The retina is the part of the eye that is sensitive to light. It is therefore very important to maintain its health in order to have good vision. Several studies, including those reviewed by the National Eye Institute, have found that large doses of some vitamins can slow the degeneration of eyesight and also heal already present damage.
Vitamin A Research
Vitamin A is an antioxidant vitamin which has proven success in helping patients with retinitis pigmentosa, i.e. progressive degeneration of the retina. According to the National Eye Institute, a 1993 clinical trial showed that participants receiving 15,000 international units of Vitamin A (a megadose) had slower retinal degeneration than other retinitis pigmentosa participants who didn't receive Vitamin A. Vitamin A is good for people at risk for or experiencing retinitis pigmentosa and for general retina health.
Night Vision
According to the Linus Pauling Institute, vitamin A is instrumental in maintaining night vision. Vitamin A, in its retinol form, moves to the retina where it is formed into retinyl ester. It is then stored until it is needed in the rod cell of the retina to form rhodopsin. Rhodopsin is important for detecting tiny amounts of light and consequently is instrumental in night vision. People who have night blindness generally have little retinol (vitamin A) which allows the eyes to take in light at night.
Vitamin A Deficiency
According to the Linus Pauling Institute, because vitamin A is necessary for detecting light in the dark, an immediate sign of a deficiency is usually impaired night vision. A deficiency may also manifest itself in Bitot's spots (keratin deposits in the tear producing area of the eye). Dry eye becomes a problem with vitamin A deficiency as well. Dry eye if untreated may cause scarring, corneal ulcers and blindness.
Antioxidants and Zinc
Age-related macular degeneration (AMD) damages the retina. According to the National Eye Institute, the risks associated with AMD reduce with megadoses of antioxidants and zinc. Risk decreased by 25 percent in an Archives of Ophthalmology clinical trial where participants received treatment "with a high-dose combination of vitamin C, vitamin E, beta-carotene and zinc." Participants with vision loss in only one eye decreased their risk of vision loss in the other by 19 percent with the antioxidants and zinc combination. This treatment proved to be great for those with AMD, but those without it or in its early stages saw no benefit.
Considerations
The utilization of vitamin A (retinol) can vary based on your levels of zinc. If you are zinc deficient, vitamin A may not function as well and your retina may be affected. According to the Linus Pauling Institute, this occurs because a zinc deficiency equals decreased production of the protein responsible for transporting vitamin A to the retina. Also, the enzyme responsible for freeing retinol from the liver decreases in activity, which means that stored retinol is trapped.
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