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. Author manuscript; available in PMC: 2014 Jul 21.
Published in final edited form as: Ocul Surf. 2009 Oct;7(4):176–185. doi: 10.1016/s1542-0124(12)70185-4

Figure 1.

Figure 1

Formation of reactive oxygen species and antioxidant defenses in the eye. Environmental exposures (such as solar ultraviolet radiation and high atmospheric oxygen) and certain pathological conditions (such as inflammation and prolonged contact lens wearing) induce the generation of reactive oxygen species (ROS) in ocular tissues. ROS are derived from diatomic oxygen (O2), including superoxide anion radical (O2−•), hydrogen peroxide (H2O2), hydroxyl (OH•), and peroxyl radicals (LOO•). ROS have high potential to react with DNA, proteins and cellular membranes, resulting in modifications of these macromolecules and consequent cellular damage. The antioxidant defense systems in the ocular surface function to combat ROS and protect ocular tissues from oxidative damage. Superoxide dismutases (SODs), catalase (CAT), glutathione peroxidases (GPXs), glutathione reductase (GR) and aldehyde dehydrogenases (ALDH3A1 and ALDH1A1) represent enzymatic antioxidants. Glutathione (GSH), ascorbic acid (VitC), α-tocopherol (VitE), NADPH and ferritin represent nonenzymatic anti-oxidants. The properties and functions of each antioxidant are discussed in detail in the text.