Fun with Refraction Click to download PowerPoint - PowerPoint Presentation

1. Fun with RefractionClick to download PowerPointKatie Clare, OD & Erin McConnell, OD

2. The Phoropter1

3. Why is Refracting Important?To help patients see the world clearlyTo rule-out underlying ocular pathologyUnexplained reduction in BCVAVisual significance of cataract, ERM, AMD, etc.2

4. Pinhole AcuityDiagnosticRefractive potentialNear pinhole potential = quick potential acuity meter (PAM)PitfallsPatients with poor understanding will have better BCVA on refractionCentral scotomaPosterior subcapsular cataract (VA worsens with pinhole)3

5. Where to Begin?RetinoscopyAutorefractionOld glasses4

6. Basic Steps of RefractionSphere Power DeterminationCylinder Axis DeterminationCylinder Power DeterminationSphere Power Refinement Binocular BalanceAdd Power Determination5

7. Sphere Power DeterminationPut autorefraction/prior Rx in phoropter (or retinoscope) and take VAFog to three lines worse than entering VA (MPMVA or maximum plus to maximum visual acuity technique)Typically by adding +0.75 sph Refine sphereOne click of minus should yield appreciable improvement in VA or approximately one line of VAEgger’s Rule“Bigger and brighter, not smaller and darker”Endpoint?Choices look equal6

8. Cylinder Axis DeterminationJackson cross-cylinder (JCC) dots should straddle the arrowFollow the white dot for (+)cyl refractionStart with 10-15° increments until reversal, then go back in 5° incrementsEndpoint?Both choices look about the same7

9. Cylinder Power Determination“Power” or P should line up with the arrows(+)cylinder refractionIf patient prefers white dot, add cylIf patient prefers red dot, subtract cylAlways start by changing cylinder by 0.50DOnce reversal, start changes by 0.25D stepsMaintain spherical equivalentFor every +0.50 change in cyl, add -0.25 sphereFor every -0.50 change in cyl, add +0.25 sphere8

10. Sphere Power RefinementSecond MPMVAAgain, start by fogging +0.75 sph, then add minus one click at a time until achieving 20/20 or BCVA9

11. Duochrome TestMonocular test on red-green screenUsually several rowsAsk patient which side of the screen is clearer/crisper/blackerIf red, add -0.25 sphere (i.e. that eye is under-minused)If green, add +0.25 sphere (i.e. that eye is over-minused)If both sides are equally clear/crisp/black, the desired endpoint has been reached10

12. Binocular BalancePatient must have binocularity Prism DissociationIsolate 20/40 lineFog +0.50 sph OURisley prisms: add 4pd BD OD and 4pd BU OSConfirm diplopic imageWhich line is darker/clearer, top or bottom?Add one click of plus to eye that is seeing darker letters until equally blurry“The image moves towards the apex”Remove prismBring down one click of minus at a time until just able to clearly see BCVAMay not work if asymmetrical BCVA11

13. Add Power DeterminationThings to consider:AgeWorking distanceRx: hyperopia vs. myopiaUse of near rod Determining Rx for specific tasks MusicSewingComputerShooting12

14. Quick and Dirty RefractingDoes the patient want new glasses?Reliable autorefractionMake sure signal strength is highBegin with addition of plus sphere. Never give minus as initial choiceDon’t touch the axis if good VA with current RxRefine cylinder power prior to cylinder axisShow binocular RxOpen both eyes and ask if they feel comfortableAdjust sphere until balancedFor add power, always ask about working distance vs. age-appropriate norm Prescribe for the patient’s needsBifocals vs. progressives vs. single vision only (SVO)13

15. Age-Appropriate Add14Patient’s AgeAdd40-45+1.00-1.2545-50+1.50-1.7550-55+2.00-2.2555++2.50 or higher

16. 15Refracting Pearls

17. Egger’s RuleEach line away from emmetropia on the Snellen chart represents roughly 0.25 diopters of ametropiaEx: If VAsc 20/40 on the Snellen chart, then rx spherical equivalent should be roughly 0.75 dioptersDoes not tell what type of ametropia (i.e. spherical and/or cylindrical), merely how much16Distance Visual AcuitySpherical Equivalent20/200.0020/250.2520/300.5020/400.7520/501.0020/701.2520/1001.50

18. Cylinder CorrectionDon’t be afraid to give full RxOften patients will achieve BCVA with full cylinder RxDo not cut cylinder unless patient is not adapting Keep axis where VA is clearestDo not push toward 90º or 180ºAmount of correction determines axis steps0-0.50D → 10-15º steps0.50-1.50D → 5-10º steps1.50-2.50D → 3-5º steps2.50D and up → 1-2º steps17

19. Case Example50yo F presents with constant monocular diplopia OU x 10 yearsNeuro-Ophthalmology workup with imaging found no cause PMH is unremarkable Current glasses Rx:OD: -1.00sph, VA 20/25OS: -0.75sph, VA 20/25Autorefraction:OD: -1.50+1.50x086OS: -1.75+1.50x105Manifest Refraction:OD: -1.50+1.25x090, VA 20/20OS: -1.50+1.50x100, VA 20/20Appreciates clear, single vision OD, OS, and OU!18

20. Just Noticeable Difference (JND)Amount of diopters that must be changed in order to discern a difference at least half the time (absolute threshold)JND = denominator of Snellen acuity/100Ex: VA 20/200 → JND = 200/100 = 2 dioptersQuick and dirty:VA >20/40 → change by 0.25VA 20/50-20/100 → change by 0.50VA <20/100 → change by 1.00 or greater19

21. Anisometropia / AniseikoniaTrial frame full RxWalk around officeWhat to look for?Double visionGradually change Rx of non-dominant eye until binocularly comfortableStress to patient the reason for cutting Rx and not to cross-cover/compare Contact lenses eliminate relative magnification differencesTilting of floorsBending of door frame, etc.20

22. Refracting AmblyopesDifficulty with crowdingLetter isolation often will achieve improved BCVADon’t forget JNDIf Rx is not amblyogenic, you must find pathology to explainConstant unilateral strabismusBilateral spherical refractive error > +4D or -6DAstigmatic refractive error >2.50DAnisometropic refractive error >1.50D in hyperopes and >2D in myopes21

23. Undilated RefractionsRepeat refractionsHigh myopia ~ 7D or higherHigh hyperopia ~ 3D or higherHigh cylinder ~ 2.50D or higherAccommodative complaintsLatent hyperopia? New presbyopesPediatricsPre/post dilation refractions22

24. Low Vision PatientsWhy refer to low vision specialist? Refraction performed with EDTRS chart and trial frameDifferent illumination In-depth discussions regarding daily visual goalsTrial variety of low vision aids; cost may be coveredOrientation and mobility therapy Utilization of physical and occupational therapistsWhere to refer?The Eye InstituteAssociation for the BlindPrivate low vision Optometrists23

25. When to Pick Up the RetinoscopePediatricsKeratoconusAphakes/scripts beyond phoropter limitsWhen things do not make senseAR dramatically differs from current glasses“It is all blurry” / “It all looks the same”DiagnosticsPoor quality of reflexCataractsIrregular corneasSurface issues24

26. Case Example33yo F presents with pressure, light sensitivity, and headache for 1 year Rx given the prior year did not relieve symptoms:OD: -1.00+0.50x105, VA 20/20-2OS: -1.00sph, VA 20/25AR at initial visit:OD: -2.50+1.75x110OS: -3.25+1.50x074Cyclo Rx:OD: +0.25+0.50x110OS: -0.50sphConcerned patient was over-minused or did not ever need Rx, then was sent to OD for undilated refraction and PCP for HA evaluation25

27. Case Example – OutcomeVAsc at follow-up was 20/25, 20/30AR at follow-up:OD: -4.25+2.75x113OS: -4.50+2.00x060Given fluctuating AR and inconsistent refraction, retinoscopy was performed and showed a scissor reflexTopography showed significant inferior steepening consistent with pellucid marginal degeneration26

28. Lens DesignAvoid switching lens design in well-adapted patientsSingle vision: distance vision only (DVO), near vision only (NVO), computer, specialty tasksUnable to adapt to bifocal (BF) or progressive addition lens (PAL)Motility issuesVertigoFlat-Top BifocalEasier to adapt than progressiveIf prism neededProgressive Addition LensNew presbyopePatients that desire increased rangeAlways discuss adaptation and tips/tricks Avoid with certain underlying ocular pathologies (e.g. advanced AMD, KCN, oculomotor deficiencies)27

29. Tips and Tricks for AdaptationBifocals and progressivesCurbs/steps/drop-offsHead positioning for near work – keep chin upGive it time, usually 2 weeks before giving upProgressivesPoint nose in direction of gazeFind the sweet spot – “trombone” per Dr. ClareFrame size/fit28

30. Repeat RefractionsReread glassesHave opticians read on manual lensometerCheck fitSegment height appropriate Pantoscopic tiltFrame size appropriateToo large induces distortions in high scriptsToo small is poor for progressivesConfirm optical centers Change in multifocal design?Consider trial framing D+N Rx29

31. ObservationsUnexplained reduced BCVA after surgeryHabitual Rx read incorrectlyAdd power in PAL – always check watermark+/- sign errorsImportance of manual lensometersPrismInduced by auto-lensometer If suspect that prism is present, always confirm by manual lensometer30

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