Age-related macular degeneration (AMD) is the leading cause of legal blindness in the United States. The disease generally occurs in people over age 50 and the risk of vision loss increases with advancing age. Nearly one-third of people over the age of 75 have some eye changes due to AMD, and about 7 percent have the advanced form in which vision is affected. Approximately 1.8 million people in the United States have vision impairment from AMD, with more than seven million additional individuals at substantial risk for vision loss.
In people who develop AMD, central vision becomes disturbed. Common symptoms include a blurred or blank spot, distortion of objects or simply blurred vision.
AMD damages the light-sensitive layer in the back of the eye called the retina. The tiny central region of the retina is known as the macula. No larger than a pencil point, it is responsible for the sharp straight-ahead vision that allows us to read, drive, and distinguish faces.
In the early stage of age-related macular degeneration, yellow fat-containing deposits called drusen form in the macula. These deposits are quite common in the normal population over 40 years of age, but become larger and more numerous in those eyes that will develop AMD.
Two forms of age-related macular degeneration are generally recognized:
In the most common form of macular degeneration, the retina, its pigmented cells, and the adjacent blood vessel layer gradually become damaged over months and years. Most people with dry AMD have little or no vision loss. However, in its advanced form, known as “geographic atrophy,” slowly progressive vision impairment can occur.
Vision loss is more rapid (usually over days, weeks, or months) and severe, and is characterized by newly formed blood vessels growing under the retina. These unwanted vessels, termed “choroidal neovascularization,” leak, bleed, form scar tissue, and commonly lead to severe loss of central vision.
While AMD can cause loss of central vision and legal blindness, it does not cause total vision loss, even in advanced cases. People with AMD may lose the ability to read, drive and distinguish fine details, but they will retain their ability to perform most other activities and maintain their independence. Magnifiers and other special optical devices can help individuals with advanced AMD maximize their visual potential.
The cause of AMD is not yet clearly understood. A combination of genetic and environmental factors contributes to the disease. Variations of several genes associated with the development of AMD have been discovered, and personal and environmental factors like age, cigarette smoking, and nutrition appear to play a role. Certain antioxidants and zinc supplements are beneficial in specific stages of the disease.