The initial diagnostic lens design should be chosen using the following criteria:
STEP 1 – What is the shape of the patient’s cornea? (Regular or Irregular Mires with Symmetrical or Asymmetrical Corneal Meridians)
STEP 2 – What is the patient’s type of cornea? (Level of Astigmatism, if any)
STEP 3 – What is your patient’s Delta K value?
STEP 4 – What is the condition of the patient’s cornea? (Eccentricity Value, Pathologies, or Surgeries)
Diagnostic Lens Selection Flow Chart:
After the applicable lens design has been selected, the BOZR (Back Optic Zone Radius) for the diagnostic lens needs to be determined. A guideline is provided on the above flow diagram how to select the BOZR by using the K-value. Round your K-value down to the closest 0.1 value.
Remember the Base Curve Selection indicated is only a recommendation. When we say fit on the flattest K, it is only a recommendation of where to start fitting a diagnostic lens. The responsibility lies with the practitioner that is still in control of the fit and can override any parameter necessary to get an acceptable fit.
Where possible, a diagnostic lens should be as close as possible to the patient’s final prescription, both to provide the patient with as natural vision as possible and to minimize the potential changes in fit and comfort1.
All the above mentioned information has been consolidated into a user friendly diagnostic lens calculator for your use:
- Rigid Contact Lens Fitting. Essential Contact lens Practice – The Vision Care Institute. p6.
