Forms of Macular Degeneration
Macular degeneration affects the retina. The retina is the paper-thin tissue lining the back of the eye. Light-sensitive cells in the retina are responsible for converting light into electrical impulses, which are then sent via the optic nerve to the brain for interpretation. In the very center of the retina is the macula. The macula contains the highest concentration of the light-sensitive cells, called cones, which are responsible for sharp, detailed, central vision that is used when driving and reading, for example. In macular degeneration, cells in the macular region begin to die, which results in blind spots and distorted vision.
There are two forms of macular degeneration: dry and wet. It is possible for a person to suffer from both forms, for it to affect one or both eyes, and for the disease to progress slowly or rapidly. Dry macular degeneration may advance and cause loss of vision without turning into the wet form of the disease. However, it is also possible for the early-stage dry form to change into the wet form of macular degeneration. Macular degeneration is the leading cause of vision loss in people over the age of 60.
Dry Macular Degeneration
The dry form is the most common type of macular degeneration. This form, in which the photosensitive cells of the macula slowly break down, is diagnosed in 85-90 percent of cases. Yellow deposits called drusen (extracellular waste products from metabolism) form and accumulate under the retina between the retinal pigmented epithelium (RPE) layer and the Bruch's membrane, 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 a blurring or spotty loss of clear, straight-ahead vision. This process does not cause any pain. In the early stages of the disease, the patient may notice slightly blurry vision. However, as more and more of the cells die, central vision worsens. In its most severe form, dry age-related macular degeneration can cause profound vision loss, severely affecting a person's quality of life. The dry form of macular degeneration has three stages:
- Early - patients have several small drusen or a few medium-sized drusen. There is no vision loss or symptoms at this stage.
- Intermediate - patients have many medium-sized drusen or one or more large drusen. Some people may need more light for tasks such as reading. A blurry spot may appear in the center of the visual field.
- Advanced - patients exhibit a large number of drusen deposits, and a breakdown of RPE, photoreceptor (light sensitive) cells, and supporting tissue in the retina. A large blurry spot occurs in the center of the visual field and can become larger and darker, eventually causing a complete loss of central vision.
Wet Macular Degeneration
Wet macular degeneration occurs when abnormal blood vessels grow behind the macula as RPE and photoreceptor cells die. 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. Straight-ahead vision can become distorted or lost entirely in a short period of time, sometimes within days or weeks. Wet macular degeneration accounts for approximately 10 percent of the cases of age-related macular degeneration, but it results in 90 percent of the cases of legal blindness. All wet macular degeneration is considered advanced.
The following BrightFocus publications provide more information:
Source: BrightFocus Foundation is grateful to Susan E. Yanni at Vanderbilt University for providing some of the above content.
Last Review: 10/04/12