Back optic zone diameter (OZD) is created by what?

Back optic zone diameter (OZD) is created by what?

• A. Optic zone diameter
• B. Radius of curvature on the anterior surface
• C. Overall diameter
• D. Base curve

Answer: (D)

The back optic zone diameter is determined by the back surface geometry of the lens. The base curve defines the curvature of the lens’s inner (back) surface, and the central optical region is carved into that back surface. How steep or flat that back surface is controls how large the central optic zone can be before the peripheral region begins, so the base curve effectively sets the back optic zone diameter. The other options describe aspects that don’t establish the size of the optical zone: the overall diameter is the total lens width, the anterior surface radius is on the front surface, and the optic zone diameter is the central region itself, not the factor that creates its size.

The back optic zone diameter is determined by the back surface geometry of the lens. The base curve defines the curvature of the lens’s inner (back) surface, and the central optical region is carved into that back surface. How steep or flat that back surface is controls how large the central optic zone can be before the peripheral region begins, so the base curve effectively sets the back optic zone diameter. The other options describe aspects that don’t establish the size of the optical zone: the overall diameter is the total lens width, the anterior surface radius is on the front surface, and the optic zone diameter is the central region itself, not the factor that creates its size.