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# NW2011 Optic of human eye

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### NW2011 Optic of human eye

1. 1. Nawat Watanachai Sakarin Ausayakhun 2010
2. 2. Visual optics  Understanding the remarkable inner workings of the eye’s optics  Problems  Complicated  imperfection  Schematic eye
3. 3. Schematic Eye  Conceptualizing the optical properties of human eye  To determine mathematic living eye models  Developed by Gullstrand, professor of ophthalmology in Sweden. Nobel Prize 1911
4. 4. Gullstrand’s schematic eye
5. 5. Reduced schematic eye  Schematic eye can be simplified even further  We can treat eye as it was a single refracting element  Ideal spherical surface separating two media of refractive indices 1 and 1.33  Known as reduced schematic eye  Nodal point =  Cornea and lens…
6. 6. Reduced schematic eye P=60 D. N=1 N=1.33
7. 7. Reduced schematic eye  D=n/f, D=(n2-n1)/f  D= 60 D., n(air)=1, n(eye)=1.33  f=n/D  Ant.focal point = 1/60 = 17mm.  Post.focal point = 1.33/60 = 22.6mm.  D = (n’-n)/f, f = (n’-n)/D =(1.33-1)/60 = 5.5 mm.  Nodal point = 22.6-17.0 = 5.6mm.
8. 8.  Schematic eye can calculate image size on retina Image size = Image distance Object size Object distance Image size = Object size Image distance Object distance
9. 9. Example  m 20 cm. retinal image? 6
10. 10.  20 cm. retinal lesion? Image size = Object size Image distance Object distance Image size = 200 mm. 17 mm. 6000 mm. Image size = 200x17/6000 = 0.6 mm. 6m
11. 11. Accommodation
12. 12. Near point (NP)  correspond accommodation retina NP w/accommodation full
13. 13. Far point (FP)  correspond retina accommodation  refraction FP w/o accommodation
14. 14. Emmetropia FP w/o accommodation NP w/ accommodation
15. 15. Myopia FP NP w/o accommodation w/ accommodation
16. 16. Hyperopia FP w/o accommodation NP w/ accommodation
17. 17. Far Point  conjugate accommodation retina Emmetropia Myopia FP FP FP Hyperopia
18. 18. Near point of accommodation  NPA Visual axis conjugate Retina accommodation  NPA amplitude of acommodation  Presbyopia accommodation progressively decrease with age  ↓ NPA ( )
19. 19. Accommodation decrease with age
20. 20. Presbyopia  Acc. loss reading required 40 ac. reserve 33 cm. acc. 1/33/100 = +3 D  20 reserve power 10 D  45 reserve spare = 3.5-3 = 0.5  fatigue 
21. 21. Accommodative amplitude  <40 yr. increase 1.00 D./ each 4 yr.  40 yr. = 6.00 D., 44 yr. = 4.5 D., 48 yr. = 3.00 D.  >48 yr. decrease 0.50 D./ each 4 yr.  <- 40(6.00 D.) – 44(4.50 D.) – 48(3.00 D.) ->  Ex. 60 yr. = 1.5 D.
22. 22. Accommodation  Accommodative range =  Accommodative amplitude A= F – N  A = accommodative amplitude  F = vergence  N = vergence FP NP FP NP
23. 23. Example  clear vision acommodative amplitude = 8.00 D. -4.00 D. • clear vision = far point – near point • Far point = 100/4 = 25 cm. • Near point = 100/(8+4) = 8.33 cm. • clear vision 8.33-24 cm.
24. 24. Myopia F N w/o accommodation w/ accommodation
25. 25. Example clear vision  +2.00 accommodative amplitude = 4.00D. • Uncorrect hyperope 2.00 farpoint = 100/2 = 50 cm. • accommodation +2.00 D. far point infinity accommodation 2.00 D. • near point 100/(4-2) = 50 cm. • clear vision 50 cm infinity
26. 26. Hyperopia F N w/o accommodation w/ accommodation
27. 27. Example  Without correction, far point is located at front of the eye and near point at eye. cm in cm in front of the  What is refractive error of this eye?  What is amplitude of accommodation of this eye?
28. 28. • FP cm 100/100 = -1 D rays) F distant correction = divergent N w/o accommodation w/ accommodation
29. 29.  FP  vergence  accom. cm FP - D NP cm  vergence   NP - D A = F - N = (-1)-(-3) = 2 D amplitude of accommodation D
31. 31. • • • cm ( accommodation 50% add 2.50 D F D) D N w/o accommodation w/ accommodation
32. 32. Example  54 accom. Amplitude -2.00 D. D • -2.00 (FP 50 cm) • AA=1 D (NP 33 cm) • accommodation 30 cm,
33. 33. Correcting myopia P f’ F
34. 34. Correcting myopia P1 F1, f1 VD1
35. 35. Correcting myopia f1 P f VD ----> f2’ > f1’ correcting lens - D (P2<P1) - D
36. 36. Correcting hyperopia f F
37. 37. Correcting hyperopia F,f
38. 38. Correcting lens and hyperopia f1 P F,f VD ----> f2 < f1 correcting lens D (P > P1 D
39. 39. Vertex distance  refractive error power  refractive error lens power VD significant change lens D VD contact
40. 40. CL power
41. 41.  Aphakic lens +12 D ( VD 15 mm) prescribe  VD Dioptric error 10 mm.
42. 42.  +12 D, F’ = 100/12 = 8.3 cm.    R VD 15 mm. 8.3 – 1.5 cm = 6.8 cm. = FP VD 10 mm. = 6.8 + 1.00 = 7.8 cm
43. 43.  P = 100/7.8 = +12.80 D  = 12.8-12.0 = 0.8 D***  *** VD error +4 D
44. 44. Example  + D mm mm power
45. 45. : f2=110 mm = 11 cm + . D power 20 mm = / =
46. 46. Cylinder and Astigmatism  Astigmatic Expression   Spherocylinder form Combined cylinder form
47. 47. Astigmatism - Corneal astigmatism - Lenticular astigmatism Toric surface
48. 48. Spherocylinder and its imagery Cornea O
49. 49. Total astigmatism Total astigmatism = Corneal astigmatism + Lenticular astigmatism O Against-the-rule astigmatism
50. 50. Total astigmatism Total astigmatism = Corneal astigmatism +lenticular astigmatism 42 40 O With-the-rule astigmatism
51. 51. Conoid of Sturm  Anterior focal line  Posterior focal line  Interval of Sturm O  Circle of least confusion  Spherical equivalent = sphere + (cylinder/ I
52. 52. Spherocylinder and its imagery
53. 53. Astigmatic dial technique  focal line retina
54. 54. Astigmatic dial technique  focal line retina
55. 55. Astigmatic dial technique  sphere retina) +Sph VA (CLC
56. 56. Astigmatism  Compound hyperopic astigmatism  Compound myopic astigmatism  Mixed astigmatism  Simple hyperopic astigmatism  Simple myopic astigmatism
57. 57. Cylinder  Plus cylinder  Minus cylinder  Power cylinder axis
58. 58. Plus Cylinder I Axis Power O O I
59. 59. Minus Cylinder O I Axis Power I
60. 60. Against-the-rule astigmatism - . x retina
61. 61. Against-the-rule astigmatism focal line focal lines - . x retina
62. 62. With-the-rule astigmatism 42 40 - . x 180 retina
63. 63. With-the-rule astigmatism 42 focal line focal lines 40 - . x 180 retina
64. 64. Cylinder  cylinder  Power  Axis  Power cylinder RE axis LE
65. 65. Example  + . D cylinder axis 180’  power +5.00 D 90’  @90  x 180’ +5.00@90’/plano@180’ optical cross
66. 66. Plus cylinder form + . sph + . x
67. 67. Minus cylinder form - + . sph - . x 18
68. 68. spherocylinder: 3 0 + . x &+ . x Combined cylinder form +3.0 0 sph 1. x Plus cylinder form 3 sph -1. x 18 Minus cylinder form +2. 0 -1 0 +1. 0 +3.0 0 +3. 0
69. 69. Transposition  minus  sphere sphere cylinder cylinder   plus cylinder axis new
70. 70. Example  form  shp + . x combined cylinder form spherical equivalent minus cylinder
71. 71. . + . x • (+2.00+1.00) -1.00 x 180’ • - . x • • Sph. Equivalent = + . + (+ . / )=+ . D
72. 72. Combined cylinder form + . + . x combined cylinder form 0’ = +3.00@180’ x 180’ = +3.00 x 90’
73. 73. Example  -4.00 -0.5 x 90’  -4.50 +0.5 x 180’  -4.50 x 90’ : -4.00 x 180’ • +2.00 -1.00 x 20’ • +1.00 +1.00 x 110’ • +1.00 x 20 : +2.00 x 110’
74. 74. The end  Confusing???