14 Accommodation and presbyopia by Dr Abid.pptx

Accommodation and presbyopia by Dr Abid..

1. CLINICAL OPTOMETRIC PROCEDURES 1 A ccomodation and presbyopia

2. Author Pirindhavellie Govender University of KwaZulu Natal (UKZN) Durban, South Africa   Peer Reviewer Bina Patel Associate Professor: New England College of Optometry, United States Project Director, Editor-in-Chief Luigi Bilotto Brien Holden Vision Institute, Public Health Division, Sydney , Australia University of Montreal, Quebec, Canada   Associate Editor Pirindhavellie Govender Brien Holden Vision Institute, Public Health Division, Durban, South Africa University of KwaZulu Natal (UKZN) Durban, South Africa   Technical Editors Vicky Larochelle , Raheema Ayob, Vicki Evans, Elaine Quinn, Kerryn Hart   Layout Editors Rajni Chhabra, Prashant Kumar   Graphics Shane Parker Brien Holden Vision Institute Foundation (formerly ICEE) is a Public Health division of Brien Holden Vision Institute COPYRIGHT © 2010 Brien Holden Vision Institute. All rights reserved. This publication is protected by laws relating to copyright. Except as permitted under applicable legislation, no part of this publication may be adapted, modified, stored in a retrieval system, transmitted or reproduced in any form or by any process, electronic or otherwise, without the Brien Holden Vision Institute’s (The institute) prior written permission. You may, especially if you are from a not-for-profit organisation, be eligible for a free license to use and make limited copies of parts of this manual in certain limited circumstances. To see if you are eligible for such a license, please visit http://education.brienholdenvision.org/ . DISCLAIMER The material and tools provided in this publication are provided for purposes of general information only. The Institute is not providing specific advice concerning the clinical management of any case or condition that may be mentioned in this publication, and the information must not be used as a substitute for specific advice from a qualified professional. The mention of specific companies or certain manufacturers’ products does not imply that those companies or products are endorsed or recommended by the Institute in preference to others of a similar nature that are not mentioned. The Institute makes no representation or warranty that the information contained in this publication is complete or free of omissions or errors.  To the extent permitted by law, the Institute excludes all implied warranties, including regarding merchantability and fitness for purpose, and disclaims any and all liability for any loss or damage incurred as a result of the use of the material and tools provided .

3. This series of lectures includes a review of: Definition & mechanism of accommodation Types of accommodation Amplitude of accommodation Presbyopia Relative Accommodation Determination of AC/A ratio

4. Definition of accommodation Changes in dioptric power of crystalline lens to maintain clear focus of object as it draws closer to the eye

5. Mechanism of accommodation Eye focused at distance Retina senses blur Sphincter muscles constrict Zonules relax Capsule bulges Lens becomes more convex

6. Accommodation reaction time Accommodation under control of Autonomic Nervous System Ciliary body = smooth muscles  slow reacting compared to EOMs (striated) According to Campell and Westheimer (1960), accommodative-reaction time Time reduced further by low levels of illumination 0.36secs + 0.09secs

7. Amplitude of accommodation Amplitude of accommodation is the dioptric equivalent of closest distance a target can be seen clearly e.g. near point is 8cm  Amplitude = 100 (in cm) 8 = +12.50D.

8. Types of accommodation Reflex accommodation Convergence accommodation Proximal accommodation Tonic accommodation Dark focus of accommodation

9. Reflex accommodation Autonomic reaction Adjustment of refractive state to a blur input to obtain & maintain sharply defined retinal image Occurs for small amounts of blur (2.00D) > 2.00D voluntary accommodation required Major component of accommodation

10. Convergence accommodation = Vergence accommodation Induced by neurological linking & action of fusional vergences Gives rise to convergence accommodation/convergence ratio (i.e. CA/C ratio) Second major component of accommodation

11. Proximal accommodation Due to influence of knowledge of apparent nearness of an object Initiated by objects within 3 meters of the individual

12. Tonic accommodation Found in absence of blur, disparity, proximal and voluntary inputs No stimulus for tonic accommodation Baseline neural innervation from the midbrain Represents normal tonus of ciliary body at rest Mean tonic accommodation in young adults is 1.00D ↓ with age due to biomechanical limits of crystalline lens

13. Dark focus of accommodation Accommodation associated with darkness Accommodative posture of eye in absence of visual stimuli Lies approx. 1.00D inside far point Explains “night myopia” or “empty field myopia”

14. Measurement of the amplitude of accommodation Several methods: Push-in-to-blur method (Push-up test) Push-out-to-clear method Minus-lens-to-blur Monocular Estimate Method (MEM)

15. Points to note All accommodative techniques performed after determination of distance Rx Distance Rx remains on during accommodation testing Factors affecting amplitude include: Target size, illumination and speed of target approach

16. Push-up test procedure Distance Rx on Done monocularly , then binocularly Uses RAF-rule RAF-rule held firmly against Pxs cheeks and tilted inferiorly from Pxs eye at 30°. Px directed to small reading print on the sliding target Target placed at far end of rule

17. Push-up test procedure Target moved slowly toward Px, stopped when Px reports blur Px asked to blink few times and try to clear print  If print clears, target moved closer until sustained blur Position of target noted centimeters and converted to dioptric value e.g. Measurement = 5cm  AMP = 100/5 = +20.00DS

18. Push-up test findings Disadvantage Over-estimation of amplitude of accommodation due to linear magnification  as target gets closer to eye, it appears larger  blur noticed later than with a smaller target Expected findings Findings compared to calculated: ( Scheiman and Wick, 2008) 18 – 1/3 age (± 2.00DS)

19. Push -out-to-clear procedure Similar to push-in-to-blur Target placed inside of near point and moved away from Px until print is no longer blurred Measurement read off the RAF-rule scale

20. Minus lens to blur procedure Test performed monocularly , then binocularly Near card held at 40cm, illuminated by overhead lamp if necessary Px instructed to view 1 line above best near VA Minus lenses added in 0.50-1.00D steps until Px reports first sustained blur

21. Minus lens to blur procedure Expected findings 2.00DS < push-up test ( Scheiman and Wick, 2008) AMP = absolute value of minus lenses cleared + dioptric value of the working distance

22. Monocular estimated method Dynamic retinoscopy (MEM) Objective evaluation of the accommodative response Used when Pxs accommodation is in active state Px fixate accommodative target at approximately 50-66 cm on retinoscope

23. MEM procedure Normal room illumination Px fixates appropriate target on MEM card attached to retinoscope Examiner moves target closer to Px while observing any change in ret reflex

24. MEM procedure Initial reflex = bright, broad, fast “with” movement  normal accommodative lag Change of reflex to narrower, dimmer and slower reflex  focusing lost  AMP exceeded Distance at which movement changes is noted  converted to dioptric equivalent = AMP

25. MEM findings Expected findings for accommodative response +0.25DS to +0.50DS ± 0.25DS ( Scheiman and Wick, 2008) Below +0.25DS or over +0.75DS  raises suspicion Requires further investigation Amplitude of accommodations as measured with MEM compares with other techniques

26. Clinical pearls Various methods of investigation can yield different values Subjective measures give larger values than objective measures due to pupil constriction Objective and subjective measures can differ by up to 2.00DS.

27. Estimation of amplitude of accommodation Hofstetter’s rule Average amplitude of accommodation, in diopters , for a patient of a given age. Measurement lower than expected  deficiency in accommodation. Average AMP = 18.5 – 1 / 3 rd Age

28. Estimation of amplitude of accommodation Duane- Hofstetter formula Probable amplitude of accommodation Considers not only average but range of minimum and maximum values Maximum amplitude = 25.0 – 0.40 x age Average amplitude = 18.5 – 0.30 x age Minimum amplitude = 15.0 – 0.25 x age

29. Points to remember For presbyopic Px: Add +1.00DS before each eye and perform procedure Final result: lens used must be subtracted from findings e.g. RAF-rule reading +3.00D, +1.00DS used for Px Amplitude = +3.00 - (+1.00) = +2.00DS

30. Points to remember For highly myopic Px: Add minus lenses before taking the readings Final result: add lens power e.g. RAF-rule reading +10.00D, -2.00DS used for Px Amplitude = +10.00 - (-2.00D) = +12.00D

31. Factors affecting Amp of A cc Original refractive state General health of the patient Vascular and Glandular defects Presbyopia Drugs Convergence problems Method of measurement

32. Presbyopia Presbyopia is gradual, naturally occurring, age-related, irreversible reduction in maximal accommodative amplitude Produces symptoms of: blur ocular discomfort asthenopia

33. Presbyopia AMP ↓ gradually from first few years of life to 55 years Usually occurs around age 40-45 years Occurs earlier in some ethnic groups, people with short arms or working distances, and hyperopes

34. Appearance and progression of presbyopia Patient’s habitual working distance Distance refractive error Visual needs of the individual Other factors: Race Gender Illumination conditions Ambient temperature Geographic factors

35. Methods to determine presbyopic add Tentative add determination Determining pxs exact requirements Fused cross cyl method

36. Tentative add determination Involves use of formula Tentative add = Age/10 – 3.50D Formula suggested for Pxs< 55yrs with average working distance of 40cm Formula does not hold for Pxs > 55yrs due to accommodation virtually zero

37. Amplitude of accommodation method Method assumes that prescription of addition should not use more than ½ to 2 / 3 of total AMP AMP determined as normal & used in formula to determine add Add = 2.50D – 2 / 3 Amp of Acc

38. Age expected addition method Uses table of expected adds based on age of Px Age in years Tentative add 40 – 42 +0.75 D 43 – 45 +1.00 D 46 – 47 +1.25 D 48 – 50 +1.50 D 51 – 52 +1.75 D 53 – 55 +2.00 D 56 – 57 +2.25 D 58 – 60 +2.50 D Antona et al. Comparing methods of determining addition in presbyopes . Clinical and Experimental Optometry 2008; 91(3).

39. Fused cross-cylinder method Subjective evaluation of accuracy of accommodative response under binocular viewing conditions Equipment Phoropter with ±0.50 D cylinder lenses Near point rod Cross cylinder grid target Adjustable illumination

40. Procedure Px behind phoropter , best distance Rx, dimly lit room Near PD set Binocular test Crossed cylinders before each eye, minus cylinder axis at 90  Px directed to grid target at 40cm Px asked to report which lines on grid appear sharper and more distinct, vertical or horizontal Horizontal lines expected to appear sharper

41. Procedure – Fused cross cyl If horizontal lines sharper  add +0.25DS lenses binocularly before eyes Continue until Px reports vertical lines appear sharper than horizontal lines Begin decreasing added plus in +0.25DS steps until both sets of lines appear equally clear If no equality  stop at highest plus lens with horizontal lines sharper

42. Recording findings Final amount of added plus lenses recorded Some cases “minus add indicated” e.g. FCC = +1.00DS

43. Expected findings Non- presbyopic patients  +0.50DS ± 0.25DS ( Scheiman and Wick, 2008) Presbyopic patients  lag of accom expected to  with age

44. Relative accommodation Relative accommodation Px’s ability to relax or stimulate accommodation Reflects interaction between Px’s accommodative-convergence system Negative Relative Accommodation (NRA) Px’s ability to relax accommodation Positive Relative Accommodation (PRA) Px’s ability to stimulate accommodation

45. Equipment Phoropter Near reading card Near point rod Illumination source

46. Procedure Px behind phoropter , distance Rx, near PD Near target  row of letters 1 or 2 lines better than near VA at 40cm Letters must be clear before beginning If not  add lenses in +0.25DS steps until letters become clear Additional lens power  tentative near add If no clarity  terminate test record NRA/PRA cannot be performed

47. NRA Performed first +0.25DS added before Px Continue adding binocularly until blur Ask px to clear target Stop at sustained blur

48. PRA -0.25DS added before px Continue adding binocularly until blur Ask Px to clear target Stop at sustained blur

49. Recording findings Note added plus lenses for NRA Note added minus lenses for PRA e.g. NRA/PRA: +2.00/-2.25 or NRA/PRA: +2.00/-2.25 through a tentative add of +1.50DS

50. Expected findings Pre- presbyopic Pxs NRA: +2.00 ± 0.50D PRA: -2.37 ± 1.00D ( Scheiman and Wick, 2008) Presbyopic Pxs Sum of the add and NRA should not exceed +2.50DS (Carlson and Kurtz, 1996) NRA and PRA may vary widely in presbyopic pxs

51. Interpretation of findings Inadequate accommodation function NRA or PRA < 1.50DS Difference between NRA and PRA of 1.00DS

52. Determining the AC/A ratio Purpose Change in accommodative-convergence that occurs when Px accommodates or relaxes accommodation by given amount AC/A ratio = key element in determination of appropriate management plan e.g. Px with esophoria at near and high AC/A ratio Rx spectacle lenses as opposed to prisms If low AC/A ratio  Rx prisms or vision therapy

53. Calculated AC/A ratio IPD = Interpupillary distance (in centimeters) NFD = near fixation distance (in meters) Hn = near phoria ( eso is plus and exo is minus) Hf = distance phoria ( eso is plus and exo is minus) AC/A = IPD (cm) + NFD(m) ( Hn – Hf )

54. Example calculated AC/A ratio IPD = 60mm Phoria at distance: 4XOP Phoria at near: 12XOP at near (40cm) Calculated AC/A AC/A = 6.0 + (0.4) (–12 + 4) AC/A = 6.0 + (-3.2) AC/A = 2.8 : 1

55. Gradient AC/A ratio Measure phoria Measure phoria second time using lens of known power either -1.00DS or -2.00Ds. Change in phoria is observed  AC/A ratio Example: Near phoria : 2SOP With added -1.00DS phoria : 7SOP  Change in the phoria is 5  AC/A ratio is 5:1

56. Expected findings Normal AC/A ratio = 4:1 (±2) Calculated AC/A ratio > gradient method