Definition:
Macular degeneration is the progressive deterioration of a critical region of the retina called the macula. The macula is a 3-5 mm area in the retina that is responsible for central vision. This disorder leads to irreversible loss of central vision, although peripheral vision (side) is retained. In the early stages, vision may be gray, hazy, or distorted.
Cause:
The exact cause of macular degeneration is unknown, but the condition develops as the eye ages. The initial site of change is not in the light-sensitive cells of the macula, but in the retinal pigment epithelium (RPE), a single layer of cells located just behind the retina close to the back wall of your eye.
Your macula is an area about two-tenths of an inch in diameter at the center of your retina. This small part of your eye is responsible for clear vision, particularly in your direct line of sight. The macula consists of millions of densely packed light-sensitive cells called cones and rods. Cones and rods have two segments: An inner segment controls cell functions and produces proteins responsive to light, and an outer segment stores and makes use of these proteins.
As the eye ages, cells in the RPE begin to deteriorate (atrophy) and lose their pigment. As a consequence, the RPE becomes less efficient in removing outer segment waste. When that happens, the normally uniform reddish color of the macula (as seen with an ophthalmoscope) takes on a mottled appearance. Drusen (yellow, fat-like deposits), begin to appear under the cones and rods. As the drusen and mottled pigmentation continue to develop, your vision gradually deteriorates.
Characteristics:
Early stage: Several small drusen or a few medium-sized drusen are detected on the macula in one or both eyes. Generally, there’s no vision loss in the earliest stage.
Intermediate stage: Many medium-sized drusen or one or more large drusen are detected in one or both eyes. At this stage, your central vision may start to blur and you may need extra light for reading or doing detail work.
Advanced stage: Several large drusen, as well as extensive breakdown of light-sensitive cells in the macula, are detected. These features cause a well-defined spot of blurring in your central vision. The blurred area may become larger and more opaque over time.
Other characteristics may include the following:
- The need for increasingly bright light when reading or doing close work
- Increasing difficulty adapting to low light levels, such as when entering a dimly lit room
- Increasing blurriness of printed words
- A decrease in the intensity or brightness of colors
- Difficulty recognizing faces
- Gradual increase in the haziness of your overall vision
- Blurred or blind spot in the center of your visual field combine with a profound drop in the sharpness (acuity) of your central vision
Your vision may falter in one eye while the other eye remains fine for years. You may not notice any or much change because your good eye compensates for the weak one.
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