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Soft Contact Lens Fitting
Fitting soft contact lenses requires considering many patient-specific factors to achieve excellent vision and ocular health. A proper fit involves selecting the correct total diameter, base curve, thickness, and material based on the patient's prescription, corneal shape, lifestyle, and health. Trial lenses are used to evaluate fit parameters like coverage, centration, movement, comfort, and vision to optimize on-eye performance while avoiding issues like tightness or looseness that could impact ocular health or vision. The goal is to find a lens that provides optimum vision and good comfort without causing any ocular insult.
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Soft Contact Lens Fitting
- 1. Soft Contact LensFitting 1
- 2. Why is fittingthe “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 health 3
- 3. Soft Contact LensFitting Parameter Selection • Total diameter • BOZR ( Base Curve) • Centre thickness • Water Content • Material Selection • Method of manufacture 4
- 4. Contact Lens FittingGuidelines • Selection of lens type –Conventional/ Disposable • Determine Lens Power • Total Diameter Selection • Base Curve selection (if required) • Trial fitting 5
- 5. Lens Power Determination •Subjective refraction e.g - -4.00/-1.00 X 180 • Spherical equivalent • Vertex distance compensation 6
- 6. Spherical Equivalent` • Ifa 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 Cylinder 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 refraction 8
- 8. Soft Contact LensFitting 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 manufacture's recommendation and select suggested diameter 9
- 9. Soft Contact LensFitting Total Diameter Selection 10
- 10. Soft Contact LensFitting 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 44 11
- 11. Soft Contact LensFitting Rule of Thumb`: (Soft Lenses) TD 0.5 mm BOZR 0.3 mm (increase) (increase) 12
- 12. Soft Contact LensFitting 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. Soft Contact LensFitting 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 lenses 15
- 14. Soft Contact LensFitting 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 distance 16
- 15. Soft Contact LensFitting Empirical Prescribing Patient data required for lens choice: • HVID • • Ks • • Spectacle Rx • • Vertex distance • • 17
- 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 – Vision 18
- 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 ideal 19
- 18. Soft Contact LensFitting` Corneal Coverage 20
- 19. Soft Contact LensFitting Centration Good Optical performance Based on Lens Diameter, Edge Design If decentered - Large lens - Steep BC 21
- 20. Soft Contact LensFitting Why is Movement Required? Movement • Removes and disperses ocular debris • • Promotes tear exchange (minimal) • • Possibly aids epithelial wetting by • mucin spreading and smoothing 23
- 21. Soft Contact LensFitting Assessment of Mobility? • Movement on a blink • Lag following eye movement • Movement on up-gaze blink • Lower lid push-up test 24
- 22. Soft Contact LensFitting Movement 25
- 23. Soft Contact LensFitting Movement 26
- 24. Soft Contact LensFitting Lens Lag A steep lens is very stable and there is hardly any lag A flat lens is less stable and therefore will lag more 27
- 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 discomfort 28
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- 27. Soft Contact LensFitting 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. Soft Contact LensFitting Effect of a Blink Too Flat : Vision BLURS after blink Flat lens Lens decenters Before Blink because of force of lid 31
- 29. Soft Contact LensFitting Tightness: What is Acceptable? 33
- 30. Soft Contact LensFitting 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. Soft Contact LensFitting Summary Choose lens that gives... 35
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