DOS_jan_2009

Contents

E5 ditorial Glaucoma

G7 uest Editorial 63 Interpretation of Humphrey Visual Field Printout

Focus Ruchi Goel, Usha Yadava, Lanalyn Thangkhiew, Manav Sachdeva

19 Management of Ocular Trauma 73 Tonopen: A Critical Appraisal

Cataract Shibal Bhartiya, Sonia Bhargav, Sumita Sethi, Shalini Mohan,
Anand Aggarwal
25 IOL Master
Retina
Prakashchand Agarwal, Chandrashekhar, G.N. Singh,
Namrata Sharma, Jeewan S. Titiyal 79 Retcam

Cornea Tinku Bali Razdan, Amit Khosla

29 Videokeratography Clinical Monthly Meeting

Noopur Gupta 83 Case 2- Non Specific Orbital Inflammatory disease:

35 Confocal Microscopy Perineuritic Variant
Vikas Menon, H.K.Tewari
Shubha Bansal, Namrata Sharma, Meena Verma, Jeewan S. Titiyal
89 Clinical Talk - Intra-operative Floppy Iris Syndrome (IFIS):
43 Specular Microscopy
A Phaco nightmare
Deepa Gupta, Ritu Arora, Jawahar L. Goyal Mahipal S. Sachdev, Charu Khurana, R. Ghosh

49 Keratometry I93 ndustry News

Monica Chaudhry, Rajni Chhabra A97 bstract

57 Acanthamoeba Keratitis F99 orthcoming Events

Sanjay Kumar Mishra, J.K.S. Parihar, Rakesh Maggon, M101 embership Form
V. Mathur, H.S. Trehan

DOS Election 3

Last date of withdrawal is 21st February, 2009 (5 p.m.) Election will be held during the Annual DOS
Conference on 22nd March, 2009.

Secretary, DOS

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4 DOS Times - Vol. 14, No. 7, January 2009

Editorial

Dear Friends,

Role of Mitomycin in Corneal and Refractive surgery

Refractive surgery has come a long way. The correction of refractive error can be accomplished both by LASIK as well as
surface ablations. However, PRK and other surface ablation procedures still have limitations, including postoperative pain,
a stronger healing response, and especially possible formation of corneal haze following surgery for high myopia. Over the
past few years topical mitromycin C (MMC) has been used to treat and prevent corneal haze in surface ablation procedures.

MMC has proven useful in several different fields of ophthalmology such as topical application of MMC in glaucoma surgery, recurrent pterygium excision,
and treatment of conjunctival and corneal intraepithelial neoplasia.

More recently, MMC was proposed as an alternative treatment for corneas with scarring or haze secondary to refractive surgical procedures. MMC application
following PRK correction is recommended only for patients who have relatively high risk of developing postoperative corneal haze which include

1. High myopia (> 65 ?m),
2. Previous corneal surgery (including PRK, LASIK, RK, or PKP),
3. Previous flap complications (such as button-holes and thing flaps), and
4. Haze development in the contra-lateral eye or
5. Cases with high rate of postoperative refractive regression (when LASIK is not indicated), including astigmatism (> 2.0D) and hyperopria or for therapeutic

purposes in patients with previous corneal haze Prophylactic use in virgin corneas:
6. Concentration: 0.02%
7. Exposure time: 12 seconds Prophylactic use following previous corneal procedures (PRK, LASIK, RK, or PKP):
8. Concentration: 0.02%
9. Exposure time: 1 minute Therapeutic purposes in patients with previous corneal haze:
10. Concentration: 0.02%
11. Exposure time: 2 minutes

There remains no consensus on the optimal concentration and exposure time for MMC treatment. Several different concentrations and exposure times have
been used based on clinical observations in patients. After use, it must be stored at -200C and preserved at the maximum of 2 weeks.

Corneal haze tends to disappear spontaneously over time, although it may take 12 to 24 months or even longer for substantial improvement. Only clinically
significant corneal haze (plus 2 or over) should be considered for treatment with mitomycin C. In all cases of postoperative corneal haze following PRK, MMC
treatment must be delayed for at least 6 months and only considered when previous steroid treatment failed.

Nomogram adjustment is recommended when MMC is used. On average, expect more correction per pulse with MMC treatment due to blockage of keratocyte
replication. On an average, monogram adjustment involves a reduction of 5% to 10% of intended correction when MMC is used.

Serious complications, such as corneal melt and sclera perforation, have been reported following MMC application after pterygium surgeries. At present, no
major complications have been reported subsequent to MMC treatment of the cornea.

Contradictory studies have been published regarding endothelial toxicity and decreased endothelial cell loss. Nassiri et al recently published a study
demonstrating clinically significant loss of endothelial cells following MMC application. On the other hand, no evidence of morphological changes or decrease
in endothelial cell density has been noted on specular microscopy with up to 5 years of follow-up in patients treated with MMC therapy up in larger series.

A synergistic effect of alcohol and MMC on keratocyte cell viability has been reported. It is recommended that manual epithelial removal with a blade rather
than alcohol, since its association leads to an increased keratocyte loss.

Almost 10 years have passed since MMC was first used in refractive surgery, and no major complications have been reported so far. At present, MMC is
considered a helpful tool for modulating corneal wound healing, which requires a careful and restricted use.

Thanking you,

Namrata Sharma
Se cre tar y,
Delhi Ophthalmological Society

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Guest Editorial

The field of ophthalmology has been evolving at a rapid pace as new technology continues to be integrated into everyday
clinical practice. The process of integration is a long, complex one that involves scientific innovations, industry, clinical
investigators, and regulatory agencies. One of the characteristic features of the development of ophthalmology is the wide
use of instruments based on the latest achievements of science and engineering for the diagnosis and treatment of
ophthalmic diseases.

The use of diagnostic resources is growing steadily as a part of standard of care in many common clinical situations.
Videokeratography devices are an evolving technology, and their use is an area of active investigation. Keratometry involves
measurement of the corneal front surface, giving a numerical measurement to the three dimensional corneal surface.
Confocal laser scanning microscopy is an optical imaging technique for obtaining high-resolution optical images. The key
feature is its ability to produce in-focus images of thick specimens, a process known as optical sectioning. With the
emergence of refractive surgical techniques, corneal pachymetry is necessary to determine suitable candidates for ablation
procedures. Furthermore, the identification of central corneal thickness as an independent indicator of glaucoma risk has
made corneal pachymetry indispensable. IOL Master non-contact optical coherence biometer allows fast, accurate
measurements of eye length and surface curvature, necessary for cataract surgery. It is a high-precision instrument
revolutionizing all previous techniques and setting a new standard for the measurement of the ocular axis.

A thorough understanding of the relationship between quantitative reliability and clinical applications of all these investigative
modalities is essential. It is important to improve the accuracy and reproducibility where needed and to standardize
measurements and nomenclature. These modalities have evolved from the need to impart objectivity to clinical diagnosis
and management. They function as important tools for the making correct diagnoses. Through these instruments, new
knowledge and research findings are adequately reflected in daily practice.

Unfortunately, when guidelines on selective and rational ordering of investigations are introduced, numerous motives for
ignoring evidence based recommendations, such as fear of litigation, or procrastination on the part of the doctor, come
into play in daily practice and are difficult to influence. It is therefore vital for eyecare professionals involved in this field
to have a good understanding of their principles and applications.

Although technology can provide significant information, investigators should remember that technology does not
replace traditional clinical examination techniques. Overuse of investigations—and there is reason to believe that some
requests are illogical—leads to overloading of the diagnostic services and over-expenditure: more efficient usage is
therefore needed. Interventions focusing on overt examples of inappropriate testing might reduce costs while
simultaneously improving quality of care. But this requires, first of all, that doctors know the principles of medical
decision making and its relevance to daily practice.

A comprehensive overview of the basic advances in techniques and diagnostic instruments needed for ocular examination
and diagnosis is being presented. Abundantly illustrated, the principles of each technique,
providing guidance on choosing the appropriate approach, explaining how to perform them,
their expanding clinical indications, offering examples of when each technique should be used,
and listing their common indications and potential pitfalls. It is recognized that all investigations
are unique and the judgment of investigators should be given preference in the implementation
of these modalities.

Noopur Gupta

Associate Editor,

Delhi Ophthalmological Society

6 DOS Times - Vol. 14, No. 7, January 2009

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Management of Ocular Trauma Focus

Dr. (Air Marshal) Dr. Yog Raj Sharma Dr. J.K.S. Parihar MS,
M.S. Boparai MS MD FRCS DOMS, DNB, MNAMS

Ocular trauma is the major cause of world wide visual impairment, and all ophthalmologists are exposed to selected aspects of ocular
trauma, dependent on their type of practice. Ocular injuries can and do occur in almost any setting, including recreational and sports
related activities, the workplace, the home, rural agricultural settings, motor vehicle accidents, and intentional altercations. The
personal impact of ocular injury is difficult to define, though the lifestyle of the affected individual may be permanently altered.

We tried to find out how ocular trauma was best managed by specialists at there centres.

(MSB): Dr. (Air Marshal) M.S. Boparai, Former Prof. of Ophthalmology, Dean and Director of Armed Forces Medical College, Pune
and Emeritus Prof. National Academy of Medical Sciences (I). (YRS): (Prof.) Yog Raj Sharma, Dr. Rajendra Prasad Centre for
Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi and Faculty, Vitreo-Retina Unit. (JKSP): (Col.) J.K.S. Parihar,
Senior Advisor Ophthalmology, Anterior Segment Micro Surgery (HOD & Professor) Army Hospital (Research & Referral) Delhi
Cantt, New Delhi. (SB): Dr. Shubha Bansal, Research Officer, Cornea and Refractive Services, Dr. Rajendra Prasad Centre for Ophthalmic
Sciences, All India Institute of Medical Sciences, New Delhi.

SB: What are the different types of Ocular injuries, SB: What is the patient profile and mode of trauma seen in
commonly seen in your practice? your institution?

MSB: It is a mixed bag of Ocular injuries consisting of trauma MSB: Patients in .service hospitals are mainly serving soldiers
inflicted at home, work places, road traffic accidents, and are relatively young. In my private practice, during
chemical bums and blast injuries. I therefore get cases festival seasons, particularly “Deepawali” and marriage
of open as well as close globe injuries, FBs, chemical seasons the profile of patients is generally under 30 years
injuries, fractures displacement of adnexal bones and with lot of children in the group. The mode of trauma in
cracker injuries. These cases can be put into two main cases that come for secondary management in our service
types. One which involve the eye/face in isolation and hospitals these days, is the result of blast injuries as a
are relatively easier to manage. The other type are the result of explosions caused by improvised explosive
ones in which eyes are involved as part of polytrauma. devices (IEDS). These are capable of causing extensive
These are difficult to manage due to requirement of damage due to flying shrapnels of various sizes.. Same
involving other disciplines in their management. mechanism operates in the explosive devices implanted
by terror groups and militants. I personally get a lot of
YRS: We get all types of referred trauma patients but our traffic related Ocular injuries which have been referred
unit mainly deals primarily with vitreo-retinal trauma to me by other ophthalmologists for further
patients. Many patients do have combined anterior management These are cases of both, open globe and
segment involvement but these are mainly dealt by close globe injuries with facial involvement. Chemical
anterior segment surgeons. Only when a clear anterior injury cases and work related injury cases are generally
segment or at least when cornea is clear is the patient in 20 - 40 years age group. During harvest season cases
seen in our unit. also come from rural areas.

JKSP: Ours is a tertiary level institution where patients are YRS: Mostly young males and children of both sexes .Patients
being transferred in from all parts of the country. In my belong to all economic backgrounds. The mode of trauma
practice, the commonest type of ocular injury is Blunt is sports related injury ,accidental injury, occupational
Trauma with or without rupture of the globe. This trauma , physical violence etc.
constitutes for almost 2/3rd of trauma cases. The
remaining cases are those with Penetrating/ Perforating JKSP: Most patients are males ranging from 02 to 20 years in
ocular injury with or without retained intra- ocular age. A large majority of injuries happen while playing at
foreign bodies (IOFB). home or in school. Young men working and involved in

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industrial procedures like grinding, lathe cutting or Keratoplasty, secondary IOL implantation, IOFB removal
hammering is the next vulnerable group. Soldiers and vitreo- retinal procedures are done for definitive
involved in blast injuries and hit by splinters constitute management.
less than 10% of cases of ocular trauma.
SB: What is your line of Management once these patients
SB: What is the management protocol followed for patients are referred to your tertiary care centre?
with Ocular Trauma?
MSB:(a) The management in the tertiary care centre is aimed at
MSB: (a)Management protocol involves a holistic evaluation of holistic rehabilitation of the patient. This involves visual
the patient including Ocular trauma. It means a general rehabilitation, cosmetic rehabilitation, physical
evaluation of the physical state, including any previous rehabilitation and psychological rehabilitation.
medical or surgical ailments / treatments. This is
important as management may require the patient to be (b) For visual rehabilitation, the anterior segment eye
put under general anaesthesia. It is also required from surgeon, vitreo-retinal surgeon, contact lens specialist
the point of view of involving other disciplines such as and oculoplastic surgeon have to work in tandem to get
maxillofacial surgeon, ENT surgeon, neurosurgeon and the best possible vision. Patient may need multiple
so on in the management. surgeries by way of stem cell / amniotic membrane grafts,
kerato- plasties, IOL implants, pupil reconstruction and
(b) From the ocular point of view, history is obtained of any so on.
previous eye disorders / injuries and the kind of treatment
that the patient may have had. Also find out the history (c) To improve cosmesis of the patient, other disciplines as
of present trauma, injuring object, chemical, weapon etc. mentioned earlier may have to been involved. Patient
If primary repair has been done; look for its nature and may need multiple skin grafting procedures.
condition. Present visual acuity is determined and visual
acuity immediately after injury is found from records if (d) Psychological rehabilitation is very important as many
available. This has a bearing on the severity of injury and patients with visual morbidity / visual blindness, lose all
future prognosis. jest for life. If a situation of this kind is becoming apparent
experts from the National Institute of visual
(c) Look for lid injuries and injury to lacrimal drainage rehabilitation, Dehradun can be associated with patient
passage~ conjunctival state, hyphaema, Ac depth, state management. This aspect is generally ignored in civil
of iris, pupillary reaction, state of lens and state of globe. institutions.
Is it an open globe or close globe injury? Examine cornea
for FBS, tears, abrasions and perforation etc. YRS: Again nothing fixed. All types of vitreo-retinal surgery is
Examination must be done under magnification. Local undertaken as long light perception is present and eye is
anaesthetic and lid retractors may have to be used. Be salvageable.
gentle and deliberate in your examination. Palpation of
orbital margins is important for any bony dehiscence. JKSP: The first step is to thoroughly assess the ocular status.
Anterior segment can simply evaluated by a detailed slit
(d) Plain film radiography is the next most important lamp examination. Assessment of the angle is difficult
assessment to look for IOFB. This is followed by USG particularly in presence of corneal scar or turbid aqueous.
and CT Scan. MRI is best avoided except in highly Gonioscopy is performed in all cases wherever feasible
selective cases involving skull /facial fracture. to look for angle recession or foreign body. In hazy media,
Ultra Sound Biomicroscope (UBM) is a useful modality
(e) Posterior segment needs to be assessed by a .vitreo- to assess the angle, ciliary body, lens capsule and the
retinal surgeon. Further management / intervention is zonules. The problem is placement of the speculum for
done based on the findings. the probe in presence of a recently sutured wound.
Anterior segment OCT should be useful in this situation
YRS: Nothing fixed. Primary repair is undertaken around the as it a non- contact technique. USG ‘B’ scan is invaluable
clock-the aim is to achieve watertight wound closure. If in assessing the posterior chamber and locating IOFB’s
the patient needs vitreo-retinal surgery ,it is generally in presence of media haze due to any reason. The further
undertaken at 10-14 days. The one exception being course of management will depend upon the findings of
endophthalmitis. In this instance surgery, if deemed ocular examination.
necessary, is undertaken at the earliest. If patient presents
late, then necessary surgery is undertaken if eye is SB: What are the difficulties faced in evaluation of patients
operable. with ocular trauma presenting at your centre after
primary management has been carried out?

JKSP: We follow a multi- tiered approach to case with ocular MSB: (a)Primary Management may not have been satisfactory
trauma. The initial primary management is performed and revision surgeries may be required
at a peripheral hospital by an ophthalmologist where
the patient first presents. Primary repair in cases of open (b) Visual assessment may not have been done at initial stage
globe injury and management of initial inflammation is and injuries not described properly to give you an idea’
done. After a few weeks, patients are transferred to a of future prognosis. Observations like state of the pupil
tertiary centre where advanced procedures like at that time may not be available.

20 DOS Times - Vol. 14, No. 7, January 2009

(c) Iatrogenic damage at the primary management stage disciplines. In some hospitals in civil a general anesthetist
may add to the actual damage and is difficult to assess. In is at a premium. Eye surgeons have to be geared to intra
open globe injuries, ointments used might get inside the disciplinary and inter disciplinary approach.
globe and cause difficulties in assessment and
management (b) Management of the patients is a time consuming affair
and long hospitalization may be necessary and even then
(d) In case of chemical/bum injuries exact nature of the visual outcome of treatment may not be satisfactory.
chemical may, not be known to help further management. Patients and his relatives need to be taken into confidence
and all aspects of treatment explained to them, lest they
(e) Recording of good history and findings at the first have wrong / undue hopes.
examination stage are very important and may be
missing. (c) Rehabilitation of trauma patients; particularly with visual
morbidity still remains the biggest challenge.
(f) Patient may be comatose and not responsive. All
required intra-disciplinary specialists hi Ophthalmology YRS: Because young population is affected, there is added
may not be available in one place and referrals may be parental and economic concern. The potential visual loss
difficult. is often difficult for the patient to accept. An existing
corneal opacity precludes effective management and
YRS: The biggest difficulty is late presentation with eye having brings to the fore our persistent shortage of donor
entered pthisis or worse persistent no light perception. corneal tissue.

JKSP: Assessment of following factors is very challenging in JKSP: Trauma affects almost all structures within the eyeball.
cases of trauma:- For example a patient may seem to be having only a
traumatic cataract with normal USG ‘B’ scan. Once we
i) Intra ocular pressure (IOP) are through with managing the cataract, retinal
examination revels that he also had macular oedema at
ii) Macular function the time of initial injury. This prevents a good visual
outcome despite adequate management of the anterior
iii) Optic Nerve function segment injuries. Involvement of multiple structures
together compounds the problem and diminishes the
Following primary repair, correct measurement of IOP chances of a good visual recovery. Reaction to any surgical
is difficult because scarring and fibrosis of corneal/ scleral intervention is far more vicious than we get to see
scar alters the dynamics of the eyeball. Thus most otherwise. Intra- operative bleeding from scarred tissues
conventional methods of measuring IOP give incorrect is more making the surgical procedures more demanding.
readings. Goldmann Applanation tonometry does not In study done in our institution, traumatic cataracts in
work in presence corneal scarring. Using a tonopen to children were noted to far poorer outcomes as compared
measure IOP is a good alternative. We have no experience to congenital and developmental cataracts. In children
with dynamic contour tonometry in cases of ocular onset of Amblyopia is very rapid and by the time
trauma. In absence of tonopen, we have to rely on Schiotz management of injuries is over, severe degree of
tonometry or clinical digital tonometry for assessment Amblyopia has already set in.
of IOP.
SB: What are your views on secondary IOL, implantation
Assessment of Macular function is another challenge for patients who have already undergone primary repair
particularly in presence of hazy media. At present there elsewhere?
is no means to evaluate macular function in presence of
corneal scarring accurately. Clinical tests like two point MSB: (a)Secondary IOL implantation for such patients is a very
discrimination or identification of coloured light points tricky question. I would not like to interfere till complete
provide us with a rough estimate of macular function. heeling has taken place and visual outcome is known.
First try a CL and see the effect on vision. If it works don’t
Similarly, evaluation of optic nerve function can be very think of secondary IOL. It is important to assess as to
difficult in hazy media. Pupillary reflexes, which are a what factors are interfering with improvement of vision.
good predictor of optic nerve function, can be altered It could be a vitreo-retinal problem and IOL may serve
due to traumatic mydriasis. Presence of perception of no purpose.
light and projection of rays will pick up cases with gross
damage to optic nerve only and partial damage maybe (b) Secondary IOL should be a well weighed decision and
missed. Visual fields can be unreliable when multiple has to be customized to each patient. I will not be keen
factors are contributing towards visual loss. Flash VEP for a PC IOL due to constraints of causing further
maybe useful in assessment of optic nerve function in astigmatism and! other aberasions due to per-existing
hazy media. fibrosis. I will rather prefer a Kelman type Ac IOL if
conditions permit.
SB: What are the challenges faced in managing cases of
Ocular Trauma? YRS: They remain a must for effective visual recovery and
must be undertaken wherever possible, if no obvious
MSB: (a)Challenges are multiple; it is a question of apt intervention contraindications exist.
at the apt time and requirement of involvement of other
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JKSP: The lens capsule ruptures at the time of initial trauma in glaucoma cases due to excessive conjunctival scaring as a
cases of penetrating/ perforating injury. Removal of result of trauma and its management. Trabeculectomy
flocculent cortical matter is mandatory during primary YRS: and Deep scleral resection with use of mitomycin-C are
repair itself as it will give rise to a severe inflammatory JKSP: worth trying. Last resort may be to glaucoma setons.
reaction if it is left behind. Generally, once the
inflammation subsides in 4- 6 weeks, secondary IOL SB: Referal to the Glaucoma expert.
implantation can be planned if other structures are
normal. If a posterior capsular frill is visible, a rigid PMMA Management of post- traumatic secondary glaucoma
single piece PCIOL is implanted in the sulcus after depends upon the cause for rise in IOP. Modulated
adequate anterior vitrectomy. Remnants of lens matter trabeculectomy can be performed in patients >50 years
should be removed as far as possible. Heparin/ Fluorane of age and those in whom distortion of Trabecular
coated PCIOL can be used in children in whom severe meshwork is minimal. Ultrasound Bio Microscope
post operative uveitis is expected. If no capsular frill is (UBM) is invaluable in assessing status of the angle. In
seen, then scleral fixated IOL can be implanted. These cases where there is advanced angle distortion, modulated
have been noted to be very safe the only complication trabeculectomy is likely to fail. In such cases, glaucoma
noted at our centre is high astigmatism. IOL power drainage devices such as Ahmed Glaucoma Valve have
calculation is inaccurate and one has to take clues from been noted to be very effective.
parameters of the other eye to arrive at the estimated
lens power. What is the management protocol regarding post-
traumatic corneal scarring and corneal opacities?

SB: How do you deal with post traumatic glaucoma? MSB: (a)Superficial corneal opacities may respond to Laser
abalation. More extensive opacities may require lamellar
MSB: (a)Important thing is to try to understand the multiple or penetrating kerotoplasty. Inspite of all this, visual
factors which may be causing glaucoma and deal with outcome is poor in most of these cases. Larger size grafts
them accordingly. Causes are different in penetrating have greater chances of failure.
injuries and close globe injuries (b) Multiple sphincter
tears of pupil, angle recession, trabecular dialysis, (b) If the opacity is too extensive and, unsightly, the chances
hyphaema, lens displacement etc are contributing factors of visual restoration are remote. In such cases cosmesis
in Non-penetrating injuries. Gonioscopy is a must but may be improved by tattooing. Desperate cases may
has to be deferred in early stages (c) Inflammation, Ac need kerato-prosthesis.
Collapse, lens damage, hyphaema, siderosis etc., are the
contributing factors in penetrating injuries. (d) Treatment YRS: Referal to a Cornea specialist.
must be directed towards management of above factors.
Use of corticosteroids, laser iridotomy and amino caproic JKSP: Linear corneal scars which are not in visual axis lead to
acid can be tried selectively standard medical glaucoma unacceptable amount of astigmatism. This needs to be
therapy can be used, although its efficiency is limited. corrected using either rigid/ toric contact lenses or limbal
Pilocarpine is best avoided, lest it closes the uveo-scleral relaxing incisions. Corneal scars in visual axis need
outflow route which may be the only drainage route in keratoplasty. Since most traumatic scars are full thickness
some cases. and associated with other anterior segment anomalies,
penetrating keratoplasty with IOL implantation or
YRS: Try to manage medically but refer to glaucoma expert at combined with a glaucoma procedure can be performed.
the earliest especially if IOP continues to remain elevated. For localized corneal scars, rotation keratoplasty can be
an alternative option but in our experience visual
JKSP: Post- traumatic secondary glaucoma can have many improvement are better with full penetrating keratoplasty.
different mechanisms. Clinicians must constantly Post- operative management in such cases must be
monitor and specifically look for it in order to detect vigorous in order to combat post- operative
glaucoma during post- trauma period. Regular IOP inflammation and rise in IOP. Since these are high risk
measurements should be carried out whenever the grafts, one must be vigilant about detecting graft rejection
patient comes for review. In the immediate post trauma early and treating it aggressively.
period, hyphema, lens matter and inflammatory material
clogging the Trabecular meshwork is a common cause of
rise in IOP. This rise in IOP can be dealt with medically. In
the later stages, angle recession, peripheral anterior
synechiae and fibrosis of Trabecular meshwork are
responsible for the rise in intra- ocular pressure. This
type of rise in IOP does not respond well to medication
and requires surgical intervention.

SB: What are the various surgical operations available in DOS Correspondent
MSB: such circumstance? Shubha Bansal DNB

It is important to know that filtering procedures are less
successful in traumatic cases compared to normal

22 DOS Times - Vol. 14, No. 7, January 2009

IOL Master Cataract

Prakashchand Agarwal MD, Chandrashekhar MD, G.N. Singh MS,
Namrata Sharma MD, DNB, MNAMS, Jeewan S. Titiyal MD

IOL master, new dimension in optical biometry, is a non-contact • Power calculation for phakic implants: calculation of iris,
optical device that measures the distance from the corneal vertex chamber angle or posterior angle supported phakic implants.
to the retinal pigment epithelium by partial coherence
interferometry. This technique relies on a laser Doppler technique • Optimisation of IOL constants can also be done.
to measure the echo delay and intensity of infrared light reflected
back from tissue interfaces. Partial coherence interferometry is Procedure
also known as optical (or ocular) coherence biometry or laser
Doppler interferometry. Laser interferometry with partial This patient data is first entered. In a overview mode for coarse
coherent light uses 780nm diode laser. Beam splitter reflects light image alignment prior to taking measurements the patient is asked
both at cornea and retina and reflected beams produce interference to look straight at the small yellow fixation light and then the
patterns. The signals are then amplified, filtered and recorded. instrument-to-patient distance is adjusted until the six light
The IOL master is consistently accurate to within + 0.02 mm or reflections on the cornea appear to be in focus. The small circle of
better, which has improved post operative refractive results. lights and the cross hairs should be approximately centered in the
Considering the fact that axial length measurements by A-scan patient’s pupil.
ultrasonography (using a standard 10-MHz transducer) have a
typical resolution of 0.10 to 0.12 mm, axial length measurements Axial Length Measurement Mode
by the IOL Master represent a fivefold increase in accuracy.
(Figure 1) Patient is asked to look directly at the small red fixation light. On
the display a cross hair with a circle in the middle appears (Figure
Instruments 2). Thus axial length measurements will be made to the centre of
the macula, giving the refractive axial length, rather than the
• SRK 2, SRK/T, Holladay, Hoffer Q, Haigis Formulas for anatomic axial length.
calculating the corneal power after refractive surgery (clinical
history method and contact lens method) Haigis-L (for myopic Measurements with and without glasses are exactly the same.
LASIK/PRK) Measurements through contact lenses lead to measurement errors
and should not be performed.

To measure aphakic eyes, pseudophakic eyes filled with silicone
oil, corresponding mode is selected from the AL settings menu.
The instrument will automatically be reset to the “phakic” mode
by changing the side (moving to other eye), or by measuring a new
patient.

Interpretation of Signal Curves

Valid signal curves are characterized by very good signals (signal-
to-noise ratio>10), clear signal (SNR>2.0) or borderline signal (SNR

Figure 1: IOL Master Zeiss V5 Figure 2: View prior to axial
length measurement
Dr. Rajendra Prasad Centre for Ophthalmic Sciences,
All India Institute of Medical Sciences, 25
Ansari Nagar, New Delhi

www.dosonline.org

Figure 3: Settings for keratometer measurement Figure 4: IOL formula
options

1.6-2.0).Along with steep rise of measuring signal several secondary • High ametropia, pupil size as well as state of accommodation

maxima are visible. do not affect the accuracy of measurement.

Keratometry • The incorporation of all operating processes from the
measurement of the parameters to the computation of the
The instrument is aligned so that the six peripheral measuring IOL through the integrated biometric formulas and lens
points are symmetrical, within the circular cross hairs and appear database in a through time savings and patient compliance.
optimally focused. Five measurements are taken within a period
of 0.5 seconds (Figure 3). Limitations

Anterior Chamber Depth Mode IOL Master is not suitable in cases of:

In this mode the system will automatically activate the lateral • In dense cataract
illumination. Throughout the examination the patient is directed • Restless patient with inability to fixate light
straight ahead on a small yellow fixation light. The keratometry • Patient with nystagmus
reading needs to be entered for ACD measurement.

IOL Power Calculation • Retinal detachment

Before the system calculates IOL options, you must have entered • Very high ametropia
the desired lens types into database. The IOL formulas HofferQ, • In severe dry eye or scarred cornea keratometry is not possible
Holladay, Haggis, SRK/t and SRK 11 are listed across the top. The • Anterior chamber depth can’t be measured in aphakic eyes.
desired target refraction can also be achieved. References
1. www.doctor-hill.com
Keratometers measure radii all IOL formulas but the Haigis,
however, expect Ks from an instrument with a keratometer index
of 1.3375 (Figure 4).

Advantages 2. Newer.Investigation of Ophthalmology, Dr. Tanuj Dada Text
• Optical biometry along the visual axis is highly accurate. Book.

First Author
Prakashchand Agarwal MD

26 DOS Times - Vol. 14, No. 7, January 2009

Videokeratography Cornea

Noopur Gupta MS DNB

The cornea is the most important refractive element of the complications from corneal dystrophies, scars, pterygia,
human eye, contributing to approximately two-thirds of its recurrent erosions, and chalazia.
optical power. The anterior surface of the cornea is the most
significant factor affecting the corneal refraction. To detect and Projection device systems
monitor the changes occurring at the anterior corneal surface,
many instruments have been devised like the von Loehman Three types of projection device systems are currently used to
keratoscope, Klein keratoscope and Placido Imaging systems. measure corneal topography, and they are categorized as Placido
Though they are economically priced, they do not provide based, elevation based, slit scanning and interferometric. All of
quantitative measurements and are not sensitive enough to detect them are capable of measuring and analyzing more than 8000 points
small but clinically significant corneal topographic features. on the corneal surface.

The keratometer was introduced with its advantages of accuracy, Placido-based systems
reproducibility, rapidity and ease of use, low cost and less
maintenance. It is able to measure the corneal radius of curvature Placido-based videokeratoscopes contain a transilluminated disc
because the anterior corneal surface behaves like a convex mirror or cone (modified Placido disc), an imaging system consisting of an
and reflects light. The major limitation to keratometry is that it is objective lens, a black and white (B&W) camera (TechnoMed utilizes
based on the false assumption that the cornea is a sphero- a color camera and color-ring system), a video frame grabber, and
cylindrical surface with a single radius of curvature in each meridian, a computer system. 3 The number of rings, thickness of the rings,
and with a major and minor axis separated by 90 degrees. However, colour and position of the rings relative to each other vary from
keratometry is not useful for measuring corneas that are likely to system to system. Most systems can be divided into “near design”
depart from sphero-cylindrical optics, as commonly occurs in and “distant design.” The near-design units typically have greater
refractive surgery, keratoconus, and many other corneal corneal coverage and require lower levels of illumination.
abnormalities.
Elevation-based systems
Corneal topography or computerized videokeratography (VKG)
evolved from the need to measure corneal curvature and Topography implies shape and requires the generation of an X, Y
topography more comprehensively and accurately than and Z coordinate system. Attempting to create such a coordinate
keratometry. Of all the technology currently available, corneal system from curvature data involves certain geometric assumptions
topography provides the most detailed information about the about the cornea. Placido-based systems generate elevation values
curvature of the cornea.1The purpose of computer-assisted by fitting the surface slope data to a pre-defined mathematical
corneal topography is to provide both qualitative and quantitative model, typically spheric, aspheric, or conic section. While reasonable
information about the corneal surface. for normal corneas, this assumption is a potential source of error
in the postsurgical or abnormal cornea.4 Currently, two systems
Standard specific applications for corneal topography include: measure corneal elevation directly: PAR Corneal Topography
System and Orbtek Orbscan. Both systems use a direct triangulation
• To screen patients prior to refractive surgery and evaluating technique to measure the anterior corneal surface. Curvature data
them after surgery are directly calculated from the elevation data without
approximations.5
• To screen patients for irregular astigmatism, corneal warpage,2
and keratoconus prior to refractive surgery; Scanning Slit Imaging: The Orbtek Orbscan uses a scanning slit-
beam and direct stereotriangulation to measure the anterior corneal
• To evaluate the cornea after cataract surgery and to surface. During the 1.5-second examination, the patient fixes on a
understand patients’ visual complaints; light source, whose reflex is aligned with the instrument axis. A
“tracking system” (software image registration) attempts to
• To direct management after penetrating keratoplasty minimize the influence of involuntary eye movement during the
1.5-second examination.
• To plan astigmatic surgery
Interferometric System
• To fit contact lenses in patients with irregular astigmatism,
and This system utilizes laser holographic interferometry fringe patterns
to depict deviation of the corneal surface. Interferometry records
• To evaluate unexplained visual loss and to determine visual the interference pattern generated on the corneal surface by two
coherent wave fronts. High accuracy is theoretically possible.

Dr. Rajendra Prasad Centre for Ophthalmic Sciences, Although this system has been commercially available for nearly a
All India Institute of Medical Sciences, decade, there is limited peer-reviewed literature available validating
Ansari Nagar, New Delhi the system, and it has yet to emerge as a practical clinical tool.

www.dosonline.org 29

represent local changes and peripheral data better than axial maps,
and can accurately determine the position and extent of the cone.

Elevation map

Elevation measurements are simply difference measurements that
calculate elevation in microns compared to a reference sphere.
Elevation data are typically displayed with a reference surface
removed to magnify the surface changes. Points above the reference
surface are positive (“hot” colors), and points below the reference
surface are negative (“cool” colors). The elevation map can help to
distinguish a steep corneal area from one that is steep because of a
protrusion e.g. keratoconus.

Refractive map

Figure 1: Normal topographic map This is also known as the Asphericity map of the cornea. It illustrates
how the corneal curvature refracts light in true diopters of power,
Formats for display of data and not curvature. This uses ray tracings and Snell’s law of optics to
perform the calculations. This map is invaluable to refractive
The interpretation of colour contour maps is based on the surgeons are useful in understanding the effects of surgery and the
recognition of the following regions (Figure 1): optical properties of the cornea. Contact lens practitioners can also
use this map in determining the optical zone for RGP lenses.
• Hot colours- Red, orange & yellow (steep zones of the cornea)
Irregularity map
• Intermediate colour-Green
This displays the distortion of the cornea using previous elevation
• Cool colours- Blue (flatter zones of the cornea) map results with best-fit sphero-cylindrical toric reference instead
of a reference sphere. The difference between the actual surface
• Corneal Power Map (Axial/sagittal) and the best-fit toric surface represents that part of the cornea that
cannot be optically corrected with a spherocylindrical lens
This is a 24 colour representation of dioptric power at various (spectacles).It shows areas that are hotter colours representing a
points on the cornea. The radius of curvature is measured 360 higher value of distortion measured in units of wavefront error. It
times for each placido disc image, from centre to vertex. enables quick diagnosis of any corneal abnormality causing poor
visual acuity.
Numerical (Curvature) map
The original algorithms used by Placido-based systems to
The corneal curvature of different areas on the cornea is shown in reconstruct the corneal surface were spherically biased. The
dioptric values with the constraint that all the centres of rotation addition of other displays (tangential and refractive power)
must fall on the axis defined by the optical axis of the improved the overall ability of videokeratoscopes to convey
videokeratoscope. The numbers are displayed in colour, in meaningful clinical data.
agreement with the colour scale being used. Ten concentric colour
zones at 1mm interval are displayed, showing data in numerical Topographical indices
values. In this map, localized changes in curvature and peripheral
data are poorly represented. Simulated keratometry (SimK)

Keratometric map The values of simulated keratometry are obtained from the greatest
mean dioptric power analyzing along each meridian the mean
It depicts the two principal meridia (K1 & K2) of the cornea at 3 dioptric power. Once the greatest value has been obtained (SimK1),
different zones i.e. central 3mm zone, intermediate 3 to 5 mm the mean value of the 90p meridian is calculated (SimK2).
zone and the peripheral 5 to 7 mm zone. It is an important map
for assessment of skewing of semi-meridians. Minimum keratometric value (MinK)

Profile map This represents the lowest value obtained along each meridian
after analyzing the mean dioptric power along each meridian.

The profile map plots the steepest and flattest meridians of the Cylinder (Cyl)
cornea along with the difference in the two, in the X-Y axis graphs.
It plots the sagittal height of the steepest axis (red) and the flat test The value of the cylinder of the surface under examination is
axis (blue) as a line graph in dioptric value. This display does not obtained from the difference in the simulated keratometric values
represent the cross-section of the cornea. (SimK1 and K2).

Tangential map Average corneal power (ACP)

This gives a better geographical representation of the cornea as This is the mean corneal power in reference to the zone of pupillary
compared to the axial corneal power map. Tangents are projected aperture. Generally, it equals the value of keratometric spherical
outwards from the centre vertex 360 degrees. Tangential maps equivalence, except in decentred surgical procedures.

30 DOS Times - Vol. 14, No. 7, January 2009

Surface Regularity index (SRI)

This represents a measurement of the local fluctuation of the
central corneal dioptric power calculated on an optical zone of
about 4.5 mm.

Surface Asymmetry index (SAI)

This represents the sum of the differences of corneal dioptric
power between corresponding points 180p from each other
calculated over the entire surface. The dioptric power of a normal
surface is distributed symmetrically.

Potential visual acuity (PVA)

This indicates a range of values of potential visual acuity which can Figure 2: Topographic map showing a tight
be expected with a particular corneal surface. These values are suture at 12 O’clock
obtained from the analysis of SAI and SRI.

Corneal abnormality index (CAI)

This index is a measurement of the corneal abnormality and takes Irregular astigmatism index (IPI)
the entire cornea into account. In the event of a spherical surface,
the value is zero, positive in case of a prolate surface and negative
in case of oblate surface.

Standard deviation of corneal power (SDP) This represents the mean of the variations in dioptric power along
each meridian of the analyzed surface.
It is calculated from the distribution of all the corneal power present
on the VKG. It is particularly required in cases where the corneal Analysed area (AA)
surface has a wide range of corneal powers e.g. advanced
keratoconus, penetrating keratoplasty and trauma. This value expresses the percentage of corneal surface covered by
the keratoscopic shots which can be processed by the instrument.
Differential sector index (DSI) The value is low in case of advanced keratoconus, corneal trauma
or immediately following corneal transplant.
This is calculated by subdividing the corneal surface into 8 segments,
each with a 45p angle. The mean dioptric power is then calculated Current Applications of Corneal Topography
within each sector and corrected on the basis of the area examined.
New segments are then defined by rotating the map through 45p Corneal topography is used to evaluate patients before and after
with intervals of 1.41, and a recalculation is done. The DSI ocular surgery, to aid in surgical planning, to assist in contact lens
represents the maximum difference between the mean of two of fitting, and in the evaluation of patients with unexplained visual
the eight segments. It is increased in cases of keratoconus. loss or visual complications from ocular disease.

Opposite sector index (OSI) Screening Patients before Refractive Surgery6,7

This represents the greatest difference of mean corneal dioptric One of the major indications for corneal topography is screening
power existing between 2 opposite sectors of the corneal sector, patients prior to refractive surgery.
divided into 8 equal segments. This index increases in cases of
keratoconus. Diagnosis of Irregular Astigmatism and Corneal warpage8

Centre/surround index (CSI) Contact lens wear can induce corneal warpage and irregular
astigmatism. Often these irregular maps can mimic keratoconus
This index expresses the difference between the mean corneal and lead to an erroneous diagnosis. Topography has been used to
dioptric power of the central 3mm zone and the surrounding zone document the resolution of corneal warpage and the return of a
(3mm to 6mm zone). This index is particularly high in cases where more normal topography with time.
there is an increase in central power such as a locally centralized
keratoconus or a reduction in peripheral dioptric power, as in the Diagnosis of Early Keratoconus9,10
case of hyperopic correction. Negative values are seen when there
is a reduction in the central dioptric power, as in myopia correction. Computerized corneal analysis has been shown to be more
sensitive in detecting keratoconus than slit-lamp examination,
Keratoconus predictability index (KPI) keratometry, and keratoscopy. While advanced keratoconus is easy
to diagnose, early or subclinical keratoconus poses a greater
This is obtained from the statistical analysis of the indices. It is diagnostic challenge. In attempts to improve the sensitivity of
considered to be a numerical estimator of keratoconus which spans computerized videokeratoscopes, a number of indices have been
from zero, when no there are no topographical characteristics of developed that suggest that keratoconus may be present. These
keratoconus present, up to 100% when all the topographical quantitative descriptors represent the classic “Rabinowitz” indices.11
characteristics relative to the keratoconus are evident. These include:

www.dosonline.org 31

Figure 3a: Topographic map depicting a typical bow- Figure 3b: Topographic map depicting a bow-tie pattern
tie pattern with against the rule (ATR) astigmatism and with the rule (WTR) astigmatism

• I-S Steepening- Keratoconic eyes typically show greater topography involved patients with high astigmatism who required
inferior corneal steepening. The I-S index is a measure of the relaxing incisions. 14 Computer-generated indices of corneal
difference between the inferior corneal curvatures (at the 3.0 asymmetry and regularity correlated well with Snellen visual acuity
mm optical zone) and the corresponding superior corneal measurements.
sector (5 points taken in each sector 3 mm from the centre
and 30p apart). Values between 1.4 and 1.9 diopters represent Surgical Planning
keratoconus suspects. Values greater than 1.9 diopters are
considered positive for keratoconus. Corneal topography is used in planning astigmatic surgery.
Symmetrical and asymmetrical bow tie pattern with against the
• Corneal Asymmetry- Central corneal curvatures of the two rule (Figure 3a) and with the rule (Figure 3b) astigmatism can
eyes that differ by more than 0.92 diopters suggest that easily be picked up. Irregular astigmatism and asymmetric
keratoconus may be present. astigmatism can be identified.

• Central corneal curvature- Keratoconus can be suspected Although corneal topography is part of standard care in many
when simulated keratometry readings are between 47.2 and common clinical situations, videokeratography devices are an
48.7 diopters. Values greater than 48.7 diopters are considered evolving technology, and their use is an area of active investigation.
positive for keratoconus. It is important to improve their accuracy and reproducibility where
needed and to standardize measurements and nomenclature. A
Evaluating Postoperative Changes in Corneal Shape after thorough understanding of the relationship between corneal
Refractive Surgery topography and optical performance would enhance patient care.

Corneal topography was developed as a way to measure the shape References
of the cornea after refractive surgery in order to understand
patients’ visual complaints and ultimately the optical performance 1. Schultze RL. Accuracy of corneal elevation with four corneal
of the cornea after refractive procedures. It was used initially to topography systems. J Refract Surg 1998;14:100–4.
evaluate patients following epikeratoplasty, then radial keratotomy
and more recently photorefractive surgery (both PRK12 and 2. Smolek MK, Klyce SD, Maeda N. Keratoconus and contact lens-
LASIK). Topography has been used extensively to evaluate post- induced corneal warpage analysis using the keratomorphic diagram.
PRK patients to identify decentrations, to evaluate and treat central Invest Ophthalmol Vis Sci 1994; 35:4192–204.
islands, and to determine the surgical effect and postoperative
regression. 3. Hannush SB, Crawford SL, Waring GO III, et al. Accuracy and
precision of keratometry, photokeratoscopy, and corneal modeling
After Cataract Surgery on calibrated steel balls. Arch Ophthalmol 1989;107:1235–9.

Corneal topography has been used to understand the effect of 4. Mandell RB. The enigma of the corneal contour. CLAO J
cataract incision placement and size. 13 It has also been used to 1992;18:267–73.
evaluate long-term stability of various cataract incisions. Tight
sutures can be easily detected and managed. (Figure 2) 5. Litoff D, Belin MW, Wynn SS, Smith RS. PAR technology corneal
topography system. Invest Ophthalmol Vis Sci 1991; 32(4
After Penetrating Keratoplasty Suppl):922S.

Corneal topography is helpful in evaluating and managing patients 6. Wilson SE, Klyce SD. Screening for corneal topographic
following penetrating keratoplasty. An early application of corneal abnormalities before refractive surgery. Ophthalmology 1994;
101:147–52.

32 DOS Times - Vol. 14, No. 7, January 2009

7. Nesburn AB, Bahri S, Salz J, et al. Keratoconus detected by 12. Wilson SE, Klyce SD, McDonald MB, et al. Changes in corneal

videokeratography in candidates for photorefractive keratectomy. J topography after excimer laser photorefractive keratectomy for

Refract Surg 1995;11:194 –201. myopia. Ophthalmology 1991;98:1338–47.

8. Wilson SE, Lin DTC, Klyce SD, et al. Topographic changes in contact 13. Koch DD, Haft EA, Gay C. Computerized videokeratographic
lens-induced corneal warpage. Ophthalmology 1990; 97:734–44. analysis of corneal topographic changes induced by sutured and
unsutured 4 mm scleral pocket incisions. J Cataract Refract Surg
9. Maguire LJ, Bourne WM. Corneal topography of early keratoconus. 1993;19(Suppl):166 –9.
Am J Ophthalmol 1989;108:107–12.
14. Koffler BH, Smith VM. Corneal topography, arcuate keratotomy,
10. Wilson SE, Lin DTC, Klyce SD. Corneal topography of keratoconus. and compression sutures for astigmatism after penetrating
Cornea 1991;10:2– 8. keratoplasty.J Refract Surg 1996;12:306 –9.

11. Rabinowitz YS, Nesburn AB, McDonnell PJ. Videokeratography of
the fellow eye in unilateral keratoconus. Ophthalmology
1993;100:181– 6.

First Author
Noopur Gupta MS, DNB

Congratulations

Congratulations to Dr. Namrata Sharma, Dr. Vishal Jhanji, Prof. Jeewan S. Titiyal, Prof. Rasik B. Vajpayee,
for their video titled ‘DALK in Hurler Schie’s Syndrome’ for being selected in “Front Row View, Series
3: Video Collection of Eye Surgery’ by American Academy of Ophthalmology.

www.dosonline.org 33

Confocal Microscopy Cornea

Shubha Bansal DNB, Namrata Sharma MD, DNB, MNAMS, Meena Verma MSc, Jeewan S. Titiyal MD

Over the past decades, the clinical application of confocal confocal microscope, which has been widely used in the biological
microscopy in ophthalmology has expanded in a progressive sciences, substitutes a low power laser as the illuminator, which
and consistent manner. The present review aims to summarize meets American National Standards Institute requirements for
the current knowledge of this technology in corneal sciences and safe use in the eye.
to provide the basis to interpret and analyze corneal confocal
images. Corneal edema may limit the effectiveness of standard specular
microscopy; however, the confocal microscope can view the
Instrument endothelium and inflammatory cells through a relatively
edematous cornea. This device can search for hyperreflective,
In 1955, Marvin Minsky1 fellow at Harvard University – developed round bodies typical for inflammatory cells, potentially avoiding
a novel microscopy technique that imaged tissue parallel to its unnecessary regrafts.8
surface. Images obtained by traditional methods are generally
oriented perpendicular to the tissue surface and collect all light Recently, a corneal confocal microscope with a z-ring adapter (z-
reflected or transmitted by the tissue, including light reflected ring Confoscan 4.0; Nidek Technologies, Padova, (Italy) claiming
from tissue depths both above and below the point of interest. to accurately measure corneal layer distance along the z-axis has
This unwanted light creates optical artifacts that diminish image been introduced in clinical practice. The constant pressure system
quality. Minsky’s invention eliminated many of these artifacts. The continuously records the pressure of the objective lens onto the
confocal microscope exploits the pinhole effect. Minsky carefully eye (which may change depending on the eye movement), and the
placed two pinholes, the first before the condenser, which focuses software automatically moves the optical head forward or
the light rays into the tissue, and the second before the eyepiece or backward. This feedback allows to maintain a constant contact
camera, which focuses the reflected light rays into an image. This pressure. (Figure 2a & 2b)
arrangement blocked unwanted light reflections2
Normal cornea confocal appearance
Minsky coined the term ‘confocal’ to describe this conjugate focal
point design. His confocal technique produced sharp images with Epithelium: Confocal microscopy measured the corneal epithelial
excellent contrast. (Figure 1) Modern confocal microscopy replaced thickness to be 54+7mm centrally and 61+5mm peripherally.9 The
the condenser with either white light or a focused laser beam, and epithelium generally comprises three cell layers – basal, wing and
the eyepiece with an electronic digital detector. Since the depth of superficial. The basal epithelial layer, derived from the perilimbal
the focal plane can quickly be changed, this permits real-time, stem cells, migrates onto the cornea and subsequently
dynamic Z-axis scanning capability. Therefore, this powerful differentiates into polygonal wing cells. These wing cells comprise
technique enabled in-vivo corneal scanning without the need for the intermediate cell layers that eventually differentiate into the
stains or dyes. Furthermore, computer technology permitted superficial epithelial cells. Within these cell layers, Langerhans cells
three-dimensional reconstructions of the images. Overall, this new appear as large, reflective, dendritic bodies. (Figure 3)
technology improved lateral and axial resolution to 1–6 and 4–
15mm, respectively, and increased magnification up to 600 times3 Basal cells measure 10–15mm in diameter and are usually uniform
in size and reflection. They form a monolayer, situated just anterior
Tandem scanning- Petran et al.4 adapted the Nipkow Disk,
originally developed for encoding and decoding telegraph
messages. This disk contains approximately 14 000 pinholes that
are systematically positioned 1800 opposite each other, allowing
simultaneous alignment with the detector and illuminator.4 When
this disk is rotated, the entire specimen can be scanned. This high
scan rate permitted the use of modern imaging technology to
view the tissue in real-time. Thus, one could view in-vivo corneal
tissue scanning on a video or computer screen.

Scanning confocal microscope- uses a single light path to create Figure 1: Diagrammatic representation of
the confocal image, which is theoretically simpler than the tandem the optical principles of confocal microscopy.
design. Koester5 and Maurice6 independently invented the
scanning slit confocal microscope that substituted a slit beam for
the Nipkow disk. In order to scan, Koester and Maurice used
movable mirrors within the microscope.7 The clinical laser scanning

Dr. Rajendra Prasad Centre for Ophthalmic Sciences,
All India Institute of Medical Sciences,
Ansari Nagar, New Delhi

www.dosonline.org 35

Figure 2a: Confoscan 4 Figure 2b: Schematic drawing showing the z-ring
(Nidek) adapter system: In the bottom right-hand, a real

picture of the z-ring adapter. (M: motor)

Figure 3: Normal Epithelium Figure 4: Superficial epithelial cells

to Bowman’s layer. On confocal microscopy, these cells reflect such as the highly reflective, beaded appearing sub-basal nerve
light poorly. The cell borders are visible, however, as highly reflective plexus.10
outlines with highly reflective cell nuclei.10
Stroma: The stoma comprises keratocytes, collagen and ground
Wing cells comprise intermediate, two to six-cell layers. These substance. The highest concentration of stromal keratocytes is
polygonal cells appear uniform in shape and size with a dark located just posterior to Bowman’s layer. Mustonen et al10
cytoplasm and bright borders similar to basal cell morphology.10 measured an anterior keratocyte density of 1058+217 cells/mm2
In general, wing cells tend to be larger than basal cells, but smaller that progressively decreased to 771+135 cells/mm2 posteriorly.
than superficial cells. Additionally, confocal imaging measured full-thickness central
keratocyte density that decreased 0.45% per year.11 Confocal
Superficial epithelial cells are generally one to two cells thick. These images demonstrate poor reflectivity of stromal keratocyte’s
cells appear flat and polygonal with light cell boundaries, subtle cytoplasm, cell boundaries and collagen substance.10 Despite this
cytoplasm reflectivity and bright nuclei.10 These cells tend to vary poor reflectivity, stromal keratocytes have bright, prominent nuclei
in diameter with the largest measuring 50mm.9 Generally, the suspended within a dark, amorphous ground substance. In
bright cells represent metabolically active epithelial cells while the addition to keratocytes, various hyperreflective nerve bundles can
dark cells signify dead or desquamated epithelial cells.9,10(Figure4) be seen weaving obliquely in between the collagen fibrils.

Bowman’s layer: It is an acellular layer composed of randomly Descemet’s membrane: Descemet’s membrane comprises the basal
dispersed collagen fibrils, measuring 12mm thick.10 On confocal lamina of the corneal endothelium. This membrane thickens
microscopy, Bowman’s layer appears as an amorphous membrane throughout life from 3–4mm at birth to 10–12mm in adulthood.12
that is difficult to image without the aid of anatomical landmarks, Unfortunately, the lack of cell nuclei and poor reflectivity prevent

36 DOS Times - Vol. 14, No. 7, January 2009

Figure 5: Corneal endothelium Figure 6: Multiple branching corneal nerves

the visualization of Descemet’s membrane on confocal microscopy therapy consist of inverse reflectivity of the basal epithelial cells,
unless significant fibrosis is present. Just as with Bowman’s layer, these changes were visible even before their detection by
however, anatomical landmarks, such as the surrounding biomicroscopy.1616
keratocyte nuclei and endothelial cells, can serve to aid in the
identification of Descemet’s membrane.10 Ciprofloxacin corneal deposits presents as highly reflective deposits
in areas devoid of epithelium.17 Stromal deposition of gatifloxacin
Endothelium: Endothelial cells are hexagonal shaped cells that crystals through a compromised corneal epithelium have also been
number approximately 500000 cells, giving an average cell count described by confocal microscopy.
of 3055 +386 cells/mm.2 Since these cells cannot replicate, the
absolute cell number decreases with age. A recent longitudinal Epithelial abnormalities like in Thygeson keratitis, fine and highly
study over 10 years demonstrated a cell loss rate of 0.6+0.5% per reflective material are visualized below the basal lamina.18 In
year in adults. On confocal microscopy, the endothelial cells usually advancing wave-like epitheliopathy), confocal microscopy discloses
appear as cell bodies without visible nuclei. This appearance is the presence of atypical, elongated, and centripetally oriented cells
similar to that of specular microscopy (Figure 5). with well-recognizable nuclei at the level of the abnormal
epithelium. At the subepithelial level, confluent hyperreflective
Corneal innervation: The cornea, especially the epithelium, is one images may be detected. With disease resolution following silver
of the most densely innervated superficial tissues in the human nitrate application at the limbus, the abnormal epithelial cells
body. For comparison, the corneal innervation is 20–40 times that disappear on confocal microscopy. In Meesman corneal dystrophy,
of tooth pulp and 300–600 times that of skin.13 Overall, the central circular, oval, or teardrop shaped hyporeflective areas in the basal
two-thirds of the corneal epithelium is five to six times more densely epithelial layer are observed. In patients with dry eyes, confocal
innervated than the peripheral cornea. Approximately 60–80 nerve microscopy revealed patchy alterations or irregularities in surface
bundles enter into the anterior one-third of the corneal stroma. epithelial cells, and abnormal subbasal nerve sprouting with
These nerve bundles branch and travel obliquely toward the sub- increased bead-like formation. In Salzmann nodular degeneration,
basal plexus that lies just posterior to Bowman’s layer.14 (Figure 6). irregularly shaped basal epithelial cells with increased extracellular
The corneal epithelium is thought to receive its innervation directly reflectivity in the nodules are seen.
from this plexus. It is estimated that there are approximately 16
000 nerve endings per 1 mm2 within the superficial epithelial layer.14 Stromal Abnormalities
Corneal nerves are highly reflective and appear as bright, reflective,
branching lines within the stroma or epithelium on confocal Stromal dystrophies usually are readily identified upon slit-lamp
images. examination. However, their confocal microscopic appearance
should be recognized, in order to avoid misinterpretation and
Epithelial Diseases erroneous diagnosis. In lattice dystrophy19 linear and branching
hyperreflective structures with changing reflectivity and poorly
Reports have documented the confocal appearances of epithelial demarcated margins are visualized in the stroma. In Reis-Buckler
or subepithelial deposits, including amiodarone, amyloid, dystrophy, multiple gray fine opacities are found in the Bowman’s
chloroquine, ciprofloxacin, gold, and iron deposits. Findings in layer region mainly in the central cornea. These opacities may
amiodarone-induced keratopathy are characterized by high extend into the anterior stroma. In granular dystrophy, deposits in
reflective, bright intracellular inclusions in the corneal epithelial the stroma present as extracellular highly reflective material
cells. The confocal microscopic appearance of the deposits separated by areas of normal tissue tissue. This hereditary
consisted of extracellular, hyperreflective, cotton candy-like condition is an allomorphic process with many alleles and a wide
material.15 Corneal epithelial changes caused by chloroquine spectrum of both slit lamp and confocal appearances. In Schnyder

www.dosonline.org 37

Figure 7: Vogt’s striae in keratoconus Figure 9: Fungal Hyphae

by confocal microscopy. In cornea farinata, small hyperreflective
particles are found in the cytoplasm of the most posterior
keratocytes.

Endothelial Pathologies

Figure 8: Fuch corneal dystrophy Conventional techniques to examine the endothelium include
specular microscopy and light or electron microscopy. While
crystalline corneal dystrophy, accumulation of reflective crystalline specular microscopy is often ineffective in visualizing the
material is observed in the anterior stromal keratocytes and in endothelium in cases of corneal edema, light or electron
association with prominent subepithelial nerves. In more advanced microscopy may only be used for ex vivo examination. Confocal
cases, dense crystals, highly fibrotic stroma, and damaged corneal microscopy, on the other hand, enables in vivo examination of the
innervations may be noted. endothelium, even in cases of moderate corneal edema. In cases
of cornea guttata or Fuchs endothelial dystrophy, cornea guttae
In keratoconus,20 Vogt’s striae (Figure 7) and folds near Bowman’s appear as roundish hyporeflective images with an occasional
membrane or disruption to Bowman’s layer may be seen. central highlight at the level of the endothelium.21 (Figure 8)
Keratocytes with long processes are arranged nearly in parallel in Decreased endothelial cell count with pleomorphism and
the area of the corneal apex. Keratocyte density is decreased in polymegathism are seen. Corneal edema may be associated with
the anterior and posterior stroma in keratoconus patients wearing bullae in the basal epithelial layer, abnormal Bowman’s layer
contact lenses. Hyperreflective keratocyte nuclei indicating presenting as diffuse bright reflection and absence of nerves, and
fibroblastic activity and haze may be detected in the stroma. lacunae and dark bands against increased background reflection
Elongated endothelial cells may be observed. Edema involving the in the stroma.
anterior stroma and the epithelium may be detected in case of
hydrops. In primary congenital glaucoma with megalocornea, a mild Confocal microscopy demonstrates the microscopic structure of
reduction of keratocyte density in the posterior stroma, a clew- the retrocorneal membranes, and subsequently allows
shaped morphology of stromal nerves, and discontinuous straightforward recognition of the nature of the membrane. In
hyperreflective structures at the level of Descemet’s membrane cases of epithelial downgrowth, cells with epithelial appearances
have been reported. Corneal degenerations may also be analyzed are the prominent features. They are recognized by their epithelial
arrangement and the presence of nuclei reflectivity. Fibrous
membrane presents as paucicellular hyperreflective images.
Posterior polymorphous dystrophy is most of the time a fortuitous
finding and asymptomatic.

Corneal infections

Treatment of corneal infections can be challenging due to delays
in accurate culture results. In an attempt to rectify this issue, early
investigators used in-vivo confocal microscopy to visualize fungus,
acanthamoeba, bacteria and microsporidium. Although, viruses
are too small to be imaged, adenovirus viral-induced subepithelial
infiltrates have been studied.

38 DOS Times - Vol. 14, No. 7, January 2009

In general, fungal infections are characterized by the presence of calculate both flap and residual bed thickness. Confocal
hyperreflective, elongated, filaments or budding yeast (Figure 9). microscopy can be used to directly visualize postoperative corneal
For example, in Fusarium solani keratitis, the hyperreflective infiltrates of inflammatory cells, distinguishing between diffuse
filaments appeared aligned in planes parallel to the anterior lamellar keratitis and infections.
corneal surface, perhaps growing between the corneal lamella.
Aspergillus fumigatus has a similar appearance, but possess Conclusion
filaments that branched at 458 angles. In contrast, acanthamoeba
appears as highly reflective, round or ovoid double-walled cyst Advantages of confocal biomicroscopy for the examination of
with a diameter of about 10–25mm.22 The classic honeycomb corneal components include the facts that; it is noninvasive,
stromal pattern manifests as optically lucent microcavities of focal facilitating examination of the same subject at different times; it
stromal destruction. Radial keratoneuritis appears as irregularly allows observation of corneal structure at high magnification; and
enlarged regions of nerve fibers. Bacteria (1.5–2mm diameter) it allows visualization of keratocytes and corneal nerve fibers.
are poorly visualized as hyperreflective bodies within the cornea. Despite these advantages for clinical application, confocal
biomicroscopy is not readily performed in all clinics and the
In infectious crystalline keratitis, needle-like deposits and crystals number of machines in use remains limited. In addition, the
have been imaged. Conversely, Nocardia asteroids – filamentous technique cannot be applied to extremely edematous or opaque
bacteria – appear as highly reflective, short, thin, beaded branching corneas, especially for observation of the deep stroma or
filaments that often branch at right angles. They are best seen at endothelium. Corneal stromal opacity, such as that associated
the edge of the infiltrate and often appear clumped together. with severe bullous keratopathy or severe stromal leukoma, results
Additional examples include Borrelia keratitis, which presented in the scattering of light emerging from the objective lens. It is
as highly reflective round objects that were arranged in straight possible; however, to perform confocal biomicroscopy in
lines, and microsporidia, which appeared as small, intraepithelial individuals in whom opacity is restricted to the overlying corneal
opacities. epithelium. Confocal biomicroscopy requires a coupling gel to
reduce light scattering at the corneal epithelium. The coupling gel
Refractive surgery allows observation of cellular components in corneas affected by
epithelial disorders, as is often the case in individuals with
Confocal microscopy has played a critical role in advancing the established Fuchs dystrophy as a result of the severity of the
management of complications and understanding corneal wound associated stromal edema. In addition, perhaps the most significant
healing after refractive surgery. Rajan et al23 used confocal attribute of confocal biomicroscopy is that it allows the detection
microscopy to study real-time cellular kinetics over 4 weeks after of minor abnormalities of the cornea that would not be revealed
photorefractive keratectomy (PRK), laser-assisted subepithelial by slit-lamp examination.
keratectomy (LASEK) and laser in-situ keratomileusis (LASIK).
Epithelial healing following PRK was completed by 92 h, whereas, References
after LASEK, the epithelial flap necrosed and was completely
replaced by 120 h. The magnitude of keratocyte loss corresponds 1. Minsky M. Memoir on inventing the confocal scanning
to ablation depth and keratocyte regeneration was delayed until microscope. Scanning 1988; 10:128–138
epithelial closure.
2. Cavanagh HD, Petroll WM, Alizadeh H, et al. Clinical and
Confocal microscopy can also reveal potential complications diagnostic use of in vivo confocal microscopy in patients with corneal
associated with relatively routine refractive surgery. Corneal haze disease. Ophthalmol 1993; 100:1444–1454.
after PRK was found to represent activated keratocytes on confocal
imaging. For example, 4 weeks after a 4D PRK and 9 D PRK 3. Jalbert I, Stapleton F, Papas E, et al. In vivo confocal microscopy of
correction, the keratocyte density had reached 98 and 111% of the human cornea. Br J Ophthalmol 2003; 87:225–236.
preoperative levels, respectively23 Thus, deeper ablations were
noted to have more activated keratocytes that remained active 4. Petran MH, Hadravsky M, Egger MD, Galambos R. Tandem
longer, which may explain the increased corneal haze and greater scanning reflected light microscope. J Optics Soc Am 1968; 58:661–
regression rates observed in higher PRK corrections. In 664.
comparison, LASIK corneas demonstrated less keratocyte loss,
but surprisingly, the stromal flap demonstrated poor keratocyte 5. Koester C. Scanning mirror microscope with optical sectioning
recovery. characteristics: applications in ophthalmology. Appl Opt 1980;
19:1749–1757
Refractive surgery can cause a postoperative dry eye syndrome
secondary to de-innervation. Confocal images demonstrate that 6. Maurice DM. A scanning slit optical microscope. Invest
the subbasal nerve density decreases 90% 1 month after LASIK, Ophthalmol Vis Sci 1974; 13:1033–1037.
but begins to recover by 3–6 months. By 2 years, however, the
nerves have regrown to approximately 50% of their perioperative 7. Kaufman SC, Kaufman HE. How has confocal microscopy helped
density. On the other hand, corneal nerve density recovers almost us in refractive surgery? Current Opinion in Ophthalmology 2006;
completely after PRK by 2 years. 17:380–388.

Other applications include examination of the LASIK flap interface, 8. Kaufman SC, Musch DC, Belin MW, et al. Confocal microscopy: a
which demonstrated benign hyperreflective material. Depth report by the American Academy of Ophthalmology.
determination of the LASIK flap interface can then be used to Ophthalmology 2004; 111:396–406

9. Eckard A, Stave J, Guthoff RF. In vivo investigations of the corneal
epithelium with the confocal Rostock laser scanning microscope.
Cornea 2006; 25:127–131

www.dosonline.org 39

10. Mustonen RK, McDonald MB, et al. Normal human corneal cell of Thygeson’s superficial punctate keratitis. Clin Experiment
populations evaluated by in vivo scanning slit confocal microscopy. Ophthalmol 32:325—7, 2004
Cornea 1998; 17:485–492
18. Chiou AG, Beuerman RW, Kaufman SC, et al: Confocal microscopy
11. Patel SV, McLaren JW, Hodge DO, Bourne WM. Normal human in lattice corneal dystrophy. Graefes Arch Clin Exp Ophthalmol
keratocytes density and corneal thickness measurement by using 237:697—701, 1999
confocal microscopy in vivo. Invest Ophthalmol Vis Sci 2001;
42:333–339. 19. Hollingsworth JG, Bonshek RE, Efron N: Correlation of the
appearance of the keratoconic cornea in vivo by confocal microscopy
12. Murphy C, Alvarado J, Juster R. Prenatal and postnatal growth of and in vitro by light microscopy. Cornea 24:397—405, 2005
the human descemet’s membrane. Invest Ophthalmol Vis Sci 1984;
25:1402–1415. 20 Chiou AG, Kaufman SC, Beuerman RW, et al: Confocal microscopy
in cornea guttata and Fuchs’ endothelial dystrophy. Br J Ophthalmol
13. Muller LJ, Vrensen GF, Pels L, et al. Architecture of the human 83:185—9, 1999
corneal nerves. Invest Ophthalmol Vis Sci 1997; 38:985–994.
21. Chiou A, Kaufman SC, Kaufman HE, et al. Clinical corneal confocal
14. Guthoff RU, Wienss H, Hahnel C, Wree A. Epithelial innervation microscopy. Surv Ophthalmol 2006; 51:482–500
of human cornea: a three-dimensional study using confocal laser
scanning fluorescence microscopy. Cornea 2005; 24:608–613. 22. Chiou AG, Kaufman SC, Beuerman RW, et al: Confocal microscopy
in cornea guttata and Fuchs’ endothelial dystrophy. Br J Ophthalmol
15. Kaufman SC, Beuerman RW, Goldberg D: A new form of primary, 83:185—9, 1999
localized, corneal amyloidosis: a case report with confocal microscopy.
Metab Pediatr Syst Ophthalmol 18:1—4, 1995 23. Chiou A, Kaufman SC, Kaufman HE, et al. Clinical corneal confocal
microscopy. Surv Ophthalmol 2006; 51:482–500
16. Slowik C, Somodi S, von Gruben C, et al: [Detection of
morphological corneal changes caused by chloroquine therapy using 24. Rajan M, Watters W, Patmore A, et al. In vitro human corneal
confocal in vivo microscopy]. Ophthalmologe 94:147—51, 1997 model to investigate stromal epithelial interactions following
refractive surgery. J Catract Refract Surg 2005; 31:1789–1801.
17. Cheng LL, Young AL, Wong AK, et al: In vivo confocal microscopy

First Author
Shubha Bansal DNB

Answer Quiz No. 7

Extra Word: GLAUCOMA

4. JUVENILE 7. GONIOSCOPY 6. MALIGNANT 1. SCOTOMA
8. NEOVASCULAR 5. IRIDOTOMY
3. SCHLEMM 2. AQUEOUS

40 DOS Times - Vol. 14, No. 7, January 2009

Specular Microscopy Cornea

Deepa Gupta MBBS, Ritu Arora MD, Jawahar L. Goyal MD

Specular microscopy is a novel way to evaluate the structure
and function of the corneal endothelium. It can be performed
using slit-lamp biomicroscope clinically as well as by using specular
microscope.

In 1968, David Maurice developed a microscope to visualize the
corneal endothelium and introduced the term specular
microscope. In 1975, Bourne and Kaufman designed the modern
non-contact specular microscope.

Both qualitative and quantitative assessment of the corneal Figure 2: Specular reflection
endothelium can be performed by specular microscope. They Vs Diffuse reflection
provide a rapid clinical evaluation of the endothelium to assess
the risk of intraocular surgery, to estabilish a diagnosis, or to decide
on treatment.

Qualitative cellular analysis identifies abnormal endothelial transparency of the medium below its surface, and the relative
structures and grades the endothelium according to cell refractive indices on each side of the surface. Specular microscope
conformation, boundaries, intersections and presence of acellular is based on the principle of specular reflection of light where the
structures. Quantitative parameters include cell size, angle of reflection is equal to the angle of incidence as seen in the
polymegathism, pleomorphism, cell perimeter and average cell figure below-
side length.

For the normal transparent cornea, most visible light incident on
the epithelial surface is transmitted. As the light passes through
the stroma, most of the incident light is transmitted through the
tissue, although a small amount is absorbed and/or scattered
(reflected through arbitrary angles) by cellular organelles. With
an increase in corneal edema the fraction of scattered light increases
and can become the dominant element thus giving rise to a "hazy"
cornea. As light strikes the posterior corneal surface, almost all of
it is transmitted into the aqueous humor. Because there is a change
in index of refraction at the endothelium-aqueous humor
interface, about 0.022 per cent of the total incident light is reflected;
this reflected light is captured by the clinical specular microscope
and forms the endothelial image.

Figure 1: The first laboratory specular As the illumination beam of the specular microscope passes
microscope used by David Maurice through the cornea, it encounters a series of interfaces between
optically distinct regions which reflect some light back.The greater
Principle & Optics the difference in index of refraction between the two regions, the
To properly interpret the endothelial photomicrographs obtained greater the amount (intensity) of the reflected light. A portion of
clinically, it is helpful to understand the optical principles of the the reflected and backscattered light is collected by the objective
specular microscope. Light striking a surface can be reflected, lens of the specular microscope and forms an image of that part
transmitted, or absorbed. Generally, some combination of the of the cornea on which the instrument is focused.
three effects occur, with the relative proportions depending on
such conditions as the wavelength of the light, the relative Figure A shows a narrow slit of light from a specular microscope
that is focused onto the posterior corneal surface. At the major
Cornea Services, optical interfaces (labeled 1, 2, and 3) much more light is specularly
Guru Nanak Eye Center, Maualana Azad Medical College, reflected back toward the image plane. Using indices of refraction
for the objective lens, saline, cornea, and aqueous humor of 1.517,
Maharaja Ranjit Singh Marg, New Delhi 1,333, 1,376, and 1.336, respectively, the fraction of light reflected
from each of these interfaces can be calculated to be 0.36% from
the objective lens-saline interface, 0.025% from the saline-corneal
epithelium interface, and 0.022% from the corneal endothelium-
aqueous humor interface. Intracorneal optical interfaces (e.g.,

www.dosonline.org 43

Figure 3: Representation of an optical section when a narrow slit (A) or a wide slit
(B) of light passes through various corneal layers and is focused on the posterior corneal surface.

As drawn, the film plane is positioned at right angles to the plane of the paper. The zones are
defined in the text. BB = bright boundary; DB = dark boundary.

between epithelium and Bowman's membrane or between stroma
and Descemet's membrane, etc) also reflect light, but the fraction
of reflected light cannot be calculated because the index of refraction
of the separate layers of the cornea has never been measured.

If a sufficiently narrow slit of incident light is used, one can generally
distinguish a bright region (Zone 1) formed by light reflected from
the lens-coupling fluid or the coupling fluid-epithelial interfaces
or both, part of the stromal region (Zone 2), the endothelial region
(Zone 3), and part of the aqueous humor (Zone 4).

The demarcation line between Zone 3 and Zone 4 that separates Figure 4: Pleomorphism
the illuminated cornea from the nonilluminated structures located
more posteriorly., is called the dark boundary (see figure above).
One side of the boundary is dark because negligible light is scattered
from the aqueous humor. In contrast, the demarcation line
between Zone 2 and Zone 3 is called the bright boundary. This
boundary separates the endothelial reflection from the overlying
illuminated corneal stroma. Since some light is scattered from the
stroma, neither side of the boundary is dark.

Of clinical importance is the width of the slit of light projected Figure 5: Polymegathism
onto the cornea by the specular microscope. If the angle of
incidence of the illuminating source is increased, a wider slit can be
used and a larger field of endothelial cells can be seen (Figure B).
However, the wider slit beam also illuminates more of the corneal
tissue anterior to the endothelium, so that the volume of
"interfering stroma" increases and more light is scattered back to
the image plane of the specular microscope. The net result is a
decrease in contrast of the endothelial image and a loss of cellular
definition. Using a narrow slit four distinct zones are seen; with a
wide slit only three zones are apparent.

Morphological parameters

The normal endothelium is usually made up of hexagonal, regular, shape.The polymorphic cells (light shading) shown below have
cells which are roughly uniform in shape. different numbers of sides than their hexagonal counterparts
(darker shading). Polymegathism is also present, with some
Pleomorphism (also known as polymorphism) refers to variation rosettes seen.
in cell shape or their deviation from the normal hexagonal

44 DOS Times - Vol. 14, No. 7, January 2009

Polymegathism refers to variation in cell sizes. It rarely occurs in
isolation without variation in cell shape. It is graded separately as
trace, mild, moderate or severe. Note the rosettes which are seen
as very small cells (dark shading) surrounded by much larger cells
(light shading). Rosettes are not a finding specific to a disease, but
rather indicate the presence of polymegathism.

Specular Microscopy: Fixed Frame Analysis

Fixed frame analysis is a technique that uses a standard size frame Figure 8: Topcon non contact specular
to count the cells. The frame is used as an overlay, counting all microscope Pre-op risk assessment
cells within the area, those touching two sides and excluding the
cells that touch the other two sides. One then divides the known Variable Frame Analysis
area of the frame by the number of cells. The test is subjective in
that the technician must pick a representative area of cells within Variable frame analysis in specular microscopy refers to the
the frame, all of which must be readily identifiable so that they can counting of cells using a variably shaped boundary to outline the
be counted. If the area of cells is irregularly shaped or doesn't fill counted cells. A computerized planimetry device is used to
the "frame", variable frame analysis can be used. measure the area. The device can then divide the area by the
In the example below of fixed frame analysis the grid is 0.01mm2. number of cells within it to arrive at a cell density. This technique
The cells are counted by marking with a dot for those to be works especially well when the countable areas are irregularly
included. The cells touching the left and bottom grids are counted shaped. The cells still need to be identified manually, generally by
while those split, but not completely included by the top and right, "clicking" on each one with the computer mouse. Since the area is
are excluded. Dividing the number of cells by the area of the grid defined by the borders of the cells, none are excluded. The
gives the cell density. For the example in Figure : [whole cells (18) computer then calculates the area and the number of cells is divided
+ partial cells (7)] divided by the frame area = 2500 cells/mm2. by the area to give the cell density.

Figure 6: Fixed frame analysis Clinical applications

Figure 7: Variable frame analysis Indications:

• Pre-op assessment of the donor cornea

• Corneal edema

• Corneal degenerations

• Corneal dystrophies

• Ocular inflammation

• Contact lens endotheliopathy

• Secondary cataracts

• Eye injuries

• Post -op management

Specular reflection using slit lamp biomicroscope

In a darkened room, the patient is asked to look straight ahead
and slit beam is projected onto the central cornea from the
temporal side. Height of beam shortened to 4-5mm and made
moderately wide. The examiner should focus the slit beam at the
level of endothelium and then slowly move it temporally towards
the catoptric image (the corneal light reflex). When the slit beam
passes in front of the catoptrics image, a bright reflex from tear-
air interface dazzles the examiner and a faint beaten metal image

www.dosonline.org 45

Figure 9: Clinical specular reflection

Figure 10: An eyebank specular to count the cell density, evaluate the morphology, and place an
microscope image on the tissue record.

of the endothelium becomes apparent. At this point, magnification Interpretation
is changed to a higher level and focused. The paving stone pattern
of endothelium becomes apparent. Comparing specular The standard printout of a specular microscope denotes the
microscope results to the slit lamp specular reflection mosaic allows following parameters:
to accurate estimate of cell counts.
• The number of cells denotes the number of cells in the marked
Specular Microscopy with Eye Bank Specular Microscopes frame

The eye bank specular microscope is designed to allow accurate • Cell density is the extrapolation of the measured density of
evaluation of corneal endothelial cells while the cornea is in-vitro cells within the frame
in a specially designed storage chamber. The specific operating
protocol for the specular microscope should be obtained from • C.V. is the coefficient of variation of the cell size which denotes
the manufacturer or their representative. The basic procedure is pleomorphism indicative of physiological stress
to place the storage chamber on the microscope stage (the holder
for the chamber). The chamber can then be positioned to make • Hexagonality is given in percentage which along with C.V. of
the light from the microscope shine on the central corneal size constitute morphometric parameters of specular
endothelium. The chamber can also usually be tilted in the stage microscopy.
to get the maximum reflected image. Using the microscope stage
the X-Y plane {tabletop} position may also have to be adjusted to • The histogram below indicate the number of cells (x-axis) Vs
maximize the reflected image intensity. Focus the image and scan area occupied by them.
the area to find a representative grouping of cells. Look for other
pathology such as guttae, folds, snail tracks, etc. at the same time. Specular microscopy in different conditions
Most specular microscopes have a means of recording the image
(Figure 11) shows a normal intact endothelium at young age. As
the age increases, cell count is found to decrease especially after
60 yrs. The mechanism of endothelial cells loss with age is not
exactly known. The presence of polymegathism, pleomorphism
and poor cell count in a donor cornea are indicative of poor quality
tissue and hence the chances of graft failure increase. (Figure12)
shows a good tissue with only mild polymegathism. Post cataract
surgery decompensation of endothelium is common (Figure 13)
and can be due to any intraoperative complication or any pre
existing pathology like fuch’s corneal dystrophy.

46 DOS Times - Vol. 14, No. 7, January 2009

Figure 11: Normal intact endothelium Figure 12: Folds with pleomorphism and
polymegathism (post op)

Figure 13: Intact donor endothelium with Figure 15: Guttatae in fuch's
mild polymegathism corneal dystrophy

Figure 14: Endothelial morphology in Figure 16: Severe polymegathism due to
Chandler's syndrome long term contact lens wear

(Figure 14) shows a patient of chandler’s syndrome showing underlying cell but abnormal neighboring cells may be seen.
abnormal epitheloid cells replacing the normal endothelial cells. Both acute and chronic endothelial changes occur with contact
The presence of these cells helps it in distinguishing from Fuch’s or lens wear. Blebs may be found in endothelium 20 min after applying
Posterior polymorphous dystrophy as the slit lamp examination the lens which gradually decrease in size. Long term wear of contact
may just reveal a fine beaten-silver appearance of endothelium in lenses having limited oxygen permeability can lead to irreversible
all. Similarly, these abnormal cells would be seen in other ICE morphological changes in form of pleomorphism and
syndromes. polymegathism (Figure 16).

Fuch’s dystrophy (Figure 15) is characterized by focal accumulations First Author
of connective tissue formed by abnormal or stressed endothelial Deepa Gupta MBBS
cells on the posterior surface of descemet’s membrane. They appear
as warts or excrescences of descemet’s membrane called as “guttata”.
These when associated with edema lead to diagnosis of fuch’s.
Endothelial cells may be visible in early stages behind a guttata.
They progressively increase in size obliterating the view of

www.dosonline.org 47

Keratometry Cornea

Monica Chaudhry BSc (Hons) Ophth., Rajni Chhabra BSc (Hons) Ophth.

Kerato = cornea, metry= measurement. It is also known as Diagram
ophthalmometry. It is used to measure the radius of curvature
of the anterior surface of the cornea.

History

In 1619 Scheiner gave the idea of measure the corneal curvature
by using two glass spheres of known radius of curvature. But it
was Ramsden in 1796 who invented keratometer by using three
essential elements of keratometer i.e. an object of known size,
doubling device and a magnifying device.

Later in 1854 Helmholtz and Javal and schiotz in 1881 modified O / I = x/f =d/f =2d /r
and improved the instrument for clinical use. The next advantage
came in 1980s with the development of auto-keratometer. Now a Hence O / I = 2d/r
day’s keraometers are merged with auto-refractors for the
convenience and there are many companies such as Topcon, Where O is the size of an object and I is the size of an image. In
Humphrey and cannon are making such duo combinations. keratometry the distance between the object and the anterior
surface of the cornea is relatively long so that the virtual image is
Clinical use located very close to the focal point of the anterior surface of the
cornea. So the distance d is approximately equal to x. where m is
Since cornea is one of the major refracting element of the eye. If the magnification. In this case equation can be written as
the shape changes by any means for example post operatively
such as cataract extraction, radial keratotomy, Lasik, keratoplasty r = 2md
or conditions like keratoconus etc. It affects the vision or sometimes
the quality of the vision by reducing the contrast. Here if d is constant, which will be for any particular instrument
then the radius of curvature of the cornea is equals to the
If sometimes there is hazy media and it is difficult to perform magnification.
refraction due to may be mid peripheral corneal opacity or lenticular
opacity, keratometry is a valuable tool. Theoretically the size of image mire can be easily measured by
keeping the graticule with in the microscope. But practically there
Patients who are going to be fitted contact lenses it is an essential was a problem in measuring the image since eye has an involuntary
to perform a keratometry to fit an appropriate lens to the eye. It movement. To overcome this problem prism was incorporated in
should be perform in all the follow up cases as well to know if
there is any change is caused to the eye due to the fit of the contact
lens

It is useful in monitoring the changes in the curvature in corneal
ecstatic disorders. However, unfortunately if the curvature changes
are significant it is difficult to measure it in advance stages through
keratometer.

It plays a major role in calculating intra ocular lens power and
because of its low cost and ease of use it is widely used.

Principle and theory

Keratometer principle is based on the reflective properties of the
cornea where cornea acts as a convex mirror. Corneal curvature is
obtained by measuring the size of an image formed by the
reflection of the cornea, of an object of known size and position,
where a measurement of the radius can be calculated

Figure 1: Baush and Lomb keratometer

Department of Contact Lens 49
Dr. Rajendra Prasad Centre for Ophthalmic Sciences,

All India Institute of Medical Sciences, New Delhi

www.dosonline.org

Figure 2: Mires out of Focus Keratometer). or variable mires with fixed doubling (eg. Javal
Figure 3: Mires in Focus Schiotz Keratometers).

Astigmatism

The cornea is aspheric in shape not spherical that means slightly
toric so to be fully specified it has to measure the curvature along
the principle meridians of the cornea. The effect of imaging mire
with a toric cornea is to magnify it by different amount in different
meridians the max and minimum magnifications being along the
two principle meridians of the cornea.

One and two positioned keratometers

Because the axis of a toric surface are always at 90 degrees to each
other most of the instrument manufacturers have designed
keratometers that incorporates two separate doubling systems
which operate in mutually perpendicular meridians. Although
these instruments still have to be rotated about their anterior and
posterio axis in order to find one of the principle meridians of a
toric cornea, once this position has been found no further rotation
of the instrument is necessary to obtain a radius measurement
along the second principle meridian. This type of keratometer is
known as one position instrument (eg Bausch and Lomb
Keratometer). Keratometers that require rotation through 90
degrees in order to measure the second principle meridian are
known as two position instruments (eg. Javal Schiotz Keratometer).
While the principle meridian of a toric lens is always at 90 degrees
to each other, those of the cornea need not be. This is because the
corneal surface more closely approximates a toric ellipse than a
toric surface and when an off axis measurement is taken of a toric
ellipse the principle meridian need not necessarily be at right angles
to each other.

Area of cornea measured

The portion of the image mire used in keratometers is not reflected
through the exact center of the cornea but from two small areas
on either side of the instrument axis. The size of these areas is
dependant upon the effective aperture of the keratometers
objective. These areas are separated by 3 mm, varying with the
design of the instrument and the radius of curvature of the cornea

the optical system of keratometer. This biprism makes two images Figure 4: Mires in focus but the
of an object and both of these images moves equally as the eye axis is not aligned
moves. However the amount of doubling is dependent upon the
position of the prism with respect to the objective lens. If this DOS Times - Vol. 14, No. 7, January 2009
distance is reduced then the extent of doubling increases and if it
is increased, the extent of doubling decreases. At a particular point
the prismatic displacement is equal to the size of the image. By
recording the position of the prism, the exact size of the image can
then be calculated.

When viewed through a keratometer with various amount of
doubling. Alignment can also be obtained by altering the size of
the mires, where amount of doubling is kept constant. Therefore
in different instruments, different ways are used such as either of
variable doubling with fixed mires (eg Bausch and Lomb

50

The cornea is a complex structure with its thickness varying from
about 0.25mm centrally to 0.8mm peripherally, and about 1.20mm
at the limbus. This results in different radii of curvature at different
points along the same meridian, with central steepening and
peripheral flattening. Asphericity varies even among different
meridians of the same cornea. Topographically, the cornea can
broadly be divided into a central and a peripheral zone. The apical
zone which is also called the conical cap or optical zone or central
zone, is the central area where the radius of curvature does not
vary by more than 1 D or 0.05 mm. This may also be defined as
the area where the refraction differ by less than 0.25D.

Figure 5: The final position This zone is about 4 mm in diameter. The majority of the normal
corneas have Spherocylindrical apical zones with maximum and
and the principle upon which the keratometer is based assume minimum radii of curvature separated by 90º, a condition known
that a cornea is spherical between these two areas where the as regular astigmatism .In most persons due to pressure applied
measurement is taken. It is a well known fact that cornea is aspheric by the lids, the vertical meridian is steeper than the horizontal one
and flatten towards its periphery. Because of this and because ( i.e. with the rule astigmatism).
different keratometers reflect their mires from different regions
of the cornea, two reading of the same cornea with two different Christopher Scheiner, in the 17th century, tried to measure the
keratometers is not exactly same. One of the other problems of refractive power of the cornea by placing the convex mirrors
the keratometry is that the radius of Curvature of the cornea is alongside the eye and noting the mirror which gave a similar image.
determined from such a small corneal area and only central corneal Ferdin and Cuignat, in 1820s, introduced the term keratoscopy
measurements can be taken. for the study of images reflected off the anterior corneal surface.
This referred to the first Purkinje image, which is a virtual and
Sources of Errors erect image, Located about 4.0mm posterior to the anterior surface
of the cornea at the level of the anterior lens capsule.
• Improper calibration of the instrument
Keratoscopy
• Faulty positioning of the patient
In 1880, Antonio Placido devised a keratoscopy target which is still
• Lack of proper fixation by patient in use. It consists of equally spaced a alternating black and white
rings with a hole in the center to observe the patient’s cornea.
• Reduced visual acuity or uncorrected refractive error of Deviations either in the shape of the rings of their concentricity
examiner would betray abnormal corneal topography. The Placisdo’s disc
has several disadvantages. Small degree of abnormalities of corneal
• Accommodative fluctuation by examiner shape are not easily identifiable with this device since the ratio of
the object to image size in this apparatus is one i.e. there is no
• Localized corneal distortions or opacities, poor tear exchange, magnification of the image. Also if the area of cornea covered is
abnormal lid position increased, either by making a larger disc or by bringing the disc
closer of the cornea, part of the object gets obscured by the nose,
• Improper eye piece focusing brow and lids. Another disadvantage is the non reflection of the
target by the cornea, thus preventing its use in cornea with epithelial
• Misalignment of mires defects and stromal ulcers etc. The unrefined Placido’s disc is thus
used only as a gross method of qualitative assessment of the corneal
Corneal Topography surface.

The cornea provides 43D of refractive power to the eye out of the Photokeratoscopy
total of 60D.As a consequence, minor alterations in its surface can
lead to significant degradation of the images formed on the retina. Gullstrand, in 1896, began the practice of photography of the
Consequently efforts have been made for a long time to evaluate keratoscopy image and called it photokeratoscopy. In this technique
the surface characteristics of the cornea, i.e., topography, in order the keratoscopic image is photographed and the size of the images
to define their role in providing optimal vision to a patient .In on the photo film can be varied to change the size of the corneal
recent times, a resurgence of interest in cornel topography has image. The corneal curvature is then measured by utilising the
occurred rather than measuring just the central cornea, mainly distance of the keratoscopic rings from the cornea, the
due to the increasing use of keratorefractive procedures and magnification of the virtual image formed by the anterior surface
contract lens fitting in patient with corneal surface abnormalities of the cornea and the focal length of the objective of the camera
because of corneal scars etc. commercially available.

The Nidek PKS 1000 or Keracorneoscope, Kera, Inc. Santa Clara,
CA covers large areas of the areas of the cornea but the central
part of the apical cap is not studied, though the use of hemispherical
target has been advocated to achieve this objective. In these

www.dosonline.org 51

photographs of the keratoscopic image, the closer the line the Adjust the keratometer until the light falls on the portion of

steeper is the corneal surface; and the farther apart the lines, the the eyelid that covers the cornea.

flatter is the corneal surface. However the corneal cylinders of
upto 3D can escape detection by the use of photokeratoscopy. 6. Now see the mires when looking into the eyepiece. Adjust the

focusing knob, alignment, and elevation to focus the mire

Keratometry: Procedure for B&L type keratometer: 7. First make the double circle into a single clear circle with the

(since this type is the most commonly used keratometer) cross in the center,

1. Adjust the eyepiece. This is the adjustment that is a must in 8. Locate the axis - turn the “horizontal” drum, until the tips of

order to increase the accuracy of measurement. Turn the the plus signs are almost touching .Rotate the keratometer.

eyepiece anticlockwise, Turn the eyepiece (clockwise) direction, until the tips of the plus signs align perfectly. Remember the

slowly, until the reticule just comes into focus, then stop. This horizontal axis is read from the horizontal mark, and the

is the correct position for your eye. vertical axis is read from the mark on top of the keratometer

2. Dim the room lights. 9. Only after the axis is aligned take the - horizontal reading by

3. Adjust the patient comfortably with their chin firmly in the turning horizontal measuring drum until the plus signs overlap

chin rest and forehead against the band. This is very important 10. The vertical reading is obtained by turning the vertical drum

when performing keratometry becauseeven small movements of until the minus signs are superimposed.

the head can lead to frustration in trying tomaintain focus. 11. Remember - The focus has to constantly be adjusted during

4. ¨Instruct the patient to look into the center of the instrument the measurement process as there are micro movements of

and occlude the other eye. the head and the eye

5. Line up the keratometer with the optical axis of the eye by 12. Record the horizontal power with its corresponding axis, and

sighting along the silver pin on the side of the keratometer. the vertical power with its axis. Like – 42.25 @ 180 / 42.75 @90.

First Author
Monica Chaudhry BSc (Hons) Ophth.

52 DOS Times - Vol. 14, No. 7, January 2009

Acanthamoeba Keratitis Cornea

Sanjay Kumar Mishra MS, DNB, J.K.S. Parihar MS, DNB, Rakesh Maggon MS, V. Mathur MS, H.S. Trehan MS

Acanthamoeba keratitis, a potentially blinding infection of the cases occur in contact lens wearers.8 The incidence of the disease
cornea, is caused by a free-living protozoan that is ubiquitous in the United States has been conservatively estimated at
in nature, found commonly in water, soil, air, cooling towers, approximately one to two cases per million contact lens users,
heating, ventilating, and air conditioning (HVAC) systems, and although these estimates need to be refined.9,10 Individuals who
sewage systems. exercise proper contact lens-care practices and non-contact lens
wearers can develop the infection. However, individuals who
Acanthamoeba species are classified into three morphologic improperly store, handle or disinfect their lenses (e.g., use tap
groups. water or homemade solutions for cleaning), swim/use hot tubs/
shower while wearing lenses, come in contact with contaminated
Group I has large cysts with rounded outer walls (ectocysts) that water, have minor damage to their corneas, or have previous
are clearly separated from the inner walls (endocysts). corneal trauma are at increased risk of infection. No known cases
of person-to-person transmission have been reported.
Group II cysts are smaller, with variable endocyst shapes.
Acanthamoeba likely invade the cornea through a physical opening,
Group III cysts are smaller than Group II cysts, with poorly such as a minor abrasion, in the corneal epithelium. Contact lens
separated walls. wear may facilitate direct inoculation of Acanthamoeba into the
eye and promote infection through mechanical or hypoxic trauma
The major human pathogens belong to Group II, although A.
culbertsoni, from Group III, is also a recognized pathogen.1 Eight
Acanthamoeba species have been isolated as etiologic agents in
Acanthamoeba keratitis: A. castellanii, A. polyphaga, A.
culbertsoni, A. hatchetti, A. rhysodes, A. lugdunensis, A. quina
and A. griffini.2,34,5

More recent genotyping work has focused on the 18S rRNA gene
of Acanthamoeba as a basis for taxonomy of the genus . Twelve
lineages referred to as T1-T12 have been identified with the
majority of the keratitis causing strains belonging to group T4,6,7

Acanthamoeba keratitis is a local infection of the eye that does not
produce systemic illness. Unlike disseminated Acanthamoeba
infection, corneal disease is not associated with
immunosuppression.

• Free living, ubiquitous. Figure 1: Trophozoite
• Commonest- A Polyphaga, A Castellani, Isolated from soil

• Water, dust

• Sewage

• Hot tubs, airfilters

• Cooling towers

• Contact lens & contact lens solution

Stage strophozoite & cyst

• Trophozoite - Mobile (Figure 1)

• Cyst - stable & highly resistant form (Figure 2&3).

Epidemiology

Acanthamoeba keratitis primarily affects otherwise healthy people Figure 2: CYST
who wear contact lenses. In the United States, an estimated 85% of

Army Hospital (Research and Referral) 57
Delhi Cantt, Delhi

www.dosonline.org

Figure 3: CYST-Papanicolou Stain • Natural immunity exists.

• Host response by acute inflammatory cells especially around
cyst & necrotic organisms. Contaminated contact lens solution
+ Microtrauma to Epithelium by contact lens

• acanthamoeba infection by trophozoite. (Figure 5)

Clinical features

• Presentation

• Blurred vision with acute pain disproportionate to signs.

• Signs

• Early

• Epithelial irregularity & infiltration pseudodendrite or
raised epithelial ridges (Figure 6 & 7)

• Radial keratoneuritis. (Figure 8)

Figure 4: Slit lamp photo; broad illumination. Figure 5: Spread to all layers.
Early epithelial stage of infection. Linear DOS Times - Vol. 14, No. 7, January 2009
configuration resembles the epithelial form
(dendritic) of herpes simplex keratitis.

to the cornea. Upon binding to mannose glycoproteins of the
corneal epithelium, Acanthamoeba secretes proteins cytolytic to
the epithelium as well as proteases that facilitate further
penetration.11,12,13,14,15 IgA antibodies normally protect corneal
epithelial cells from Acanthamoeba infection; however, certain
Acanthamoeba species are capable of producing proteases that
lead to antibody degradation.16

Because the timing of exposure to Acanthamoeba is difficult to
assess and because the time required to establish infection is highly
dependent on the size of the inoculum, the incubation period for
Acanthamoeba keratitis is difficult to determine; it is thought to
range from several days to several weeksImages of Acanthamoeba
Keratitis (Figure 4)

Pathogenesis

• Exposure to contact lens - 70-85%

• Corneal trauma.

58

Figure 6: Non Specific Infiltration Figure 8: Perineuritis

Figure 7: Epithelial Ridges Figure 9: Disciform Keratitis

• Stromal infiltration, , (Figure 9) satellite lesion, disciform • PAS & methenamine silver.
lesion, ring infiltrate (Figure 10)
• Confocal microscope - confirmatory pear shaped cyst &
• Conjunctival follicles. irregular trophozoite. (Figure 11)

• Preauricular nodes. • Phase contrast (Figure 12) Microscope

• Late PCR and Corneal Biopsy

• Stromal opacification Transported in : Page saline with sample of contact lens saline &
• Scleritis case.-Ideal. Alternative media is buffered charcoal yeast extract
• Descematocele formation agar-Lower efficacy (72%)20
Diagnosis
E-coli on non nutrient agar (1.5%) at 25 and 37 degree C, May
require up to 14 days to grow - Create track by eating E Coli.

• Clinical features Pathology

• Lab • Cystic & active trophozoite form

• Gram & Giemsa stain • Trophozoite bind to Epithelium

• Calcofluor white stain - stains wall of cyst. • Thining & necrosis of Epithelium
• acridine orange. • Collagenolytic Enzymes released
• Immunofluorescent antibody stain. • Inflammation, necrosis & oedema of stroma

www.dosonline.org 59

Figure 10: Ring Ulcer Figure 12: Wrinked Double Walled
Cyst-Pathognomonic

Figure 11: Confocal Microscopy • Ointment 3.5 mg/g

Differential diagnosis • Azoles - destroys cell wall
• Diagnosis By Exclusion
• Herpetic keratitis - no systemic association • Clotrimazole, suspension, 1%
• Fungal
Treatment • Fluconazole, solution, 0.2%
Agents
• Cationic Antiseptics - inhibits membrane function • Ketoconazole, oil solution, 5%

• Chlorhexidine, Solution, 0.02% • Miconazole, solution, 1%
• Polyhexamethylene, Solution, 0.02%
• (PHMB)-BAQUACIL • Initially - hrly x 48 hrs.
• Aromatic Diamidines - inhibits DNA synthesis
• Propamidine isethionate, Solution, 0.1% Gradually reduced over weeks 4-6 times x several months.
• (BROLENE) Persistence of corneal and scleral inflammation characteristic of
• Pentamidine isehionate, Solution 0.1% (PENTAM ) acanthamoeba cyst may be due to necrotic protozoa and amoebic
• Aminoglycoside - inhibits protein synthesis cyst rather than active trophozoite:therefore, excessive prolonged
• Neomycin Solution, 1.75 mg/ml and aggressive antiamoebic treatment may merely prolong the
morbidity of disease.21
60
Corticosteroid - reduces inflammation.Very Cautious use (While
continuining anti-amoebic agents): Prevents encystment of
Trophozoite in vitro and may therefore enhance effectiveness of
Topical treatment22. Topical steroids have shown to prolong
effective treatment and used in specific conditions like
Limbitis,Scleritis and uveitis.23

Course & outcome

Majority eradicated by medical therapy.

• Treatment of Complications

• Scleritis:-consider immunosuppressant with steroids/
cyclosporine.

• Corneal Scaring:- Two Types

Therapeutic Penetrating Keratoplasty

Indications

• Non resolving

• Severe inflammation & necrosis

Optical Penetrating Keratoplasty

• Performed once treatment is complete and cornea is sterile

DOS Times - Vol. 14, No. 7, January 2009

Initial approach nonrelevant Acanthamoeba strains isolated from contact lens-
wearing keratitis patients in Austria. J. Clin. Microbiol.
• Chlorhexidine or PHMB+ neomycin or propamidine / 2000;38:3932-6.
pentamidine isethionate imidazole as third agent.
8. Parmar DN, Awwad ST, Petroll WM, Bowman RW, McCulley JP,
Prevention Cavanagh HD. Tandem scanning confocal corneal microscopy in
the diagnosis of suspected Acanthamoeba keratitis. Ophthalmology.
These guidelines should be followed by all contact lens users to 2006;113:538-47.
reduce the risk of eye infections, including Acanthamoeba keratitis:
9. Schaumberg DA, Snow KK, Dana MR. The epidemic of
• Visit your eye care provider for regular eye examinations. Acanthamoeba keratitis: where do we stand? Cornea. 1998;17:3-
10.
• Wear and replace contact lenses according to the schedule.
prescribed by your eye care provider. 10. Stehr-Green JK, Bailey TM, Visvesvara GS. The epidemiology of
Acanthamoeba keratitis in the United States. Am J Ophthalmol.
• Remove contact lenses before any activity involving contact 1989;107:331-6.
with water, including showering, using a hot tub, or swimming.
Extended-wear contact lens users should discuss concerns 11. Jaison PL, Cao Z, Panjwani N. Binding of Acanthamoeba to
with their eye care provider. [corrected] mannose-glycoproteins of corneal epithelium: effect of
injury. Curr Eye Res. 1998;17:770-6. Erratum in: Curr Eye Res
• Wash hands with soap and water and dry before handling 1998;17:1036.
contact lenses.
12. Morton LD, McLaughlin GL, Whiteley HE. Effects of temperature,
• Clean contact lenses according to the manufacturer's guidelines amebic strain, and carbohydrates on Acanthamoeba adherence to
and instructions from an eye care provider. corneal epithelium in vitro.Infect Immun. 1991;59:3819-22.

• Use fresh cleaning or disinfecting solution each time 13. Yang Z, Cao Z, Panjwani N. Pathogenesis of Acanthamoeba keratitis:
lenses are cleaned and stored. Never reuse or top off old carbohydrate-mediated host-parasite interactions. Infect Immun.
solution. 1997;65:439-45.

• Never use saline solution and rewetting drops to disinfect 14. Hurt M, Niederkorn J, Alizadeh H. Effects of mannose on
lenses. Neither solution is an effective or approved Acanthamoeba castellanii proliferation and cytolytic ability to
disinfectant. corneal epithelial cells. Invest Ophthalmol Vis Sci. 2003;44:3424-
31.
• Store reusable lenses in the proper storage case.
15. Leher H, Silvany R, Alizadeh H, Huang J, Niederkorn JY. Mannose
• Storage cases should be rinsed with sterile contact lens induces the release of cytopathic factors from Acanthamoeba
solution (do not use tap water) and left open to dry after castellanii. Infect Immun. 1998;66:5-10.
each use.
16. Leher HF, Alizadeh H, Taylor WM, Shea AS, Silvany RS, Van Klink
• Replace storage cases at least once every three months. F, Jager MJ, Niederkorn JY. Role of mucosal IgA in the resistance to
Acanthamoeba keratitis. Invest Ophthalmol Vis Sci. 1998;39:2666-
References 73.

1. Pussard, M., and Pons, R. Morphologie de la paroi kystique et 17. Biddick CJ, Rogers LH, Brown TJ. Viability of pathogenic and
taxonomie du genre Acanthamoeba (Protozoa, Amoebida). nonpathogenic free-living amoebae in long-term storage at a range
Protistologica. 1977;13:557-98. of temperatures. Appl Environ Microbiol. 1984;48:859-60.

2. Centers for Disease Control (CDC). Acanthamoeba keratitis 18. Neff RJ, Neff RH. The biochemistry of amoebic encystment. Symp
associated with contact lenses--United States. MMWR Morb Mortal Soc Exp Biol. 1969;23:51-81.
Wkly Rep. 1986;35:405-8.
19. Brandt FH, Ware DA, Visvesvara GS. Viability of Acanthamoeba
3. Yu HS, Kong HH, Kim SY, Hahn YH, Hahn TW, Chung DI. cysts in ophthalmic solutions. Appl Environ Microbiol.
Laboratory investigation of Acanthamoeba lugdunensis from patients 1989;55:1144-6.
with keratitis. Invest Ophthalmol Vis Sci. 2004;45:1418-26.
20. PenlandRL,WilhelmusKR. Laboratory diagnosis of Acanthamoeba
4. Simitzis-Le Flohic AM, Hasle DP, Paniagua-Crespo E, Colin J, Keratitis using buffered charcoal-yeast extract agar. Am J
Lagoutte F, Donval A, Bellon C. Acanthamoeba keratitis. Ophthalomology. 1998;126(4):590-2.
Epidemiologic and parasitologic study. J Fr Ophtalmol. 1989;12:361-
6. 21. Yang YF,Matheson M,Dart JK. Persistence of Acanthamoeba
antigen following Acanthamoeba Keratitis. Br J Ophthalmology.
5. Ledee DR, Hay J, Byers TJ, Seal DV, Kirkness CM. Acanthamoeba 2001;85:277-280.
griffini. Molecular characterization of a new corneal pathogen.
Invest Ophthalmol Vis Sci. 1996;37:544-50. 22. O'Day DM, Head WS. Advances in management of keratomycosis
and Acanthamoeba Keratitis.Cornea. 2000;19(5):681-7
6. Stothard, D.R., Schroeder-Diedrich, J.M., Awwad, M.H., Gast, R.J.,
Ledee, D.R., Rodriguez-Zaragoza, S., Dean, C.L., Fuerst, P.A., and 23. Bacon AS, Frazer DG, Dart JKG. A review of 72 consecutive cases
Byers, T.J. The evolutionary history of the genus Acanthamoeba of Acanthamoeba Keratitis.Eye.1993;7:719-25
and the identification of eight new 18S rRNA gene sequence types.
J. Eukaryot. Microbiol. 1998;45:45-54. First Author
Sanjay Kumar Mishra MS, DNB
7. Walochnik, J., Haller-Schober, E., Kolli, H., Picher, D., Obwaller, A.,
and Aspock, H. Discrimination between clinically relevant and

www.dosonline.org 61

Interpretation of Humphrey Visual Field Printout Glaucoma

Ruchi Goel MS, DNB, FICS, Usha Yadava MD, DNB, Lanalyn Thangkhiew MS, Manav Sachdeva MBBS

Visual field assessment is an integral part of glaucoma diagnosis If the visual acuity is good but the foveal threshold is low, there
and management1. The usefulness of the field charts may be an early damage to the fovea. (Figure 7 & 8) A low visual
primarily depends on the perimetrist who is responsible for acuity but good foveal threshold indicates need for refractive
explaining the test to the patient and also its alert monitoring. correction for perimetry as follows:
Also important is to keep in mind the learning curve of the patient
(Figure 1 & 2) and the need to repeat the initial field to ensure a • With a plus lens for distance, a spherocylinderical combination
consistent defect. The final assessment would still depend on the calculated by incorporating the usual add for the age is used.
clinical judgment which cannot be replaced by any machine
however accurate. • Distant sphere : Plano to -3.00D(HFA-I)/-3.25 D(HFA-II)

For initial examination, 30-2 or 24-2 white size III testing with • Calculated near correction if plus, is used along with
SITA standard when available (or Full Threshold, when SITA cylindrical power.
Standard is unavailable) is appropriate. When a short test is needed,
24-2 testing with SITA Fast (if not available then Fastpac –lacks • Calculated near correction if minus, only cylindrical
GHT) is used. For follow up, 30-2 is preferable because 24-2 power is used.
provides less number of points (Figure 3). When most or all the
points in the arcuate region between 10 and 30 degrees have • Distant sphere >3 D: Near correction for perimetry is calculated
threshold sensitivities of near 0dB the central 10-2 pattern is done. by using the full add.
(Figure 4&5) The test points in 10-2 are spaced on a 2-degree grid
(68 points), as compared to 6-degree spacing of 30-2 and 24-2.
This helps in picking up progression in subsequent fields.

When vision is limited to the central 5 degrees, the Macula Test is
performed which consists of a square grid of 16 points, 2 degrees
apart, centered around the point of fixation. The Macula test
supplements the 24-2/30-2 programs if the defect impinges on
fixation though there are still measurable locations outside the 5
degrees.

The stimulus size can be increased from size III to size V when
most of the points have thresholds 10dB or less in any of the
programs to detect any further deterioration. Size V (1.72 degrees/
64mm2) increases the sensitivities at normal points by 7-8dB as
compared to size III stimulus (0.43 degrees/4mm2). The normal
blind spot is 5 degrees wide and 7 degrees tall and about 200 size
III stimuli and twelve size V stimuli can fit in the blind spot.

Interpretation

To proceed systematically, the entire field is divided into eight Figure 1: Central 24-2 Threshold Test showing
zones. (Figure 6) excessive False positive errors leading to unreliable

Zone 1: This consists of the strategy used, patient’s name, date of field done for the first time
birth, correction used, visual acuity and pupil size (which should
be at least 2.5 to3mm).

Zone 2: The visual acuity is correlated with the foveal threshold
(normal value 34-38 dB) mentioned in this zone. Fifty decibels is
the dimmest target the perimeter can project. A young and
perimetrically experienced person can probably see the 40dB target
that too at fovea.

Glaucoma Services,
Guru Nanak Eye Center, Maualana Azad Medical College,

Maharaja Ranjit Singh Marg, New Delhi

www.dosonline.org 63

Figure 2: Central 24-2 Threshold Test repeated after Figure 4: Central 24-2 Threshold Test showing
3 months was reliable showing a learning curve excessive field loss with only central island
remaining threatening the macula

Figure 3: Total Deviation Plot of 30-2. Reliability criteria
The area enclosed shows points tested in 24-2
Fixation Losses: As mentioned in this zone are determined by
which are lesser in number projecting approximately 5% of the stimuli on the blind spot by
the Heijl Krakau blind spot method. Fixation loss >20% indicate
low test reliability. The blind spot is located by the perimeter by
giving catch trials at its usual location. If the patient responds to
these, successive stimuli are presented to locate the top, bottom
and sides of the blind spot which is indicated by a triangle in the
print out. High FL rates often are due to patient misalignment
rather than to unsteady fixation.

Besides the value of fixation losses mentioned in this zone, the
perimetrist observation and gaze monitor provide a continuous
testing of fixation. The gaze monitor uses image analysis methods
to locate the center of pupil and location of the corneal reflection
image of an infrared source. At the beginning of each test, a gaze
monitor initialization procedure calibrates and adjusts the system
to the individual patient during which the patient is required to
look at the fixation point without blinking for 20 seconds. The gaze
direction is noted only during stimulus presentation. The gaze
tracker record appears at the bottom of printout and not in this
zone. Errors are indicated as upward deflections from the baseline
with full scale being equal to 10 or more degrees of fixation error.
Downward deflections indicate absent pupil images or corneal
reflexes, usually caused by a blink. The gaze track shows poor

64 DOS Times - Vol. 14, No. 7, January 2009

Figure 5: Central 10-2 Threshold Test of the same patient Figure 6: The field is divided into 8 zones for
with stimulus size III. Stimulus size V could have been interpretation
used to document progression in future fields

fixation in figure 1 throughout the test showing multiple upward On the Numerical Plot: The zero indicates that the patient has the
deflections from base line. expected threshold for age. A positive number denotes a higher
sensitivity and negative number a lower senstivity than the average
False Positive Errors(FP): This is the ratio of false positives to for age.
false positive trials. The patient ‘s response to the mechanical sound
in the absence of stimuli is recorded. Although an upper limit of The Probability Plot predicts the chances of such an abnormality
33% is allowed, but even 10-15% FP can make the field unreliable. occurring in the normal population. The blackest dot indicates
Figure 1 shows a trigger happy patient with high false positives. that less than 0.5% of the normal population would be expected to
have such a depression in those areas.
False Negative Errors(FN): The False Negative rate is the
proportion of visible stimuli to which the patient fails to respond The Total Deviation Plot highlights any scotoma that may be
because of inattention. This is tested by presenting stimuli 9dB present, involving a large area of the field.
higher brighter than the threshold sensitivity already measured at
that location. FN>33% indicate ‘low patient reliability’ but even Zone 5: The Pattern Deviation Plot exposes any localized defects
10-15% may make the fields unreliable. High FN errors result also which may be masked by either generalized depression or elevation
from fatigue, poor fixation and malingering. of the hill of vision by making an adjustment of the threshold
values according to the ‘General Height` of the visual field. For
Zone 3: The Gray Scale highlights areas which need to be looked at both 30-2 and 24-2 patterns, only the 51 points of 24-2 pattern are
in detail. It is also useful if there are gross false positive or false considered ignoring three locations nearest to the blind spot. Of
negative errors. This zone should not be used for diagnosis. the 51 points, the seventh highest sensitivity value relative to age
(Figure 9) normal (85th percentile) is taken to represent the height of hill of
vision. The deviation of this point from its normal value is
Zone 4: Total Deviation Plot: It is a point by point difference of the subtracted from the deviation from normal of all tested points.
patient’s threshold from those expected in age corrected normals. The pattern deviation of the seventh best point thus becomes
It draws attention towards the ‘overall sinking` of the hill of vision zero. In 10-2 pattern, all the points are considered.
which could be caused by media opacities such as cataracts
(Figure 10), refractive errors, corneal opacities and miosis. It is There are both Numerical and Probability Plots. We try to look
depicted by a numerical and a probability plot. for abnormal points in a cluster. If there are abnormal points in

www.dosonline.org 65

Figure 9: Central 24-2 Threshold Test with excessive
False negative errors leading to unreliable field. The
gray scale shows a ‘clover leaf pattern’ characteristic of

patient who performs well initially but becomes
progressively less responsive

Figure 7: Central 24-2 Threshold Test showing a
good visual acuity of 6/6 but a low foveal threshold

indicating a macular lesion

Figure 8: Fundus photograph of the same Figure 10: 30-2 SITA standard showing generalized
patient showing a macular lesion depression of field due to cataract

total deviation plot which persist in the pattern deviation plot, Deviation(MD), the Pattern Standard Deviation(PSD), the Short

they are scotomas which have been revealed after adjusting for Term Fluctuation (SF) and the Corrected Pattern Standard

any depression in the hill of vision. (Figure 11 & 12) Deviation(CPSD).

Zone 6: The global indices provide inference of the visual field as a The Mean Deviation: It is calculated by average of all the numbers
single value. There are four such global indices namely Mean in the Total deviation Plot and signifies overall severity of the field

66 DOS Times - Vol. 14, No. 7, January 2009