Ocular oxidants and antioxidant protection.

Oxidative damage and antioxidant protection in ocular tissues has not been reviewed recently. Metabolism in the eye is of increasing interest because the organ is highly susceptible to damage by sunlight, oxygen, various chemicals, and pollutants. Interest is expected to increase because of an aging Western world population and a continued depletion of stratospheric ozone. Hydrogen peroxide is discussed because it is both a byproduct and a source of free radical reactions and is normally present in the aqueous humor. The metabolism of reactive oxygen species by enzymes, nutrients, pigments, and low molecular weight scavengers is evaluated. Ascorbic acid, because of its high concentration in the eye, is thought to be a primary substrate in ocular protection; progress in determining the mechanisms by which it is recycled and maintained in the useful, reduced state is discussed. Recent information is included about antioxidants not previously known to be present in the eye, and some importance is placed on the properties of the vitreous humor and tear fluid because of the previous lack of emphasis on these.