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SUCCESSFUL TORIC GP DESIGN AND FITTING

SUCCESSFUL TORIC GP DESIGN AND FITTING. GPS AND HIGH ASTIGMATISM. With > 2.00D corneal cylinder the following problems can occur with a spherical GP: • Flexure • Decentration • Corneal Warpage • Corneal Desiccation • Lens Awareness. Sphere lens on toric eye….

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SUCCESSFUL TORIC GP DESIGN AND FITTING

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  1. SUCCESSFUL TORIC GP DESIGN AND FITTING

  2. GPS AND HIGH ASTIGMATISM With > 2.00D corneal cylinder the following problems can occur with a spherical GP: • Flexure • Decentration • Corneal Warpage • Corneal Desiccation • Lens Awareness

  3. Sphere lens on toric eye… …toric lens on same toric eye.

  4. BACK SURFACE VS. BITORIC • Both indicated with ≥ 2.50D corneal cyl • Back surface toric only lenses have a toric back surface (identical in curvature to a bitoric) as verified with a radiuscope • Back surface torics induce a residual cylinder equal to about one-half of the back surface cylinder of the lens due to differences in refractive indices between lens and tear film

  5. BACK SURFACE TORIC: INDUCED CYLINDER • BST induces cylinder equal to 1/2 of back surface cylinder • If there is 3.5D of back surface cyl, induced is (-1.50) to -1.75D x 180; this will be present via over-refraction • On lensometer there will 3/2 x back surface cylinder or 5.25D

  6. Back Surface Toric • BST is the lens of choice when the corneal toricity is ATR and the RA is one half the back surface toricity (ie., patient has ATR cylinder and the refractive cyl = 1 1/2 times the back surface toricity)

  7. BITORICS • When you correct for induced cylinder (ie, in previous example, add +1.75 x 180) on front surface, you have a bitoric design • Provides good centration; should fit like a spherical lens on low astigmatic cornea • Provides good vision • Results in good corneal integrity • When induced cylinder (only) is corrected, this results in a spherical power effect

  8. FITTING • Empirical • Diagnostic

  9. EMPIRICAL • Mandell-Moore Guide: easy empirical method of determining base curve radii and powers • Mandell-Moore bitoric interactive guide is available from the GP Lens Institute at: • www.gpli.info • 1-800-344-9060

  10. Case #2 • Spectacle Rx – 4.00 – 4.00 cx 180 • Corneal Measurements 42.50/46.00 @ 90

  11. Mandell-Moore Bitoric Lens Guide - Per eye 1 Keratometry 2 Spectacle Rx (Minus Cyl Form) Flattest K Sphere Steepest K Sph + Cyl Power Power 3 Enter K 4 Enter Spectacle Power 5 Vertex Adjust Line 4 6 Insert Fit Factor (-) (+) (-) (+) Add Line 3&6 5&6 3&6 5&6 7 Final CL Rx Base Curve Power Base Curve Power Case #2

  12. Bitoric Lens Fit Factor Corneal Cyl Fit Flat Meridian Fit Steep Meridian 2.0 Diopters On K (0 D) 0.50D Flatter 2.5 Diopters 0.25D Flatter 0.50D Flatter 3.0 Diopters 0.25D Flatter 0.75D Flatter 3.5 Diopters 0.25D Flatter 0.75D Flatter 4.0 Diopters 0.25D Flatter 0.75D Flatter 5.0 Diopters 0.25D Flatter 0.75D Flatter Case #2

  13. Mandell-Moore Bitoric Lens Guide - Per eye 1 Keratometry 42.50 @ 180 46.00 @ 90 2 Spectacle Rx (Minus Cyl Form) - 4.00 – 4.00 x 180 Flattest K Sphere Steepest K Sph + Cyl Power Power 3 Enter K 4 Enter Spectacle Power 5 Vertex Adjust Line 4 6 Insert Fit Factor (-) (+) (-) (+) Add Line 3&6 5&6 3&6 5&6 7 Final CL Rx Base Curve Power Base Curve Power Case #2

  14. Mandell-Moore Bitoric Lens Guide - Per eye 1 Keratometry 42.50 @ 180 46.00 @ 90 2 Spectacle Rx (Minus Cyl Form) - 4.00 – 4.00 x 180 Flattest K Sphere Steepest K Sph + Cyl Power Power 3 Enter K 42.50 46.00 4 Enter Spectacle Power 5 Vertex Adjust Line 4 6 Insert Fit Factor (-) (+) (-) (+) Add Line 3&6 5&6 3&6 5&6 7 Final CL Rx Base Curve Power Base Curve Power Case #2

  15. Mandell-Moore Bitoric Lens Guide - Per eye 1 Keratometry 42.50 @ 180 46.00 @ 90 2 Spectacle Rx (Minus Cyl Form) - 4.00 – 4.00 x 180 Flattest K Sphere Steepest K Sph + Cyl Power Power 3 Enter K 42.50 46.00 4 Enter Spectacle Power - 4.00 - 8.00 5 Vertex Adjust Line 4 6 Insert Fit Factor (-) (+) (-) (+) Add Line 3&6 5&6 3&6 5&6 7 Final CL Rx Base Curve Power Base Curve Power Case #2

  16. Mandell-Moore Bitoric Lens Guide - Per eye 1 Keratometry 42.50 @ 180 46.00 @ 90 2 Spectacle Rx (Minus Cyl Form) - 4.00 – 4.00 x 180 Flattest K Sphere Steepest K Sph + Cyl Power Power 3 Enter K 42.50 46.00 4 Enter Spectacle Power - 4.00 - 8.00 5 Vertex Adjust Line 4 - 3.75 - 7.25 6 Insert Fit Factor (-) (+) (-) (+) Add Line 3&6 5&6 3&6 5&6 7 Final CL Rx Base Curve Power Base Curve Power Case #2

  17. Mandell-Moore Bitoric Lens Guide - Per eye 1 Keratometry 42.50 @ 180 46.00 @ 90 2 Spectacle Rx (Minus Cyl Form) - 4.00 – 4.00 x 180 Flattest K Sphere Steepest K Sph + Cyl Power Power 3 Enter K 42.50 46.00 4 Enter Spectacle Power - 4.00 - 8.00 5 Vertex Adjust Line 4 - 3.75 - 7.25 6 Insert Fit Factor (-) 0.25 (+) 0.25 (-) 0.75 (+) 0.75 Add Line 3&6 5&6 3&6 5&6 7 Final CL Rx Base Curve Power Base Curve Power Case #2

  18. Mandell-Moore Bitoric Lens Guide - Per eye 1 Keratometry 42.50 @ 180 46.00 @ 90 2 Spectacle Rx (Minus Cyl Form) - 4.00 – 4.00 x 180 Flattest K Sphere Steepest K Sph + Cyl Power Power 3 Enter K 42.50 46.00 4 Enter Spectacle Power - 4.00 - 8.00 5 Vertex Adjust Line 4 - 3.75 - 7.25 6 Insert Fit Factor (-) 0.25 (+) 0.25 (-) 0.75 (+) 0.75 Add Line 3&6 5&6 3&6 5&6 7 Final CL Rx 42.25 - 3.50 45.25 - 6.50 Base Curve Power Base Curve Power Case #2

  19. -8.00 46.00 -4.00 42.50 Step 1 – 4

  20. -8.00 46.00 -7.25 -4.00 42.50 -3.75 Step 5 - Vertex

  21. -8.00 46.00 -7.25 -4.00 42.50 -3.75 Step 6 – Fit Factor 0.75 Fit Factor 0.25 Fit Factor

  22. -8.00 46.00 -7.25 -4.00 42.50 -3.75 Step 7 +/- Fit Factor 0.75 FitFactor -6.50 45.25 0.25 Fit Factor -3.50 42.25

  23. tear lens • 43.25 41.00 Rx: -1.00-3.00 X 180 K’s: 41.00/ 44.00 @ 090 OAD: 9.2 mm Contact Lens -4.00 -3.25 44.00 -0.75 -1.00 plano -1.00 41.00 Order: BC: 41.00 (8.23mm)/ 43.25 (7.80mm) BVP: -1.00/ -3.25 Difference in base curve (D): 2.25 D Difference in lens powers: 2.25D Conclusion:Spherical Power Effect Design

  24. BASE CURVE RADII DETERMINATION • Base curve radii are not typically equal to the K values: • For example: if K’s are 44.00/47.50; • Select BCR = 43.50/46.50 • This allows for a slight amount of toricity which assists in tear pumping and centration

  25. DIAGNOSTIC FITTING • Polycon SPE (Ciba Vision) is an excellent diagnostic set (or a similar set from a CLMA member laboratory) • Three different sets: 2D, 3D & 4D back surface cylinder • Recommend 3D set: (40.50/43.50 to 45/48D in 0.50D steps; powers = Pl/-3.00D)

  26. SPE DIAGNOSTIC FITTING • Select diagnostic lens 0.12 to 0.50D FTK • Perform spherical over-refraction • Add OR to powers in the flat and steep meridians of diagnostic lens

  27. SPE EXAMPLE K’s = 44.00/47.50 Spectacle Rx = -3.75 - 4.00 x 180 Vertex = -3.75 - 3.50 x 180 Diagnostic Lens = 43.50/46.50; Pl/-3.00D Over Refraction = -3.25DS Final Contact Lens: 7.76/7.26; -3.25/-6.25

  28. CYLINDER POWER EFFECT • If the patient has residual astigmatism resulting in blurred vision with spherical OR, a cylinder power effect bitoric is recommended • This lens must remain stable on the eye as any rotation could blur vision

  29. CYLINDER POWER EFFECT POWER DETERMINATION (Silbert): If axes are at or near the principal corneal meridians, add the appropriate power in the refraction to the air power of the corresponding meridian in the diagnostic lens, then order.

  30. CPE EXAMPLE • +0.50 - 4.00 x 170; 42/45 • DX SPE = 41.50/44.50, Pl/-3.00D If VA = 20/30, perform Sph-Cyl OR OR: +1.00 - 1.00 x 170 20/20 Add +1.00 to plano = +1.00D Add Plano to -3.00 = -3.00D

  31. OTHER CONSIDERATIONS: PERIPHERAL CURVES < 4D corneal toricity, use spherical pc’s add 1mm to mean value of BCR for SCR add 2mm to SCR for peripheral curve radius • If > 4D corneal toricity = toric pc’s add 1mm to BCR for secondary curve radii add 2mm to SCR for peripheral curve radii

  32. POOR CANDIDATE A difference of 15˚ or more between corneal cylinder axis and spectacle axis (irregular astigmatism)

  33. CLINICAL CASES

  34. CASE ONE • 23 year old law student desiring new spectacles as vision is not great with current glasses; has been 8 year GP lens wearer (about 10 hrs/day) • Refraction:OD -2.25 - 4.00 x 180 20/20 OS: -2.75 - 1.75 x 180 20/20 OD: 44.00 @ 180; 47.50 @ 090 OS: 43.50 @ 180; 45.25 @ 090

  35. CASE ONE • Empirical: Mandell-Moore • Diagnostic Fitting (SPE) • What diagnostic lenses? • 43.50(7.76)/46.50(7.26) Pl/-3.00D • If over-refraction is -1.75DS, what are powers? • -1.75/-4.75

  36. CASE ONE • What about Lens Material? • Low Dk F-S/A • What about Center Thickness? • Equal to spherical lens of more + power meridian (approx. .16mm) • What about Diameter? • Same as spherical (9.4mm)

  37. CASE ONE • What about peripheral curves? • With <4D of corneal toricity, use spherical pc’s • Add 1mm and 3mm to Mean BCR • PC’s = 8.50mm & 10.50mm

  38. CASE TWO • 16 year old spectacle wearer who has been wearing soft torics for sports • Refraction: OD +0.75 - 5.50 x 180 20/20 • OS: +1.00 - 5.50 x 180 20/20 • Keratometry: OD 41.50 @ 180; 47.00 @ 090 • OS: 41.50 @ 180; 47.00 @ 090 • SLE: Grade 2 papillary hypertrophy OU • Vascularizationx 2mm inferiorally OU

  39. CASE TWO • What SPE diagnostic lenses to use? • 41.00(8.23mm)/44.00(7.67mm) Pl/-3.00D • If OR = +1.25DS OD & +1.50DS OS • What are the powers to order? • OD: +1.25/-1.75; OS: +1.50/-1.50D

  40. CASE TWO • What would be the fluorescein pattern? • Mild dumbbell pattern OU • What changes would you make in BCR • Steepen steeper curve & add minus; for example, change to 41D(8.23mm)/45(7.50mm) & add 1D to steeper meridian power • What would be the final lens powers? • OD: +1.25/-2.75; OS: +1.50/-2.50D

  41. CASE TWO • What peripheral curves would you order? • If ≥4D of corneal toricity, add 1mm and 3mm to each base curve • Toric Peripheral Curves: 9.2/8.5; 11.2/10.5mm

  42. CASE THREE • 19 y/o male college student with symptoms of eyestrain • Spherical GP wearer x 4 years • Refraction: -0.50 - 2.00 x 180 OU 20/20 • Keratometry: 42.00 @ 180; 45.00 @ 090 OU • SLE: Inferior decentration; dumbbell fluorescein pattern

  43. CASE THREE • What SPE diagnostic lenses to use? • 41.50/44.50 Pl/-3.00D • If OR = +1.00 - 1.00 x 090 20/20, what are the final powers? • Pl/-2.00D

  44. GP LENS INSTITUTE RESOURCES • Mandell-Moore Bitoric Design • Quinn powerpoint forthcoming • Patient Brochures • GP Clinical Guide • On-Line Symposium; 2nd Tuesday night at 8PM (central time) on gpli.info • Feb. 10th (Quinn, Newman): “Bitoric Lens Design and Fitting”

  45. SUMMARY • Use Mandell-Moore and/or SPE diagnostic set • Low Dk F-S/A material • “Try it . . .You’ll like it”

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