POSTED OCT 3, 2002
Mouse over the image to see an approximation of what an exudative (wet) AMD sufferer might see when trying to focus on the newscaster's face.
You get old, and it may get you. "It" is age-related macular degeneration (AMD), a strange disease that's the leading cause of blindness among those 60 and older.
Macular
degeneration destroys the macula, the site of fine-grained central vision.
Patients with a bad case of AMD cannot recognize faces. They cannot
read the Why Files or drive.
Signs of this common and essentially untreatable disease appear among 30 percent of Americans over 70 -- about 14 million people. Up to 5 percent of these people will get the more severe, "wet, or exudative" version of AMD - which causes blindness in the center of vision.
Both forms of the disease will only grow more prevalent as the population grays. By 2025, AMD could be blinding 900,000 to 3 million Americans -- unless someone can unravel the cause and learn to prevent or treat it.
Right now, only a charlatan can claim to fully understand AMD. Despite considerable progress in recent years, the views of
cause, prevention or treatment are rather primitive. About the only "medicine"
for the early stage is a vitamin cocktail that seem associated with reduced
symptoms. Recently, a large multi-centered clinical trial
sponsored by the National Eye Institute did show that vitamins can reduce
the risk of severe vision loss by 25 percent in some patients with AMD. They are,
in other words, slightly better than a shot in the dark.
Treatment for the blinding "wet" variety of AMD -- where new blood vessels grow under the retina and leak fluid that kills light-sensitive cells -- has been, until recently, even less promising.
AMD is a mysterious disease, and even its name is misleading, since the cell death can spread beyond the macula at the center of the retina. New studies indicate that the rods, which see in black-and-white toward the periphery, start to decline early in the disease, damaging night vision.
The good news is that in the past few years, researchers have uncovered major new clues that could, with luck, lead to real understanding and real treatments for AMD. The Why Files explored the subject at a September conference sponsored by the non-profit Research to Prevent Blindness.
U.S.
National Library of Medicine.
A glance at the basics
AMD comes in two varieties:
Dry AMD starts with the appearance of drusen (fat deposits) under the retina. Cell deaths occur in the retinal pigment epithelium, an essential support structure for the retina, and in the rods and cones, which detect light. While dry AMD may only blur the vision, each year a few percent of cases convert to the dreaded "wet" form.
We've described a general picture of damage inside the eye, but today, prevention and treatment are hobbled by a wobbly understanding of what's really taking place. Beyond vitamin cocktails, the best an ophthalmologist can recommend for dry AMD is watching and waiting. If your vision seems to be slipping away, that's less than satisfactory.
The options for wet AMD - which may destroy vision in just weeks -- are even less comforting. Doctors can zap the new blood vessels with a hot laser, hoping to cook them and block the flow of blood. A new and improved option is "photo-dynamic therapy," in which a laser activates a light-sensitive dye in the blood, causing a toxic reaction that closes new blood vessels.
Needed - some understanding
Most eye doctors would agree that treatments for wet
AMD are desperate measures. Hot lasers burn blind spots in the retina,
causing black holes in the critical central vision. Hot lasers and photo-dynamic
therapy may only temporarily close the actual leak. And in a few weeks, a regrowth
of blood vessels may require more treatments, more cost, and, worst of
all, the possibility of more retinal damage.
"For the majority of patients, what we have right now is better than nothing," says AMD researcher Karl Csaky of the National Eye Institute, "but it's not much better."
After years of floundering in the dark, however, scientists
have begun using new scientific techniques to gain a sharper picture of
the disease process. The new theories about why and where the blood vessel
form could lead to major advances in treatment, and perhaps more important,
in preventing this blinding disease.
"If you look at what's in clinical trials, and in phase I [early-stage] trials, and in the lab, there is a lot coming down the road" in potential AMD treatments, says Csaky.
For example, a study announced as we go to press indicates that the drug RhuFab V2 restored significant vision to wet AMD patients, in a 64-patient trial (see "New Drugs Show..." in the bibliography). After the three-month trial, the average patient could see two lines further down on a vision test, while the untreated controls lost one line. The genetically engineered drug, made by Genentech, must pass further tests before approval.
A major fringe benefit of improved treatment for AMD would be a better understanding of diabetic retinopathy, the leading cause of blindness among the middle-aged. Although it's caused by the excess blood sugar of diabetes, this blinding illness also features the growth of leaky blood vessels.
But let's return to our starting point. With any luck, before you get old, research doctors will have painted a better picture of why macular degeneration starts, and how it can be stopped. This is not something most retina specialists would have predicted 10 or even five years ago.
Inflammatory words? What's the immune system got to do with AMD?
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Terry Devitt, editor; Sarah Goforth, project assistant; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive
©2002, University of Wisconsin, Board of Regents.