There’s more to good vision than meets the eye. Our eyes are extremely complex in their structure and function.
Nutrition's Role for Eye Health
Age-related macular degeneration (AMD) was identified as a disease of the retina, there have been ongoing debates among ophthalmologists, optometrists and researchers regarding the role of nutrition in protecting against the disease and possibly slowing its progress. The Age-Related Eye Disease Study (AREDS) results support vitamin supplementation for those who already have AMD.
One aspect of AMD that makes credible scientific studies difficult is the fact that the disease, particularly the "dry" form, progresses slowly over a long period of time - years or even decades. When it is finally identified, the nutritional history of patients is indeed "history." How much can they remember about their diet 20 or 30 years earlier? How reliable is their memory? Researchers could track the diet of a certain segment of the general population for decades on the chance that a small percentage of this group will develop AMD. But this would be prohibitively expensive and would impose unwarranted burdens on the participants.
Despite this difficulty, a body of information on long-term eating habits has been accumulating, some of it coming from research not originally undertaken for AMD. For example, there are a number of long-term studies that have been tracking the health, lifestyles, and habits of tens of thousands of people in relation to the incidence of cardiovascular disease. When AMD shows up in these studies, the individual's dietary and nutritional habits over time may shed light on the origins and development of the disease in these specific cases. The AREDS study began 10 years ago and there is a similar one underway for women, looking at carotenoid intake.
Recent research, focused on changes in the retina, suggests that the progress of AMD could be slowed if patients were treated with appropriate dietary supplements. Since moderate intake of vitamins is not harmful, many physicians offer patients the option of taking them in case they may prove helpful. Others prescribe particular regimens to their patients and feel strongly about their potential.
The Role of Antioxidants
Both patients and physicians are hoping that antioxidant vitamins and minerals will prove to be useful in the prevention and treatment of AMD. Basic research shows that metabolic activities within cells can produce highly reactive species of oxygen known as free radicals or unstable oxygen that the body needs to fight infections and stop inflammation. These free radicals also react with and damage "innocent bystander molecules," such as DNA, proteins, lipids, and carbohydrates. The retina is prone to continuous oxidative damage because of the high level of polyunsaturated fatty acids (lipids) in the photoreceptors, cells which lie in the outer segment membranes. To counteract the oxidative process, our bodies produce free radical scavengers by converting the free radicals into stable compounds before they interact with cell membranes to produce damage. When the amount of free radicals in the body exceeds the capacity of the scavengers, aging and injurious processes begin. This degeneration is called oxidative stress.
Antioxidants that may protect against AMD are:
vitamins E, C, and A
phytochemicals-carotenoids and xanthophylls; especially lutein and zeaxanthin.
assorted minerals and vitamins including selenium, zinc, magnesium, glutathione,Vitamin B6 and folic acid
enzymes involved in the oxidative process.
Lutein and Zeaxanthin for Eye Health
The substances you are most likely to hear touted as protection from AMD are lutein and zeaxanthin. There are two carotenoid pigments: carotenes, which are derived from tuberous vegetables like carrots, sweet potatoes, yams, and winter squash, and xanthophylls, which come from plant leaves. Lutein, a xanthophyll, is found in marigold flowers, spinach, kale, collard and mustard greens, egg yolks, and certain hormones. Plants produce many types of xanthophylls, but lutein is the only one that accumulates in the eye. Closely related to lutein, zeaxanthin seems to produce thicker, more protective macular pigment. In a 15-week study, people given a diet high in fruits and vegetables which are rich in lutein and zeaxanthin demonstrated increased plasma levels of these nutrients and increased density of their macular pigments. The control group, given a diet low in these carotenoids, did not show these increases.
Lutein accumulates in the very center of the retina, forming the macula lutea. It helps filter out the blue spectrum of sunlight, which can increase drusen. Everyone has varying amounts of lutein. Zeaxanthin in the diet is present with lutein. It may end up being even more important and research is ongoing.
According to a recent report, it is not genetic factors, but the dietary consumption and absorption of lutein that determines the density of protective yellow macular pigment at the back of the eyes. Yellow lutein, by virtue of its location in front of the central photoreceptors, protects the rods, cones, and retinal pigment epithelial layer from oxidative damage caused by unfiltered sunlight. The density of brown melanin in the iris and retina is genetically-determined and may be a factor in protecting against macular disease. Melanin appears to be a secondary defense against oxidative damage caused by blue light.
Some experts believe that lutein acts like a pair of sunglasses. It protects the macula from the oxidative effects of ultraviolet light. The more unfiltered sunlight that reaches your retina, the more lutein is used up defending your delicate retinal tissues. This is why wearing ultraviolet light protection is so important. It may help to preserve the lutein in your eye. It is important to remember that contact lenses and eyeglasses, unless specifically marked, do not filter out the potentially harmful ultraviolet rays of sunlight. Nor do all sunglasses offer the same kind of protection. Be mindful of this when you buy your next pair and ask an optician to verify the UV protection of your glasses.
A reasonable approach would be to increase the level of lutein in your eyes and to protect them from ultraviolet light at the same time. This may conserve the lutein and keep it available to fight other oxidative stress.
Lifestyle recommendation for healthy eye
consume a nutritionally balanced diet
curtail consumption of alcoholic beverages
engage in regular cardiovascular exercise
protect their eyes from blue/ultraviolet light with sunglasses