The EyeCare Connection

abstracts and answers to commonly asked questions

Nutr ition and the Eye

A number of nutrients, vitamins, minerals and amino acids, have been identified as important to the health of the eyes. Some of this is very new information and the issue has not been seriously addressed until recen tly.

Vitamin A and Beta Carotene

The need for vitamin A in the human vision system was identified almost 100 years ago. The biochemistry was clearly identified over fifty years ago, making vitamin A the first vitamin carefully examined; hence the reason why it is called A. Another related micro-nutrient, lutein, was discovered only months ago to be involved in the biochemistry of human vision!

Vitamin A starts out as beta-carotene, one of the family of plant chemicals known as carote noids, which also includes lutein, zeaxanthin and many others. When we consume vegetables containing beta carotene (dark green leafy types: spinach, kale, broccoli, cauliflower, cabbage, mustard and collard greens, as well as yellow-orange vegetables lik e carrots, cantaloupe, pumpkin, yellow squash, etc.), our bodies convert it to the various other forms of vitamin A called retinols. Some are used for skin and ligament repair, others for transporting enzymes and proteins, and some of it is used in the bi o-electrical process of vision. Beta-carotene is also one of the anti-oxidants which acts as a free-radical scavenger, helping to eliminate damaged cells within our bodies. There is evidence that this type of reaction is important in fighting certain canc ers and regulating the aging process.

Beta Carotene and the Eye

In the eye, beta-carotene is converted to the aldehyde form of vitamin A called retinaldehyde (or retinal for short). It becomes bound to a protein called opsin. This combined m olecule resides in the rods and cones, the photoreceptors of the retina which lines the back of the eye. When light strikes a photoreceptor, the retinaldehyde is converted from the -cis isomer form to the -trans form. This initiates a transient excitation of electrical energy which travels along the optic nerve. The electrical signal ultimately reaches the occipital cortex in the brain. The electrical information is processed into what we perceive as vision. Meanwhile, back at the photoreceptor, the split apart retinal-opsin is being rejoined and is ready for another photon of light to start the same process all over again!

As long as adequate amounts of beta-carotene are available in the retina, the photoreceptors are ready to fire off electrical in formation to the brain. People with vitamin A deficiency experience night blindness, or more commonly, poor adaptation to vision in low light situations. As the depletion of beta carotene increases, the quality of vision decreases. In extreme cases this r esults in blindness. Some people with night vision disorders also experience glare and haze under normal light levels because brightness information is not correctly processed as visual data.

A specific hereditary disease, retinitis pigmentosa causes similar symptoms in the early stages. Symptoms are related to retinal/opsin metabolic deficiency secondary to the primary degenerative pigmentary changes and reulting destruction of the photoreceptors. Treatment with massive doses of beta-carotene and vi tamin A acids has been shown to be effective in the early stages of the disease.

Other vitamins and micro-nutrients and the eye.

Evidence continues to mount supporting the theory that at least two other carotenoids, lutein and zeaxanthi n play a key role in age-related macular degeneration. ARMD is a condition which causes decreased visual acuity and blindness in older adults. Researchers at Harvard Medical School compared the dietary habits of patients diagnosed with ARMD to those with other eye pathologies but without ARMD. They found a direct correlation with increased consumption of carotenoids and decreased risk of ARMD.

Science has long accepted the role of beta carotene's related compounds in retinal neurological processin g, but recent studies indicate that some of the other carotenoids may have more profound effects on the aging eye. Vitamin C in its many forms (acids and mineral-bound acorbates) is also important in tissue repair and as an anti-oxidant. Along with the an tioxidant minerals: selenium, chromium and the polypeptide glutathione (and its related amino acid glutamine), these nutrients may provide the key to maintaining better visual function in later life.

Dietary concerns: How much is enough?

One issue that is not clearly understood is the relationship between consumption of these nutrients and the resulting bio-availability to the eye tissues. For some people, taking large quantities of these nutrients does not increase its presence in the eye. For others, just eating vegetables does the trick. Some researches feel that when the key to making these important micronutrients easily available to the eye is found, the aging process within the eye may be halted. This may eliminate presbyopia (n ear vision focusing problems in people over 40), cataracts (the clouding of the crystalline lens) and macula degeneration (loss of active photoreceptors in the retina).

For now, people with age-related macular degeneration are encouraged to take suppl ements consisting of:
5-15mg beta-carotene,
100-400 IU tocopherol vitamin E,
500-1000 mg vitamin C, 50% as calcium ascorbate,
15-45 mg zinc,
25-40mcg selenium
5-50mg l-glutathione

A number of products have recently become available with these micronutrients. They are marketed under the brand names: OcuVites, EyeVites, OcuCaps, I Caps Plus and others. If you consider purchasing them, first check your regular multi-vitamin/mineral supplement and your anti-oxidant supplement. You may already be getting appropriate levels of these important nutrients.

Lutein is just now becoming available in tablet form. Remember that the carotenoids and most minerals are readily available in vegetables! There is increasing scientific ev idence that obtaining these from natural dietary sources may provide better tissue absorption as you are getting other related compounds as well. That is how the effects of lutein were discovered! Also, eating whole foods is good for you. They provide a s ource of fiber and protein---the way nature intended for you to get your nourishment. Supplements are, however, appropriate for certain people who would not ordinarily be able to get adequate amounts of these important nutrients or who have metabolic defi ciencies which prevent their absorption.

Certain medications may interact with micro-nutrients. It is a good idea to consult with a physician or dietitian before beginning special nutritional therapies.