Free radicals and aging of anterior segment tissues of the eye: a hypothesis.

A hypothesis is proposed that aging processes in the eye occur as a consequence of degradation of enzymes that normally metabolize and detoxify hydrogen peroxide and other free radicals. The loss of enzyme activity allows hydrogen peroxide, which normally occurs within eye fluids, and free radicals to induce irreversible deleterious effects on different eye tissues. These processes may lead to cataract formation in the lens, loss of corneal endothelial cells, modification of the glycosaminoglycan secretory patterns of the cells of the trabecular meshwork, and other changes associated with ocular aging. These processes may be exacerbated during inflammation when oxidation products increase. Considerable circumstantial evidence points towards hydrogen peroxide as one of the major chemicals involved in the induction of these changes. Much remains to be determined to definitively identify this chemical or free radicals as the primary inducers of tissue alterations that occur in aging eyes.