SOFT CONTACT LENS FITTING AND EVALUATION

Contact lens

1. Soft contact lens fitting SHAHLA THESNIM.K

2. Fitting characteristics of soft contact lens is a complex interaction of various ocular factures and definitely need proper understanding of the fitting techniques. It is the fitter responsibility if the patient develops complications due to improper fitting

3. Factors which affects lens fit Modulus of elasticity (thin lenses are more flexible and move less on the cornea) Manufacturing method Water content (high water content-more flexible-less movement) Keratometric readings (patient with same k readings can also have different lens parameters.)

4. Lid tonus Tear film(lens will dehydrate on dry eye and will move less ,hypertonic tear causes lens to dehydrate thus move less) NB : predicting from the empirical calculations can go wrong ,so it is better to evaluate the fitting on trial lens method.

5. The ideal soft contact lens fit Coverage Centering Movement Too much tight will leads to limbal compression Loose will leads to unstable vision and discomfort

6. Fitting steps

7.  History  Initial eye examination-SLE  Refraction, 4:1  Keratometry  HVID  Other tests like tear film assessment , sensitivity, etc  Selection of trial lens based on the following criteria

8. Steps for calculations

9.  BC  Power  Diameter  T ype of trial lens

10. BC Measure corneal curvature-convert in to millimeter  Add 1mm to mean k Eg :- 43.0@180/43.50@90 =7.85/7.76 =7.80 7.80+1=8.80mm (Typical base curve ranges from 8.1 to9.1mm in 0.1 step ) NB:Thin lenses need lesser addition can depend manufactures guidelines If there is only 2 or 3 base curve are available in the trail set then select a lens with base curve closest to the required base curve.

11. Power Lens selected should have power as close as possible to the refractive correction,or else maximum with in +-4D Cylinder should not be more than 0.75or 4:1 ratio 3 basic step to calculate expected power is Transpose to minus cyl Sph . equivalent VD correction for more than 4 D

12. Eg :- Spectacle power/Refractive correction Contact lens power Remark -2.50DS -2.50/-0.50 @ 180 -8.00DS -8.00/-1.00 @ 90 +2.00/+0.50 @ 90 -2.50DS -2.75DS -7.25DS -7.75DS +2.25DS Same as spectacle power.<4.00D Spherical equivalent Compensate VD. >4.00D Spherical equivalent, then compensate VD Transposition , spherical equivalent

13. Selection of power from trial set It is usually not possible to have all powers in all base curve Basic trial set having following powers 1. -3.00 used for 0 to -6.00 spectacle power 2. -10.00 used for -6.00 to -14.00 spectacle power 3. +3.00 0 to +6.00 4. +10.00 +6.00 to +14.00 NB: select the trail lens with closest required power

14. DIAMETER Diameter- HVID+2mm Typical soft lens dia ranges from 13 to 14.5mm in 0.50 step(normal corneal size can fit in this range) Smaller and larger corneas may need different dia , so usually the lens is custom made by lathe cutting.

15. LENS THICKNESS Based on the thickness can be classified as Thick 1mm to 1.5mm Thin 0.6 to 1mm Ultra thin <0.6mm Thick lens Thin lens Suitable to mask cylinders Easier to handle Reduce oxygen transmissibility High transmissibility Do not mask astigmatism Greater tendency to dehydrate(not suitable for dry eyes)

16. Evaluation of Fit

17. Place the trail lens on the eye Although the patient with soft lens will adapt easily wait for some time before evaluating fit.(usually 5 min after insertion ) Some patients may need more time to psychologically adapt to the lens.

18. Patients comfort response after 5minuts Fairly comfortable – probably good fit Uncomfortable - predicts loose fit(excess movement) Very comfortable – May be steep or tight (immobile)

19. corneal coverage Slit lamp, diffuse illumination, eye in primary position, lens should show full corneal coverage about 1 to 2mm beyond limbus before ,after and during the blink. Full coverage (1 - 2mm from the limbus ) – Ideal Greater than 2 mm – lens too large Corneal exposure – lens too small

20. lens centration  should be reasonably centered , extending equal distance beyond limbus in all directions  Centered in all position of gaze – ideal  Decentered with corneal exposure in any position of gaze- steep , loose or dia may be small.

21. Lens movement Essential for proper tear exchange and removal of debris Patient asked to look straight in primary gaze and asked to blink normally. Movement is estimated during blinking with slit lamp diffuse light in a moderate to high magnification .

22. Movement will depend the type of lens ,its design and thickness. (should follow manufactures guideline) 0.2mm to0.4 mm movement during blinking for thin lens(modern thin designs) 1mm to 2 mm movement for thick lens(lathe cut lens)

23. O ther tests to asses lens movement 1. Push up test  Patients looks straight and examiner pushes the lens up vertically through the pressure of lid IDEALFIT EASY DISPLACEMENT SMOOTH RECOVERY TIGHT FIT RESISTANCE TO DISPLACEMENT TIGHT FIT LOOSE FIT EASY DISPLACEMENT ERRATIC RECOVERY

24. 2. Lens Lag on up gaze  Patient asked to loo up and lens move down slightly –Lag  1 to 1.5 mm - Ideal

25. 3. Edge Alignment  Edge of the lens is observed with reference to the conjunctiva.  If the edge is sliding smoothly and aligning with conjunctiva is the ideal.  If indent on conjunctiva - tight or steep  If it stands off - loose

26. Other responses from patient to estimate fitting relationship  Vision before and After blink vision will remain same and clear in both - Ideal If vision clears with blink – steep If vision gets blur with blink - flat fit

27. Keratometry and retinoscopy with the lens on the eye can also be performed. Clarity of mires is observed before and after blinking  If mires clears with blink-steep  If mires blurs with blink- flat

28.  I f first chosen trail lens is not show adequate fit , find and refit another lens  Fitting can be changed on BC Dia Thickness A ltering the lens if ideal fit is not achieved

29. If the fit is flat Make it steep by either:- Decrease the base curve, leads to high sag or Increase the diameter, leads to high sag

30. If the fit is steep Make it flat by either:- I ncrease the base curve, leads to Less sag or decrease the diameter, leads to less sag

31. Rule of thumb Applied for altering the base curve and dia without changing the fitting relationship 0.3mm change in the base curve = 0.5 mm change in Diameter Eg : 8.3mm BC,13.5 mm dia 8.6mm BC, 14.00 mm dia Same fitting relationship

32. Over refraction  Refraction over trial lens  Algebraically add power Note aditional power needed should be less than 4D  If residual astigmatism is present and vision is not acceptable with spherical equivalent then fit toric lens EG: POWER OF THE TRAIL CONTACT LENS : - 3.00DS OVER REFRACTION : +0.50DS FINAL LENS POWER TO BE ORDERED: +2.50DS

33. Over-refraction and visual acuity A normal over-refraction should take place with binocular balancing. The refraction should have a clear endpoint and visual acuity should be stable and crisp. Variations of this could indicate a poor lens fit, and the use of the retinoscope to confirm is recommended.

34. Final Order  BC  Power  Diameter  Water content  Tint  Material  Manufacturer COMPANY NAME AND BRAND NAME OF CL OR

35. SUMMARY 1. Measure KR HVID 2.Determine contact lens parameters Base curve Diameter Power 3.Select trail lens type 4. Assess fitting after lens settles on the eye Coverage C entration Movement Patient comfort 5. Assess vision Over refraction 6.Ordering the lens

36. THANK YOU