Increasing the overall optical diameter (OAD) of a GP lens affects sagittal depth how?

Increasing the overall optical diameter (OAD) of a GP lens affects sagittal depth how?

• A. SAG decreases
• B. SAG unchanged
• C. SAG increases
• D. SAG is not affected by OAD

Answer: (C)

Increasing the overall optical diameter means the lens must cover a larger arc of the cornea while keeping the same central curvature. The sagittal depth is basically how high the lens edge sits above the corneal surface. When you widen the diameter, the edge travels farther from the center, so the edge height increases. Geometrically, for a fixed base curve radius, the sagitta (the height of the arc at the edge) grows as the diameter grows, roughly described by s ≈ D^2/(8R) for small sizes. So the sagittal depth increases with a larger OAD.

Increasing the overall optical diameter means the lens must cover a larger arc of the cornea while keeping the same central curvature. The sagittal depth is basically how high the lens edge sits above the corneal surface. When you widen the diameter, the edge travels farther from the center, so the edge height increases. Geometrically, for a fixed base curve radius, the sagitta (the height of the arc at the edge) grows as the diameter grows, roughly described by s ≈ D^2/(8R) for small sizes. So the sagittal depth increases with a larger OAD.