soft contact lens fitting

Soft contact lens fitting

Md. Nooruz ZamanM.Optom, (FIACLE), (PhD)

Factors which affects lens fit Modulus of elasticity Manufacturing method Water content Keratometric readings Lid tonus Tear film

Fitting steps History Initial eye examination-SLE Refraction, 4:1 Keratometry HVID Other tests like tear film, sensitivity,PAH

etc Selection of trial lens

The parametrs of lens is selected on following BC Power Diameter Types of lens

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)

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)

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

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.

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

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

Lens Lag Patient asked to loo up and lens move

down slightly –Lag 1 to 1.5 mm - Ideal

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

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

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

Over refraction Refraction over trial lens Algebraically add power Note- aditional power needed should be

less than 4D If cyl required –fit toric

Final Order BC Power Diameter Water content Tint Material Manufacturer