Age-Related Macular Degeneration

What is age-related macular degeneration?

Age-related macular degeneration (AMD) is a progressive disorder of the tiny central part of the retina, called the macula (See Anatomy of the Eye), that gradually destroys central vision, making reading or driving difficult or impossible. Although some peripheral vision remains, a person with macular degeneration has increasing difficulty in reading, watching television, or even recognizing friends.

Because it is an age-related disease, the incidence of AMD is growing as the mature population increases. An estimated 400,000 Americans develop a serious form of the disease every year.

What causes AMD? What are the risk factors?

Although the macula occupies only 2 percent of the retina, it contains about 25 percent of the light-sensing cone cells, which are specialized for daylight vision. AMD occurs when this central part of the retina and the layer of cells underneath it, which is the retinal pigment epithelium, begin to deteriorate, for reasons that are not clear. Genetics may play a role in some cases, because the disease can run in families.

There are two forms of AMD, dry and wet. The "dry" form, which accounts for 85 percent to 90 percent of all cases, does not cause blindness but does cause a loss of central vision that can produce grayness, haziness, or a blind spot in the central area of vision. In the dry form of the disease, tiny white deposits called drusen accumulate in the retina, and there is a thinning of macular tissue. The cause is unknown, although lifetime exposure to sunlight and smoking may increase the risk. In "wet" AMD cases, which account for 10 percent to 15 percent of all cases, abnormal blood vessels grow under the retina, scarring or destroying retinal tissue and often causing sudden blindness. The wet form causes most AMD-related blindness.

What are the symptoms?

The symptoms of AMD are blurred vision, loss of color perception, a dark or empty spot in the center of the field of vision, and seeing crooked lines that are really straight. The condition can be diagnosed in several ways: with an ophthalmoscope, a slit lamp lens, an Amsler Grid test, photographing the back of the eye, fluorescein angiography, and/or macular pigment density testing. People over the age of 65 are advised to see an ophthalmologist once a year for a complete eye examination, and any sudden change in vision should be reported to an ophthalmologist. If dry AMD is detected, close follow-up is recommended to monitor for indications of the wet form.

What treatments are recommended for AMD?

Several techniques are used to treat wet AMD:

Laser photocoagulation surgery uses a powerful beam of light to attack the abnormal blood vessels. Early diagnosis is important because this treatment is effective only in the early stages of the disease. The surgery often does not stop the progression of abnormal blood vessels, so repeat treatments are needed. The surgery can destroy some healthy tissue, causing some loss of vision.
Still somewhat experimental, photodynamic therapy uses verteporfin (brand name Visudyne), a photosensitive dye that goes to the abnormal blood vessels. Light from a low-powered laser triggers a chemical reaction that destroys the blood vessels. Photodynamic therapy generates less heat than photocoagulation, and thus causes less damage to healthy tissue.
Another treatment involves surgery to detach the retina and rotate it, so that the macula is no longer in the region of abnormal blood vessel growth.
Surgery can also be used to remove the abnormal blood vessels.
Thalidomide, notorious for causing birth defects, is being tried as a treatment because it blocks blood vessel development.

What can be done to decrease the likelihood of developing AMD?

There is evidence that chemicals called antioxidants, which include vitamins C and E, can protect the macula. So can carotenoids, which include beta-carotene, and the mineral selenium. Field trials to determine whether vitamin therapy can be effective against macular degeneration have begun. The National Institutes of Health has started a study to determine whether estrogen replacement after the menopause can prevent or slow the progression of AMD.