In the calculation example, what does OZ stand for in the equation OZ + 2(ICW) + 2(PCW) = OAD?

• A. Optical Zone
• B. Optical Zone Diameter
• C. Overall Zone
• D. Optical Zenith

Answer: (B)

The OZ term is Optical Zone Diameter. In this calculation, the central clear portion of the lens that provides vision is the optical zone, and its diameter is what OZ represents. This diameter is added to the widths of the zones on either side of the optical zone (two inner corneal widths and two peripheral corneal widths) to give the total lens diameter, or OAD. So the formula shows how the central optical area plus the surrounding peripheral zones come together to define the overall size of the lens.

Other options don’t fit the concept here: Optical Zone alone doesn’t specify a measurement, Optical Zone Diameter is the correct diameter term, Overall Zone isn’t a standard descriptor in this context, and Optical Zenith isn’t related to lens sizing.