A secondary/intermediate curve is flatter or steeper than the base curve?

• A. Steeper
• B. The same as base curve
• C. Flatter
• D. Cannot determine

Answer: (C)

In a multi-curve gas permeable lens, the fit is built from several concentric curves: the base curve sits closest to the cornea and is chosen to match its curvature. The secondary (intermediate) curves are flatter than this base curve, meaning they have a larger radius. This flatter progression toward the periphery creates a gradual slope from the center to the edge, which helps maintain central clearance while providing proper peripheral alignment and tear exchange. If the intermediate curves were steeper than the base curve, the lens would press more on the cornea and disrupt fit; if they were the same or steeper, the lens wouldn’t achieve the desired grazing and edge control. So, the secondary/intermediate curve is flatter than the base curve.