Visual acuity

Basics of visual acuity and refracting surfaces of eye ; including components, factors affecting visual acuity.
For visual acuity charts refer my other ppt of visual acuity.

1. VISUAL ACUITY OPTOM PRATIKSHA PATIL

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3. TOTAL POWER OF THE EYE? CORNEA – 2/3 rd eye power (+44.00D) LENS- 1/3 rd eye power (+16.00D) OPTOM PRATIKSHA PATIL

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12. VISUAL ACUITY OPTOM PRATIKSHA PATIL

13. HOW WILL YOU QUANTIFY VISION? Visual function assessment / vision components? OPTOM PRATIKSHA PATIL

14. HISTORY 1679- Hooke Early 19 th century- Purkinje & Young 1863 – Professor Hermann Snellen OPTOM PRATIKSHA PATIL

15. CONCEPT OF VA Visual acuity(VA) is the spacial resolving capacity of visual system. It express the angular size of detail that can just be resolved by observer. OPTOM PRATIKSHA PATIL

16. VISUAL ANGLE VISUAL ANGLE IS THE ANGLE SUBTENDED AT THE NODAL POINT OF THE EYE BY THE PHYSICAL DIAMENSION OF THE OBJECT IN THE VISUAL FIELD OPTOM PRATIKSHA PATIL

17. Visual angle ? At nodal point? Minimum angle required to see at retina? OPTOM PRATIKSHA PATIL

18. COMPONENTS OF VA Minimum visible or detectable acuity Minimum resolvable acuity Minimum recognizable acuity Minimum discriminable acuity or hyperacuity OPTOM PRATIKSHA PATIL

19. Minimum Visible/Detectable Refers to the smallest object that one can detect. OPTOM PRATIKSHA PATIL

20. Minimum resolvable Refers to the smallest angular separation between neighboring objects that one can resolve. OPTOM PRATIKSHA PATIL

21. Minimum recognizable Refers to the angular size of the smallest feature that one can recognize or identify. OPTOM PRATIKSHA PATIL

22. Minimum discriminable or hyperacuity Refers to the angular size of the smallest change in a feature (e.g. a change in size, position or orientation) that one can discriminate. Fig.: Two “ hyperacuity ” configurations: Vernier acuity ( A) and bisection acuity ( B). In both cases, the subject’s task is to judge the relative position of the features. OPTOM PRATIKSHA PATIL

23. (A) (B) (C) (D) OPTOM PRATIKSHA PATIL

24. FACTORS AFFECTING VISUAL ACUITY Stimulus/ object Related Luminance / illumination Contrast Geometry of letters Time of exposure of the target Influence of wavelength Interaction effect OPTOM PRATIKSHA PATIL

25. Observer Related Area of the retina stimulated Pupil size Accommodation Effect of eye movement Refractive error Optical element Developmental aspect FACTORS AFFECTING VISUAL ACUITY OPTOM PRATIKSHA PATIL

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27. OPTOTYPES OPTOM PRATIKSHA PATIL

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30. REFERENCE: Borish’s clinical refraction(William J. Benjamin) 2nd ed. OPTOM PRATIKSHA PATIL

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36. Specification of visual acuity OPTOM PRATIKSHA PATIL

37. T ERMINOLOGY Snellen’s Fraction Decimal notation Minimum Angle of resolution(MAR) LogMAR Visual Acuity Rating(VAR) Visual efficiencies OPTOM PRATIKSHA PATIL

38. Snellen’s Fraction Angular size of optotypes VA=testing distance/distance at which Optotype subtend 5min of arc Eg. 20/200 feet or 6/60 m E 5min of arc 6 meter testing distance OPTOM PRATIKSHA PATIL

39. Snellen’s Fraction 20/200 means : test distance - 20 feet and the smallest letters that could be read would subtend 5 minarc when at a distance of 200 feet. The angular size of such letters at 20 feet is 50 minarc. 20/200, 40/400, 10/100, 5/50, and 6/60 are all visual acuity scores that represent the same angle (letters subtend 50 minarc); OPTOM PRATIKSHA PATIL

40. Decimal Notation Gives single number to quantify an angle. Does not indicate test distance. Eg. 20/200 = 0.1 ; 20/20 = 1. OPTOM PRATIKSHA PATIL

41. Minimum angle of resolution(MAR) Expressed in min of arc. Indicates angular size of critical detail within just resolvable optotype. Critical detail= ⅕ of letter height. MAR= 1/ decimal acuity value Eg.20/40 = 2 min of arc OPTOM PRATIKSHA PATIL

42. LogMAR : It is common Logarithm of MAR (logMAR) 10 Eg. VA= 20/20 MAR= 1 min of arc, so logMAR = 0 When VA is better than 20/20, logMAR is negative. OPTOM PRATIKSHA PATIL

43. Visual acuity rating Derived from the logMAR values. VAR = 100-50(logMAR) OPTOM PRATIKSHA PATIL

44. Visual efficiency Visual efficiency scale used to quantify visual loss for legal & compensation purpose. AMA later used VE scale for quantifying loss in visual field & ocular motility. VE= 0.2 (MAR-1)/9 VE for visual acuity 6/6 is 1.0, for visual acuity 6/60 is 0.2 OPTOM PRATIKSHA PATIL

45. Visual Acuity Assessment VA is tested by different ways depending upon age group: Infant:- less than 1 year Toddlers:- 1-2 year Children:- 2-12 year Adolescents:- 12-18 year Adult:- more than 18 year OPTOM PRATIKSHA PATIL

46. Visual Acuity test in adolescent OPTOM PRATIKSHA PATIL

47. Snellen’s chart OPTOM PRATIKSHA PATIL

48. Reference: Textbook of visual science and clinical optometry - Bhattacharya , 2009 OPTOM PRATIKSHA PATIL

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51. CLINICAL TESTING OF VISUAL ACUITY OPTOM PRATIKSHA PATIL

52. CHART FORMAT OPTOM PRATIKSHA PATIL

53. TESTING DISTANCE Testing distance is 6 m. Patient is asked to read the chart with each eye separately. When patient is able to read upto to 6m line the VA is recorded as 6/6 it is normal. Similarly depending upon the line that the patient can read from distance of 6m patient vision is recorded as 6/9 , 6/12 , 6/18, 6/24 , 6/36 and 6/60. OPTOM PRATIKSHA PATIL

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55. If patient cannot see the top line from 6m patient is asked to slowly walk towards chart till he can read the top line. Depending upon distance at which patient can read the top line patients VA is recorded as 5/60 , 4/60 , 3/60 , 2/60 and 1/60. If patient is unable to read the top line from 1m, Patient is asked to count fingers of examiner his or her vision is recorded as CF-3’, CF-2’, CF-1’ or CF close to the face depending on the distance at which he counts fingers. OPTOM PRATIKSHA PATIL

56. When patient fails to count finger, the examiner moves his or her hand close to the patient’s face. If patient appreciates the hand movement (HM), VA is recorded as HM positive. When the patient cannot distinguish the hand movements, the examiner notes whether the patient can perceive light (PL) or not. If yes, vision is recorded as PL positive and if not it is recorded as PL negative. If PL positive then ask the patient from which quadrant light is coming. OPTOM PRATIKSHA PATIL

57. TESTING PROCEDURE OPTOM PRATIKSHA PATIL

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61. Near charts Testing distance of near Chart is 35-40 cm OPTOM PRATIKSHA PATIL

62. Jaeger’s chart : In this chart, prints are marked from 1 to 7 and accordingly patient’s acuity is labeled as J1 – J7, depending upon the print one can read. Roman test chart : consists of “Times Roman” type font with standard spacing and the near vision is recorded as N5, N6, N8, N10, N12, N18, N36 and N48. OPTOM PRATIKSHA PATIL

63. Reduced Snellen’s near vision chart : the graded thickness of the letters of different lines is about is 1/17th of the distance vision chart letters. M notation Chart :In this chart, prints are marked from 0.4 to 4 accordingly the patients visual acuity is labelled 0.4M to 4M, depending upon the print one can read. OPTOM PRATIKSHA PATIL

64. Roman test chart Jaeger’s chart OPTOM PRATIKSHA PATIL

65. References Borish’s Clinical Refraction- William J Benjamin Adler’s physiology of the eye , 11th ed. - William M Hart, jr Theory & practice of optics & refraction- A K Khurana Clinical visual optics - Bennett & Rabbetts’ Primary care optometry - Theodore Grosvenor OPTOM PRATIKSHA PATIL

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