What Is It?
Macular degeneration is a common cause of blindness and vision impairment among people older than 50 in the United States. This condition also is called age-related macular degeneration, or AMD. AMD damages the macula, a small part of the eye’s light-sensitive retina, the layer of tissue that sends vision signals to the brain. Because the macula is responsible for seeing sharp details directly in the center of the field of vision, damage caused by AMD can interfere with:
- The ability to see straight ahead, necessary for driving and viewing distances, such as when recognizing faces or watching television
- Fine, detailed vision, necessary for reading newsprint, sewing, working with crafts and making repairs
Macular degeneration is characterized by deposits known as drusen that develop in the macula, although the reason these deposits accumulate is not known. There are two ways to lose vision as a result of macular degeneration. Both occur during the early stage of the disorder.
- Dry (nonneovascular) AMD — About 90 percent of people who lose significant vision from AMD have this form of the illness. In dry AMD, the layer of cells under the retina stops functioning well, causing the light-sensing cells that overlie drusen to dysfunction or disappear over time, producing subtle and, later on, overt blank spots in an eye’s central vision.
- Wet (neovascular) AMD — In wet AMD, delicate new blood vessels begin to grow beneath the retina and can leak blood and fluid into the macula, causing scarring. Damage from the blood vessels, blood and fluid, and scar tissue can occur in a very short period of time, causing rapid loss of vision over days to weeks and continued loss of vision over time. This aspect of the disease is probably responsible for about 90 percent of the cases in which AMD has led to legal blindness.
Age is the most important risk factor for AMD, and the early stage (drusen) currently affects approximately 3.5 million to 10 million people in the United States older than 65. The exact number depends on how drusen is defined. Only a small percentage of people in their 50s have AMD. This percentage increases dramatically in people aged 75 and older. In that age group, about 10 percent have the advanced form of AMD that causes vision loss. AMD also may be slightly more common in women and in those with a family history of AMD. Caucasians may be at greater risk of developing the wet form. Cigarette smoking and risk factors for cardiovascular disease, such as high levels of blood cholesterol, may be additional risk factors for AMD.
Dry AMD sometimes does not cause any symptoms, or it can cause minimal loss of central vision clarity. In a small number of cases, it gradually advances to cause more significant blurring in the center of the field of vision. In these more advanced cases, faces and printed words become hard to recognize.
As a first symptom of wet AMD, straight lines or edges appear crooked and images become blurred. In some cases this is followed by a central blind spot, as in dry AMD. However, unlike in dry AMD, this vision loss usually occurs rapidly.
AMD generally does not affect side vision, even in advanced cases, so patients can function independently. Other people may not perceive any problem with the person who has AMD. People who have AMD appear to see normally but actually may have difficulty recognizing friends. This can lead to social difficulties. About 15 percent of people with vision loss from AMD experience visual hallucinations. That is, they see things, such as people and patterns that are not there.
Your doctor will ask questions about your health history and about any risk factors you might have for AMD. He or she then will perform a thorough eye examination, including tests of visual acuity and, in some cases, an Amsler grid test. An Amsler grid is a drawing of vertical and horizontal lines with a dot in the middle. You are asked to stare at the dot. If you have AMD, some of the lines will appear bent or distorted.
AMD is a lifelong illness. However, only a small fraction of people with early nonneovascular AMD do not develop advanced AMD with vision loss.
Although there is no proven way to prevent AMD, you can help to prevent AMD-related loss of vision by having regular eye examinations after age 40.
There is no effective treatment for dry AMD. Although some studies suggest that certain vitamins and minerals may help to prevent the development or progression of the disease, it is still too early to tell for sure if there is any benefit, and the chance of causing harm is unknown. Some patients with wet AMD can be treated with thermal laser surgery, which burns the retina to confine the damage. Another possible treatment is photodynamic therapy with verteporfin (Visudyne), which can damage the new blood vessels more selectively with less harm to the retina than might occur with thermal laser surgery. There are new types of medications being evaluated, as well as surgeries to remove the new blood vessels or to move the center of the macula to a healthier location.
Patients who have lost vision from AMD may be able to use low-vision aids to read. Low-vision aids include both optical devices (magnifying spectacles, handheld magnifiers, stand magnifiers, computer monitors with large type) and nonoptical devices (books and newspapers with large print, talking computers, high-contrast watch dials, enhanced lighting).
New research is being done to identify genes that may be responsible for AMD, to see how vitamins and minerals or laser may prevent or treat the disease, and to find new treatment regimens for wet AMD. Studies supported by the National Eye Institute, a part of the U.S. National Institutes of Health (NIH), also are investigating ways to operate on the retinal tissue in eyes affected by AMD.
When To Call A Professional
Call your doctor immediately whenever you notice any change in your vision, especially if this change has happened suddenly and interferes with your ability to read newsprint or to recognize people’s faces.
In general, everyone older than 40 with no eye problems should have a thorough eye examination every two years. If your doctor believes that you are at high risk of vision loss from AMD, you may wish to keep a copy of the Amsler grid at home for screening purposes.
Because dry AMD develops slowly, most people who have it continue to lead normal lives, especially if only one eye is significantly affected. Of patients with wet AMD, only a small fraction, perhaps 5 percent to 10 percent, may be candidates for thermal laser surgery, with an additional 20 percent to 30 percent for photodynamic therapy with verteporfin, depending on the extent, location and composition of the new blood vessels under the retina.
by David A. Scott, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.