Wednesday, September 28, 2011

Diet’s Effects on Eyes

By Dr. Terry Tucker 
Tucker Vision Center 

We all grew up knowing that carrots are good for our eyes.  Carrots, among other deeply colored vegetables and fruits, are rich in sources of beta carotene, the plant-based building block for vitamin A, which is required to form rhodopsin, the visual pigment that allows people to see in the dark.

Medical science is now learning a lot more about the influence of diet on vision.  Not only carrots and vitamin A, but other potentially important nutrients including  two related carotenoids, lutein and zeaxanthin; vitamins C and E; and docosahexanoic acid, or DHA, found primarily in fish oil.
The evidence for the effects of these nutrients on visual development and prevention of sight-robbing eye disease is not conclusive, strong hints from recent research may justify dietary improvements.  Even if some of these changes turn out to be only minimally helpful to the eyes, they have other health benefits.

DHA evidence from premature babies suggests a role in visual development.  Infants born eight or more weeks early arrive fat-free, lacking both a reserve and stored energy and the fatty acid DHA, which is essential for normal visual (and brain) development.
DHA normally accounts for more than one-third of fatty acids in the retina of the eye as well as in the brain’s gray matter.  The retina develops rapidly in the final months of pregnancy and in the first six months of infancy.

Fetuses begin to acquire large amounts of DHA only in the last three months of pregnancy.  Unless a premature baby is fed breast milk (which naturally contains DHA) or formula fortified with DHA, the child’s visual acuity is likely to be compromised.  Studies indicate premature babies fed formula fortified with fish oil developed visual acuity similar to that of term infants and preterm infants fed breast. From these studies it appears that fish oil (omega 3) is a vital part of the diet and could help to keep the eye healthy.

Two common sight-robbing disorders, cataracts and age-related macular degeneration, have been linked in several studies to dietary deficits of nutrients.  Maintaining an adequate intake of these nutrients may not prevent the eye disorders, but it can’t hurt.

Age-related eye disorders:  Nearly everyone who lives long enough develops cataracts, a clouding of the eye’s lens that reduces the ability to see clearly.  The main cause is believed to be oxidative damage by so-called free radicals caused by exposure to sunlight.  Thus, antioxidants, which act as scavengers for free radicals, are believed to be protective.

One antioxidant nutrient, vitamin E, occurs naturally in the lens, and in animal studies, supplements of vitamin E have slowed the rate at which cataracts form.  In several studies in people, higher rates of cataracts occurred among those whose intake of vitamin E was low.

Vitamin C, another antioxidant found in the lens, has also prevented cataracts in animals.
The strongest evidence for eye benefits from dietary ingredients involves the carotenoids lutein an zeaxanthin, found in large amounts in the lens and retina.  Lutein may help prevent cataracts through its ability to absorb damaging ultraviolet light, blocking oxidative damage. 
Perhaps even more important, these carotenoids may prevent and even partly reverse otherwise untreatable damage to the macula, the area in the center of the retina that allows people to see whatever is in the center of their visual fields.  

Lutein and zeaxanthin are most prominent in dark green leafy vegetables.  Some experts recommend eating at least half a cup of one of those nutrients.

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