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.
