See Longer with C

Cataract is a condition in which the lens of the eye becomes clouded, eventually leading to blindness. Because oxidation of the lens proteins appears to play a central role in the formation of age-related cataracts, scientists have investigated the possibility that dietary antioxidants could prevent or delay the disease. Initially, working with eye tissue in the laboratory, they found that vitamin C could slow the chemical reactions that make certain lens proteins clump together. The researchers then gave the vitamin to animals to see if it would retard cataract formation. It did.

Most recently, researchers have attempted to determine whether vitamin C could prevent or delay cataract formation in humans. By comparing women who took vitamin C supplements with women who didn't, they discovered that women on vitamin C for at least 10 years were only 23% as likely to develop cataracts as women who did not supplement. (The mean dietary intake of vitamin C for those not taking supplements was 130 milligrams per day—about two times the recommended amount, but less than one-third the average intake of the women taking supplements.)
Based on information in: American Journal of Clinical Nutrition 1977; 66:911-6