagnosed with total CRAO in the right eye and normal fellow eye.Compared to the ERG pattern in Fig. 5a and 5b, more diminished
responses in dark-adapted and light-adapted ERG, including PhNR amplitude, were observed in this case of total CRAO.

retinal detachment, and ophthalmic artery occlusion.4,13-15 Factors Affecting ERG
ERG changes in patient with central retinal artery occlusion
are shown in (figure 5a,b,c). In retinal detachments, ERG ERG responses can vary with age, sedation, sex and
amplitudes correlate with the amount of healthy retina.13 technique used by various laboratories. Attenuation of
Type 1 congenital stationary night blindness has abnormal b-wave up to 50% can occur in anaesthetized children. Peak
dim scotopic ERGs and type 2 has abnormal dim and bright amplitude and implicit time of ERG occurs in young age and
scotopic ERGs.16 The b/a-wave ratio is useful in diagnosing declines slowly with age especially after age 55–60.19 ERG
congenital stationary night blindness.17 responses may be more in women than men and reduced in
high myopes.20-21 Another limitation of the FERG is that, as it

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is a mass potential from the whole retina, at least 20% of the Resulting waveforms are similar to the FERG consisting
retina has to be affected to see noticeable change.4 of an initial negative wave (N1 or a-wave), followed by a
positive deflection (P1 or b-wave) and a second negative
Photopic negative response (PhNR): The PhNR is a slow deflection (N2 or c-wave). mfERG has five concentric rings:
negative potential that follows the b-wave under light ring 1 corresponds to the fovea, ring 2 to parafovea, ring 3 to
adapted conditions. It originates from retinal ganglion cells perifovea, ring 4 to near periphery and ring 5 to the central
and thus useful in early detection of glaucoma. part of the middle periphery. It also provides display of the
signal amplitudes in a three-dimensional ‘hill of vision' with
Oscillatory Potential the largest signals corresponding to fovea(figure 7).

Oscillatory Potentials (OP) are series of high frequency, Indications
low amplitude wavelets seen on the ascending limb of
b-waves in both scotopic and photopic bright flash ERG mfERGs can be useful in detecting localized disease in the
recordings. They are thought to reflect activity initiated by macular, paramacular or discrete peripheral retina. It is
the interactions between bipolar cells, amacrine cells, and useful in diseases like age-related macular degeneration,
ganglion cells in the inner retina. An OP abnormality means macular holes, hydroxychloroquine toxicity, retinitis
either delay of implicit time or reduction of amplitude, or pigmentosa, branch retinal artery occlusion, fundus
both. A selective OP abnormality is observed in the early flavimaculatus, Stargardt’s disease and acute idiopathic
stage of diabetic retinopathy or diseases of retina such as blind spot enlargement.28 mfERGs are better than FERG in
central retinal vein occlusion. quantifying retinal toxicity due to ethambutol, chloroquine,
or hydroxychloroquine (figure 8).4,27 The classic finding
Pattern ERG (pERG) of chloroquine or hydroxychloroquine toxicity is a ring
scotoma between 5 and 150of fovea.29 mfERG may detect
Full-field ERG is a diffuse retinal response and PERG is earlier progression of glaucoma than automated perimetry.30

recorded for central stimulus subtending 30° (grey box) or Pitfalls

15° (black box) of the central retina respectively. The pattern Similar to ffERG. The presence of a depression in area
of expected blind spot shows fixation to be adequate.28
ERG (pERG) uses contrast reversing pattern stimulus Decreased amplitudes are found in old age and high
myopes.28
(checkerboards) to assess macular retinal ganglion cell
Figure 6: Normal electrophysiological traces. P50 component and the larger
(RGC) activity. Ocular media clarity, proper refraction and N95 are seen in the normal PERG. The figures are using an intensity of 3.0 cd
s/m2 for photopic ERGs, an intensity of 10 cd s/m2 for maximal response, and
undilated pupils are important for pERG measurement.
80 mcd s/m2 for the rod-specific traces.
Over time, the dark checks become light, and the light

checks become dark (at a rate of 4 reversals per second). It

has three main components: N1 at 30 ms, P1 at 50 ms, and

N2 at 95 ms (figure 6).22 Ganglion cell activity represents N2

and outer retinal activity represents P1. As the N2 signal

originates from retinal ganglion cells and their axons, it

helps in detecting optic nerve disease.23,24 PERG helps in

differentiating anterior ischemic optic neuropathy from optic

neuritis and also in differentiating retinal from optic nerve

disease. Factors affecting PERG are same as FERG including

sex and age.25 The pERG is also abnormal in diabetic

retinopathy and idiopathic intracranial hypertension.

Multifocal ERG

The multifocal ERG (mfERG) detects many local ERG
responses, typically 61 or 103, within central 30 degrees.
This detects dysfunction within the macula which may be
missed by ffERG. mfERG responses are recorded under
light-adapted conditions. The mfERG cannot replace ffERG.
If diffuse retinal damage or rod pathway dysfunction is
suspected, then ffERG should also be done.

Technique

Electrodes and their placement can be same as described
for ffERG and eyes should be dilated with normal room
illumination.26 The retina is stimulated at 61or 103 hexagonal
elements with a central fixation point of which 50% are
illuminated on each frame and are displayed in 300 radius
on liquid crystal display.26 The hexagonal pattern is scaled in
size to produce same amplitude across the retina with central
hexagons being smaller than peripheral.26 The hexagonal
pattern alternates between black and white at a rate of 75Hz
in a pseudorandom sequence, called binary m-sequence.

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should not be used as it may give false results. Three

electrodes are placed: Oz (active/positive electrode placed

at occiput), Fz (reference/negative electrode at forehead)

and ground electrode placed at Earlobe/vertex/mastoid.

Flash VEP using small flashes of light in a dim room are

more useful than pattern stimulus in infants or patients with

media opacities, poor cooperation, poor fixation or poor

acuity.31 Pattern reversal VEP is done on undilated patients

which are refracted for distance, whereas flash VEP is done

on dilated patients.31 The signals of 100–200 responses are

averaged and amplified to obtain peak, amplitude and

latency. Waveforms

The waveform is measured as an initial negative peak(N1),

followed by a large positive peak (P1) and a second negative

peak (N2). Pattern reversal latencies are recorded as N75

(N1), P100 (P1), and N135 (N2)(figure10). The components of

the flash VEP are negative N2 peak (90 ms) and the positive

P2 peak (120 ms)31(figure11). Pattern onset/offset VEPs have

Figure 7: Normal multifocal ERG. Source: Evaluation of hydroxychloroquine positive wave c1(75ms), negative c2(125 ms) and positive
retinopathy with multifocal electroretinography27
c3(150 ms).

Figure 9: Screen showing pattern reversal VEP. Source:Gurunanak Eye Center.

Figure 8: Evaluation of hydrochloroquine toxicity with mfERG. Figure 10: pattern reversal VEP waveforms showing N75 and N135 as negative
Source: Evaluation of hydroxychloroquine retinopathy with multifocal peaks and P100 as positive peak.

electroretinography 27 Indications

Visual-Evoked Potential Optic nerve function is best assessed by VEP, whereas it is not
of much use in postchiasmatic disorders. With optic nerve
The VEP is a large positive polarity wave generated by dysfunction, P100 latency is prolonged most commonly
occipital lobe in response to visual stimulation which begins but decreased amplitude can also be seen in optic atrophy.
at retina and ends at visual cortex. VEP is sometimes more sensitive than clinical assessment in

Technique

The VEP measures one eye at a time with scalp electrodes
placed over the occipital region. It is used to quantify the
functional integrity of optic nerve, pathway to visual cortex
and occipital cortex. The patient visualizes a display with
a central fixation point and high contrast, equal sized
and numbered black and white checkerboard-patterned
stimuli which are placed 50–150 cm away, depending
on the size of the display.31 A pattern reversal stimulus
is most reliable with black and white checks reversing
at rate of 2 per second (2 Hz)31 (figure 9). Large checks

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Figure 11: Flash VEP waveform is evaluated by measuring peak-to-peak both check widths, with only a small response to large check
amplitude between negative wave (N75) and positive wave near (P100). A widths, and in F-VEP broad and slightly low amplitude
significant decline in flash VEP is considered if there is decrease in peak-to- present. The PhNR is relatively preserved, but does not
peak distance between N75 and P100 by at least 50% from the reference fall below the a-wave. This shows severe bilateral retinal
ganglion cell (RGC) and optic nerve dysfunction, with some
amplitude. preservation of peripheral RGC function. Optic neuritis:
The PERG shows normal P50 components but mildly
reduced N95 components in both check sizes. The PR-VEP
is atypically delayed with normal amplitude and F-VEP is
also normal. The PhNR is markedly reduced. Overall, there
is optic nerve dysfunction with mild degeneration to RGCs
centrally, with marked peripheral RGC dysfunction.

Macular dystrophy: The PERG P50 of 30° field is well
defined, but that of a 15° field is absent showing severe
macular dysfunction localized to central 15° field. The
PR-VEP of 50′ check widths has normal peak-time with
borderline amplitude and loss of PR-VEP to small check
widths. The F-VEP and PhNR are within normal limits.

Figure 12: Pattern reversal VEP of a patient of multiple sclerosis causing decreased amplitude in left eye compared to right eye showing more involvement of left
optic nerve. Source:Guru Nanak Eye center.

detecting optic neuritis, especially once improvement has retina to area 17 of occipital cortex. Bilateral abnormal
occurred clinically.32 Pattern reversal VEP is more useful VEP can be due to chiasmal or retro-chiasmal lesions. An
in detecting conduction delay secondary to demyelination abnormal unilateral VEP suggests an optic neuropathy
(figure 12).33 The McDonald criteria for diagnosis of multiple if ocular disease is ruled out. Other factors are electrode
sclerosis recommend use of VEP when MRI shows at least placement, scalp thickness, attention, fixation, mental
four but not more than eight T2 lesions consistent with activity, refractive error, pupil size, fatigue, state of dark
MS.34 VEP amplitudes in stroke patients are reduced in the adaptation and background illumination.40-44 VEP can be
ischemic area when compared with the nonischemic area of abolished by sedation or anesthesia and carbamazepine has
brain.35 VEP can be predictive of visual recovery in traumatic been shown to prolong P100 latencies.45
optic neuropathy, with decreased amplitudes and increased
latencies indicating worse visual acuity (figure 13).36 It detects Electrophysiological findings of a normal person and in
visual status in infants or young children and in cases of various diseases is shown in (figure 14).
media opacities.37 P100 latency is better indicator than color
vision and visual field in early stages of hydroxychloroquine The first row is showing normal findings of PhNR, PERG (to
maculopathy without ocular symptoms or fundus changes.38 30° and 15° fields), pattern reversal visual evoked potential
It is useful in objective measurement of refractive error.39 (PR-VEP) (to 50′ and 12.5′ check widths) and flash visual
evoked potential (F-VEP).

Pitfalls LHON: The PERG demonstrates normal P50 components
but markedly abnormal N95 components which do not fall
VEP can detect optic nerve dysfunction but cannot explain below the baseline and in 15° field the P50 is also reduced
the cause. It is best used as an adjunct to clinical history, with early peak-time. The PR-VEP is severely declined in
examination and imaging. VEP detects the pathway from

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Figure 13: flash VEP of a patient showing decreased amplitude and increased latency in both eyes after occipital trauma to 1year old having traumatic optic
neuropathy. Source: Guru nanak eye center.

Figure 14: demonstrating the electrophysiological findings in a normal person, and in patients with Lebers Hereditary Optic Neuropathy, Optic Neuritis and
Macular dystrophy respectively. Source: Clinical electrophysiology of the optic nerve and retinal ganglion cells.46

Overall, it shows localized macular dysfunction in the 15° Figure 15: The multifocal VEP stimulus display: the dartboard pattern consists
field with preservation of surrounding 15–30° field. The of 60 sectors, each with a checkerboard pattern of 16 checks, eight white (200
normal N95:P50 ratio and PhNR indicates normal RGC and cd/m 2 ) and eight black (3 cd/m 2 ). The entire display subtended a diameter
optic nerve function. of 44.5°, and the central 12 sectors fell within a diameter of 5.2° of the foveal
center. Source: Study for analysis of the multifocal visual evoked potential.
Multifocal Visual Evoked Potential
Korean J Ophthalmology37
The multifocal VEP (MfVEP) uses a 60-sector checkerboard
that covers the central 220 and electrical responses to pattern
stimuli are recorded (figure 15).

Technique

Compared with conventional VEP, MfVEPs are made of
electric responses from a wider region of the visual field
(40–500 radius), so it is capable of detecting a broad range of
optic nerve damage.37 It can detect local defects.37

Indications/pitfalls

MfVEP is useful in optic neuropathies, such as glaucoma
and correlates with defects seen on automated perimetry.47
It is an objective topographic assessment of the visual field

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in glaucomatous and non-glaucomatous optic neuropathies near 2:1. Ratio of less than 1.7 is considered abnormal between
and useful in patients with unreliable visual field.48 Also, it light peak and dark trough. Normal pigment epithelium
shows defects not detected on automated perimetry in optic and normal mid-retinal function, both are required for light
neuropathies.48-49 Pitfalls are same as that of standard VEP. rise of potential. Most common use of electrooculogram is
confirmation of Best disease.
Sweep Vep
Identification of best disease is done by appearance of an
It is mainly useful for the examination of non-verbal children egg-yellow fundus and is confirmed by recording both
and malingering patients. Here, the program generates electroretinogram (ERG) and electrooculogram (EOG). The
a pattern stimulus that is alternated at a high temporal ERG will be normal whereas EOG will be abnormal. The
frequency rate (5 to 15 Hz), producing a steady state visual EOG can also be used for tracking eye movement.
evoked response. It detects a response very rapidly. For
measuring visual acuity, the size of the pattern is reduced Conclusion
rapidly.20 different pattern sizes are presented in succession
within 10 seconds. This sweep of the spatial resolution Various electrophysiologic tests are helpful in
domain provides estimation of visual acuity by the smallest ophthalmology, each having different indications. The
pattern size producing a response. FERG is very useful in diffuse retinal disorders, whereas
the MfERG is better in localized disease. VEPs is useful for
Technique diagnosing optic neuropathies, nonorganic visual loss, and
evaluating retinal function of infants or children. MfVEP acts
It starts by producing a cartoon to attract the attention of the as an objective test for visual field defects in glaucomatous
child which is followed by the presentation of a checkerboard and non-glaucomatous optic neuropathies. Sweep VEP
with large dimensions. After which, operator trigger sweep provides estimation of visual acuity in non-verbal children
stimulations that generate a rapid succession of 20 different and malingering patients.
patterns of decreasing sizes.
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E-ISSN: 2454-2784  P-ISSN: 0972-0200 96 Delhi Journal of Ophthalmology

DJO Vol. 32, No. 4, April-June 2022

Theme section

Biomicroscopic Lenses to Visualise Posterior Segment

Khushboo Chawla, Shraddha Raj Shrivastava

Guru Nanak Eye Centre, Maulana Azad Medical college & assoc. Hospitals New Delhi, India.

Ophthalmology is a unique field allowing the clinician a non-invasive ‘window’ to the organ of interest as the eye and especially
its posterior segment hide’s information, not just about eye-related issues but also about the patient’s general well-being.

Although newer technologies like Optical Coherence Tomography (OCT) and other retinal imaging modalities have
Abstract revolutionised the diagnosis and management of posterior segment pathologies, they are still not a replacement for the

easily available, affordable and portable hand-held lenses. By utilising the optics of these lenses, we are able to visualise the
remote areas of the eye especially the fundus, in order to facilitate any therapeutic interventions. This article focuses on the
various types of lenses used for posterior segment evaluation which are important tools in every ophthalmologists’ arsenal.

Delhi J Ophthalmol 2022; 32; 97-103; Doi http://dx.doi.org/10.7869/djo.778

Keywords: Lens, biomicroscopy

The optical system of the patient's eye - the cornea
and lens, together provide so much convergence that
ordinarily we cannot see the retina using a slit-lamp. At
most, the slit lamp can view upto the anterior vitreous.
So, auxiliary lenses for slit-lamp examination of the
retina are required to nullify these intervening optical
effects caused by the patient’s eye.1 During indirect
ophthalmoscopy the divergent rays from the patients
eye are focused between the hand held condensing lens
placed just above the patient’s eye.

Classification Of Lenses For Posterior Segment
Examination

The various lenses used in clinical ophthalmology can be
divided in to Diagnostic(figure 1) and therapeutic (figure 2)
lenses

Figure 1: Different categories of diagnostic lenses used in posterior segment
evaluation

Figure 2: Schematic representation of Therapeutic lenses used in posterior segment treatment

E-ISSN: 2454-2784  P-ISSN: 0972-0200 97 Delhi Journal of Ophthalmology

DJO Vol. 32, No. 4, April-June 2022

1. Non-Contact Lenses +90 D lens – Relatively wide field of view with a good
resolution.(Figure 4C)
a. Convex Lenses - Examination of the retina using the slit-
lamp with these lenses placed in front of the patient’s - Posterior pole examination for general diagnosis and
eye, is called indirect slit-lamp double aspheric lenses bio small pupil examination,.
microscopy. Typically, the +60D, +78D, and +90D(Figure
4) fundus lenses are used for comprehensive fundus - Diameter ring - 26mm, ideal for dynamic fundoscopy.
evaluation. ie dynamic observation of the fundus in all directions
possible by moving the condensing lens, scleral
These are double aspheric lenses (so it does not matter indentation etc.
which side is held towards the patient), forming a real,
inverted and laterally reversed aerial image of the - Working distance from the cornea - 6.5mm.
fundus(Figure 3).

Figure 3: Fig.3 High-power plus lenses for slit lamp indirect ophthalmoscopy Figure 4: (A)+60 D lens (B)+78 D lens (C)+90 D lens
(eg, 60 D and 90 D fundus lenses) held in front of the eye produce an inverted
aerial image of the retina within the focal range of a slit-lamp biomicroscope.1 Delhi Journal of Ophthalmology

POWER ∞ MAGNIFICATION∞ 1/FIELD OF VIEW

High powered lenses provide a large field of view but lesser
magnification, e.g. the +90D lens provides a bigger field of
view but lesser magnification than +78D lens.

Magnification is calculated under the assumption that the
patient’s eye is a +60D optical unit.

Field of view = (Dioptric Power of the lens x 2)

Magnification = Power of eye x magnification of slit lamp/ Power of the lens

Stereopsis = Magnification / 4.

Brief Technique: With the patient seated comfortably at the
slit-lamp, the illumination and observation system kept co-
axial, and magnification kept at 10X or 16X, the light beam
(4mm wide with brightest light intensity) is focused on
the patient’s pupil. The condensing lens is then aligned at
around 5-10 mm from the patient’s cornea and the slit-lamp
is pulled backward gradually towards the examiner until
the fundus is visualized. To view the peripheral retina, the
patient is asked to look into appropriate positions of gaze as
with standard indirect ophthalmoscopy.

+60 D lens – Introduced by Volk Optical in the early 1980s.4
- High magnification views of the posterior pole for

detailed optic disc and macula imaging. (Figure 4A)
- Ideal for optic nerve head examination as lens offers

higher magnification near 1x.
- Diameter -31mm, facilitates easy handling.
- Working distance from the cornea - 11mm.

+78 D lens – Single lens providing an ideal balance between
magnification and field of view (Figure 4B)

- Working distance from the cornea - 7mm.

E-ISSN: 2454-2784  P-ISSN: 0972-0200 98