This document discusses optical biometry measurements and their use in determining appropriate intraocular lens (IOL) calculations and selections. It provides an overview of biometry techniques such as ultrasound and optical methods, compares their accuracy advantages, and outlines considerations for different eye anatomies and conditions. Formulas for calculating IOL power are examined, including preferences for different eye lengths. Challenges in post-refractive surgery patients are also addressed.

1. Optical Biometry Measurements for Future IOL’sAaron Graham, BA, CCOA

2. Financial Disclosure

3. Ground Rules

4. The GoodExclusive Эксклюзивные Exclusif ExclusivaSuperior верхний Supérieur SuperiorElite Элитные élite elisiónSpecialist Специалист Spécialiste Especialista

5. The Good

6. The Good

7. The Good

8. The Good

9. The Good

10. The Good

11. The Good

12. The Good

13. The Good

14. Good καλός Buono Versus έναντι Contro Bad κακός Cattivo

15. The BadIndifferent Безразлично Indifférent IndiferenteInferior Нижняя Inférieur InferiorGeneric родовой Générique GenéricoApathetic апатичный Apathique Apático

16. The Bad

17. The Bad

18. The Bad

19. The Bad

20. The Bad

21. The Bad

22. The Bad

23. The Bad

24. The Bad

26. Finer PointsEstimates of the resolution of the human eye are some where around 576 mega pixels (24000 x 24000 pixels) for a 120 degree field of view.

27. However, it must be noted that the human eye itself has only a small spot of sharp vision in the middle of the retina, the fovea centralis, the rest of the field of view being blurry.

28. The angle of the sharp vision being just few degrees in the middle of the view, the sharp area thus barely achieves even a single mega pixel resolution.

29. The experience of wide sharp human vision is in fact based on turning the eyes towards the current point of interest in the field of view, the brain thus perceiving an observation of a wide sharp field of view. First surgical procedure 6th century B.C.

30. "couching", in which a curved needle was used to push the lens into the rear of the eye and out of the field of vision. The eye would later be soaked with warm clarified butter and then bandaged.

31. Couching continued to be used throughout the Middle Ages and is still used in some parts of Africa and in Yemen.

32. 1748 First lens extraction (Modern Era)

33. 1884 First local anesthetics (Cocaine Drops)

34. 1940 First IOL (Harold Ridley)

35. 1960 PhacoemulsificationCataract Surgery Saga

36. StatsAccording to surveys of members of the American Society of Cataract and Refractive Surgery, approximately 2.85 million cataract procedures were performed in the United States during 2004 and 2.79 million in 2005.Eye MeasurementsAverageRangeAxial Eye Length 23.5mm 22.00-24.5AC Depth 3.24mm Varies with ALLT 4.25mm up to 6.9 w/catPachymetry 0.55mm Keratometry 43.0-44.0 Usually within 1D of each other

37. Normal Measurements23.5mm12.5mm245 μm4.25 mm*3.24 mm0.5 – 8mm550μmK: 43 - 44 D*LT is Age dependant andcontinuously growing

39. A-Scan MethodsContact Method – Contact Biometry is the most common technique used for measuring eye length, but is by far the most inaccurate. This method requires placing the A-Scan probe directly on the Cornea. This will result on Corneal compression and the amount of compression will vary depending on the experience and technique of the user.

40. Studies have shown that this method can result in erroneous eye length measurements between 0.14mm and 0.36mm too short. (.25D - .75D)

41. Immersion Method – The Immersion method of Ultrasound Biometry is by far the most accurate way to measure the AL of the eye using Sound. This method requires that the probe is placed in a “bath” of saline solution directly over the eye. With the immersion of the probe the cornea is not touched thus eliminating the compression errors.

43. Optical Biometry – Uses Optical Low-Coherence Reflectometry, a similar technology that is used in OCT devices. This technology results in highly accurate measurements of the eye using light in comparison to sound. The added benefit is that this technology is also non contact and can be performed with the patient sitting comfortably in a chair without the need for any topical anaesthesia, and without the risk of damage to the cornea.

44. The Down SideSince optical Biometry uses light there is a higher probability of the “scatter” effect. Meaning that if the light beam is reflected prior to the RPE then the signal returning to the device sensor will be very weak if detected at all. This will result in low SNR. Patients with Dense PSC, Extreme Corneal Abnormalities, or White Cataracts are very tough to measure.Long EyesOptical up to 40mmUltrasound 45mm (Up to 60) < 5% of patients have AL > 26mm

45. Lenstar LS 900 (Haag-Streit)

46. IOL Master (Carl Zeiss)

47. OA 1000 (Tomey) to be launched 2000?Manufacturers

48. Optical Biometer Features

49. Patients demand at least 20/20 vision after surgery

50. Multifocal / Accommodating IOL’s

51. Toric lenses

52. Patient specific anatomical anomalies

53. Very Long / Short Eyes / AstigmatismModern Technology / Knowledge

54. Measurement along the Visual AxisVisual axis(Patient fixates on the measurement beam)Ultrasound BiometerTheoretical Optical Axis≈ 90°Optical BiometerVisual axis

55. What about the “Dust Cover”?aka CorneaTo ensure proper K value along central visual axis Keratometry should be measured at the same time as Axial Length.

56. Poor Alignment* Image courtesy of Karen Bachman and Cara Fletcher from the Cincinnati Eye Institute

57. 40.75 / 43.50 35.25 / 40.50 39.25 / 43.25 37.50 / 42.00 44.75 / 45.25 * Measurements obtained using Reichert Manual Keratometer Model # 12990

58. 42.12 D37.88 D41.25 D39.75 D45.00 D

59. IOL DataAlcon SN60WF

60. SRK/T using 119.05

61. www.doctor-hill.com

62. AL = 23.50

63. CCT + AD = 3.7923.0 D27.5 D24.0 D25.5 D19.5 D

64. +3.50 D+7.00 D+ 4.50 D+6.00 D0.00 D

65. US vs. optical BiometryAxial length

66. US Biometry accuracy ±0.04 mm (theoretical)±0.1 to 0.12 mm (real)

67. Optical Biometry accuracy ±0.03 mm (theoretical) ±0.03 mm (real)

68. US depends on user (0.1mm ≡ 0.28 D)

69. Compression of the eye

70. Misalignment of the probe

71. Achievable accuracy in post-op. refractive error

72. US Biometry based St. Dev.: 0.8D

73. Optical Biometry based St. Dev.: 0.25 to 0.5DUS vs. Optical BiometryCorneal Curvature

74. US Biometry requires a 2nd device

75. Anterior Chamber Depth

76. Compression of the anterior chamber (US)

77. Misalignment of the probe (US)

78. Contact (US) vs. Non contact (Optical)

79. Transmission of bad germs (US)

80. Risk of corneal injuries (US)

81. Compression of the eye (US, unless immersion)

82. No limitation with the cataract penetration (US)US vs. optical BiometryWhy is Optical- Superior US Biometry:

83. Higher Accuracy

84. Non contact

85. All measurements in one device

86. Operator independent

87. Speed

88. Patient comfort