The cornea's contribution to refractive power is approximately:

The cornea's contribution to refractive power is approximately:

• A. +60 D
• B. The cornea contributes +43 D
• C. 0 D
• D. -43 D

Answer: (B)

The cornea provides the majority of the eye’s refractive power because its curved surface creates a large bend when light passes from air into the optical medium of the cornea. The air-to-cornea interface, with a big refractive index jump (about 1.00 to around 1.376) on a short radius of curvature, yields roughly +43 diopters of converging power. This is the main focusing element of the eye; the crystalline lens adds about +17 diopters, bringing the total to about +60 diopters. The positive sign means light is focused forward toward the retina. So +43 diopters best represents the cornea’s contribution. The total eye power is around +60 D, zero would imply no focusing effect, and a negative value would indicate divergent power, none of which describe the cornea’s contribution.

The cornea provides the majority of the eye’s refractive power because its curved surface creates a large bend when light passes from air into the optical medium of the cornea. The air-to-cornea interface, with a big refractive index jump (about 1.00 to around 1.376) on a short radius of curvature, yields roughly +43 diopters of converging power. This is the main focusing element of the eye; the crystalline lens adds about +17 diopters, bringing the total to about +60 diopters. The positive sign means light is focused forward toward the retina. So +43 diopters best represents the cornea’s contribution. The total eye power is around +60 D, zero would imply no focusing effect, and a negative value would indicate divergent power, none of which describe the cornea’s contribution.