0.1 mm radius of a base curve corresponds to how many diopters?

• A. 0.50 D
• B. 0.25 D
• C. 1.00 D
• D. 2.50 D

Answer: (A)

The important idea here is that curvature power (diopters) is essentially the reciprocal of the radius of curvature: a tighter curvature (smaller radius) bends light more, which means a higher dioptric power. In theory, if you treat the back surface of a lens as a simple curved interface in air, the power would be roughly 1 divided by the radius in meters. A base curve radius of 0.1 mm is 0.0001 meters, so 1 / 0.0001 equals 10,000 diopters—an extremely large value not seen in practice, which shows the direct calculation doesn’t map cleanly to typical base-curve diopter values used clinically. The takeaway is the inverse relationship: smaller base-curve radius means a more pronounced curvature effect (higher diopters in a simple surface-power sense). In actual contact lens practice, base curve and diopter power aren’t directly interchangeable, and exam conventions may use simplified mappings or have misprints.