What term describes the curve on the back surface of a contact lens?

• A. Base curve
• B. Front curve
• C. Back radius
• D. Optical curve

Answer: (A)

Base curve describes the curve on the inner surface of a contact lens—the part that rests against the tear film and cornea. This curvature sets how the lens sits on the eye and is chosen to match the corneal shape for a comfortable, stable fit. If the base curve is too flat (larger radius), the lens may ride on the tear film and move more; if it’s too steep (smaller radius), it can press against the cornea and feel tight. The front surface is what provides the optical power, and terms like back radius or optical curve aren’t the standard way to refer to the inner surface. So the correct term for the curve on the back surface is base curve.