What is Age-Related Macular Degeneration?
Age-related macular degeneration (AMD) is a retinal degenerative disease that causes a progressive loss of central vision. AMD is the most common cause of vision loss in individuals over 55. An estimated nine million people in the U.S. either have AMD or are at substantial risk of developing it.
What are the symptoms?
The macula is a small region in the center of the retina, which enables a person to see fine detail. Light sensing cells in the macula, known as photoreceptors, convert light from the visual field into electrical impulses and then transfer the impulses to the brain via the optic nerve. Central vision loss from AMD occurs when photoreceptor cells in the macula degenerate. People with AMD may first notice a blurring of central vision, especially during tasks such as reading or sewing. Also, straight lines may appear distorted or warped. As the disease progresses, blind spots may form within the central visual field. In most cases, if one eye has AMD, the other eye will develop the disease. The extent of central vision loss varies depending on the type of AMD — dry or wet.
What is dry AMD?
Dry AMD accounts for about 90 percent of all cases, and normally affects vision less than wet AMD. Dry AMD is sometimes called atrophic, nonexudative, or drusenoid macular degeneration. A characteristic of dry AMD is the accumulation of tiny protein and fat-containing “drusen” deposits in a thin layer of cells beneath the photoreceptors in the retina called Bruch’s membrane. The origin of drusen is unknown, but they may be from waste products of various cells and tissues of the retina. Drusen may interfere with the health of the macula, causing progressive degeneration of the photoreceptor cells. Drusen deposits can, however, be present without vision loss.
Reduction in central vision from dry AMD occurs gradually over many years. Vision may even remain stable between eye examinations. People with dry AMD do not usually experience a total loss of central vision but tasks that require finely focused vision may become more difficult.
Research suggests that medium- and large-sized drusen present a greater risk for the progression of dry AMD to wet AMD. Wet AMD causes more severe vision loss. Although no standard therapies currently exist to treat dry AMD, several clinical research trials are evaluating methods, including laser treatments, to reduce their size.
What is wet AMD?
Wet AMD accounts for about 10 percent of all cases of macular degeneration. Wet AMD is also called choroidal neovascularization (CNV), subretinal neovascularization, or exudative or disciform degeneration. In wet AMD, abnormal blood vessels grow beneath the macula. These vessels leak blood and fluid into the macula that damage photoreceptor cells. Wet AMD often progresses rapidly and can cause substantial loss of central vision.
What treatments are available for wet AMD?
Excellent progress is being made in understanding, predicting, and treating wet AMD. Scientists have discovered new causes of the disorder — including genetic and environmental factors — as well as possible risk indicators. Numerous pharmaceutical companies are developing wet AMD treatments. Researchers are also studying cell transplantation to preserve and/or restore vision.
In June 2006, the FDA approved a drug called Lucentis for the treatment of wet AMD. Results from a large, two-year study showed that Lucentis halted vision loss in more than 90 percent of individuals with the wet form of age-related macular degeneration (AMD). In addition, Lucentis restored vision in 33 percent of those study participants. FFB has funded dozens of research projects to better understand the mechanisms that lead to vision-robbing blood vessel growth in wet AMD, giving companies like Genentech, maker of Lucentis, clear targets for the development of AMD treatments.
Numerous clinical research trials are being conducted to evaluate other promising treatments for wet AMD.
If you have been diagnosed with wet AMD, visit www.FightBlindness.org for a list of treatments and clinical trials. FFB recommends that patients always discuss study participation with a health care provider before enrolling.
How does nutrition affect AMD?
The Age-Related Eye Disease Study (AREDS), conducted by the National Eye Institute, revealed that a dietary supplement containing a combination of vitamins and minerals could help reduce the risk of advanced wet AMD and vision loss in people who are at greatest risk.
The AREDS study found that high levels of antioxidants and zinc can reduce the risk of developing advanced AMD by about 25 percent. The specific daily amounts of antioxidants and zinc used by the study researchers were 500 milligrams of vitamin C; 400 International Units of vitamin E; 15 milligrams of beta-carotene (often labeled as equivalent to 25,000 International Units of vitamin A); 80 milligrams of zinc as zinc oxide; and two milligrams of copper as cupric oxide. Copper was added to the AREDS formulations containing zinc to prevent copper deficiency anemia, a condition associated with high levels of zinc intake. Please visit www.nei.nih.gov/amd for more information about the AREDS recommendations.
AMD may also be related to dietary fat, according to scientists studying people with early- and intermediate-stage disease. They found that study subjects who reported eating lower amounts of vegetable and animal fat were less likely to develop advanced AMD.
However, fish and nuts can slow the progress of AMD. Studies have revealed that eating fish — which is high in healthful omega-3 fatty acids — has a protective effect. Though nuts are also protective, researchers did not determine which nuts, or how much of them, should be consumed.
Carotenoids are also possible protectors against AMD. Researchers found that the more dietary lutein and zeaxanthin — two carotenoids found in green and colorful vegetables — you eat, the lower the likelihood you have of developing advanced AMD. These carotenoids are highly concentrated in the macula and may be protecting it from damage.
What are the risk factors?
The exact causes of both dry and wet AMD are not completely understood. However, genetics, diet, cigarette smoking, bright sunlight, cardiovascular disease, and hypertension are considered to be possible risk factors for AMD.
Is AMD an inherited disease?
Researchers are discovering that genetics appears to be a major factor in more than half of the cases of AMD. In March 2005, three independent research groups — including one funded by FFB — discovered a gene called Complement Factor H (CFH) that appears to be linked to at least 50 percent of all cases of AMD. Prior to this landmark discovery, FFB-funded researchers discovered other genes that appeared to be linked to AMD, though these genes were implicated in a smaller number of cases than CFH.
What is the Amsler grid?
Along with regular examinations by an eye doctor, people can evaluate their eyesight for possible symptoms of AMD using a simple home testing device known as the Amsler grid. The Amsler grid, consisting of parallel and perpendicular lines, looks much like a sheet of graph paper. By focusing on a marked spot in the middle of the grid, it is quite easy to detect blurred or distorted vision. While the Amsler Grid is not a substitute for an expert medical diagnosis, it does allow people to check their eyesight regularly for possible symptoms of AMD. To receive a free Amsler Grid, please call The Foundation Fighting Blindness.
Download a copy of the Amsler grid here.
What low-vision aids are available?
As central vision declines, people with AMD may benefit from low-vision aids like magnifying glasses and special lenses, screens that enlarge small print, text-to-speech and speech-to-text computer software programs, and any number of other specialized technologies. Low-vision experts can also help individuals adapt daily living skills. Low-vision specialists are available through ophthalmology centers and physician referrals.