DOS Times - DOS Times - Vol 26 No. 3

Subspeciality - Refraction and Spectacle Prescription

to the eye there will be an increase If a problem occurs, it will generally be 4. Relate symptoms/signs to cause
in the field of view through the two discovered when a patient first tries on Oncewehaverelatedthesymptoms/
zones. their spectacles at the time of collection.
However, problems may also occur / signs to the cause, it will be easy to
Facial wrap: Increased facial wrap be noticed several days or weeks after take the appropriate action to solve
also works by bringing the various dispensing the spectacles. the person’s problem.
zones closer to the eye. Some of the common complaints
Patients can often feel agitated, (Symptoms / Signs) reported are -
4) Measurements disappointed or upset that their • Distance blur
spectacles are not meeting their • Blur at near
Two important (mandatory) expectations. Solving their problem • Small reading area
measurements needed to fit a in a calm and confident manner will • Dizziness, wobble, swim
PAL are the monocular pupillary reassure them that we are in control of • Peripheral waviness
distances and the heights. the situation. • Need to tilt head or need to turn

The above measurements can be Prevention is better than Cure -Better head to see clearly
obtained manually using a PD ruler still, it is best to anticipate and avoid
/ pen torch or through devices like potential problems by ensuring Possible Causes
pupilometer, Height measuring accurate prescribing and dispensing
System, etc. methods (always use the best practice While there may be other possible
methods) causes that we can add to this list,
Modern Personalised PAL are fitted the main causes of problems with
with more individual parameters Problem solving goes through 4 step progressives are:
and hence an advanced measuring systematic approach
device (Visioffice, Eyepartner ,etc.) • Incorrect monocular PDs
will be helpful 1. Identify the problem that the • Incorrect fitting height
patient is experiencing with their • Inappropriate frame selection
Accuracy of these measurements spectacles. • Poor or insufficient frame
plays a vital role on the PAL wearer’s
Vision, field of Vision and comfort. This may be done through asking adjustment
the person specific questions and • Inaccurate refraction
5) Lens Ordering observing their behaviour while
they are wearing their spectacles. Incorrect PDs and heights are by
It’s important to ensure that after all far the most common causes of
the above measurements are taken, 2. Be aware of possible symptoms/ problems.
to verify all the major viewing signs
areas of the selected lens brand falls Trends In PAL
within the frame. Often a person will tell you the A number of technical innovations
problem that they are having with have recently impacted the field of
This can be verified by using the their spectacles. Most of the time, progressive addition lenses (PALs). Some
“layout” chart of that specific the information they tell you or of them are the W.A.V.E Technology,
brand. Coincide the fitting cross of the change in their behaviour may proprietary technology that is similar
each frame (dummy lens) with the be sufficient for you to identify to that used in laser surgery. By digitally
corresponding cross on the layout and solve their problem. However, scanning the entire surface of the lens
chart to check if the distance, sometimes the problem may and digitally surfacing with point by
intermediate and the near zones are be subtle and will need further point accuracy, the most complex optics
well within the frame area and no investigation; such cases are often can be created. By introducing wave
portion is cut out. more difficult to diagnose. If you front surface technology, we are able
are able to diagnose these problems, to achieve a lens that reduces and/or
Problem Solving you will stand out over your eliminates high order aberrations,30%
competitors. wider field of vision in the intermediate
There can be more than one source zone and Unsurpassed sharpness in
of error in prescribing, fitting and 3. Understand possible causes of low-light conditions
dispensing of progressive lenses. symptoms/signs
Problems may arise from refraction / Eyecode is a stunning breakthrough
prescription errors, monocular PD or To diagnose the problem a person and is at the forefront of innovation.
fitting heights and frame selection. is having with their spectacles, it
Alternatively, a problem which a person is important to be aware of all the
may experience with their spectacles possible causes of the symptoms/
may simply come from a lack of patient signs a person may experience.
education too.

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 51

Subspeciality - Refraction and Spectacle Prescription

Currently, all lenses that are d) Dominant Eye It is critical that the Eye Care
manufactured assume every person has New measuring technologies enhance Practitioners actively recommend
the same Eye Rotation Centre (ERC), precision and personalization Progressive Lenses and help patients
when in fact it can vary by up to 30%. techniques. And personalisation of PAL (wearers) to SEE MORE and DO MORE.
The dynamic 3D eye measurement is brings in sophistication to the category References
based on pinpointing the exact Eye on the whole. • Ophthalmic Optics Files-Progressive
Rotation Centre that is unique to every
person and this heralds a new era in lens Conclusion lens - Dominique Meslin
personalisation. We are living in a Digital Era with more • Points De Vue
and more people glued to different • Essilor Academy
To name a few path breaking digital devices. Use of Digital Devices
innovations – Xtend technology, has heavily impacted on the way we Corresponding Author:
Nanoptix , Synchroneyes- all these have work, shop, communicate and so on.
taken the PAL experience to a greater With dramatic increase in the usage Ananthalakshmi. N
level of digital devices, it is also essential for Head - Education & Professional Services
ophthalmic lens technology to evolve Essilor India Pvt. Ltd
Today lenses are dispensed with more to meet today’s need. Outdated options
personalised measurements some of like Bifocals, reading glasses cannot
which include manage today’s increasing visual
demand. On the other hand, today we
a) Eye Data: Pupillary distances, have Progressive Lenses, which are not
heights, Eye rotation centre only designed ergonomically, it also
combined with lots of innovation and
b) Frame data –Frame fitting impactful technology. All these make
parameters, - Frame position Progressive lens a Right Choice for the
Presbyopia.
c) Behavioural data: Head –Eye Ratio,
Near Vision Behaviour, Reading
distance

52 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Ametropia - Optical
Considerations for CL Wear

Vamshu Bhat, Optometrist, M.Optom Nilesh Thite M.Optom, FIALCE, FAAO

Ametropia is “a refractive condition In Refractive Ametropia, the correcting a minus meniscus lens is located
in which light fails to fall on retina plus lens make retinal image size larger a short distance behind the back
when accomodation is at rest, infinity in hyperopia and minus lens make surface. Therefore the back vertex
and retina of both the eye’s are not it smaller in myopia, as compared to of a plus meniscus lens would have
conjugate.”. It is also classified as ‘Axial’ standard emmetropia by about 16-17% to be located somewhat closer than
& ‘Refractive’. for every dioptric correction. 14 mm from the cornea & a minus
meniscus lens would have to be
In Axial ametropia, the refractive Knapps Law & Its Limiatation placed farther than 14 mm from the
component (cornea or crystalline According to Knapp’s law, “When a cornea.
lens) is standard but an axial length is correcting lens is so placed before the
either too long (axial myopia) or too eye that its second principal plane 3. The refracting power of the eye
short (axial hyperopia) whereas, in coincides with the anterior focal point must be equal to that of the standard
Refractive ametropia it’s vice-versa, of an axially ametropic eye, the size of emmetropic eye.
the axial length is standard but one the retinal image will be the same as
of the refractive component is either though the eye were emmetropic.”. The 4. The shape factor of the correcting
excessive (refractive myopia), or too retinal image size will not be different lens must be unity (in reality
little (refractive hyperopia). between the two eyes, no matter what the shape factor for a plus lens is
amount of axial ametropia exist, when normally greater than 1, whereas
The amount of ametropia is indicated the spectacle lens is placed at the eye’s the shape factor for a minus lens is
by the dioptric value of the distance anterior focal point. normally less than 1).
from the far point of accommodation to In order to apply this law, certain
the spectacle plane. conditions are required: An additional factor to be considered is
1. The emmetropia must be purely that Knapp’s law applies only to induced
Image size in corrected aniseikonia. As an ametropic eyes may
Ametropia axial. suffer anatomical aniseikonia, due to
2. The correcting lens must be located the differences in receptor densities for
While correcting ametropia, the the two eyes (this would be particularly
dioptric combination of correcting lens so that its secondary principal point expected in axial ametropia, the density
is placed in primary focal plane of the coincides with the primary focal of the receptors being spread out in a
eye resulting in shift of retinal image point of the eye. The position of large axially ametropic eye and more
and size. the principal planes moves as the closely packed in a small, hyperopic
“bend” of a lens is increased moving eye). This condition, in addition to the
In pure Axial Ametropia (myopia or toward the surface with the greatest four conditions listed above, makes
hyperopia), the size of the retinal image curvature. The secondary principal the clinical application of Knapp’s law
formed by the combination become point of a plus meniscus lens is a somewhat inexact procedure. In the
same as of an emmetropic schematic located a short distance anterior case of axial ametropia corrected by a
eye. The retinal image size enlarges in to the front surface of the lens contact lens the power of a contact lens,
an axial hyperopia and reduces in an &the secondary principal point of fitted “On-K,” can be considered as equal
axial myopia. to the ocular refraction.

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Subspeciality - Refraction and Spectacle Prescription

Changes in accommodation to contact lenses results in increased be equal with the result that the retinal
accommodation with back vertex image size for each eye is essentially
& convergence when myopes power being included, which is why equal to that of the standard emmetropic
early presbyopic, moderate-to-high eye. If spectacle lenses are worn, the
shifts from spectacles to CL’s myopes always need an increased power spectacle magnification produced by
in their contact lenses before they need the lenses will bring about an inequality
In myopes, spectacles gives base-in it in their spectacles. High myopes can in the sizes of the two retinal images
prism experience at near which moves sometimes survive presbyopia without with the result that relative spectacle
the image further away & looking away ever needing progressive spectacles. magnification for each eye will differ
from the optical center of the lens also from unity and a significant amount
reduces the power, effectively reducing of aniseikonia will be induced. But if
the accommodative demand. The shift contact lenses are worn rather than
spectacles, the lenses will bring about
very little magnification with the result
that relative spectacle magnification
will differ little from unity, and a
minimum amount of aniseikonia will
be induced. In summary, prescribing
contact lenses is the ideal treatment
of choice, if one wishes to minimize
induced aniseikonia.

Reference

1. Troy E. Fannin, O.D., Theodore
Grosvenor, O.D., Ph.D., Clinical Optics,
Butterworths

2. Kate Gifford, Phd, Bappsci(Optom)Hons,
Refractive Focus – The Near Refractive
State, Contact Lens Spectrum, Volume:
33, Issue: November 2018, Page(S): 12, 13
Accessed On 18 Jan 2020

3. Joseph I. Pascal New York, N.Y.,
Retinal Image In Axial And Refractive
Ametropia, Brit. J. Ophthal. (1955), 39,
380.

4. Cliffword W. Brooks, Irvin M. Borish,
System For Ophthalmic Dispensing,
Third Edition, Butterworth-Heinemann
Isbn-13: 978-0-7506-7480-5, Isbn-10:
0-7506-7480-6

Correction with SPECTS & Cl aniseikonia being induced. If corrected Corresponding Author:
Axial Ametropia: In this, the equivalent by contact lenses, the magnification is
powers (corneal power and lens power) much less than spectacle lenses with Vamshu Bhat
are the same for the two eyes but the result that the relative spectacle Sharp sight Eye Hospital , Delhi
the retinal image sizes are different magnification for each eye will
due to the axial length difference. If differ significantly from unity and a
spectacle lenses are worn, the retinal significant amount of aniseikonia will
image size difference will be offset by be induced. So, prescribing spectacle
the spectacle magnification produced lenses will be the ideal choice of
by the correcting lenses, resulting (as treatment, if one wishes to minimize
stated by Knapp’s law) in the relative induced aniseikonia.
spectacle magnification for each eye Refractive Ametropia: In this, the axial
being essentially unity and in little or no lengths of the two eyes are considered to

54 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Refraction in Accommodation and
Convergence Anomalies - Case
Studies

Jameel Rizwana Hussaindeen, M.Phil Opt, Ph.D., FCOVD-I, FAAO
Lecturer, Optometry Unit, Dept of Surgical Sciences, Faculty of Medical Sciences, University of the West Indies

Uncorrected refractive errors are known to cause a wide Illustration 2
variety of visual symptoms including blurred vision, *NPC – Near point of convergence; NPA – Near point of
headache, and asthenopic symptoms. Compounded with accommodation
a binocular vision dysfunction, there is an increased risk of The baseline binocular vision assessment points out to the
worsening of symptoms as well as deterioration of binocular fact the near points of accommodation are way below the
functions. In this article, two cases of such nature are being age expected norms.1 Though the near point of convergence
discussed with emphasis to management of refractive error as appears borderline, given the fact that the accommodation
the first step in the sequential management process. amplitudes are reduced, the accommodation parameters need
The approach to assessing a patient with a binocular vision to be investigated in details prior to making any diagnosis.
dysfunction is illustrated through a conceptual model (Figure
1). This model considers the assessment of comprehensive eye Illustration 3
examination that represents the assessment of the integrity of
the visual system followed by refraction as the fundamental
components. This is then followed by accommodation and
vergence assessment that represents visual efficiency, and the
top most part of the assessment represents evaluation of the
visual information processing system and reading assessment
carried out as and when required. This is just a conceptual
model and does not represent a standard hierarchical
approach and clinical discretion is highly recommended.

Illustration 1: Conceptual framework to managing dysfunctions
of binocular vision

Case 1 *MEM – Monocular estimate method dynamic retinoscopy;
A 20-year-old college student reported with complaints of AF: Accommodative facility (with +/-2.00 DS accommodation
eyestrain associated with reading and using computers. The flippers)
symptoms began after 30 minutes of near work and was also This patient has uncorrected hyperopia that could have
associated with intermittent blurred vision at distance after potentially impacted the accommodation amplitudes,
prolonged near work. His unaided visual acuity was 6/6, N6 in response and dynamics giving the clinical picture of ill-
both the eyes and he has never used glasses so far. Rest of the sustained accommodation. As seen in Illustration 2,
eye health examination was normal and the patient’s medical prescribing the optimal refractive correction has ensured
history was unremarkable. restoring the accommodation amplitudes, and response.

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Subspeciality - Refraction and Spectacle Prescription

To push maximum plus in young subjects, Borish delayed focusing binocularly through minus lenses at near leading
subjective acceptance technique is of great clinical value.2 to a diagnosis of convergence excess.3 The high AC/A ratio
A follow-up at 12 weeks is recommended to re-assess the confirms the same suggesting the potential benefits of added
binocular vision parameters following refractive adaptation.3 plus lenses at near to reduce the excessive convergence and
In the presence of asthenopic symptoms, and abnormal thus the near esophoria. Based on the AC/A ratio, a near
binocular vision parameters, vision therapy can be initiated.4 addition of +1.25 DS was resulted in orthophoric alignment
Case 2 at near, and improved the key binocular vision parameters
A 22-year-old student who was pursuing his medical (Illustration 5).
education reported with complaints of double vision while
focusing through microscope. He was pursuing Dentistry and A follow-up at 12 weeks was done that showed the stability
had intense visual demands related to the medical training. of improved binocular vision parameters and reduced
He has been using a Myopic prescription since Grade 8, and asthenopic symptoms. The patient was very happy with
also reported progression in Myopic refractive error. His best bifocal lenses and reported improved focus even at distance
corrected visual acuity was 6/6, N6 in both the eye. Rest of the especially when he had to copy down notes from the distance
eye health examination was normal and the patient’s medical screen in the medical school sitting at the farthest row. Vision
history was unremarkable except for Obesity. therapy aiming at improving accommodation facility and
divergence amplitudes at near was also initiated with an
Illustration 4 intention to wean off bifocals in the long run. The patient and
*NPC – Near point of convergence; NPA – Near point of parents were counselled regarding the same.
accommodation
He was using a glass prescription of OD: -4.50 DS/ -1.50 DC X Both these cases are just snapshots of many such cases
180 and OS: -4.75 DS/ -1.25 DC X 170 for the past 3 months. that an eyecare professional encounters in their practice.
His cycloplegic refraction values were same as the glass The importance of optimal refractive correction can never
prescription. be underestimated and understanding how this impacts
accommodation and vergence parameters needs to be
understood by every eye care practitioner. A simplified
approach that enables the assessment and management is
proposed through a conceptual framework in this article
that I hope would help in incorporating binocular vision
assessment as part of a routine eye care assessment especially
when the patient presents with asthenopic symptoms.

References

1. Hofstetter H. Useful agEamplitude formula. Optom World 1950;
38: 42–45.

2. Borish IM. Comments on a “Delayed Subjective” Test. Am J
Optom Arch Am Acad Optom 1945;22:433-36.

3. Scheiman M, Wick B. Clinical Management of Binocular Vision:
Heterophoric, Accommodative and Eye Movement Disorders.4th
ed. Philadelphia: Lippincott Williams & Wilkins; 2014.

4. Hussaindeen JR, Murali A. Accommodative Insufficiency:
Prevalence, Impact and Treatment Options. Clin Optom (Auckl).
2020 Sep 11;12:135-149. doi: 10.2147/OPTO.S224216. PMID:
32982529; PMCID: PMC7494425.

*MEM – Monocular estimate method dynamic retinoscopy; Corresponding Author:
AF: Accommodative facility (with +/-2.00 DS accommodation
flippers); NFV – Negative fusional vergence; PFV- Positive Dr. Jameel Rizwana Hussaindeen
fusional vergence; AC/A – accommodative convergence to Lecturer, Optometry Unit
accommodation ratio Dept of Surgical Sciences, Faculty of Medical Sciences
^ Reported binocular diplopia with minus lenses University of the West Indies

The patient’s binocular vision (Illustration 4) points out
to the fact that the patient has reduced near negative
fusional vergence amplitudes, near esophoria, and difficulty

56 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Difficult Situations in Refraction

Monica Chaudhry, B.Sc, M.Sc Optometry FIACLE
Consultant Optometrist and Educator

There are situations in refraction which VD well-adjusted in trial frame technique in hazy medias with high
need special consideration, some of before beginning the subjective errors.
these situations are highlighted as acceptance. i) Other common observation with
clinical pearls in this article. high myopic cases is associated
e) The maximum power lens should retinal degeneration and
Refracting high refractive be placed in the back slot while subnormal visual acuities. Low
errors. taking acceptance. vision devices should be provided
This technique is similar like any when best corrected visual acuities
normal refraction but needs patience f) Possible Media haze: high refractive are subnormal.
and careful examination while doing errors may have associated j) Progression of myopia: It is
retinoscopy. anomalies haze media’s or poor commonly seen that children
vitreous quality. If there is poor with high myopia have tendency
a) The starting points the reflex is media the clarity refraction or of progression. Every millimeter
going to be dull – proceed by retinoscopy maybe done by increase in axial length results
holding a +8.0 or –8.0 spherical reducing the working distance to in approximately three diopters
lens if the reflex is still unclear go 50 centimetres’ increase of myopia. An average of 0.5
further by holding a –16 or +16 lens diopter increase in early childhood
and refracting through them . The g) Dilation of Pupil helps in high is normal. Myopia control is matter
high minus glow will be detected errors to achieve the neutralising of concern, and all measures should
with either of the lenses .There point. Weak cycloplegic like be adopted two control progression
are cases which are even up to Tropicamide works fine in high in children. Retinal examination is
-30 dioptres seen in practice keep errors of myopia in young adults important while refracting these
trying higher spherical power lens in children however there is no myopes on regular basis.
just to be sure you have not missed compromise to having a good
on the high refractive error. cycloplegic as a baseline refractive Our old theory of under correcting
error. Hyperopes specially children the myopia in children is potentially
b) The auto refractors in high should be always refracted under harmful leading to further
prescriptions usually are beyond cycloplegia. Follow up visits of progression of myopia rather than
range and fall short of the true error. hyperopic refraction decision to put inhibiting it.
in cycloplegia can be individualised
c) Prefers using a trial frame instead depending upon the change seen Best practice pearl:
of phoropters. This gives better by refracting over the glasses. If
possibility of patient to see through the change is significant proceed • Patient’s current spectacles are best
the centre with the natural head to repeat under cycloplegia. If the form of starting point for subjective
postures. change is not significant one may refraction in high errors.
just attempt a subjective refraction
d) The vertex distance should be by doing overfraction technique. A • Over refraction or doing the
well adjusted for the patient on study by Jeorge et.al stated that an retinoscopy over the present
the trial frame and preferably experienced clinician, retinoscopy habitual prescription is a good
as close as possible to the eye. In is more accurate than automatic starting point
case of patient using glasses the refraction and gives a better starting o -The technique of over refraction :
same vertex distance should be point to noncycloplegic refraction. have the patient wear the current
maintained while refracting or
subjective acceptance. Ensure h) Autorefractor is a good beginning
point followed by bracketing

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Subspeciality - Refraction and Spectacle Prescription

spectacles, put an occluder by Induced Myopia c) If Diplopia is documented during
may be even inserting a paper The refractive error shifts towards refraction the aim should be to
behind the spectacle and add myopia in conditions like Nuclear binocular balance the prescription
a halberg clip Holder over the cataracts, pharmaceutical agents such that patient does not
refracting eye. Begin with your like pilocarpine morphine, opium, experience it with prescribed
working distance lens and see corticosteroids, anti-hypertensives, oral glasses. Contact lens should be
if the reflex is neutralised in contraceptives etc. or in conditions like proactively recommended in such
both the meridians. A residual diabetes with significant variation in cases.
power or astigmatism can be blood sugar level. Several case reports
immediately recognized and of transient drug-induced myopia have d) Worth 4 dot test is important and
refraction can be fine-tuned. been reported. These cases have been all-subjective test monocular and
For example: associated with secondary angle closure binocular balancing should be well
Patients glasses are -16.00 Dsph / -1.00 X glaucoma and other ocular conditions performed.
90 .The over refraction is - 1.5 Dph so such as choroidal detachment,
the final spectacle prescribed will be maculopathy, retinal folds or even iris e) A child with anisometropia must
–17.50 Dsph / -1.00 X 90 claw lens implants. Discontinuation be prescribed full correction
Image 1 : halberg clip of medications in most cases leads to followed by occlusion therapy for
complete resolution of the anatomic amblyopia. Once the visual acuity
Spectacle dispensing pearls shift. is best corrected achieved contact
The spectacle lens selected should be lens should be recommended.
minimized weight by using plastic Patients with induced myopia report
lenses specially the high index ones. blurred distance vision and onset is f) If there is suppression in amblyopic
Small size frames are preferred to dependent on the causative agent. eye correction can be given in
improve the appearance. Back vertex Refraction of such cases may be variable, spectacles but contact lenses
distance PD are important part of and patients should be informed off are still advised considering the
spectacle dispensing. ARC coating such variations over the period of cosmetic appearance
is mandatory for all higher myopes. medication. Spectacles should be less
Frames should be preferably adjustable expensive material and as far as possible g) If there is diplopia or alternate
notepads where the minor adjustments the causative agent maybe first stopped separation full correction in
on dispensing of spectacles can be done. and then prescription given. glasses will not be tolerated partial
Contact lenses as far as possible should correction to suppress the non-
be recommended to high refractive Anisometropia and dominant eye in the spectacle is
errors as they have far better optical Aniseikonia recommended, however contact
performance enhanced field and quality Anisometropia is defined as a condition lens is the solution.
of vision. in which the refractive error of one eye
differs from that of the other and the h) The binocular balancing with
suggested difference should exceed one Borish technique can produce
diopter. Anti-metropia is the condition incorrect results while doing
when one eye is hyperopic, and the other subjective testing. Duochrome
eye is myopic. Anisometropia of around dissociation test is better in such
2 diopters and 1 diopter in hyperopes cases. The patient is not asked to
is often seen to be associated with compare the sharpness but the
amblyopia and strabismus, however two Duochrome charts produced
its severity depends on the degree. by dissociation should show that
Assessment of binocular functions and red letters are just clearer than
its grade is important while dealing green or red and green are equally
with such patients. clear on both the images. If there is
a) Such patient is likely to present discrepancy the sphere it is adjusted
monocularly till the images show
subnormal binocular function both red and green are equally clear
status. in two images.
b) Stereo acuity is usually reduced,
Fusion is weak, and the refraction i) Full correction is prescribed to
should aim at keeping the binocular children below 8 years of age who
functions to the best. would need amblyopia therapy do
not compensate or under correct by
giving Plano or under correction in
the amblyopic eye.

j) Anisometropia induced due to

58 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

incorrect calculation of IOL power Refraction pearls based on type of Congenital cataract: congenital
is less frequently observed these cataract. cataracts require immediate surgery and
days however if such a situation prescription of spectacle in the aphakic
arises best corrected spectacle Nuclear cataracts: myopia is induced eye as soon as possible post the surgery
prescription or any anisometropic in such cataracts and it is common to Infants and children proceed towards
optical solution should be tried. have higher minus prescriptions or amblyopia and nystagmus with poor
Prismatic effects symptoms may changing minus prescriptions which visual outcomes if timely spectacles
be reported, and symptoms and will improve the visual acuity for a are not prescribed. The growth of the
glasses may be intolerable to some patient who desires to wait for the eyeball leads to rapid reduction of
patients. cataract surgery. Retinoscopy in the plus power hence refraction must be
center will reflect the opacity and the repeated every two months in these
k) Axial versus refractive peripheral neutralization of the reflex babies.
Anisometropia: If the cause is will be different or lesser minus from
axial, the and the difference in the final acceptance. DRY retinoscopy Traumatic cataract: Once removed
axial length matches the difference or subjective testing is preferred is invariably associated with corneal
of refractive error in the two eyes method in such cases. Auto refraction injuries and scars. While doing
theoretically such patients tolerate may not match the final prescription retinoscopy the reflex is irregular
full corrections binocularly and well and cylindrical powers may be and show opacities which hinder in
there is minimal aniseikonia overestimated by AR. achieving the best corrected visual
induced in such cases. Prescribing Tinted spectacles, contrast enhancers acuity. The pinhole visual acuity
full correction in hence may not and glare cutting filters help such may not be achieved due to irregular
produce diplopia or suppression. patients to certain extent. astigmatism induced. Rigid gas
However, the issues of cosmetic permeable contact lens should be
appearance maybe a concern Cortical cataracts: reflex in such advised to restore the visual acuity in
Contact lenses, or refractive surgery cataracts is dull and shows areas of case pin hole acuity is better.
have studied to still better solution. lenticular opacities which create
inaccuracy in estimation of neutralizing Co-management and surgical
It is generalized that binocular point during retinoscopy. The central referral for cataract
functions are subnormal if the, if the glow is generally good and should be
retinal image difference is more than the area of focus. Undilated refractions Incapacitation is the key for patient’s
5% or there is difference of more are again preferred choice in cortical decision for surgical referral.
than 2.5D between both the eyes. cataracts. Best corrected visual acuity Optometrist should attempt to bring
will vary with or without dilation in in best corrected visual acuity with
Cataract most of the cases. binocular functions and near visual
Cataract leads to subjective quality of acuity achieved. Glare and reduced
vision loss specially in Posterior sub Subcapsular cataracts: variation of contrast even with 6 /6 vision are
capsular cataract. Variation is obvious visual acuity with pupil size is common bothersome to the patient and can be
in different lighting conditions. The complaint with such cataracts. Glare the criteria for referral. Anisometropia
decision for surgical intervention and variability in visual acuity with induced due to cataract even with best
depends on the incapacitation of the variation in illumination should be visual acuities achieved is sometimes
patient. A good refractionist can guide explained as part of this problem and an indication for surgery. Visual acuity
this through. The objective refraction patient counseling is important during should not only be considered achieved
may not be accurate and aberrations spectacle prescription. Retinoscopy for distance but for near also while
in the reflex lead to only a rough without dilation would give a faint dealing with cataract cases.
estimation in most of the cases. AR is central glow and estimating the
a useful tool to know the beginning refractive status may not be accurate by Aphakia
point of subjective refraction and it objective methods. Dilated refraction Aphakic eyes are very less frequently
depends a lot on the type of the cataract. and acceptance under dilation may seen these days however seldom a case
In general, the refractionist should not not match the typical normal eye. or two may be reporting for refraction.
miss to record the best corrected VA Near visual acuity is most important Such patients present with high plus
both for near and distance uniocular to be recorded and understood as this power spectacle with increased retinal
and binocularly along. The induced is the deciding factor for surgery even. image size, reduced field of view,
anisometropia and binocular status Low vision devices magnification an increased aberrations and poor cosmetic
estimation is the key to refer to the enhanced illumination recommended acceptance.
surgeon for further management. for patient who plans to defer the
surgery. Since the astigmatism in an aphakic

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Subspeciality - Refraction and Spectacle Prescription

eye is mainly Corneal, performing Cylinders which enhance visual Patients who have partial visual
keratometry is a good starting point for acuity are recommended in school gain after cataract surgeries should
cylindrical value estimation. Back vertex going age. A handheld autorefractor be prescribed additional plus near
correction is important factor while is also useful. Low vision addition correction has long with other low
taking acceptance. Reading addition and optical correction is required vision devices.
is must as there is no accommodation in young children over the reading
in the eye. The reading addition will glasses. Recommended spectacle lenses Ectopia Lentis Or Subluxated
depend upon the best corrected visual should be plastic, aspheric with anti- Lens
acuity and the reading distance. In case reflection and UV protection coating. Dislocation of lens partial or complete
of moderate to low astigmatism, full A headband with sides removed and a is seen in ectopia lentos or in cases
cylinder can be prescribed. cord tied helps supporting the frame of trauma. Surgical intervention of a
and taking the weight away from dislocated lens depends upon a good
- Plastic, aspheric, UV protection the nose. Visual acuity assessment refraction. It is usually seen that
with anti-reflection coating is the with suitable pediateric charts are patience have astigmatism myopic
choice of spectacles in aphakes important documentations. Binoculars shift and fluctuating vision between
function assessment should be done the aphakic and phakic portion of the
- Progressive spectacles are on each visit and amblyopia should be eye. Monocular diplopia may also be
recommended instead of bifocals simultaneously taken care of. present. This eye is also at high risk
with glaucoma and vision is subnormal
Pediatric aphakic children should be Pseudophakia in most of the cases.
monitored with the changes every
two months. Progressive. or flat top Small incisions surgeries permit us to The key is to refract both the aphakic
bifocals maybe suggested in such cases prescribe the spectacle as early as day and the phakic portion of the eye.
occlusion therapy if needed. An infant one of cataract surgery. Prescribing near Anisometropia and high astigmatism
aphakic eye is usually around + 22 correction based on the occupation with binocular imbalance sometimes
diopters and they may be prescribed and functional needs of the patient is leads to a compromise visual acuity
extra plus so that they are prescribed important component of pseudophakic and hence the best corrected spectacle
for near rather than distance. Bilateral refraction. Keratometry gives us the prescription is binocularly imbalanced.
aphakes need progressive lenses to clue to the astigmatism quantity and its The visual acuity also fluctuates with
start with bifocal glasses when the axis. the changing illumination and depends
child is around two years of age. Add on the dislocation position of the lens
low vision devices wherever necessary. Difficult situation in pseudo phakic from the pupil.
Ignore small cylinders and prefer giving arises when the other non operated
spherical equivalents. eye is high myopic or refractive error. Steps in refracting such eyes
Such cases will have to be dealt like
Contact lenses should be tried in any anisometropic where contact lens 1. Record visual acuity, unaided,
children there are high oxygen silicone becomes imperative in retaining visual monocularly and binocularly
hydrogel lenses which are very safe for equity post the surgical indication in before starting they dilation.
paediatric aphakic eyes. Spectacles are that other eye due to anisometropia.
not possible in unilateral cases and its Surgeons chose to however go for 2. Do dry acceptance and there are 3
imperative to prescribe the contact lens refractive surgery or implant for good possible situations that may be seen
to prevent amblyopia or suppression binocular balancing. Progressive without dilation lens is subluxated
.Silicone hydrogel disposable are spectacles should be advocated in to a position that the
available and can be fit these eyes. The pseudophakes . Some surgeons prefer
power of the spectacle needs frequent to give a monovision to patients who - aphakic portion is only seen
monitoring and changes usually 2 have bilateral cataract surgeries. through the non dilated pupil,
monthly up to one year of age and 3
monthly till 4 or 5 years of age. Glare is a common problem in pseudo - both aphakic and phakic areas
phakic eyes, prescribing photochromic are seen, or
Retinoscopy pearl in pediateric lenses with anti-reflection coating or
aphakic child - begin with a + 20 tinted lenses which are glare reducing - the phakic area is visible only.
diopter lens while doing objective maybe supplemented to the patient
retinoscopy. Cycloplegia is not if such symptoms are observed. All 3. Attempt with high plus or minus
required hence dry retinoscopy on spectacle lenses should be 100% UV lens to detect the reflex ,in case the
a week cycloplegic like tropicamide protective. reflex is very dull.
maybe used. Ignore small cylinders up
to one diopter in infants and toddlers. 4. Subluxation usually give rise to
oblique cylinders.

5. Record acceptance without dilation.

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Subspeciality - Refraction and Spectacle Prescription

6. Dilate next step take acceptance achieving reasonably good visual acuity Malingering
in both the phakic and aphakic with opacities which cover the central
portions. pupil maybe recommended. Such clinical pictures of malingering
are seen in history of anxiety and some
7. The decision of visual rehabilitation Albinism emotional purposeful nature. School
and surgical intervention will going children under mental stress
depend upon the best corrected Use a partial or translucent occlude and avoidance of studies are common
visual acuity and good functionality instead of a full black occluder as the examples seen in clinical practice.
achieved with the best correction in amplitude increases while taking
either phakic or aphakic form monocular acceptance with full Test to substantiate the malingering
occlusion. Also , prefer using a trial are
Corneal Opacities frame in patients with albinism rather
than a phoropter in patients with 1. Ocular movements are full and
Corneal opacity maybe of various nystagmus. well formed in all directions in
grades and the visual outcome depends patients with good visual acuity in
upon the intensity and the location of Retinoscopy under cycloplegia is both the eyes.
the opacity. important the reflex is very pale
coloured, and iris is trans illuminated. 2. A Prism base out is put in front of
Refraction pearls are quite like those Patient usually have photophobia and the eye it will normally move the
seen in irregular cornea attribute poor cooperation in bright eye inward involuntarily. A blind
light retinoscopy. Fixation is also poor, eye will not be able to make such a
- to begin with record visual equity and they usually have subnormal visual movement.
unaided and then with pinhole. acuities. Being fast in such patients is
important so that the photophobia may 3. A plus 10 lenses is placed in front of
- Strat with dry retinoscopy and not distract them. It is expected to find the good eye such a lens has a focus
focus through the visual axis while moderate to high refractive errors in at 20 – 25 centimetres. A reading
determining the neutralization albinism associated with astigmatism. card with fine print is held at that
point. Subnormal visual acuity patients need distance and is gradually moved
the low vision magnification for near away while the patient is engrossed
- Auto refraction may give poor .Correcting the refractive error does in reading. If he continues to read,
results and the patient may not improve the visual acuity quantity and he is doing so with his other eye
be able to fix. Handheld ones are reduces the amplitude. Spectacle lenses which is malingering as blind eye.
relatively better than the table with glare cutting filters and 100%
mounted ones in opacities. ultraviolet protection with tinted lenses 4. Friend test - a patient wearing
supports the patient in reducing glare red and green goggles is advised
- Keratometry again is no clue for the and augmenting vision quality. to read friend in the visual equity
astigmatism. box a patient with good binocular
Nystagmus vision will be able to will be able to
- The reflex would be dull in most of read that.
the cases and hence the neutralising Refracting a nystagmoid is sometimes
objective retinoscopy is very vague . a nightmare. Fixations are poor and 5. Testing for partial blindness in one
examiner has to be amazingly fast eye can be done by varying the
- Subjective refraction is the key. and prompt. Achieving a neutral point visual acuity distance by moving
Determine the spherical best vision accurately may not be possible in all the chart and then corelating with
sphere. Use an astigmatic fan, cases. Use a translucent or a frosted the quantity read.
stenopic slit or cross cylinder to occlude to cover the other eye while
refine the cylindrical correction taking the subjective acceptance. Use 6. Total or partial blindness in both
trial frames instead of autorefractors the eyes malingering can be tested
- Check the binocular vision status . Vision is subnormal and such cases with base in prism placed in front
with WFDT should be worked up like a low vision of one eye. If the vision is present
patient. Full cycloplegic refraction is then eye will move outward and
- Pinhole acuity in corneal opacity imperative for a first-time refraction of a then inward when the prism is
is important as it estimates the best nystagmus eye. Patient may be allowed removed. Optokinetic nystagmus
corrected visual acuity that can be to have head posture while taking drum also helps us find out total
achieved with rigid contact lenses. the nystagmus because the patience blindness in both the eyes.
achieve the null point while doing this.
Rigid gas permeable contact lenses are 7. Visual field in malingers can be
mainstay treatment in corneal opacity detected with the kinetic test
and should be strongly recommended. types.

Referral for an optical iridectomy in

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Subspeciality - Refraction and Spectacle Prescription

Pseudomyopia or spasm of with non-cycloplegic photoscreening. Friedman NE, Frane SL, Lin WK, et
accommodation Strabismus . 2001; 9: 59–70. [CrossRef] al. Accommodation, acuity, and their
Pseudomyopia is a result of increase [PubMed] relationship to emmetropization in
in ocular refractive power due to over infants. Optom Vis Sci. 2009;86:666–76.
stimulation of eyes accommodative yy Suryakumar R Bobier WR. The yy Kahmeng Chung, Norhani Mohidin,
mechanism or simply because of ciliary manifestation of noncycloplegic Daniel J. O’Leary, Undercorrection of
spasm. The sign and symptoms are a refractive state in pre-school children myopia enhances rather than inhibits
distance blur which is usually transient is dependent on autorefractor design. myopia progression, Vision Research,
or a history which is very recent onset Optom Vis Sci . 2003; 80: 578–586. Volume 42, Issue 22, 2002, Pages 2555-
of blur distance vision. Clinically the [CrossRef] [PubMed] 2559,
eye will give more myopic acceptance yy Winn, B., Ackerley, R.G., Brown,
than it is. yy Rajavi Z Parsafar H Ramezani A Yaseri C.A., Murray, F.K., Paris, J. and John,
M. Is noncycloplegic photorefraction M.F.S. (1988), Reduced aniseikonia
To verify this condition refraction applicable for screening refractive in axial anisometropia with contact
under cycloplegia is performed . Strong amblyopia risk factors? J Ophthalmic Vis lens correction§. Ophthalmic and
cycloplegics are recommended than Res . 2012; 7: 3–9. [PubMed] Physiological Optics, 8: 341-344.
weaker ones. Recording of visual acuity yy David R Weakley, The association
under cycloplegia is imperative this yy Jorge, Jorge; Queirós, António; Almeida, between nonstrabismic anisometropia,
is the true visual acuity without the José BParafita, Manuel A. retinoscopy/ amblyopia, and subnormal binocularity,
accommodation spasm. Dry refraction Autorefraction: Which Is the Best Starting Ophthalmology, Volume 108, Issue 1,
will not be equitable and will be Point for a Noncycloplegic Refraction?, 2001,
higher minus acceptance than what Optometry and Vision Science: January yy Vincent, S.J., Collins, M.J., Read,
is expected. AR under cycloplegia and 2005 - Volume 82 - Issue 1 - p 64-68 S.A. and Carney, L.G. (2014), Ocular
dry is significantly variable . If such doi10.1097/01.OPX.0000150182.91410.97 characteristics of anisometropia. Clin
cases are given prescription under Exp Optom, 97: 291-307.
the accommodative spasm condition yy Kaimbo Wa Kaimbo, Dieudonne. (2014). yy Skiadaresi E, McAlinden C, Pesudovs K,
, it may lead to further problems Transient Drug-Induced Myopia. SAJ Polizzi S, Khadka J, Ravalico G. Subjective
and accommodation anomalies. The Case Reports. Volume 1. 105. Quality of Vision Before and After
management of such cases is to prescribe Cataract Surgery. Arch Ophthalmol.
the acceptance as detected under yy Güell, José & Morral, Merce & Gris, Oscar 2012;130(11):1377–1382. doi:10.1001/
cycloplegia and there is no requirement & Elies, Daniel & Manero, Felicidad. archophthalmol.2012.1603
for Post mydriatic test. Vision therapy (2012). Transient myopic shift after
and visual hygiene are advised along phakic intraocular lens implantation. Corresponding Author:
to relax the accommodation. Certain Journal of cataract and refractive surgery.
severe cases extra plus edition may 38. 1283-7. 10.1016/j.jcrs.2012.04.020. Prof Monica Chaudhry
be given to relax the accommodation. Advisor & Adjunct Professor,
Excessive near work should be avoided yy .AIOS Guidelines 2018. 76th. Coimbatore: G.D Goenka University ,
in such cases. AIOS; 2018. Paediatric Eye Examination Founder -Learn Beyond Vision
and Paediatric Refraction. Preferred Gurugram
References Practice Pattern. AIOC

yy Liang CL Hung KS Park N Chan P Juo yy Mayer DL, Hansen RM, Moore BD, Kim
SH. Comparison of measurements of S, Fulton AB. Cycloplegic refractions
refractive errors between the hand-held in healthy children aged 1 through
Retinomax and on-table autorefractors 48 months. Arch Ophthalmol.
in cyclopleged and noncyclopleged 2001;119:1625–8.
children. Am J Ophthalmol . 2003; 136:
1120–1128. [CrossRef] [PubMed] yy Monga S, Dave P. Spectacle prescription
in children: Understanding practical
yy Cordonnier M Kallay O. Non-cycloplegic approach of Indian ophthalmologists.
screening for refractive errors in children Indian J Ophthalmol. 2018;66:647–50.
with the hand-held autorefractor
Retinomax: final results and comparison yy Kulp MT, Ying GS, Huang J, Maguire M,
Quinn G, Ciner EB, et al. Associations
between hyperopia and other vision and
refractive error characteristics. Optom
Vis Sci. 2014;91:383–9.

yy Sainani A. Special considerations for
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Ophthalmol Res. 2013;1:169–73.

yy Mutti DO, Mitchell GL, Jones LA,

62 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Refraction and Binocular Balance
of Accommodation

Md Oliullah Abdal, M. Optom, Co-founder & Director, Bynocs
Jinal V Shah, B.Optom, PGDOVS, Consultant Optometrist Bynocs

Humans perceive the world 1. Prism-dissociated blur balance Remove the Risley prisms and
binocularly, hence during refraction, of accommodation: check visual acuity, decrease the
only monocular subjective refraction fog in each eye in steps of 0.25DS till
does not accommodate the needs of This test balances the maximum visual acuity is received
the patient. The refraction has to be accommodation in both eyes
balanced binocularly, keeping the using prisms while relaxing the This test is better performed using a
accommodative and vergence demand accommodation in both eyes. phoropter than a trial frame due to
in check thereby providing comfortable, Risley prisms are introduced in excessive changes in lenses.
maximum vision. This holds true front of both eyes with 3PD base
especially in case of children who have up in one eye and 3 PD base down 2. Monocular fogging balance
active accommodation. in front of the other eye while the (Modified Humphriss):
patient fixates at 6/12 row of letters.
Binocular balance of accommodation A +1.00DS lens is added in front One eye is fogged using a +1.00DS
is done after monocular subjective of one eye making the fixating lens or until the visual acuity
refraction is completed. Binocular line appear just blurred. Add plus drops by 3-4 lines, the other eye
balancing helps in ensuring that the lenses in steps of +0.25DS in front which becomes the testing eye is
state of accommodation remains of the other eye till both the lines introduced a +0.25DS lens and is
balanced between both the eyes. appear equally blur and a balance asked whether the target appears
is achieved. If 1 line appears clearer just as clear or better without,
Performing this test helps especially in than the other, add +0.25DS lens if the patient accepts the plus
cases of latent hyperopia, psuedomyopia in front of the eye with the clearer power, an additional +0.25DS lens
and antimetropia where over minus or image. is introduced. The plus lenses are
under plus may have occurred during introduced till the patient can no
monocular subjective refraction. The Figure 1. Patient undergoing prism- longer accept anymore plus power.
use of an occluder may have stimulated dissociated blur balance of accommodation The same procedure is repeated for
the accommodation in non-testing using a phoropter the other eye.
eye thereby increasing the equivalent
accommodation in the eye being tested. This test is extremely useful
in relaxing accommodation in
In such cases, all the latent plus power patients who suffer from latent
that may have been compensated for by hyperopia.
accommodation becomes manifest.
Figure 2.Patient undergoing modified
Binocular balance of accommodation Humphriss test to balance accommodation
is not advised when the visual acuity
is unequal, if the patient is monocular
or strabismic. It is also not advised in
patients who do not have an active
state of accommodation eg. presbyopia,
psuedophakia and aphakia

There are various techniques that can
be done for binocular balancing, they
are:

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Subspeciality - Refraction and Spectacle Prescription

If an additional minus lens 4. Turville Infinity Balance (TIB): of latent hyperopia, it is beneficial
is required to balance the After monocular subjective to use the Modified Humphriss
accommodation it is indicative that technique for binocular balancing.
the monocular subjective refraction refraction is finished, the occluder 2. In case a patient accepts a minus
might have been wrong. is removed from the trial frame. lens in Modified Humphriss, it
The patient is asked to close his one might be time to go back and check
This test is preferred over prism eye and keep his head steady while monocular subjective refraction.
dissociation test when using a trial the septum on the mirror is moved This is because it indicates an under
frame. till one half of the visual acuity correction of myopia.
chart is covered. Both eyes should 3. In cases of myopia, over-correction
3. Humphriss Immediate Contrast see different halves of the visual can easily happen during
(HIC): acuity chart and the end goal is that monocular subjective refraction as
both halves are equally clear. If one patients cannot differentiate if the
One eye is fogged using a +1.00DS half is clearer than the other then targets become actually clear or just
lens or until the visual acuity drops the best vision sphere procedure is smaller and blacker. In such times,
by 3-4 lines. In front of the testing repeated for the eye with the least doing a binocular balance will help
eye a +0.25DS lens in introduced clear vision. in removing all the extra minus that
for 1 second and then removed the patient might have accepted.
immediately, and replaced with Figure 4. Diagrammatic representation of 4. The benefit of binocular balancing
a -0.25DS lens for 0.5 seconds TIB. is that it replicates a real-life
and then removed immediately. LE RE - Patient’s position, C - Chart binocular viewing scenario in
The patient is asked if the image behind patient, M - Mirror, P - Reflected clinical settings. Thereby, helping
was clearer in lens 1 or lens 2. If image of chart us maintain a correct state of
the patient prefers the plus lens, Amongst all the tests mentioned accommodation and vergence.
additional plus power is added above, the most effective test is the 5. Although polaroids can be used
till the patient rejects the plus. If modified Humphriss as it is really to perform binocular balancing
the patient prefers the minus lens, easy for the patient to appreciate the test, it is often not preferred as the
he’s asked if the target appeared balance and it can easily be done in luminance in each eye decreases to
actually clear or just smaller and clinic while using a trial frame or a 50% and it isn’t economical for the
darker. Minus lens is only added if phoropter. Additionally, in cases like practioner.
the patient confirms that the target latent hyperopia, psuedomyopia and
definitely appears clearer. The test antimetropia, this test helps in relaxing Corresponding Author:
is then repeated for the other eye. the accommodation that may have
been stimulated during monocular
Figure 3a. Patient undergoing HIC with subjective refraction.
+0.25DS lens in front of testing eye

Figure 3b. Patient undergoing HIC with Clinical pearls Md. Oliullah Abdal
-0.25DS lens in front of testing eye 1. Modified Humphriss relaxes Co-Founder & Director
Bynocs
the state of accommodation 102, Maryland Corner, TV Chidambaram Marg,
to its maximum level, thereby Sion, Mumbai, 400022
manifesting all the hyperopia that
might have been compensated by
accommodation. Hence, in cases

64 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Rapid Objective Refraction
Technique in Babies

Md Oliullah Abdal, M.Optom, Fellow Lvpei, Co-Founder and Director Bynocs
Faiza Bhombal, B.Optom, Fellow Lvpei, Consultant optometrist Bynocs

Background sharply focused. The size and location ophthalmoscope minimizing costs
The paediatric population with of the pupillary crescent is noted as when compared to a photoscreener, 4)
refractive error needs regular hyperopic, myopic or astigmatic. can potentially screen a large population
assessment. Determining pediatric In myopic group the pattern of crescent within a short period as the test does
refraction is challenging when is inferior and the size will be more not take long to administer 5) the test
compared to older group. Correcting than 1mm. In hypermetropic and has good sensitivity 6) with experience
a child’s refractive error prevents or emmetropic group the crescent will the sensitivity and specificity improves
treats amblyopia which ultimately be superior but in hypermetropia the 7) the investigator can proceed with the
helps to avoid irreversible vision size will be more than 2 mm and in additional examination using the same
loss. In subjective refraction children emmetropia it is less than 2mm. In the ophthalmoscope.
unreliable response and variable astigmatic group the crescent will be
accommodation can lead to wrong anywhere. Radical Retinoscopy
diagnosis and prescription of glasses. Advantages with the Brückner test If in the Bruckner test inferior crescent
Objective refraction with the help of - 1) it is a relatively easy and simple is noticed that is the myopic group,
ophthalmoscope and retinoscopy can test to administer, 2) can train radical retinoscopy becomes useful. In
help in determining refractive status in persons with no or minimal prior this method the examiner moves closer
pre verbal children. It requires special experience to administer the test, 3) to the patient until neutralised glow
skill set to perform objective refraction can be administered using only a direct achieved. Reciprocal of that neutralised
on them. In the article different distance is noted as magnitude of
methods are explained that can be easily
learned and used in screening pediatric refractive error. This
refractive error objectively. may involve a working
distance as close as
Bruckner’s Test 20cm– 10cm. At such
The Brückner test is a simple and quick close working distance
method to detect anisometropia. It the practitioner must
is an objective test performed using be careful to stay as
a coaxial light source such as direct close as possible to the
ophthalmoscope and the optical patient’s visual axis
principle is essentially that used in the otherwise larger error
development of the photoscreener. of cylinder power is
Brückner’s test is a dark room procedure. introduced.
Examiner is one meter away from the
subject. Both eyes of the subject are Enhancement
simultaneously illuminated using a
direct ophthalmoscope with the patient Technique:
looking directly at the ophthalmoscope.
The examiner looked through the direct Enhancement
ophthalmoscope and adjusted the technique combines
lens dial until the pupillary reflex was changing the
illuminating system
with properties of the
viewing system with
the minimal use of

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Subspeciality - Refraction and Spectacle Prescription

lens. In hyperopic eyes, it is possible Rotation of the sleeve will not change 3. Radical Retinoscopy is done by
to narrow the beam on the retina the width of the reflex if the eye has a decreasing working distance to
sufficiently so that its borders can be spherical hyperopic refractive error. enable the reflex to be seen easier
seen despite the magnification (cross- Only a thin reflex is seen in the pupil. in cases of miotic pupils or opaque
hatched) of the viewing system. The Perhaps the most important and ocular media. It can also give you
amount that the sleeve is moved and practical point about enhancement is refractive error estimate in Myopes
the width of the facial intercept permit this—if the reflex cannot be enhanced, by converting the working distance
estimation of the amount of hyperopia. there cannot be more than +1.50 of in dioptre.
If the reflex inside pupil gets thinner by residual hyperopia.
changing the sleeve width, it suggests 4. In enhancement technique, low
significant refractive error. Clinical Pearls degrees of hyperopia can be
A sharply focused reflex can be seen 1. Bruckner’s Test is one of the fastest estimated by focusing the streak
in the pupil when the sleeve is raised within the pupil, using the vergence
toward the point at which the beam screening test to identify the control, and comparing the width
becomes parallel and enters an eye and refractive status of the eye. It is also of the beam visible within and
working distance lens that still requires useful in detecting amblyogenic outside the pupil.
more than 1.50-D hyperopic correction. factors such as strabismus and
This occurs because the focal point of density of amblyopia. 5. All these methods are effective
the retinoscope lies near the focal point 2. One needs to remember to across age group and plays very
of the patient’s eye. This makes the dim the room illumination important role in pre verbal
width of the focused filament image during the procedure and both children. One needs to be aware
on the retina and effectively prevents eyes are illuminated with the of the working distance as the
the appearance of a magnified image. ophthalmoscope simultaneously accuracy of the test largely depend
from a distance of 1 meter. on it.

Corresponding Author:

Md. Oliullah Abdal
Co-Founder & Director
Bynocs
102, Maryland Corner, TV Chidambaram Marg,
Sion, Mumbai, 400022

66 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Refraction in Keratoconus

Jeetesh Gurnani, D. OPTOM, B. OPTOM,
Executive Manager of Educational Programs, International Association of Educational Programs
Gurnani Chashma Ghar

Keratoconus is the condition of Supplementary symptoms are due Objective Refraction
extremes where corneal thinning and to a crazy marvel known as, “high When we perform auto refractometry
ectasia are the primary progressive order aberrations” that come from on keratoconus patients, the mires
changes, ultimately resulting in an irregular cornea. These will root show distortions, even in mild cases of
alterations in the corneal shape and thus ghosting, shadows, and inclusive corneal ectasia. We need to rule out it
affecting the refraction. It stimulates us distortion to vision that a simple pair with the poor tear film quality, because
to extend our limits of clinical skills, of glasses or soft contact lenses cannot same situation is seen in lower TBUT.
while challenging our ability to manage treat. Therefore, while taking the visual
difficult conditions. acuity of the keratoconus patients, we Retinoscopy shows traditional scissors
must not practice direct lighting over reflex because of irregular refraction
Acuity Charts and Stenopic Slit- the charts, in demand to duck glare occurring due to cone formation.
Symptoms of keratoconus includes problems.
blurred vision. Now this isn’t the Keratometry mires are also distorted and
emblematic blurred vision that an Double vision and distortion are the degree varies as per the severity of the
ordinary patient who just needs glasses two chief criminals specifically when condition. Also because of the limited
might experience. Frequently patients the cone is in the pupillary zone. So the central 2-4 mm corneal measurements,
with keratoconus develop extreme best way to overcome this issue while keratometry proves to be of negligible
myopia (near sightedness) with refracting is to use the stenopic slit. importance in such cases.
identically high irregular astigmatism. Letter chart is used when performing
This causes their vision to be distorted refraction with stenopic slit. Some Corneal Topography is the best way
than just regular blur. experts also suggest that use of Landolt to assess the corneal refraction in
C chart or T and E chart can be used. keratoconus. It aids us to gain the
T or E chart is recommended because knowledge of entire surface including
stem of T or E is beneficial to confirm the shape, radius of curvature, dioptric
the meridional orientation. In cases values and beyond. Refractive maps
of keratoconus, there is irregular in topographers benefit us to plot
astigmatism. Slit can be used to isolate the corneal power at various points
the two primary meridians which are that serves as a pearl in keratoconus
obliquely oriented. refraction. It correspondingly springs
simplified data about the principal
meridians of irregular astigmatism.

Source: Keratoconus can cause Double Source: Magnetic disks | definition of Source: (765) Quick guide to the manage-
Vision - Centre for Sight magnetic disks by Medical dictionary ment of keratoconus: Part 13 - YouTube
(thefreedictionary.com) (Sinjab Academy)
Objects tend to have shadows around
them or even look double. Patients
report glare and haloes at night time.
Regrettably, if scarring of the cornea
has occurred secondary to keratoconus,
then there is amplified haziness and
a reduction in contrast sensitivity.

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Subspeciality - Refraction and Spectacle Prescription

meridians that will guide us to our
management strategy.

2. Retinoscopy: In retinoscopy, we
measure the power of meridians.

Source: Preoperative Pentacam 4 map refractive of a patient with keratoconus... | Download Source: (765) Quick guide to the manage-
Scientific Diagram (researchgate.net) ment of keratoconus: Part 13 - YouTube
(Sinjab Academy)

We can determine the most accurate
axis using retinoscopy. Scissoring
reflex is the earliest clinical sign in
keratoconus.

Steps of Refraction in 1. Topography: Corneal topographer Source: (765) Quick guide to the manage-
Keratoconus provides us four related maps, ment of keratoconus: Part 13 - YouTube
1. Topography namely sagittal curvature (front), (Sinjab Academy)
2. Retinoscopy elevation (front), corneal thickness, So, to refract by surpassing this
3. Subjective refraction elevation (back); that helps us to scissoring reflex, we just need to rotate
4. Over refraction read the real corneal refraction the slit to the perpendicular axis, and
5. Fine tuning in corneal ectatic conditions then continue with the traditional
6. Comparison with Total Corneal including the true astigmatism retinoscopy using spherical lenses until
of cornea at various points. We the reflex is neutralized.
Refractive Power (TCRP) usually do this by studying the
7. Binocular balancing amount of refraction in zones with
8. Measuring potential acuity (if cone as a centre especially the 5 mm
zone, that involves pupil as well.
needed) It also gives the data of principal

Source: Preoperative Pentacam 4 map refractive of a patient with keratoconus... | Download Source: (765) Quick guide to the manage-
Scientific Diagram (researchgate.net) ment of keratoconus: Part 13 - YouTube
(Sinjab Academy)

68 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Now, if there is a break in the pupillary Source: (765) Quick guide to the manage- components to reconfirm that the
band and the outer or projected streak, ment of keratoconus: Part 13 - YouTube previously determined refraction
then we need to rotate the outer streak (Sinjab Academy) was correct or not. We generally do
to align with the inner one. We start with the most correct axis this by retinoscopy. We can also do
that we have obtained by performing this step subjectively.
Source: (765) Quick guide to the manage- retinoscopy. Rotate the slit to achieve 5. Fine Tuning: Fine tuning is done
ment of keratoconus: Part 13 - YouTube the clearest meridian as the patient’s using Jackson’s Cross Cylinder in
(Sinjab Academy) response. Now we begin with adding traditional manner. Cylindrical
By this we can reach the most accurate spherical lenses until we obtained the axis is first tuned and then the
axis. maximum visual acuity. cylindrical power. The only
difference in keratoconus is the
Source: (765) Quick guide to the manage- Source: (765) Quick guide to the manage- power of JCC is more than +/- 1.50
ment of keratoconus: Part 13 - YouTube ment of keratoconus: Part 13 - YouTube D because the just noticeable
(Sinjab Academy) (Sinjab Academy) difference in these patients is much
After that, we can determine the power Now rotating the higher than the normal patients.
by altering the spherical power until we slit opposite to the For fine tuning the spherical power,
get the characteristics of a neutral glow. current axis, to get we do the conventional duochrome
And this will give us the end point of the best corrected test.
retinoscopy, noting the correct power visual acuity at that 6. Comparison with Total Corneal
with axis. axis. We keep on Refractive Power Maps: Corneal
3. Subjective Refraction: Recording adding lenses over Manifest Refraction (CMP) is
the previous lens compared with the Manifest
the uncorrected visual acuity and until the maximum Refraction (MR), we have obtained
starting with two line above it. possible acuity is subjectively. Now we can overlook
Using the stenopic slit, we cover all achieved. the spherical component as that
the meridians of the cornea except Now transpose to is being compensated by the axial
the meridian being tested. equate it in sphero – length but in general there is no major
cylinder format. difference between the cylindrical axis
4. Over Refraction: Manipulations and power of the CMP and MP. And if
it occurs, then we need to go with all the
are done in sphere and cylinder above steps very thoroughly to recheck
the refraction.
CMP is nothing but the projection of
prescription at spectacle plane onto
cornea plane. This can be done by two
paths, Inward Translation and Outward
Translation.

Source: (765) A Quick Guide to Reading
Corneal Tomography: Part 4 - YouTube
(Sinjab Academy)

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 69

Subspeciality - Refraction and Spectacle Prescription

Any K readings will affect myopic correction as -0.8 per -1.00 We all know that 43.50 D is considered to be normal corneal
Dioptres refraction. More than that means steeping or the resultant
curvature myopia.

Source: (765) A Quick Guide to Reading Corneal Tomography: Part Source: (765) A Quick Guide to Reading Corneal Tomography:
4 - YouTube Part 4 - YouTube
(Sinjab Academy) (Sinjab Academy)
For example, For example,

Source: (765) A Quick Guide to Reading Corneal Tomography: Part Source: (765) A Quick Guide to Reading Corneal Tomography:
4 - YouTube Part 4 - YouTube
(Sinjab Academy) (Sinjab Academy)
Path 2 is Outward Translation, that can be elaborated as
conversion of Corneal Refraction (CR) based on K reading to SEQ: Spherical Equivalent
Assumed Manifest Refraction (AMP) at spectacle plane.
7. Binocular Balancing:
Source: (765) A Quick Guide to Reading Corneal Tomography: Part Always remember that Binocular Balancing is done only
4 - YouTube
(Sinjab Academy) if the spectacles are the mode of correction and can be
performed after achieving monocular end points of the
refraction.
8. Measuring Potential Acuity: It becomes must when the
corrected visual acuity is or less than 0.6
We do this usually by using trial rigid lenses. Visual Acuity
measurement is very important because it helps us in decision
making. Whether to go with spectacles at the current severity
or RGPs or other options may help the patient.

The Manifest refraction is the key to the lock called
keratoconus. The value of general automated refraction is less

70 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

important in this case unlike in normal 6. h t t p s : / / w w w . h e a l i o . c o m / Management Specialist, Corneal
patients. Depending upon the degree ophthalmology/journals/jrs/2018- Tomography Expertise.
of irregular astigmatism, and patient’s 1-34-1/%7Ba768a875-a94e-
desire we can now plan a management 4021-960c-ea479deba5dd%7D/ Corresponding Author:
with regular contact lenses, speciality autorefraction-versus-manifest-
contact lenses or just by prescribing a refraction-in-patients-with-keratoconus Jeetesh Gurnani, (B Optom)
pair of spectacles. Gurnani Chashma Ghar, Prayagraj
7. Diagnostic Procedures in
References Ophthalmology Second Edition

1. Keratoconus: Causes, Symptoms, (Authors: H V Nema, Nitin Nema)
Diagnosis, and Treatment (webmd.com)
8. w w w . p e n t a c a m . c o m / u s / s t a r t /
2. Keratoconus: Causes, symptoms and technology/topography-maps.
treatment | All About Vision html?utm_content=aktionsbox

3. Making Sense of the Irregular Cornea 9. (765) Sinjab Academy - YouTube:
(reviewofcontactlenses.com) Virtual academy containing videos
about refractive surgery, keratoconus
4. Management of Keratoconus (nih.gov) and corneal topography created by
5. Autorefraction Versus Manifest Mazen Sinjab. Mazen M Senjab - MD,
MSc, CABOphth, PhD, FRCOphth
Refraction in Patients With Keratoconus (London) Professor of Ophthalmology in
- PubMed (nih.gov) Damascus University, Anterior Segment
and Refractive Surgeon, Keratoconus

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 71

Awards

Awards

Awards

Speakers

Speakers

Speakers

Speakers

Speakers

Speakers

Speakers

Speakers

MCQ Quiz DOS Times Quiz

Monica Chaudhry, Professor , BSc, MSc optometry INSTRUCTION
• The Quiz questions are designed to help you self
DOS refraction and spectacle prescription
Self reflection assessment assess on the refraction speciality on the topics
covered in this issue.
• The quiz can also be accessed through the QR code
as a google form link through your smartphone
and answered through digital mode
• If you select the incorrect response you can retake
the quiz until the correct response is responded.

1. Which of these is not a binocular balancing 1 point 5. Retinoscopy done when accommodation is 1 point
technique 1 point active is called .......... to find the lag or lead 1 point
alternate occlusion, 1 point of accommodation. 1 point
prism-dissociated blur balance Static retinoscopy
fogging technique MEM
Humphriss immediate contrast method Dyanmic retinoscopy
Radical retinoscopy
2. If significant latent nystagmus is present
the other eye should be occluded during 6. Which examination can be done through
refraction with– Telehealth
opaque occluder optical dispensing
pin hole occluder retina evaluation
translucent occluder assess colour vision
Jackson Cross Cylinder Refraction
all of the above
3. When a patient with Myopia presents with
near esophoria over the prescription, the 7. Which of the statement is FALSE for
first step to management would be Cyclopentolate
Cycloplegic refraction to rule out can cause side effects like redness of the eye,
overcorrection of Myopia eye irritation, blephroconjunctivitis and
Under correct the prescription immediately psychosis
Remove the Myopic prescription available in 5 and 10 % drops
Prescribe near addition effect comes in 20-30 mins
effect lasts for 2-24 hrs
4. Bifocal lens design with minimum image
jump is 8. Retinoscopy is based on
Executive bifocal design Badal’s principleb
C segment Contour matching
D segment Focaults principle
Round segment Imberts principle

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 83

DOS Times Quiz

9. Transpose -1.0Dpsh / -3.0 Dcyl X 20 1 point 15. Jackson’s cross cylinders : which of the 1 point
-1.0Dpsh / +3.0 Dcyl X 20 statment is INCORRECT
-4.0.0Dpsh / +3.0 Dcyl X 110 the handle is 45 degrees to the axis
-1.0.0Dpsh / +3.0 Dcyl X 110 a 0.50 JCC means +0.25 / -0.50 D cyl
-4.0.0Dpsh / +3.0 Dcyl X 20 it is used to determine the axis of the
cylindrical power
10. Which of the following is best process 1 point is used to determine the power of the sphere
followed while refracting high refractive
errors 16. Which of the following is INCORRECT for 1 point
keeping vertex distance at 14 mm ARC Anti reflection coating
use halberg clips and overrefract improves cosmesis
giving undercorrection helps to minimise or eliminate ghost images
using phoropter is better than trial frame is improtant for high index powers
method enhances tint of the spectacle

11. Which of the statement is FALSE for 1 point 17. A 15 year child, with excessive near work 1 point
LogMAR chart and digital screen use complains of blurred
Same no of letters in each line distance vision since one month and
Non uniform progression of letter detected to have -1.0 Dsph acceptance on
Regular spacing between lines and letters dry refraction .
Greater accuracy prescribe the -1.0 as early as possible
rule out spasm of accomodation by
12. Measurements required to fit PAL 1 point cylcoplegic refraction
successfully are 1 point prescribe undercorrection around 0.50
Pupil height only Advise contact lenses
Binocular Pupillary Distance and Heights
Monocular Pupillary Distance and Heights 18. A 4 year old child 6/9 VA with eso deviation, 1 point
near reference circle for the first time when refracted under
cylcoplegiaa , shows retinocsocpy findigns
13. Cycloplegic Drug of choice for refraction in under cylcoplegia as +3.0 Dsph Both eyes.
an adult is The prescription guidelines is
Tropicamide treat strabsimus first
Tropicamide and phenylneprine
Hom Atropine prescribe full correction under cycloplegia
Cyclopentolate subtracting only the working distance

undercorrect to +2.0 Dsph and prescribe

over prescribe for distance +4.0

14. The following statements are true except 1 point 19. The normal range of lag of accommodation, 1 point
in dynamic retinocopy is
Contrast sensitivity is expressed in log units +0.25DS to +0.75DS
+0.50DS to +1.00Ds
Michelson contrast is used for grating charts -0.50DS to +0.50DSd
-0.25DS to -0.75DS
Sine wave indicates sudden change in
contrast

dModulation Transfer Function is
represented by ratio of image contrast over
object contrast

84 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

DOS Times Quiz

20. A near esophoria higher than distance, 1 point 24. To assess the accommodation response, 1 point
with a high accommodation convergence which of the below tests is appropriate?
to accommodation ratio is indicative of Push-up amplitude of accommodation
Accommodation excess Monocular estimate method retinoscopy
Convergence excess Accommodation facility
Convergence insufficiency Negative relative accommodation
Accommodation insufficiency

21. The Four steps of subjective refraction : put 4 points 25. Which contrast sensitivity chart uses 1 point
them in order square wave gratings?1
Cambridge
first second third fourth Arden
step step step step FACT.
CSV-1000
Binocular balance

Astigmatic
correction

monocular 26. While peforming the retinoscopy, If the 1 point
end point movement of the reflex and the intercept
are in the opposite direction, its known as
Spherical correction With motion
Against motion
22. Monocular spherical end point is achieved 1 point Neutral
by Swirl
Duochrome test
Fogging test 27. By knapps law , If the ametropia is Axial in 1 point
none of the above origin, then prescribing of contact lenses
both duochrome and fogging is the treatment of choice if one wishes to
minimize induced aniseikonia. And in
23. Which statement is CORRECT based on 1 point Refractive anisometropia spectacle lenses
Gaussian curve for distribution of refractive is the treatment of choice to minimize
errors: induced aniseikonia
True
the mean would shift towards emmetropia False
the mean would shift towards hyperopia
the skewness would firstly be slightly

negative, and
At last the skewness becomes strongly

positive for post-teenage years.

Corresponding Author:

Prof Monica Chaudhry
Advisor and Adjunct Prof G D Goenka Unviersity,
Retd Sr T Officer AIIMS,
Ex HOD Amity University ,
Ex Director School of Health Sciences
Ansal University ,
Ex Chairman Optometry Council of India

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 85

Tearsheet

Sharpen your Refraction
Knowledge

Monica Chaudhry, B.Sc, M.Sc Optometry , FIACLE
Consultant Optometrist and Educator

Emmetropia : ideal refractive state of the eye Expected Visual acuity and child development

Ametropia: refractive power does not produce this precise Age Optokinetic Force preferential VEP
focus (Months) Nystagrnus looking
Presbyopia is the age-related decrease in accommodative 6/120 6/90
ability 1 6/90 6/6
Refraction : To establish the power of the corrective lens that 6/6
will achieve this accurate focus when positioned in front of 6 6/18 6/45 6/6
the eye. The right prescription is determined for each patient
as an individual and is balanced binocularly. 12 6/12 6/30

36 6/6 6/6

20 feet or 6 m distance is used for measuring VA because it A Spherical lens has same power in all meridians. A
approaches optical infinity. cylindrical lens has power in two meridians.The power is
6/6 means : normal individual can read at 6 m and so can the 90 degrees from its axis.
person with 6/6 vision. 6/36 vision means the person will be Spherical equivalent calculation: Add algebraically the
able to see this at 6 m which a normal person can see clear a sum of the sphere power with half of the cylinder power
36 m

CONVERSION OF SNELLEN ACUITY Eg : -2.50 D sph / -1.0 Dcyl x 90 = -3.0 Dpsh .
Transposition : Plus-Minus Cylinder Conversion eg
INTO LOGMAR, AND METRIC UNITS 1. -3.00 D Sph / -1.50 Dcyl x30 °
Steps
logMAR SNELLEN SNELLEN
(METRIC)

1.0 20/200 6/60 1. Add the cylinder power to the sphere algebraically
{Add spherical -3.00 and cylindrical power -1.50 = -5.0 }
0.9 20/160 6/48
2. Change the sign of the cylinder from plus to minus or
0.8 20/125 6/38 from minus to plus (+ 1.50 D cyl :Sign Changed)

0.7 20/100 6/30 3. Change the axis by 90 degrees: Add or subtract 90
6/24 degrees {eg 120° (30°+90°)}
0.6 20/80 Eg 2 3.00 D Sph / -1.50 Dcyl x30 ° Final Transposed Power
0.5 20/63
6/20 is -5.00 / +1.50 x 120

0.4 20/50 6/15

0.3 20/40 6/12 Steps in subjective refraction
0.2 20/32 6/10
0.1 20/25 6/7.5 • Visual acuity aided and unaided
0.0 20/20 6/6 • Starting point - retinoscopy, autorefraction, or the patient’s

current glasses
• Best vision sphere - fogging and Duochrome

86 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Tearsheet

• Astigmatism cylindrical power determination – Cross cylinder / Progressive addition lens PAL- Progressive addition
astigmatic fan lenses are one piece lenses that vary gradually in surface
curvature from a distance portion to a plus addition in the
• Monocular end point lower near portion. Unlike bifocal or trifocal lenses, there is
• Binocular balancing uninterrupted vision without any visible line of demarcation..
Near vision and addition if required There is a Distance, intermediate and near zones of a typical
Sequence progressive lens where the wearer has clear vision at all
monocular sphere, cylinder axis, cylinder power, and sphere. distances
Success is achieved in instructing properly and relaxing Prescribing in children : key deciders
accommodation . - Match Normal range refractive error range in child’s age
- Does the amount of refractive error interrupt the
Preventing over minussing
1. Cycloplegia – patient is unable to accommodate functional vision
2. Fogging - starting the refraction from a position of extra plus - prescribing glasses interfere with the normal process of

spherical power. Plus power is then removed, stopping as soon as emmetropisation
the letters on the acuity chart are read correctly Polycarbonate and Trivex is the choice for paediatric spectacle
3. The duochrome test – uses principle of chromatic aberration - material. Less weight and high impact resistance
The red and green sides of the screen should appear equally clear. Relationship of AC/ A ratio and prescription in children
Red add minus, green add plus (mnemonic RAMGAP) with Eso deviation
- Normal AC/A ratio (<5:1), prescribe full correction as
Symptoms and possible diagnosis on
refraction achieved under cycloplegia :
Blur vision : refractive error, amblyopia , spasm of - High (>5:1) AC/A ratio : will correct the distance deviation,
accommodation , malingering
additional plus ( as bifocal )may be required for near
Asthenopia : uncorrected refractive error, phorias,
convergence insufficiency, accommodation anomalies Classification of Total Hyperopia

Strabismus and amblyopia : anisometropia

Retinoscopy: procedure
• Reduce room illumination
• Ask patient to fix far off at a fixation target just behind examiner
• Scope with retinoscope and locate the axis .
• Identify – With , Against reflex
• Neutralize movement of the reflex
• Record your retinoscopy findings
• Subtract working distance
Presbyopia : is decrease in accommodative facility. A plus
corrective lens is prescribed as reading addition over an
accurate distance prescription. An add of +2.0 to +3.0 dioptres
is given in an intraocular (monofocal ) implant.

Near vision : Measure uniocular and then binocular .
Asymmetric add may suggest incorrect distance prescription

Prescribing add depends on Reading range and habitual
reading distance .

Add above +3.50 is given for patients with low vision so as to
magnify the objects.

Bifocal types : round , Flat top and Executive

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 87

Tearsheet

Table : Dioptres criteria to prescribe glasses in children

Infant age above 2 years
and above

Myopia - 4.0 and above -3.0 and above

Hyperopia + 6.0 and above + 4.50 and above

Hyperopia with Eso +2.0 and above +1.50 and above

Astigmatism -3.0 and above - 2.0 and above

Anisometropia above 2 diopters should be considered for
prescription

Astigmatism classification Aetiology of myopia
• WTR : With-the-rule astigmatism :Vertical meridian is Axial - increased axial length of eye ball

steeper, plus cylinder axis is at 90 degrees (+- 20 o) Curvature - increased curvature of the cornea
• ATR : Against the Rule astigmatism :horizontal meridian
Index - increased index of lens
is steeper , plus cylinder axis is at 180 degrees (+- 20 o)
• OBLIQUE : meridian between 120 and 150 degrees and 30

and 60 degrees.
Regular Astigmatism. When horizontal and vertical
meridians are at right angle to each other.

Irregular Astigmatism. When the two meridians are not Accommodation excess - occurs due to spasm of
perpendicular , and this cannot be corrected by cylindrical accommodation
spectacle lenses. Positional - anterior placement of the lens in the eye ball
- Mild astigmatism : <1 D
- Moderate astigmatism : 1.00 to 2.00 D
- Severe astigmatism :more than 3.0 diopters

Lens material Index Specific gravity Abbe value Benefits Recommendation
Glass 1.52 2.54 60 Good optics Low cost ,Heavy , breakable , least
recommended
CR 39 / std plastic 1.49 1.32 58 Good optics Almost any prescription , preferably low
Less powers , add scratch resistant coating
expensive

Polycarbonate 1.59 1.20 32 High impact Children
resistance Any occupation with trauma risk
Thinner than
standard CR

Trivex 1.53 1.11 43 Very high Special recommendation in high trauma
impact risk
resistance

High index plastic 1.60 1.34 37 Thin High powers
Lightweight Less expensive than 1.7 index
ARC coating essential

High index plastic 1.70 2.99 32 Thinner than High powers
1.60 Expensive
Lightweight ARC coating essential

Common Surface treatments / coatings of the spectacle lenses
1. Anti-reflection coating (ARC)
2. Scratch resist ance coating
3. UV coating 4.Hydrophobic coating

88 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Tearsheet

Sample prescription slip
XYZ Clinic
Address :
Name ............................................................................................................................................................................................ Date..........................................
Age ......................... Sex ........................... Address .......................................................................................................................................................................

Sphere Cylinder Axis Prism and base Visual acuity

Distance
Near

Remarks ....................................................................................................................................................................... Signature

Prescribed for
o Continuous wear
o Near only
o Distance Only
o Wear as required
Recommendation
o Scratch resistant plastic
o Plastic /high index plastic / polycarbonate
o UV protection
o ARC coating / Hydrophobic coating / Blue cut
o Tint
o Glass
Monucular PD …………………………………………………………
Frame specifications ………………………………………………

Corresponding Author:

Prof Monica Chaudhry DOS Times - Volume 26, Number 3, November-December 2020 89
BSc, MSc Optometry
Consultant Optometrist and Educator
Founder Learn Beyond Vision

www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

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Subspeciality - Refraction and Spectacle Prescription

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