In many species, ascorbate (vitamin C) is found throughout the eye in concentrations that are high relative to those in other tissues. In addition to blocking UV light in the aqueous humor, ascorbate is thought to function synergistically with vitamin E to terminate free radical reactions. Vitamin C functions as an electron donor, reducing oxidized elements and molecules. It has been proposed that vitamin C can react with the vitamin E radicals formed when vitamin E scavenges free radicals. Vitamin E radicals are then regenerated to form native vitamin E. The vitamin C radicals resulting from this regeneration can be reduced by nicotinamide adenine dinucleotide (NADH) reductase, with NADH as the electron acceptor. Ascorbate is found at high levels in the aqueous humor as well as in the vitreous, where it also functions to reduce oxygen levels (see Chapter 11, Fig 11-6).
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Reddy VN, Giblin FJ, Lin LR, Chakrapani B. The effect of aqueous humor ascorbate on ultraviolet-B-induced DNA damage in lens epithelium. Invest Ophthalmol Vis Sci. 1998; 39(2):344–350.
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Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.