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Challenging Refraction
This document discusses various aspects of refractive error assessment and management. It begins by defining refractive error and describing its causes and treatment options. It then discusses the distribution of refractive errors in the normal population. Several sections provide details on objective refraction techniques like retinoscopy, including prerequisites, procedures, troubleshooting difficulties, and the importance of retinoscopy. Guidelines are provided for prescribing for various refractive error types and patient characteristics.
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Challenging Refraction
- 1. Pearls to prescribing ChallengingRefraction Indra P Sharma Optometrist10/28/2016
- 2. Refractive Error • Resultof 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 10/28/2016
- 3. Hypermetropia 50% Emmetropia 25% Myopia< 1D 13% Myopia> 1D 12% Ref:Borish IM, Clinical Refraction , Ed 3: 861-937 Refractive Error distribution in normal population 10/28/2016
- 4. What is Refraction? 10/28/2016 Objective Refraction Retinoscopy Static (Refraction with inactive accommodation) Dynamic (Refractionwith active accommodation) Autorefractometry Refraction – estimation of refractive status of the eye
- 5. Objective refraction • Refractiveerror is determined without the effort of the patient. • Gold standard: Retinoscopy 10/28/2016
- 6. 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. 10/28/2016
- 7. Why is retinoscopyimportant? • 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.10/28/2016
- 8. Retinoscopy Prerequisites • Semi-darkroom • Trial box and frame • Retinoscope • Fixation target • Working distance • Cycloplegia 10/28/2016 Retinoscopy Procedure
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- 11. 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. 10/28/2016
- 12. 1. Reflex maynot be visible 10/28/2016
- 13. 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 10/28/2016
- 14. 2.Varying/Changing retinoscopic findings With oragainst? ……Its confusing 10/28/2016
- 15. 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 10/28/2016
- 16. 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 10/28/2016
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- 18. 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 10/28/2016
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- 20. Possible Causes Solutions 1.Irregularastigmatism 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 10/28/2016
- 21. Relationship between Visual Acuityand 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 10/28/2016
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- 23. Possible Causes Solutions 1.Positiveaberration(in normal accommodating lens) 1. Increase retinoscope illumination to decrease pupil diameter 2.Concentrate on the central bright glow and ignore the peripheral glow 2.Negative aberration (more in lenticular nuclear sclerosis) 1. Increase retinoscopic illumination 2. Perform dilated retinoscopy 10/28/2016
- 24. Prescribing guidelines for HyperopicCompensation Consideration Management Birth 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 10/28/2016
- 25. Consideration Management options Ciliarytonicity 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 10/28/2016
- 26. Astigmatism Management Type Visualacuity 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 10/28/2016
- 27. High-Degree Astigmatism • Highdegree 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’ • Ascribed to genetic disposition • Pressure of the upper eyelid on the cornea With-the- rule • Considered congenital • Precursor to conical corneal distortionOblique 10/28/2016
- 28. High spherical withlow 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 10/28/2016
- 29. General guidelines toglass 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 10/28/2016
- 30. 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. 10/28/2016
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