Macular Degeneration, leading cause of irreversible vision loss in the United States. This incurable condition attacks the central portion of the retina, the part of the eye that receives light patterns and transmits them to the brain. Macular degeneration progressively damages or destroys the part of vision used for reading and seeing fine details, while leaving the peripheral vision generally unaffected. People who have this disorder develop an area of vision loss that increases in diameter until they are unable to read or even see groups of two to three words at normal reading distance. Macular degeneration usually develops in both eyes, with one eye generally more affected than the other.
Although children can develop forms of macular degeneration such as Stargardt's disease, 99 percent of the cases occur in older people. Age-related macular degeneration (AMD) may affect as many as 15 million Americans over the age of 50, and one-fifth of people over 75 show at least some symptoms. This article focuses on AMD, the most common form of the disease.
AMD targets the most sensitive part of the retina, a cluster of cells called the macula located directly in its center. There are two forms of AMD, dry AMD and wet AMD. In the dry form, which accounts for about 90 percent of AMD cases, the macular cells slowly waste away, causing gradual vision loss. In most cases this vision loss progresses no further than permanent blurring of the central field of vision. In the wet form, abnormal growth of blood vessels beneath the macula causes bleeding and scarring. The result is severe damage to the macula that may completely destroy the patient’s central vision.
Ophthalmologists (medical doctors with special training in diagnosing and treating eye disorders) diagnose AMD with a thorough eye exam. Visible light imaging and infrared imaging, procedures that use cameralike devices that make it easier to see abnormal blood vessels, are useful in identifying wet AMD. An ophthalmologist injects a patient with fluorescent dye that travels to the eye through blood vessels. These imaging devices snap a series of 15 to 30 pictures over a five-to ten-minute period that track the progression of dye leakage from damaged blood vessels beneath the macula.
Although the cause of AMD is still unknown, people with light-colored eyes or a family history of macular degeneration are more vulnerable to AMD. Through research on the mutated gene that causes Stargardt’s disease, scientists have discovered what they believe to be a genetic trigger for the disease. Researchers have found that 16 percent of AMD patients have alterations in this same gene. Through this growing body of research, many scientists now consider heredity to be a significant risk factor in AMD. Some evidence suggests that smokers—particularly women—and people who spend a great deal of time outdoors without eyewear that offers protection from the sun’s ultraviolet rays may have a higher rate of AMD. Hypertension also appears to increase a person’s risk of developing AMD.
No treatment is available for most cases of macular degeneration. In a small percentage of early-stage cases of wet AMD, laser surgery can seal off the leaking blood vessels to slow vision loss, but the leaks frequently recur. Medical researchers are experimenting with cellular transplants designed to replace damaged macular cells with healthy cells. New drug treatments being studied include the use of thalidomide, which slows the growth of blood vessels.
Sparse scientific evidence exists to support controversial theories that nutrition and other lifestyle factors can reduce the risk or progress of macular degeneration. However, researchers believe that vitamins A, C, and E may slow the progression of the disease.
As scientists continue to search for ways to prevent this disease or halt its progression, patients must rely on special magnifying devices that help them read and watch television. High-powered eyeglasses, handheld or mounted magnifiers, telescopes, special illumination lamps, and extra-large type are all available to AMD patients, and new devices are under development. However, people who develop this disorder generally continue to live very independent lives and can still drive if their vision complies with vision regulations for day and evening driving.
