A Closer Look
By Lexie Verdon
Macular degeneration destroys a person's central field of vision and is the leading cause of blindness in Americans over the age of 60. Although the disease does not interfere with peripheral vision (which allows side views), it eventually takes away patients' ability to drive, read, see faces or perform other common daily activities. The National Eye Institute estimates that nearly 2 million of the 34 million Americans over the age of 65 suffer from macular degeneration.
The macula, which is damaged by the disease, is a section of light-sensitive cells about the size of a pinhead in the middle of the retina, next to the optic nerve.
There are two forms of the disease. About 90 percent of patients have the "dry" form in which the macula cells slowly deteriorate and vision is gradually lost. In the "wet" version, fragile blood vessels begin to grow beneath the macula and then leak, causing scarring that damages the macula. Vision loss in this form of the disease is often very quick.
The cause of the disease is unknown, but some research suggests it might be related to exposure to sunlight. It also strikes more whites than blacks and more women than men. And it is more common among smokers.
There are no preventive measures for macular degeneration and no way to restore vision after the damage has been done. There are also no treatments for the dry form of the disease. Patients with wet macular degeneration, however, are sometimes treated to help stop the bleeding. The Food and Drug Adminstration approved verteporfin (Visudyne) in April for this. The drug is injected into a patient's arm and then 20 minutes later, a laser light is activated into the patient's eye for about 90 seconds to seal the blood vessel. Prior to the use of verteporfin, physicians sometimes used lasers directly on the blood vessels, but that was effective in only a small number of patients and had the potential to cause further damage.
Research into the cause of macular degeneration is looking at environmental and genetic factors, including studies by scientists at the National Eye Institute on placing genes into the retina that might help protect it from macular degeneration. The institute, part of the National Institutes of Health, is also funding the Age-Related Eye Disease Study of 4,700 patients that officials hope will help explain how macular degeneration develops, what risk factors are involved, and perhaps provide treatment options. The study is expected to be completed in September, 2001, according to Emily Chew, a medical officer at the Division of Biometry and Epidemiology at the eye institute.
As part of the study, Chew said, researchers are looking at what effect dietary factors, especially vitamins C and E, beta-carotene and zinc, may have on macular degeneration, especially the dry form. Some people believe that these ingredients may be protective, but there is little evidence so far.
Lutein, another ingredient found in green, leafy vegetables, concentrates in the retina and lenses of the eyes, and some researchers have theorized that it might be help prevent macular damage. Studies on this are beginning, Chew said. The supplement was not common when the Age-Related Eye Disease Study began, and it was not included in that major research. "It will be many years before we know" if lutein supplements are helpful, Chew added. The eye institute in March advised caution, saying there is little scientific evidence that the over-the-counter supplements provide any protection for the eyes.
Drug companies also are continuing studies, Chew said, especially on the wet form. Among the areas of interest are new types of laser treatments and compounds that could be applied to help prevent blood vessel formation.
Advances in basic science, new technology and the increasing interest of an aging American population have helped propel studies of macular degeneration. "There's a lot of things happening [in the research]," Chew said. "It's more exciting than it's been for 10 years."