There are two forms of AMD: dry and wet. It is possible for a person to suffer from both forms and for the disease to progress slowly or rapidly.
Dry macular degeneration is the most common type of AMD. This form, in which the photosensitive cells of the macula slowly break down, is diagnosed in 85 to 90 percent of cases. Yellow deposits called drusen (waste products from metabolism) form and accumulate under the retina, between the retinal pigmented epithelium (RPE) layer and the Bruch's membrane, the blood-retina barrier which supports the retina. Drusen are often found in the eyes of older people, but an increase in the size and number of these deposits is frequently the first sign of macular degeneration. Over time, drusen are associated with deterioration of the macula and the death of RPE and photoreceptor cells, resulting in blurring or a spotty loss of clear, straight-ahead vision.
Dry AMD may advance and cause loss of vision without turning into the wet form of the disease. It is also possible for early-stage dry AMD to change into the wet form of the disease.
Wet macular degeneration is usually preceded by the dry form of the disease. This wet form occurs when the Bruch's membrane begins to break down, usually near drusen deposits, and new blood vessels grow. This growth is called neovascularization. These vessels are very fragile and can leak fluid and blood, resulting in scarring of the macula and the potential for rapid, severe damage. The neovascularization disturbs the natural organization of the light-detecting photoreceptor cells and their associated RPE cells, eventually leading to their death. Straight-ahead vision can become distorted or be lost entirely in a short period of time, sometimes within days or weeks. The wet form accounts for approximately 10 percent of all cases of AMD, but it results in 90 percent of the cases of legal blindness. All wet AMD is considered advanced.
This content was last updated on: May 27, 2015
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