Ascorbic acid in the eye

E, (Robertson et al. 1989), or B2 (Prchal et al. 1978) may be more susceptible to cataract formation in general. The concentration of ascorbic acid in the aqueous humor of adult animals is generally higher than that in young animals (Kinsey et al. 1945). Ascorbic acid concentration in the eyes of... 

It seems clear that ascorbic acid enters the eye as a constituent of aqueous humor. From there it can be shifted into the cells of the lens and also into the endothelial monolayer which lines the inner surface of the cornea. It is likely that some ascorbic acid diffuses from the aqueous humor into the vitreous cavity. However, McGahan (1985) suggested that ascorbic acid may also enter the vitreous humor from other sources perhaps some passes out of the retina. In most species, the concentration of ascorbic acid in the vitreous humor is the same as that in aqueous humor or slightly lower (DiMattio, 1989a McGahan, 1985 Varma and Richards, 1988). 

There must also be a second mechanism of ascorbic acid transport through certain specialized cells, difierent from the diffusion of dehydro-ascorbic acid followed by intracellular reduction. There are no indications that dehydroascorbic acid is involved in the renal tubular absorption of ascorbic acid, and, contrary to earlier conclusions, it appears that the concentration of ascorbic acid into the aqueous humors of the eye occurs in the form of ascorbic acid itself. 

The ascorbic acid concentration in the eye is also relatively high. The main task of ascorbic acid is the protection of the sulfhydryl groups of several proteins and of the polyunsaturated fatty acids of the outer segments of color-sensitive eye pigments (Tso etal., 1984). 

The finding that the human lens and the intraocular fluids maintain a high ascorbic acid level has led investigators to propose that ascorbic acid plays a special role in the eye, perhaps to make up for the lack of antioxidant protection that comes normally with a blood supply or perhaps to meet the special needs of transparent tissues that may face unusual biochemical damage as a consequence of light exposure. It should be noted, however, that not all species concentrate ascorbic acid in... 

Ascorbic acid is photosensitive and unstable in aqueous solution at room temperature. During storage of foods, vitamin C is inactivated by oxygen. This process is accelerated by heat and the presence of catalysts. Ascorbic acid concentration in human organs is highest in adrenal and pituitary glands, eye lens, liver, spleen, and brain. Potatoes, citrus fruits, blade currants, sea buckthorns, acerola, rose hips, and red paprika peppers are among the most valuable vitamin C sources [1,2]. 

There are no approved pharmacologic treatments for atrophic AMD. The Age-Related Eye Disease Study showed that a supplement containing ascorbic acid 500 mg, vitamin E 400 IU, beta carotene 15 mg, zinc oxide 80 mg, and cupric oxide 2 mg reduced the rate of clinical progression of all types of AMD by 28% in patients with at least intermediate macular degeneration. No benefit was seen in patients with earlier stages of age-related maculopathy however, the duration of the study may have been insufficient to detect this benefit.25... 

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