Research Focuses on Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in older populations in the US, so it’s no wonder that researchers nationwide are trying to zero in on its causes and find new treatments.

At the Froedtert & Medical College Eye Institute, scientists and ophthalmologists are involved in studies and clinical trials that seek to find cures for macular degeneration, or at least to limit the vision-impairing impact of this progressive disease.

“Named after the Latin word for ‘spot’, the macula is the small but critical patch of light-sensing cells in the retina,” says the Eye Institute. “The macula provides our acute central vision. When the macula degenerates, central vision diminishes, even to the extent that some patients are unable to read, drive a car, recognize faces or colors or see much of anything at all.

Each year in the United States, more than 200,000 people develop macular degeneration. It is an epidemic that has researchers around the globe scratching their heads, baffled by their inability to find either cause or cure.”

“Wet” and “Dry” Degeneration
The National Eye Institute notes that age-related macular degeneration is associated with aging, fair skin, light iris color, hypertension, smoking, arteriosclerosis, prolonged exposure to sunlight, and family history of AMD. Most victims experience the effects of AMD after age 55.

The disease has two types, a "dry" form and a "wet" form, based on the absence (dry) or the presence (wet) of abnormal growth of blood vessels under the retina. More than 80% of people with AMD have the dry form. While there is no proven treatment for the dry type, the loss of vision tends to be milder and the disease progression is rather slow.

The wet form afflicts about 15% of AMD patients. For these people, the growth of abnormal blood vessels under the retina can cause leakage, bleeding and scarring, resulting in more rapid and severe vision loss. About 80% of severe vision loss is due to the wet form, compared to 20% due to the dry form.

A number of new clinical trials being performed at the Froedtert & Medical College Eye Institute have to do with injecting a substance called “anti veg-f“ (vascular endothelial growth factors) into the vitreous of the eye to prevent the proliferate growth of retinal blood vessels that cause the "wet" form of macular degeneration.

Melanin May be Key to Maintaining “Young Eyes”
While researchers may still be unsure as to its causes, they’re less baffled about AMD than they were even a few years ago as the potential treatment roles of melanin, anti-oxidants in general, and growth factors are becoming more clearly defined.

In 2002, Janice Burke, PhD, the Medical College of Wisconsin’s Marjorie and Joseph Heil Professor of Ophthalmology, began a five-year study of the role melanin may play in the development of macular degeneration. Eyes, skin and hair get their color from the pigment melanin, which also helps protect tissue from damage caused by exposure to sunlight.

Dr. Burke believes that melanin serves another important protective role in the eye by functioning as an antioxidant. “I study retinal pigment epithelial cells (RPE), which support photoreceptor cells (those that let you see),” said Dr. Burke, whose study is funded by a $1.125 million grant from the National Eye Institute.

“RPE cells contain melanin,” said Dr. Burke, “which we believe may act as an antioxidant in young eyes, protecting cells from oxidative damage. As we age, however, melanin may change to a pro-oxidant. It then no longer protects, but may actually cause damage.

“Determining what protects and what damages RPE cells is an important area of investigation because damage to RPE cells can ultimately lead to photoreceptor degeneration and blindness,” said Dr. Burke.

General interest in dietary antioxidant vitamins has been growing over the past few decades with the recognition that oxidative processes can damage cell membranes and DNA.

In collaboration with the Medical College of Wisconsin’s Biophysics Research Institute, Dr. Burke hopes to discover an intervention, dietary or otherwise, to help maintain the function of natural antioxidants during the aging process.

Nutrients Reduce the Risk of Vision Loss
Results released in 2002 from the National Eye Institute’s Age-Related Eye Disease Study showed that high levels of antioxidants and zinc significantly reduce the risk of advanced age-related macular degeneration and its associated vision loss.

The study found that people at high risk of developing advanced stages of AMD lowered their risk by about 25% when treated with a high-dose combination of vitamin C, vitamin E, beta-carotene and zinc. In the same high-risk group – which includes people with intermediate AMD, or advanced AMD in one eye but not the other eye – these nutrients reduced the risk of vision loss caused by advanced AMD by about 19%. For those study participants who had either no AMD or early AMD, the nutrients did not provide an apparent benefit.

The Froedtert & Medical College Eye Institute stresses that the nutrients are not a cure for AMD, nor will they restore vision already lost from the disease. They will, however, play a key role in helping people at high risk for developing advanced AMD keep their vision.

Surgical and laser treatment options are also used to treat AMD and continue to be refined to minimize negative effects on the macula and other parts of the eye.

The Age-Related Eye Disease Study involved 4,757 participants, 55-80 years of age, in 11 clinical centers nationwide.

Dan Ullrich
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.