The eyes are the first to go, the old adage says. And that means more than simply struggling to read the fine print as we grow older. Aging increases the risk of macular degeneration, the leading cause of vision loss in older Americans.

Age-related macular degeneration, or AMD, causes sight loss in the central field of vision, although peripheral vision remains intact. Central vision is what enables us to read, drive a car, recognize faces, and other activities that call for clear vision straight ahead.

As our eyes age, cells in the "macula" may begin to deteriorate. The macula is the small, central part of the retina that allows us to see fine detail clearly. Deterioration usually begins in just one eye, but may eventually spread to the other. Researchers don't yet know exactly what causes the deterioration, although research suggest that inadequate nutrition, smoking and sun exposure are significant risk factors. [See side bar].

The risk of AMD typically begins to escalate after age 50. Studies show about 14 percent of people aged 55 to 64 have some form of AMD; that grows to nearly 20 percent for those ages 65 to 75. But after age 75, AMD strikes nearly 40 percent of seniors.

An estimated 13 million Americans over age 40 currently have some signs of AMD, and at least 1.2 million of those are at risk of serious vision loss from the more advanced stages of the condition.

Wet v/s Dry

There are two distinct types of AMD, commonly called "wet" and "dry" AMD. Dry AMD is by far the most common, accounting for about 90 percent of cases. It occurs when small, yellowish deposits called "drusen" begin accumulating under the macula. These deposits break down the macula's light-sensing cells, causing distorted vision in that eye. While dry AMD usually does not cause a total loss of vision, its slow progression should be monitored carefully, since it could lead to the more severe "wet" form of AMD.

"Wet" AMD accounts for just 10 percent of AMD cases, but causes the most severe vision loss. An estimated 200,000 new cases of wet AMD are diagnosed annually. It occurs when tiny, abnormal blood vessels begin growing behind the retina, toward the macula. These fragile, abnormal blood vessels damage the macula as they leak blood and fluid, hence the term "wet." In contrast to the dry form's relatively gradual pace, wet AMD causes sudden and severe vision loss, often within weeks or months of the initial symptoms.

Symptoms

Vision loss from AMD is painless, so sufferers don't realize anything is wrong until they experience significant vision loss. The most common symptom of dry AMD is slightly blurred vision. You may also find you need more light for reading or other detailed tasks, or have difficulty recognizing faces at a distance.

As AMD progresses, you may notice a blurred spot in the center of your field of vision. However, because AMD often begins in just one eye, these symptoms may not be noticeable unless or until the condition spreads to both eyes.

With the wet form of AMD, an early symptom is that straight lines appear to be wavy. This distortion is caused by the newly formed blood vessels leaking fluid under the macula. A sudden blind spot, or rapid loss of central vision, is another classic symptom.

The most common diagnostic tool used to detect AMD is the Amsler grid, a checkerboard-like grid with a dot in the center. To someone with AMD, the grid's straight lines may appear wavy or distorted.

Research and Treatment

To date, there is no cure for AMD. However, researchers are making remarkable strides in treating wet AMD. Some patients have been treated with laser surgery to seal leaking blood vessels in their eyes. While the treatments do not reverse their vision damage, they do stop further vision loss. One drawback of the laser surgery is the scarring of retinal tissue that may occur. However, the FDA recently approved "photodynamic therapy," a treatment that uses a special drug and a non-thermal laser. This form of laser treatment seals the leaky blood vessels without scarring retinal tissue.

Studies are also underway on a new category of drugs to treat wet AMD. The drugs, which are injected directly into the eye, act on a protein that triggers the growth of abnormal blood vessels in the eye. While more studies are required, preliminary results appear to show that AMD-related vision loss can be stopped or even reversed with periodic injections of the drugs.

Dr. Steven Schwartz, chief of the retina division of UCLA's Jules Stein Eye Institute, has worked with several of these new drugs. He told the Associated Press, "For the first time in my career, I have actually been able to restore vision to patients who otherwise would never be able to get back their central vision."

Prevention is the most promising option to avoid AMD. First, limit your exposure to sunlight by wearing sunglasses and brimmed hats. Stop smoking, or better yet, don't start. Limit the amount of saturated fats and cholesterol in your diet.

Improving your diet will not only reduce your risk of AMD, but also slow any deterioration already present in your eyes. Increasing your intake of zinc can prevent cellular damage, as will eating foods rich in nutrients called "carotenoids." The best foods are green, leafy vegetables, such as kale, raw spinach, and collard greens. These simple guidelines can help your eyes stay healthy and bright for a lifetime.