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05/02/2023
Pearls to prescribing Challenging
Refraction
Indra P SharmaOptometrist
05/02/2023
Refractive Error• Result of a mismatch between optics and the
growth of the eye
• Combination of genetic and environmental influences
• NOT considered an eye disease
• Treatment includes spectacles, contact lenses, and refractive surgery
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Hyperme-tropia50%
Emmetropia25%
Myopia< 1D13%
Myopia> 1D12%
Ref: Borish IM, Clinical Refraction , Ed 3: 861-937
Refractive Error distribution in normal population
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What is Refraction?
Objective RefractionRetinoscopy
Static
(Refraction with inactive
accommodation)Dynamic
(Refraction with active
accommodation)
Autorefractometry
Refraction – estimation of refractive status of the eye
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Objective refraction• Refractive error is determined without the
effort of the patient.• Gold standard: Retinoscopy
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Retinoscopy –The name
• Commonly used synonyms for retinoscopy are “skiascopy” and “skiametry”
• Other synonyms seen in literatures were “umbrascopy”,“pupilloscopy” and “retinoskiascopy”
• The term “retinoscopy” (vision of the retina) was initiated by Parent in 1881.It has been generally accepted in English-speaking countries.
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Why is retinoscopy important?• First technique that determines the patient’s
refractive status.
• Serves as a starting point for subjective refraction.
• It can be performed on infants, mentally infirm, low vision patients, uncooperative or malingering patients.
• Heavily reliable for the prescription of optical correction.
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Retinoscopy Prerequisites• Semi-dark room• Trial box and frame• Retinoscope• Fixation target
• Working distance• Cycloplegia
Retinoscopy Procedure
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Troubleshooting Difficulties during
retinoscopy
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Difficulties in retinoscopy• Some refractions are easy; some are
extremely difficult
• It is an art that requires practice and can’t be totally learnt from books
• Certain difficulties encountered during retinoscopy.
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1. Reflex may not be visible
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Possible Causes Solutions
1. Opaque/hazy ocular media
1.In most cases, it is overcome by use of mydriatics*
2.Small pupil 1.Use of mydriatics*
3.High degree of refractive error.
1.Follow-up case: Check PGP to get a rough estimation
2.First Examination :If reflex is dull, try -7 first and then + 7.If reflex still dull proceed to 15D or 20 D, untill in the range of visible reflex and proceed from there.
* Perform all indicated investigation and rule out contraindication before dilating
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2.Varying/Changing retinoscopic findings
With or against?……Its confusing
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Possible Causes Solutions
1. Wandering fixation 1.Give a specific fixating target
2.Abnormally active accommodation
1.Fogging technique
2.Cycloplegic refraction may be required in young patient
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Role of Cycloplegics
• Atropine 1% ointment – tds x 3 days ( reserve this to infants or convergent squint)
• Cyclopentolate or HA 2% drops – 1 hour before : 10 mins interval 3times
• Tropicamide – 30 mins before , 5 mins interval 3 times
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3.Scissor Reflex
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Possible Causes Solutions
1. High Astigmatism 1.Rotate the retinoscopic beam to find angle where scissor reflex is minimum.
2.Nebular corneal opacties
1.Increase retinoscopic illumination to decrease pupil diameter.2. Spot retinoscopy may help
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4.Conflicting or triangular shadows
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Possible Causes Solutions
1.Irregular astigmatism 1.Do keratometry and subjective refraction and prescribe minimum power that gives maximum visual acuity
2.Keratoconous 1. Relate refraction to visual acuity.2. Perform corneal topography 3. Perform keratometry and
subjective refraction
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Relationship between Visual Acuity and Refractive Error
Relationship between Visual acuity and refractive error Snellen Visual Acuity Uncorrected Spherical
Error(DS) Uncorrected Cylindrical
Error (DC) 6/6 (20/20) <= 0.25 <= 0.25 6/9 (20/30) 0.50 1.00 6/12 (20/40) 0.75 1.50 6/18 (20/60) 1.00 2.00 6/24 (20/80) 1.50 3.00
6/36 (20/120) 2.00 4.00 6/60 (20/200) 2.00- 3.00 >= 5.00
Source: Borish’s Clinical Refraction ,Bennett and Rabbetts
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5. Spherical aberration.
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Possible Causes Solutions
1.Positive aberration(in normal accommodating lens)
1. Increase retinoscope illumination to decrease pupil diameter2.Concentrate on the central bright glow and ignore the peripheral glow
2.Negative aberration (more in lenticular nuclear sclerosis)
1. Increase retinoscopic illumination2. Perform dilated retinoscopy
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Prescribing guidelines for Hyperopic Compensation
Consideration ManagementBirth to 6 years
No compensation, except for strabismus, suppression or poor school performance
6 to 20 years No compensation, except for strabismus, suppression or poor school performance, near asthenopia or acuity loss; prescribe cautiously with liberal cut in + power
20 to 40 years Compensate for complaints , with moderate cut in plus power for distance, yet full compensation for near activity
40 + years Usually compensate with full plus power with near add for presbyopia
Esotropes Fully correct , with possible near correction
Exotropes Partially correct to minimize secondary exo problems
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Consideration Management optionsCiliary tonicity
Cut about +1.0 D from ‘wet’ refraction
Patient age The younger the patient the more liberal cuts from plus power.
Prescription History
For first prescription, plus power should be cut from wet refraction for adaptive purpose
Residual accommodation
If less than 1.oD,good cycloplegic effect. So liberal plus cut from wet refraction
Dry Refraction
The closer the dry refraction is to the wet, the less likely to cut plus power in the final prescription
Guidelines in Cycloplegic Refraction Prescribing
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Astigmatism ManagementType Visual acuity Symptoms Management Adaptation
Low Little reduction Near asthenopia, distance driving fatique
Prescribe if symptomatic
Minimal
Small amount with-the-rule
Little reduction Near asthenopia Prescribe if symptomatic
Minimal
Large amount with-the-rule
Reduction at far and near
Blur vision at distance and near
Prescribe to increase visual acuity
Pronounced
Against the rule Slight reduction at far and near
Near asthenopia, slight near blur
Prescribe if symptomatic
Moderate
Oblique Little reduction Near asthenopia Prescribe if symptomatic
Moderate
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High-Degree Astigmatism• High degree astigmatism(>0.75D) causes
asthenopia as well as decreased vision• They are usually with-the-rule or oblique.
• Pt exhibit ‘fixed squint’ or ‘squeezing of lids’
With-the-rule• Ascribed to genetic
disposition• Pressure of the upper eyelid
on the cornea
Oblique• Considered congenital• Precursor to conical corneal
distortion
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High spherical with low astigmatism• Necessary to estimate if cylinder is
causing patients symptoms• Correct cylindrical or not?- initially matter
of diagnostic judgement• Often large spherical correction provides
satisfactory acuity• Patient symptoms on subsequent
evaluation will possibly indicate weather the initially omitted should be prescribed
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General guidelines to glass prescription
• Aim for 6/9 or better.• If less than one line improvement in vision there is
no real benefit in prescribing new glasses.• Convergence insufficiency/ exophoria Low myopic full correction Hypermetropia- Undercorrect• Low hyperopes, especially the young-Do not
prescribe until symptomatic.• Patient must always be counselled about the
intention of lens correction
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Points to Ponder• Retinoscopy is a combination of art and
science.
• The importance of a good refraction can never be undermined.
• There is NO SUSBTITUTE to retinoscopy.
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