The Why Files The Why Files --

Diet and blindness

POSTED 30 JUN 2005
Originally posted 1996.

AMD: The blinding disease
The macula is a delicate, light-sensitive tissue at the back of the eye. Site of the finest vision, it's the only region of the retina that can read or recognize faces. Photo of child with face blurred outWith age, a mysterious and hard-to-treat disease called age-related macular degeneration (AMD) can destroy the light receptors in the macula. As many as 1.7 million elderly Americans have AMD, according to Research to Prevent Blindness, and about 230,000 of them are legally blind.

When you have a serious case of age-related macular degeneration, your world may look like this. Photo: National Eye Institute, NIH

In serious cases, damage to the macula makes it impossible to read or recognize faces. With 100,000 to 200,000 light-sensitive nerve cells packed into each square millimeter, the macula is the only place with vision detailed enough for these critical tasks.

eye and quoteThe good news is that AMD almost never leads to complete blindness. The bad news is that lost vision cannot be restored (although laser surgery can slow the destruction in some cases).

Today's disease toll will likely intensify as the population continues to gray, and AMD is an intense focus of interest among eye doctors. A recent genetic insight may lead to ways to prevent or treat AMD. In the meantime, scientists are wondering if a diet that's low in fat or high in antioxidants could slow -- even prevent -- the irreversible damage.

An arterial question?
Let's start with fat. The retina is full of tiny blood vessels, and fat deposits in the arteries -- atherosclerosis -- help set the stage for high blood pressure, stroke and heart disease. The possible link between fat deposits and blindness got some support from a 1995 Dutch study, which found that a high rate of AMD among people who had atherosclerotic plaques in neck arteries (see "Age-Related Macular Degeneration Is..." in the bibliography.

diagram showing parts of eyeThe macula, site of the finest vision, is damaged or destroyed in AMD. Graphic: National Eye Institute, NIH

Also during the 1990s, Julie Mares, a professor of ophthalmology at the University of Wisconsin-Madison, participated in a study of diet and AMD (see "Relation Between..." in the bibliography). Mares and her colleagues related eye disease to diet among about 2,000 people in Beaver Dam, Wis. People who recalled eating a high-fat diet 10 years earlier had an 80 percent higher chance of having drusen -- globby fat deposits in the retina that are often an early sign of AMD. "This was the first study to find a link between fat in the diet and AMD," says Mares. "It raised the possibility that what we eat not only affects our chances of getting major, life-threatening illnesses, but also affects degenerative processes that can diminish our quality of life."

Could antioxidants fight AMD?