Eye

Abstract

The eyeballs are composed of three concentric layers: (1) an outer layer, consisting of the sclera and the cornea; (2) a middle layer, consisting of the choroid, the ciliary body, and the iris; and (3) an inner layer, the retina, consisting of the inner retina proper and the outer pigment epithelium. The eyeballs are filled with a transparent gel, the vitreous body. For visual function, the light must pass through several refractive media: the cornea, the aqueous humor, the lens, the vitreous body, and finally reaching the retina. The first layer of the inner retina is consisting of photosensitive cells, rods and cones. The second layer is an intermediate layer of photosensitive cells consisting of bipolar neurons which connect rods and cones to ganglion cells. The final layer is composed of the ganglion cells with long dendrites and which form the optic nerve, through which signals of visual sensing are sent to the visual cortex. UV radiation is one of many causes of oxidative eye damage. Vitamin C level in the eye physiologically is found at rates of 10–40 times higher than in human plasma. Vitamin C levels in aqueous humor and vitreous humor are 200~500 μM and 2 mM, respectively. The concentration of vitamin C in aqueous humor decreases with age in patients with age-related cataracts. Vitreous concentrations of vitamin C are impaired in diabetic patients. Serum levels of vitamin C are lower in patients with diabetes than in normal controls. As diabetic retinopathy progresses, the vitreous concentrations of vitamin C level are decreased. Vitamin C may play an important role in UV-induced lens pathology.