- DETERMINE THE FITTING AND CENTRAL CURVE VALUES FROM TOPOGRAPHY OR KERATOMETRY READINGS.
- EVALUATE THE DIAGNOSTIC LENS
Central / Mid-peripheral fit
Look for 0.020mm to 0.030mm central clearance with alignment in the midperipheral area. Change the fitting curve/central base curve relationship to achieve the desired fit.
Making changes to both the fitting and the central base curve values at the same time can get confusing. When making a change, it is recommended to change only one curve value at a time.
First, trial fit to determine which FITTNG CURVE value gives you the desired alignment in the mid-peripheral area. When doing so, select a CENTRAL BASE CURVE that allows sufficient clearance (2.00D to 3.00D steeper than flattest post surgical corneal curvature) ensuring no central touch. Ignore the central tear layer profile at this stage.
Second, with the correct FITTING CURVE VALUE in situ, progressively flatten the CENTRAL BASE CURVE value to achieve the desired 0.002mm to 0.003mm clearance over the post surgical central area.
For more information on how the curves interact with each other, please refer to the section included in this guide (FITTING CURVE / CENTRAL BASE CURVE INTERACTION).
Peripheral / Edge fit (Edge lift)
Once you have achieved the desired central and mid-peripheral fit, assess the peripheral / edge fit. Look for a peripheral band of 0.5mm to 0.7mm in width. Order Flat or Steep edge lifts accordingly. When the inferior quadrant is significantly steeper then the superior quadrants, causing excessive lift at 6 o’clock consider ordering a lens with ACT (Asymmetric Corneal Technology). For more information on ACT please refer to the section included in this guide.
The standard diameter is 10.5mm. Reducing the diameter will release some pressure in the mid-peripheral area and allow the lens to move more freely, conversely, increasing the diameter will increase pressure in the mid-peripheral area, improve centration and reduce lens movement.
- Perform over-refraction in normal light conditions
- Begin with ±1.00D steps
- Refine with ±0.50D and ±0.25D
- Order lenses with the following parameters:
- Central base curve
- Fitting curve
- Peripheral edge configuration
- Lens power