Vitamin A and Eye Health
Topic
How does vitamin A help maintain eye health in the cornea and convert light energy in the retina?
Major Statement
The presence of vitamin A in our diet is crucial for healthy eyes. Vitamin A is acquired by animal and plant sources of food and they are stored in the liver. The forms of vitamin A which are retinol, retinal, and retinoic acid are then transported to where they are needed. Retinal is transported to the eyes because its role in the body is to aid in vision. Some retinal is stored in the cornea and the rest is stored in the retina. In the cornea, retinal helps to maintain a clear, moist, and healthy cornea. In the retina, retinal is used to convert light energy into electric impulses that send messages to the brain. Without vitamin A, these functions cannot take place. As a result, vision problems will occur and eventually blindness can happen.
Forms of Vitamin A and Conversion of Vitamin A compounds
- Retinoids- Present in animal foods.
- Carotenoids- Present in plant foods and they are a precursor to vitamin A.
- Vitamin A stored in the liver as retinyl ester.
- Beta carotene can split and yield two molecules of vitamin A.
- These molecules include retinol and retinal.
- Retinol is the alcohol form of vitamin A and can be converted to retinal.
- Retinal is the aldehyde form of vitamin A and can be converted back to retinol or it can convert to retinoic acid.[unique_solution]
- Once retinal converts to retinoic acid and cannot be reversed.
- Retinal is transported from the liver to the eyes to aid in vision.
Role of Vitamin A in the retina
- Retina-The innermost membrane of the eye which is composed of several layers.
- Retinal helps convert light energy into nerve impulses.
- Retinal binds to opsin.
- Rhodopsin absorbs light.
- Retinal changes from cis to trans (electrical impulse).
- Sends info to optic nerve.
- Most retinal converts back and regenerates rhodopsin.
- Some oxidized to retinoic acid.
- Need for vitamin A foods to replenish losses to retinoic acid.
Role of Vitamin A in the cornea
- Cornea- Transparent membrane covering the outside of the eye.
- How the cornea absorbs vitamin A physiologically is still poorly understood.
- Epithelial maintenance
- Helps maintain crystal clear outer window.
- Prevents ulceration.
Vitamin A RDA, Deficiency, and Toxicity effects in the eye
Night blindness- Occurs because there is a lack of vitamin A in the retina. Eyes cannot transition from a bright environment to an area of low light.
Xeropthalmia (Full Blindness)
Xerosis-Inadequate mucus protection. (Dry and Hard Cornea)
Keratomalacia- Softening of cornea. (Irreversible)
Toxicity-change of vision/blurry vision.