Overview
Macular degeneration is the progressive deterioration of the macula, the small central area of the retina. The central macula, the fovea, is responsible for fine-detail vision and has the highest concentration of color receptors (i.e., cone cells).
The most common type of macular degeneration is called age-related macular degeneration (AMD), because it usually develops in patients over the age of 55. A rare form of macular generation, called juvenile macular degeneration (JMD), occurs in younger patients, including infants and children. JMD is an inherited disorder caused by mutated genes.
Incidence and Prevalence
Macular degeneration is diagnosed every 3 minutes in the United States. It occurs in about 10% of people over the age of 50, and about 33% of people over 75. AMD is most common in Caucasians of European decent and is more prevalent in women. Every year 1.2 million people with macular degeneration lose part of their central vision, and 200,000 suffer complete loss of central vision in one or both eyes.
Age-Related Macular Degeneration
Because AMD primarily affects central vision, patients usually do not lose vision completely, even at very advanced stages. This disorder can make it difficult to read, drive, work at a computer, and perform other activities that require clear central vision. AMD occurs in two forms, dry and wet.
Dry (atrophic)—This form of AMD accounts for 85–90% of all cases. The earliest sign of AMD is the development of waste material deposits, called drusen, that appear as tiny orange or yellow dots among the retinal pigment epithelial (RPE) cells. These deposits are initially tiny and few in number, but they may grow larger and become more numerous. The presence of drusen does not necessarily signal vision loss, and many people with drusen continue to have good vision for decades. As dry AMD progresses, mild to moderate visual acuity loss may occur.
Over time, patches of RPE cells may die, leaving "bare" spots. This is called geographic atrophy and results in vision loss in the affected areas of the retina. If these patches become large and involve the fovea, visual acuity can deteriorate to the point of legal blindness. Geographic atrophy is a severe form of dry macular degeneration.
Wet (vascular)—The wet form accounts for approximately 10% of cases but is responsible for the vast majority of severe, AMD-related vision loss. Vascular macular degeneration begins as the dry form and progresses to the wet form when abnormal blood vessels develop. In wet AMD, abnormal blood vessel growth is triggered by mechanisms that are not completely understood. The new vessels are very delicate, break easily, and bleed and leak fluid into surrounding tissue. This can damage the macula very quickly and may cause central vision loss in a short time. The risk for progression from dry to wet AMD is approximately 14-87% over 5 years and depends on many factors.
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Original Date of Publication: 02 Feb 2002
Reviewed by: Stanley J. Swierzewski, III, M.D.
Last Reviewed: 04 Dec 2007
Macular Degeneration, Overview, Types reprinted with permission from vision.healthcommunities.com
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