For a flat GP lens, how should the optic zone diameter (OZD) be adjusted?

• A. No change
• B. Smaller
• C. Proportionally larger
• D. Larger

Answer: (D)

The optic zone diameter is the part of the lens that carries the refractive correction and must stay aligned with the pupil as you blink and move your eyes. When a GP lens is flatter than ideal, it tends to sit more on the cornea with more movement, which can cause the optic zone to shift off the visual axis. Increasing the optic zone diameter helps ensure the pupil remains covered by the corrective central zone across gaze and eyelid dynamics, improving centration and reducing edge-related blur or halo effects. In short, a larger optic zone diameter provides more stable, consistent vision with a flat fit.