January 2, 2004.
By: Virgil Williams and Ron Eisenberg,
Sstaff physicians at Highland General Hospital in Oakland.
Q: What is macular degeneration?
A: The eye is made up of three major layers: an outer layer (sclera and cornea), middle layer (choroid, iris and ciliary body) and inner layer (retina).
The sclera is the tough white outer portion of the eyeball. Although not visible to us, its continuation to the front of the eye as the cornea is the structure we see as the "whites of the eyes.
The choroid lies just inside the sclera and continues to the front of the eyeball as two structures: (1) the iris, which surrounds the pupil and gives the characteristic color to the eye; and (2) the ciliary body, the muscle that focuses the lens.
The retina forms the innermost portion of the eyeball. It contains special cells (rods and cones) that are responsible for translating the light that enters our eye into an electrical impulse, which is then transmitted to the brain to form a visual image. The macula is a small area of the retina where there is absorption of light that has a short wavelength. The macula is the site of detailed fine vision (20/20 vision). Even only a few millimeters away, visual acuity drops off.
Macular degeneration is probably the most common cause of blindness in the elderly. Although the exact cause of this condition is unknown, arteriosclerosis, certain drugs and several gene defects can lead to similar problems. Macular degeneration is more common in women, Caucasians and those who smoke cigarettes.
Macular degeneration can be divided into two types: "dry" and "wet." In dry macular degeneration there is gradual, progressive loss of vision in both eyes. In contrast, in wet macular degeneration (90 percent of cases) the visual loss is rapid and more severe, first affecting one eye and then the other over a period of several years. Over time, the layers of the retina are separated by an accumulation of fluid that may lead to retinal detachment. The fluid may resolve with a variable amount of visual improvement.
But often there is resulting scar tissue that produces permanent visual loss. It should be noted that the visual loss only affects the central portion of the eye; peripheral vision is maintained.
Laser treatment may benefit some patients with "wet" macular degeneration by reducing or delaying progression of the disease. Unfortunately, there is no specific treatment for "dry" macular degeneration. Visual aids may benefit individuals affected with either type.
Virgil Williams and Ron Eisenberg are staff physicians at Highland General Hospital in Oakland.
©1999-2003 by MediaNews Group, Inc. and ANG Newspapers
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