Soft Contact Lens Fitting


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Soft Contact Lens Fitting

  1. 1. Soft Contact Lens Fitting1
  2. 2. Why is fitting the “whole patient” necessary?• Successful fitting involves complete set of parameters• Most critical, patient must achieve excellent vision and maintain ocular health• Many factors must be considered for success: – Compliance to lens wear and care schedules – Lifestyle issues and environment – Overall patient physical health3
  3. 3. Soft Contact Lens Fitting Parameter Selection • Total diameter • BOZR ( Base Curve) • Centre thickness • Water Content • Material Selection • Method of manufacture4
  4. 4. Contact Lens Fitting Guidelines • Selection of lens type –Conventional/ Disposable • Determine Lens Power • Total Diameter Selection • Base Curve selection (if required) • Trial fitting5
  5. 5. Lens Power Determination• Subjective refraction e.g - -4.00/-1.00 X 180• Spherical equivalent• Vertex distance compensation6
  6. 6. Spherical Equivalent`• If a patient has low astigmatic refractive errror in addition to myopia or hyperopia, a spherical soft lens may be prescribed. The Rx is based on a calculation known as the “spherical equivalent.” SE = Sphere + ½ Cylinder7
  7. 7. Vertex Distance Compensation • Effective lens power changes depending on the distance from the cornea; e.g.spectacle vs. contact lens • Utilize vertex distance compensation chart to determine proper contact lens power from spectacle refraction8
  8. 8. Soft Contact Lens Fitting Total Diameter Selection • Measure HVID (Horizontal Visible Iris Diameter) Then either: • Add 2mm to HVID and select trial lens set with nearest diameter or • Follow manufactures recommendation and select suggested diameter9
  9. 9. Soft Contact Lens Fitting Total Diameter Selection10
  10. 10. Soft Contact Lens Fitting Effects of Diameter S2 > S1 > S3 same BOZR S 1 S2 D 1 D2 ‘Original Fit’ ‘Steeper’ flatter BOZR same BOZR S 4 S 3 D 4 D 3 ‘Same’ ‘Flatter’ S11 S 44 D 11 D 4411
  11. 11. Soft Contact Lens Fitting Rule of Thumb`: (Soft Lenses) TD 0.5 mm BOZR 0.3 mm (increase) (increase)12
  12. 12. Soft Contact Lens Fitting Base Curve Selection Measure Ks (mm) then add either: • 0.8 mm to flattest K • 1 mm to average of Ks • 4 D flatter than average K Select lens of nearest Base Curve from trial set or . . .Select Trial lens Base Curve as per manufacturer’s recommendation 13
  13. 13. Soft Contact Lens Fitting Trial Lens Fitting• Regarded as essential by some• Allows the feel of a lens experience• Patient reaction is assessable• Needs to be performed in average illumination (pupil size) - assessments made with the aid of good illumination - low to moderate magnification• Now easier and safer - disposable trial lenses15
  14. 14. Soft Contact Lens Fitting Trial Lens Fitting • Select trial BVP nearest to vertex corrected spectacle Rx result • If only ± 3.00 D (or similar) available use appropriate type ( ie plus or minus) • If Rx high but only low Rx trial lenses available, consider getting more appropriate trial lenses ) • If large difference between trial and Rx, remember to correct over-Rx for vertex distance16
  15. 15. Soft Contact Lens Fitting Empirical Prescribing Patient data required for lens choice: • HVID • • Ks • • Spectacle Rx • • Vertex distance • •17
  16. 16. Optimizing On-Eye Performance • Trial Lens is placed on the eye and allowed to settle 10-15 minutes • On-eye lens performance is evaluated based on the universal fitting criteria: – Corneal Coverage – Centration – Lens movement – Comfort – Vision18
  17. 17. SOFT LENS FITTING The need for Corneal Coverage • Mechanical, prevention of trauma • • Physiological - corneal exposure - corneal dessication - tear film disturbance, lens & eye wettability • About 1 mm symmetrical overlap is ideal19
  18. 18. Soft Contact Lens Fitting` Corneal Coverage20
  19. 19. Soft Contact Lens Fitting CentrationGood Optical performanceBased on Lens Diameter,Edge Design If decentered - Large lens - Steep BC21
  20. 20. Soft Contact Lens Fitting Why is Movement Required? Movement • Removes and disperses ocular debris • • Promotes tear exchange (minimal) • • Possibly aids epithelial wetting by • mucin spreading and smoothing23
  21. 21. Soft Contact Lens Fitting Assessment of Mobility? • Movement on a blink • Lag following eye movement • Movement on up-gaze blink • Lower lid push-up test24
  22. 22. Soft Contact Lens Fitting Movement25
  23. 23. Soft Contact Lens Fitting Movement26
  24. 24. Soft Contact Lens Fitting Lens LagA steep lens is very stableand there is hardly any lagA flat lens is less stableand therefore will lag more 27
  25. 25. Comfort • A critical factor of contact lens success • Steeper (tighter) fitting lenses may be more comfortable • Flat (loose) fitting lenses may cause lid sensation and discomfort28
  26. 26. Vision29
  27. 27. Soft Contact Lens Fitting Effect of a Blink Too Steep : Vision CLEARS after blink Steep lens Before Blink Lens conform to central cornea after Blink (due to lid force)30
  28. 28. Soft Contact Lens Fitting Effect of a Blink Too Flat : Vision BLURS after blink Flat lens Lens decenters Before Blink because of force of lid31
  29. 29. Soft Contact Lens Fitting Tightness: What is Acceptable?33
  30. 30. Soft Contact Lens Fitting Tightness: What is Acceptable?• Lens Immobile• Conjunctiva Indentation• Blood flow constriction in peri-limbal vessels• Low grade inflammation• Vision better immediately after blink 34
  31. 31. Soft Contact Lens Fitting Summary Choose lens that gives...35
  32. 32. Optimum vision36
  33. 33. Good comfort37
  34. 34. No ocular insult38