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# Contact Lens Optics

. Convert to Minus cylinderAdd the sphere to cylinderReverse sign of cylinderAdd 90 degrees to axisExample:-5.50 1.50x80 becomes-4.00-1.50x170. . Vertex all powers >4D to corneal planeVertex equation:Fcornea=Fspec/(1-dFspec)F=powerd=vertex distance in metersMust vertex both meridians

## Contact Lens Optics

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### Presentation Transcript

1. Contact Lens Optics Melanie A Pickett, O.D.

2. Convert to Minus cylinder Add the sphere to cylinder Reverse sign of cylinder Add 90 degrees to axis Example: -5.50+1.50x80 becomes -4.00-1.50x170

3. Vertex all powers >4D to corneal plane Vertex equation: Fcornea=Fspec/(1-dFspec) F=power d=vertex distance in meters Must vertex both meridians Example: -5D Rx at 15mm -4.62=-5.00/[1-(.015X5)]

4. Soft Contact Lenses Spherical Disposables Dailies Toric Disposables Dailies Custom Multifocals

5. Soft Contact Lenses Sphericals Essentially no tear layer Must have tear exchange for health Does not change refractive status

6. Soft Lenses Variety of powers -20 to +20 Use spherical equivalent for up to 3 steps of cylinder

7. Soft Contact Lenses Torics Now in XR series- extended series up to -6 cyl Toric Multifocal 2 designs Prism ballasted Thin zone design

8. Soft Toric Most all toric designs have marking indicators on surface. 3,6,9 o’clock 6,12 15 degrees apart Can be used to identify lens- Tyler’s/contact lens quarterly

9. Soft Toric LARS rule Left Add, Right Subtract Fitting: Fit to vertexed spec RX then use LARS to adjust for contact to eye interaction. Also should match overrefraction Toric Track

10. Soft Contact Lenses Material HEMA – 1st soft Dk dependent on hydration i.e. higher water content =higher Dk D=diffusion coefficient k=solubility coefficient Dk=“Oxygen permeability” Dk=8-30 Early lenses B&L Acuvue

11. Soft Contact Lens Materials Non-HEMA Dk 12-30 Dk less dependent on hydration Better for dry eye patients CSI Proclear

12. Soft Contact lenses Silicone Hydrogel Dk independent of hydration Dk=60-150 Dk in order (high to low) Focus Night & Day Biofinity Acuvue Oasys O2 Optix Purevision

13. Soft Contact Lenses Parameters Power Base Curve – typically 1-2 choices Flatter – Asian eyes, smaller eyes, less vault Diameter (13.8-14.5mm) Optical zone diameter Material Center thickness – comfort and hydration Only power and BC is adjustable – rest cause a change in type of lens selected

14. 4 groups of classifications Group 1= low water/ non-ionic Group 2=high water/non-ionic Group 3=low water/ionic Group 4=high water/ionic Low water=38-50% - low evap, low DK High water =60% - high evap, thick, use in dry eye

15. Extended Wear Soft Lenses Open eye =21% oxygen Closed eye =7% oxygen Overnight with closed eye & CL Some swelling expected 4-5% safe 10-15% folds 15-20% pathological

16. Fitting Soft Lenses Evaluation: Fitting Movement -Want .5 to 1mm of movement on blink- too tight conjunctival drag Centration Lag- position of contact on sup and side gaze Edge appearance

17. Edge Appearance

18. Changes to fit Go to looser fit: Need to decrease sagittal depth How?

19. Looser Fit Decrease sagittal depth Corneal flattens in periphery Flatten base curve Decrease diameter Opposite for tighter fit

20. Summary of Market Total Share of Market by Manufacturer J&J – Acuvue – 50% Copper-23% Ciba-18% B&L – 16% In US dailies now about 10% As of Q2 2007 silicone hydrogel>Hema lenses

21. Where is the optics?

22. Not a lot Tear layer non-existent in soft contact Accommodative demand Convergence demand Astigmatism issues Spectacle magnification

23. Accommodative Demand Accommodation: Difference of vergence at the first principle point of the eye(1.35mm behind the cornea) between rays from infinity and rays from a near point myopes in CL hyperopes in CL

24. Accommodative Demand AD=(verg N-Verg Infinity) Accom need=1/focal length (m) In contacts no vertexing Verg N= Accom + Power RX Verg infinity=power of Rx lens In glasses – have to vertex Verg N=(accom +power Rx) vertexed Verg Infinity=power of spec (vertexed)

25. Accommodative Demand Back to Vertex equation: Fcornea=Fspec/(1-dFspec) d=vertex distance in meters Example: What is the accommodative demand of -9 D viewing an object at 40cm?

26. Accommodative Demand CL’s: 2.50D AD=Verg N-Verg infinity =(11.5-9)=2.5 1. Verg N=9 + accom need(1/focal length) 2. Verg Infinity=9 Glasses:1.45D AD=Verg N-Verg Infinity=(9.37-7.92)=1.45D 1. Verg N=9.37 2. Verg Infinity = 7.92

27. Accommodative Demand Simply 1. find accom need (1/focal length) 2. CL or glasses CL=accom demand=accom need Glasses= [rx +accom need (vertexed)] –[rx(vertexed)]

28. Accommodative Demand What is another scenario where we are inducing more accommodative demand for myopes?

29. Convergence Demand As eyes converge contact moves with eyes – spectacles do not. Convergence demand in contact lenses vs. glasses More with myopes in CL Less with hyperopes in CL Spectacle lenses induce prism

30. Convergence Demand Spectacles – myopic lenses induce BI prism – aid reading Hyperopic lenses induce BO prism- more difficult for near work

31. Convergence Demand Prentice’s Rule: P=(dxD)/10 P=induced prism d=distance from optical center D=power of lens

32. Astigmatism CL vs. glasses: Less meridional aniseikonia created with contact lenses due to correction at corneal plane. Making the next choice: Soft vs. Hard Answer lies in where the astigmatism is located. Mostly lenticular = soft better choice

33. Astigmatism First convert minus cyl Second vertex Refractive astigmatism=corneal astigmatsim+lenticular astigmatism Compare: Rx=refractive ( or total) K’s = corneal astigmatism If lenticular astigmatism>corneal - SOFT

34. Astigmatism Example: -4.00+0.50x090 with K’s: 42.50/44.00 1. Convert: -3.50-0.50x180 2. vertex if needed 3. refractive =corneal+lenticular Refr= 0.50x180 Corneal=1.50x180 Lent= Best choice???

35. Relative Spectacle Magnification Spectacle Magnification=1/(1-aF) F=power of lens a=distance in meters from lens to entrance pupil of eye (3mm behind corneal) Example: +14.00 D lens, 15mm vertex Spec mag=1/(1- 0.018x14)=1.33

36. Relative Spectacle Magnification In Contacts versus glasses: Mag=1-dF d=vertex distance F=spectacle power Example: +14.0 D lens, 15mm vertex Mag=1-(0.015x14)=.79 or 21% less mag with CL

37. Image Size Anisometropia- monocular aphakes Mag is reduced as the forward facing plus lens is moved closer to site of former lens. Most mag=glasses<cl<pcIOL Telescope In aphakics- reversed Galilean telescope helps equalize the image Correct phakic eye with CL to Inc image size Over + CL add minus to spec RX

38. Complications CLARE/SLACH Treatment Ulcer

40. Complications Neovascularization Allergy- Environmental vs. solution Dry eye Epithelial split- Acanthamoeba

41. Acanthamoeba

42. Hard Contact Lenses

43. Original – PMMA Polymethylmethacrylate Now – rigid gas permeable

44. Power Cross Tear layer- 2x players Posterior tear layer= curvature due to front surface of cornea Secondarily to assumed equal index of refraction for tears and corneal tissue Anterior tear layer=curvature due to back surface of contact lens Thus Power of TL =CL BC- corneal K

45. Power Cross Minus Cylinder Base Curve–K- readings= Tear Layer TL+Spec Rx(vertexed if necess) =CLRX

46. Power Cross Each of these calculations must be performed for each meridian separately If 2 different powers are obtained order spherical equivalent If residual cylinder is >.75 rethink RGP vs. bitoric

47. Tear Lens K readings =Diopters Radius =mm R=337.5/K Example K=42.5 R=337.5/42.5=7.95

48. Example PT: Manifest ref: -3.25-1.00x180 K’s:44.50 @090/43.50@180 Order? 44.00/-4.00/9.2

49. Tear Lens Tear layer functions as a lens Power of tear lens .25D for every.05mm radius of curvature difference b/w BC and corneal Rule: SAM/FAP Steep add minus/Flat add plus

50. Tear Lens SAM/FAP Example: Spec=-3.00 K=43.25(7.80) BC of RGP=42.5(7.95) RGP =.75 flatter than K Order:-2.25/7.95/9.0 On K fit – Use base curve of flatter meridian

51. Parameters of Change Power Base Curve OZ Diameter Peripheral curves Ct Blend Can change each independently in RGP

52. Hard Contact Lenses Power= Change Base curve by flatten – need to increase rx by equal amount (-)

53. Hard Contact Lenses Base Curve Flatten BC =Decrease sag depth OZ= optical zone If large pupil Shadows Blend Diameter 9.0-11.0 Increase diameter= increase edge lift

54. Hard Contact Lens PC= Peripheral curves Secondary Tertiary For comfort Edge lift CT= Center thickness Request – again for comfort Polycon design

55. Hard Contacts Bitorics Greater than 3D of astigmatism Rx= 2 base curves/2 powers Ordering Match K’s Match sph and total rx in cyl meridian Warpage Example= +1.00-4.50x135/K=43/47.25 Order:(+1.00)(-3.50)/44x47.25/9.0

56. Hard Contacts Materials Boston ES (Dk=18) Boston XO (Dk=100) Boston XO2 (Dk=150) Increase DK increase lens buildup

57. Fit & Evaluation Position: Lid attached/Apical/Korb- Under upper lid- best comfort Intrapalperal- Large fissure

58. Fit & Evaluation Centration: Centered/temporal/nasal Falls down and out=too flat

59. Centration

60. Fit & Evaluation Fluorescein eval Clearance Edge lift

61. Fluorescein Pattern

62. Fluorescein

63. Alignment

64. Wettability Lathe cut Cleaning – at night

65. Wettability

66. Plasma Surface Treatment Started offering in late 2005 Aids in early wetting for sure- lenses are shipped wet How long lasting is the effect? Claim 6-9 months Boston Cleaner contra-indicated

67. Plasma Treatment Is really just “super cleaning” Can prove better wetting – clinically for weeks Shipped wet

68. RGP Complications 3 & 9 staining- Assoc w/ low riding CL Decrease edge lift Increase diameter GPC- Giant papillary Conjunctivitis Corneal warpage- spec blur Acanthamoeba

69. GPC

70. Use of Contacts in Clinical Practice

71. Corneal Keratoconus Salzmann Nodules Post transplant, RK, Lasik Bandage contact lens Ortho K

72. Keratoconus How to fit a GP to Keratoconic cornea K’s & spec Rx Trial lenses set Rose K Soper McGuire Apex Goal – improve VA, comfort, corneal health 3 point touch- apical, 3 & 9

73. Keratoconus

74. Keratoconus

75. Synergeyes 4 series – including post surgical and KCN lens Need significant, definite apical clearance Opposite to normal fit Versus piggybacking

76. Synergeyes

77. Corneal Bandage contact lens Abrasions, erosions, burns Enhances comfort Only SH lenses Procedure code 92070 Fitting of contact lens for treatment… Fee includes supply of the lens

78. Orthokeratology Definition: the reduction or elimination of myopia, hyperopia, or astigmatism through the programmed application of custom designed lenses Non-surgical Reversible- complete within 3 months Safe corneal molding

79. Glaucoma Bleb leak- post trab Bleb avoidance RGP Soft Infection risk Aniridia

80. Pediatrics Aphakics EW Parent Involvement

81. Questions?

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