Sunlight and cortical cataract.

We undertook a prospective clinical study to test our initial impression that cortical opacities are seldom present in the upper part of the lens. Data analysis revealed that of 174 eyes having cortical opacities, only 15 (8.62%) had opacities in the area of the lens between the 10- and 2-o'clock positions. Lid retraction, defined as upper lid position at or above the limbus, was seen in 13 (88.66%) of these eyes. Our study indicates that in the absence of lid retraction, cortical opacities are very rarely seen in the upper segment of the lens, a segment that is normally covered by the upper lid. This suggests a protective effect of the upper lid against cortical opacities, and indirectly it supports the theory that senile cortical opacities may be the result of thermal damage to the lens.