The optic zone diameter should be larger than the pupil by about how many millimeters?

• A. 0.5
• B. 1
• C. 1.5
• D. 2

Answer: (B)

Having the optic zone extend around the pupil by about one millimeter gives a safety margin so the pupil stays entirely within the lens’s clear optical area as lighting changes. Pupil size varies with light: it’s smaller in bright conditions and dilates in dim conditions. If the optic zone is only about the same size as the pupil or only slightly larger, a dilated pupil can begin to encroach on the peripheral zone of the lens, leading to blur, halos, or faint edge effects. A margin of roughly 1 mm helps ensure the entire pupil remains within the optic zone even when it dilates, providing more consistent vision and reducing nighttime disturbances. Too small a margin increases the chance of aberrations at the edge of the optic, while a much larger margin isn’t necessary for typical GP designs and isn’t required to achieve reliable vision.