optic zone diameter

optic zone diameter 

Diameter of the optic zone (front or back) of a contact lens measured to the surrounding junction. It is commonly specified in millimetres. Specifically, there are the back optic zone diameter (BOZD), formerly called back central optic diameter (BCOD), and the front optic zone diameter (FOZD). It is often difficult to measure these dimensions due to the blending of the line separating the zones, especially for the back optic zone diameter. The region surrounding the central optic zone is the peripheral zone. If there is more than one, the zones will be numbered first, second, etc., beginning with the zone immediately surrounding the central optic zone. The diameter of each peripheral zone is referred to as the back (or front) peripheral zone diameter (BPZD). See blending; total diameter; edge lift.