Subjec've Refrac'on. Dr Cesar Carrillo

Transcription

1 Subjec've Refrac'on Dr Cesar Carrillo May, 2014 Vien'ane/NOC **Disclaimer** The images contained in this presenta5on are not my own, they can be found on the web

2 VISION ASSESSMENT VISUAL ACUITY OBJECTIVE REFRACTION BINOCULAR BALANCE RX PRESCRIPTION SUBJECTIVE REFRACTION 2

3 OUTLINE MONOCULAR SUBJECTIVE REFRACTION SPHERE DETETMINATION MAXIMUN PLUS TO MAXIMUN VISUAL ACUITY (MPMVA) PLUS /MINUS TECHNIQUE FOR BEST VISION SPHERE DETERMINATION DUOCHROME TEST THE FAN AND BLOCK TEST ALTERNATIVE TECHNIQUES

4 MONOCULAR SUBJECTIVE REFRACTION Determina5on of refrac5ve correc5on of pa5ent based on their responses to the addi5on of various lenses One eye is occluded while the refrac5ve correc5on of the other eye is determined Only possible with pa5ents who can communicate effec5vely

5 SUBJECTIVE REFRACTION Should be performed under condi5ons that simulate pa5ent s normal viewing situa5on (pupil size, illumina5on)

6 MONOCULAR SUBJECTIVE REFRACTION Advantages Easier to learn than binocular refrac5on Is the preferred technique when you start to learn subjec5ve refrac5on Disadvantages Limited in that the occluder can lead to less relaxa5on of accommoda5on Over- minusing or under- plussing the refrac5ve correc5on Not latent nistagmus or cyclodevia5on

7 SUBJECTIVE REFRACTION Procedure: 1. Explain procedure (no wrong answer) 2. Sit or stand off to the pa5ent s side 3. Set phoropter or trial frame (PD, Rx) 4. Occlude lea eye

8 SUBJECTIVE REFRACTION 5. Determine the Best Vision Sphere:MPMVA (phoropter); Plus/ Minus (trial frame) 6. Duochrome test (circle of least confusion) 7. Determine the cylinder axis (JCC)

9 SUBJECTIVE REFRACTION 8. Determine the cyl power (JCC) 9. If the cyl axis or power change a lot, repeat the Best Vision Sphere 10. Measure VA 11. Repeat steps 5-10 for the lea eye

10 SUBJECTIVE REFRACTION 12. <60 y.o. perform binocular balance of accommoda5on: (Prism- dissociated blur balance of acc; Monocular fogging balance; HIC; TIB) 13. Compare VA (subjec5ve Rx other eye)

11 SUBJECTIVE REFRACTION Recording: No use degree sign (15 can look 150) Use x no axis Axis Monocular VA - Ph Vertex distance for correc5ons >4 D (equivalent sphere) Examples: Vertex distance 11mm RE: +6.00/ x 35 6/6+1 LE: +6.25/ x 145 6/6 OD: / x /15 OS: DS 20/15-1 RE: /- 0.50x100 6/12 PhNM LE: / x 75 6/4 Vertex distance 12 mm OD:- 7.50/- 2.25x35 20/70 Ph20/30 OS: /- 1.50x150 20/20

12 MONOCULAR SUBJECTIVE REFRACTION Interpreta'on: Compa5ble with re5noscopy (young pt. more posi5ve/less minus than re5noscopy) Less posi5ve/more nega5ve (latent hyperopia pseudomyopia) = cyclo Inconsistent results = technique error

13 SUBJECTIVE REFRACTION Common errors: Not monitoring VA (change in lens power = expected change in VA) Poor pa5ent instruc5ons Losing control of accommoda5on Allowing the pa5ent to direct the test Not recheck results

14 SUBJECTIVE REFRACTION MAXIMUN PLUS TO MAXIMUN VISUAL ACUITY (MPMVA) Used to determine best vision sphere as part of subjec5ve refrac5on and to determine op5mal spherical correc5on The pa5ent is fogged or blurred by adding plus lenses to the re5noscopy result. VA improve decreasing + or increasing -

15 MPMVA Used to ensure that the circle of least confusion is on the re5na prior to the use of the JCC technique

16 MPMVA Advantages Accommoda5on is well controlled Using a phoropter the lens changes can be made quickly and easily Disadvantages Care must be taken to ensure that the best vision sphere is not under- minused or over- plused prior to the use of JCC as inaccurate determina5ons of as5gma5sm can occur

17 MPMVA Procedure: 1. Oclude the lea eye 2. Determine RE VA 3. Add DS or more un5l lost 4 lines of VA(fogged) 4. If the VA is 6/12 or worse: young and older pa5ents

18 MPMVA Young pa5ents: able to accommodate = good distance VA Poor VA young pt: re5noscopy result is over- plussed or under- minused. The eye is already fogged. Go to step 5 Over 55 yo: re5noscopy result could be reducing VA (to minus or to plus). Use ±0.50DS lenses to determine Over plussed/under- minused (already fogged) or over- minused/under- plussed add +lens to fog

19 MPMVA 5. Reduce amount of fog by 0.25 DS and check VA improves 6. Con5nue to reduce the amount of fog in 0.25 DS steps and stop when there is no improvement in VA

20 MPMVA Pa5ents do no give perfect answers Present lens changes several 5mes un5l you obtain reliable responses Make sure your instruc5ons are accurate and your technique is good If a pa5ent is unable to tell any difference with 0.25 DS, then use 0.50 DS or even larger steps

21 SUBJECTIVE REFRACTION THE PLUS /MINUS TECHNIQUE FOR BEST VISION SPHERE DETERMINATION Low- powered plus sphere and minus sphere lenses (0.25 DS) are added in a systema5c manner to the pa5ent s re5noscopy result un5l the best visual acuity is obteined

22 PLUS /MINUS TECHNIQUE FOR BEST VISION SPHERE DETERMINATION Advantages: Easier than the MPMVA when using a trial frame as fewer lens changes are typically required Disadvantages: No provide a good control of accommoda5on in young pa5ents One or more check tests are needed

23 PLUS /MINUS TECHNIQUE FOR BEST VISION SPHERE DETERMINATION Procedure: 1. Occlude right eye. Direct pa5ent s aten5on to the best acuity line. Add D. Ask: are leuers clearer, more blurred or the same?

24 PLUS /MINUS TECHNIQUE FOR BEST VISION SPHERE DETERMINATION 2. If VA improves or remains the same: exchange the spherical lens that is in the trial frame for one that has DS added (i.e DS/ DS). Do not remove the plus lens un5l the new lens has been inserted to avoid accommoda5on (i.e in trial frame insert lens first, and then remove the DS lens)

25 PLUS /MINUS TECHNIQUE FOR BEST VISION SPHERE DETERMINATION 3. Con5nue adding plus lens power in DS steps, un5l VA first blurs. Stop at the most plus/least minus lens that does not blur VA 4. If VA blurs with a DS lens, then do not add it 5. Direct the pa5ent s aten5on to best VA line. Add and ask again(clear, blur or same)

26 PLUS /MINUS TECHNIQUE FOR BEST VISION SPHERE DETERMINATION 6. If VA improves or remains the same: exchange the spherical lens that is in the trial frame for one that has DS added (i.e DS/ DS). Do not remove the plus lens un5l the new lens has been inserted to avoid accommoda5on (i.e in trial frame insert lens first, and then remove the DS lens)

27 PLUS /MINUS TECHNIQUE FOR BEST VISION SPHERE DETERMINATION 7. Add further minus lenses (in D steps) only as long as the VA improves 8. If a young pa5ent reports VA improved with the lens, but not VA improvement ask: Do the leuers definitely look clearer, or just smaller and blacker? If just look smaller and blacker, do not add the DS

28 PLUS /MINUS TECHNIQUE FOR BEST VISION SPHERE DETERMINATION 9. If the pa5ent reports no change or a worsening of VA, do not add the Duochrome check 11. The blur check. Place +1.00DS over the final best vision sphere. If the original VA is 6/4, then VA with blur to about 6/12+ with the +1.00DS. If VA is beter than 6/12 = over- minused/under- plussed. Recheck

29 DUOCHROME TEST Based on the principle of longitudinal chroma5c aberra5on, were light of shorter wavelength (green, 535nm) is refracted more by the eye s op5cs than light of longer wavelength (red, 620nm)

30 DUOCHROME TEST An eye in a mildly myopic state (- 0.25D) will see the target on the red filter more clearly An eye in a mildly hyperopic state (+0.25D) will see the target on the green filter more clearly

31 DUOCHROME TEST Can be used at two points during the subjec5ve refrac5on: 1. Aaer the ini5al determina5on of the best vision sphere and prior JCC 2. Recheck the best vision sphere aaer JCC and prior to finalising refrac5ve correc5on

32 DUOCHROME TEST Advantages: Disadvantages: Quick and easy Some pa5ents (older) technique give poor results and always prefer one Works in a majority of colour (oaen red) pa5ents No all charts provide appropriate red and green wavelength light

33 DUOCHROME TEST Procedure: 1. Occlude one eye. Turn off the room lights 2. Q: Are the rings (leuers/dots) clearer and blacker on the red or on the green, or are they about the same?

34 DUOCHROME TEST 3. If the rings on the green look clearer, add DS un5l you obtain balance 4. If the rings on the red look clearer, add DS un5l you obtain balance 5. If more than ± 0.50 DS is needed to balance the clarity of the rings, this usually indicates that the duochrome test is unreliable (ignore results)

35 DUOCHROME TEST 6. Prior to use JCC: If the clarity of the rings changes from green to red with or red to green with DS, leave a young pa5ent on the green (ac) 7. Aaer JCC and prior to finalising: If the clarity of the rings changes from green to red with or red to green with DS,note the addi5onal power to leave a young pa5ent on the red

36 DUOCHROME TEST 8. Use the addi5onal lens power suggested by the duochrome test and double check whether this addi5onal power is preferred by the pa5ent using MPMVA or the plus/minus technique Should not be used as the arbiter of the final refrac5ve correc5on

37 SUBJECTIVE REFRACTION CYLINDER AXIS AND POWER DETERMINATION: 1. JACKSON CROSS- CYLINDER 2. THE FAN AND BLOCK TEST 3. SIMPLE AXIS ROTATION 4. CLOCK DIAL TEST

38 THE FAN AND BLOCK TEST

39 THE FAN AND BLOCK TEST JCC should not be the only subjec5ve test for the determina5on of as5gma5sm Not all pa5ents will be able to respond accurately to the demands of the JCC Mul5ple objec5ve measurements of as5gma5sm (re5noscopy, keratometry, autorefrac5on and vertometry)

40 THE FAN AND BLOCK TEST Advantages: Accommoda5on is well controlled as the pa5ent is fogged prior to the use of the procedure ensuring that the circle of least confusion and both focal lines are in front of the re5na Disadvantages: Is less accurate at determining small cylinders than the JCC Only available with wall charts

41 THE FAN AND BLOCK TEST Procedure: 1. Determine the best vision sphere 2. Occlude the untested eye 3. Remove the cyl determined from re5noscopy from the right eye and add to the sphere. Circle of least confusion is now in front of the re5na. If re5noscopy cyl was correct, both focal lines will be in front of the re5na

42 THE FAN AND BLOCK TEST 4. Draw an analogy between the lines of the fan and the hours of a clock, and ask the pa5ent if any of the lines of the fan appear clearer and darker than the other lines?

43 THE FAN AND BLOCK TEST 5. If the pa5ent reports that all the lines are equally clear (or blurred) then fog by a further D and ask again. If they equally clear or blurred, then this suggest there is not as5gma5sm 6. If some lines are reported as clearer, point the arrow that joints the blocks towards the clearest line

44 THE FAN AND BLOCK TEST 6. Adjust the arrow un5l its two barbs appear equally clear. One block should be clearer than the other 7. Ask the pa5ent to look at the clearer block and add DS and ask if the block blurs (if not add extra+0.50ds)

45 THE FAN AND BLOCK TEST 8. Set the cyl axis in trial frame/phoropter at the axis indicated by the arrow. Add nega5ve cyl at this axis un5l the blurred block just become as clear as the other 9. Reduce the plus fogging sphere 10. Repeat for the lea eye

46 ALTERNATIVE TECHNIQUE Simple axis rota'on: If you are confident of the need of cylinder power (as5gma5sm noted in re5noscopy and/or autorefrac5on; reduced VA with the best sphere result), but uncertain about the cyl axis, simple axis rota5on may be useful

47 SIMPLE AXIS ROTATION Ask the pa5ent to view the smallest line of VA they can see Rotate the correc5ng cyl axis clockwise un5l pa5ent report blur leters. Note Rotate the axis an5- clockwise un5l pa5ent report again blur leters. Note The cyl axis is the midpoint between this two blur points. i.e.25 and 55 (40)

48 ALTERNATIVE TECHNIQUE Clock dial test

49 CLOCK DIAL TEST Similar to fan and block steps 1 to 5 Procedure: 1. Determine the best vision sphere 2. Occlude the untested eye 3. Remove the cyl determined from re5noscopy from the right eye and add to the sphere.

50 CLOCK DIAL TEST 4. Draw an analogy between the lines of the fan and the hours of a clock, and ask the pa5ent if any of the lines of the fan appear clearer and darker than the other lines? 5. If the pa5ent reports that all the lines are equally clear (or blurred) then fog by a further D and ask again. If they equally clear or blurred, then this suggest there is not as5gma5sm

51 CLOCK DIAL TEST 6. Axis determined by mul5plying the smaller of the two clock dial values of the most clear lines by 30 (i.e. 2 and 8 axis is 60 (2x 30)) 7. Increase cyl power un5l the most blurred lines are clear

52 ALTERNATIVE TECHNIQUE Sunburst or fan dial test

53 RX PRESCRIPTION VISUAL ACUITY OBJECTIVE REFRACTION BINOCULAR BALANCE RX PRESCRIPTION SUBJECTIVE REFRACTION (SPHERE DUOCHROME CYLINDER) 53

54 PRESCRIBING At the end of an eye examina5on you will have to answer one of the following ques5ons: 1. What prescrip5on (Rx) should be given? 2. Does a pa5ent with small refrac5ve correc5on need spectacles or contact lenses? 3. Is a small change in refrac5ve correc5on necessary? Does the pa5ent need to update their lenses?

55 PRESCRIBING Subjec5ve refrac5on result is not a perfectly repeatable measurement and can vary up to 0.50 D from test to test Only if you can make a significant improvement in their VA but some5mes the pa5ent may want slightly blurred vision (presbyopic myope may prefer to be slightly under- corrected at distance so thy can read with spectacles)

56 PRESCRIBING Always compare against the pa5ent s spectacles Ask the pa5ent whether they like the change in vision or not

57 PRESCRIBING Non- progressive myopes: Do not always push the plus and give maximun plus They tend to wear their Rx only for driving at especially at night Be extremely careful of reducing a myopic Rx in older non- progressive myopes. This is the most common reason for failure of spectacle lens acceptance

58 PRESCRIBING Hyperopes: Only prescribe the full hyperopic Rx if the pa5ent is presbyopic, esotropic or has esophoria (convergence excess) Consider prescribing a par5al Rx sufficient to remove any symptoms The amount will depend upon the pa5ent s symptoms, age, manifest and latent hyperopia

59 PRESCRIBING Latent hyperopes: Prior to cyclopegic refrac5on asses the effect of giving extra plus over the manifest dry Rx This will indicate how much extra plus the pa5ent is likely to be able to tolerate before distance blur becomes to great

60 PRESCRIBING It is easier to make big changes in Rx in younger pa5ents In pa5ents over 25 years old, be careful of making changes over 0.75 D

61 PRESCRIBING Presbyopes: General rule: Not increase >0.75 D Large increases in older pa5ents tend not to be tolerated and can lead to an increase in falls

62 PRESCRIBING Cylinder changes: 0.25 cyl should be prescribed when sphere is low and/or if the pa5ent has precise and repeatable responses Changes in power are more tolerable if the axes are not oblique (no >0.50 DC) Changes in axis should never be large for large cyl (trial frame use) Poor adaptors = small changes

63 PRESCRIBING Anisometropia: Less 1 D does not cause problems Young pa5ents = full Rx Best correc5on = contact lenses Anisometropia > 4D + Amblyopia age >10 VA < 6/36 = balance lens Alterna5ng vision= not spectacles

64 PRESCRIBING Should you prescribe a small Rx (+0.50)? If there are not symptoms related to the use of the eyes = no If the pa5ent does a lot of detailed work and/ or detail- oriented personality = yes If the Rx has effect on binocular vision = yes (heterophoria compensated)

65 htp://youtu.be/g5ubaum_t00 htp://youtu.be/xtzpkwtikbo htp://eyeontechs.com/new/wp- content/uploads/2009/04/re5noscopysimulator.swf htp://youtu.be/ezoopkzwndk htp://youtu.be/zjlydi7ifqc

66