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soft contact lens fitting

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soft contact lens fitting

  1. 1. Soft contact lens fitting Md. Nooruz Zaman M.Optom, (FIACLE), (PhD)
  2. 2. Factors which affects lens fit  Modulus of elasticity  Manufacturing method  Water content  Keratometric readings  Lid tonus  Tear film
  3. 3. Fitting steps  History  Initial eye examination-SLE  Refraction, 4:1  Keratometry  HVID  Other tests like tear film, sensitivity,PAH etc  Selection of trial lens
  4. 4. The parametrs of lens is selected on following  BC  Power  Diameter  Types of lens
  5. 5. Steps for calculations  K in mm  Add 1mm to mean k  Power- 1. transpose to minus cyl 2. Sph. equivalent 3. VDC for more than 4 D  Diameter- HVID+2mm (13 to 14.5mm)
  6. 6. Evaluation of Fit  Patients comfort response - Fairly comfortable – probably good fit - Uncomfortable - predicts loose fit(excess movement) - Very comfortable – May be steep or tight (immobile)
  7. 7. Corneal coverage Slit lamp, diffuse illumination, - eye in primary position, lens should show full corneal coverage about 1 to 2mm beyond limbus - Full coverage (1 -2mm) – Ideal - Greater than 2 mm – lens too large - Corneal exposure – lens too small
  8. 8. Lens centration  Equally centered in all distance beyond limbus in all directions.  Centered in all position – ideal  Decentered with corneal exposure in any position of gaze- steep or loose, dia may be small.
  9. 9. Movement  Patient asked to look straight in primary gaze and asked to blink normally.  Movement is estimated in diffuse light and moderate to high magnification with blink.  0.2 – 0.4 mm ---- ideal
  10. 10. Push up test  Patients looks straight and examiner pushes the lens up vertically through the pressure of lid  40-60% IDEAL  Easy displacement- smooth recovery – ideal fit  Resistence to displacement – may not recenter – tight fit  Easy displacement- Erratic recovery – Loose fit
  11. 11. Lens Lag  Patient asked to loo up and lens move down slightly –Lag  1 to 1.5 mm - Ideal
  12. 12. 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 cornea- tight or steep  If it stands off - loose
  13. 13. Other responses  Vision before and After blink- - If ideal vision will remain same and clear - If vision clears with blink – steep - If vision gets blur with blink- flat fit  Keratometry and retinoscopy with the lens on the eye can also be performed. Clarity of mires is observed  If clears with blink-steep  If blurs- flat
  14. 14.  Alter the lens if ideal fit is not achieved  Fitting can be changed on - BC - Dia - Thickness - Rule of thumb- 0.3mm change in the base curve = 0.5 mm change in Diameter
  15. 15. Over refraction  Refraction over trial lens  Algebraically add power  Note- aditional power needed should be less than 4D  If cyl required –fit toric
  16. 16. Final Order  BC  Power  Diameter  Water content  Tint  Material  Manufacturer

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