What are the Symptoms?
As noted above, the symptoms are distortion of vision (typically straight lines or objects appear wavy or crooked), a dark spot, and blurring of vision. Later, there is a loss of reading vision. This can prevent one from reading, seeing well enough to drive, and/or loss of the ability to recognize the features on a friend’s face. Preservation of peripheral vision permits patients to see large objects and to retain ambulatory vision.
How is it Diagnosed?
AMD is diagnosed by an eye care professional, either an ophthalmologist or optometrist. The diagnosis is based on the characteristic symptoms and signs as noted above. Very important to the diagnosis is actually viewing the changes in the retina by examination with a special instrument, an ophthalmoscope. Other tests are sometimes performed. These include Amsler grid testing and a fluorescein angiogram. In a fluorescein angiographic study, a special dye is injected into a vein in the arm, and photographs are taken of the dye as it passes through the vessels in the back of the eye. This allows the ophthalmologist to identify the abnormal choroidal blood vessels which are causing the problem.
Macular degeneration is one of the leading causes of decreased vision in the United States in patients over age 50. The ability to see fine detail and to read depends on the health of the eye. The macula is a small region of the retina. The fovea is the center of the macula and is the most sensitive part. In age-related macular degeneration, or AMD, sight-threatening changes occur in the macula. These changes occur only rarely in people under 50 and most commonly occur in people over age 60. The degenerative changes that occur fall into two categories, “wet” and “dry” changes. “Dry” signs of AMD include the accumulation of drusen (tiny yellow-white lumps) on the undersurface of the retina, loss of cells in the macula, and deterioration of the pigmented cells under the retina. Of the people with AMD, 80% to 95% have the “dry” type. Some individuals with “dry” AMD can have nearly normal sight, whereas others may notice distortion and blurring while reading. There currently is no known treatment to slow or stop the changes that occur with “dry” AMD. There is an ongoing study to determine if supplemental vitamins and minerals are beneficial, but the results will not be known for some time. Dietary spinach or other green leafy vegetables may help to slow down AMD as well. The “wet” form of AMD is also know as the neovascular or exudative type. Between 5% and 20% of all people with AMD have this form, and they may experience a more rapid loss of vision. In the “wet” form, new blood vessels develop beneath the retina in a layer of tissue called the choroid. These new vessels grow into the macula from the choroid. This process is called choroidal neovascularization or a choroidal neovascular membrane. Generally, the new blood vessels develop at the outer edge of the macula and extend in towards the fovea. These new vessels leak fluid which accumulates under the retina and separates the retina from the underlying layer, creating a localized retinal detachment. The retinal cells in the affected area do not function normally. A person with this typically sees straight lines as wavy or crooked and later in the disease may note a blind spot which corresponds to the area of the macula affected. This process of new vessel formation can also lead to bleeding and scarring, which may produce a permanent loss of reading vision. However, side or peripheral vision is rarely affected.
As mentioned, there is no known treatment for the “dry” form of AMD, although multivitamins and certain dietary elements (such as spinach or collard greens) may help reduce the risk. However, visual aids, such as magnifying lenses with extra bright light, special telescopic or prism glasses, and closed circuit TV, can all be of use in improving reading vision in some patients with the “dry” type of AMD. Patients with the “dry” type of AMD may develop abnormal blood vessels and progress to the “wet” type of AMD. In the “wet” type of AMD, laser therapy is helpful in destroying the abnormal blood vessels, in some cases. This treatment is called laser photocoagulation. A fluorescein angiogram is first done to locate abnormal blood vessels. If the abnormal blood vessels are in a “safe zone,” intense light energy from a laser is focused onto the abnormal blood vessels. If the blood vessels are totally destroyed, this helps preserve vision by preventing the further bleeding or leakage of fluid. Unfortunately, not all patients with “wet” type of AMD are candidates for laser therapy. Sometimes a separate type of angiogram (indocyanine green or ICG angiogram) can be used to determine if treatment is possible. Once a patient has received laser treatment for AMD, they must continue to have regular examinations of the retina so that any additional growth of new vessels can be detected and treated. If the patient notices any new symptoms, he should be examined promptly. Patients with the “dry” type of AMD, as well as patients who have been successfully treated with the “wet” type of AMD, should check their own eyes by using the Amsler grid (a piece of white paper with lines on it in a grid pattern). Patients should check their vision daily by covering one eye and viewing the grid. It helps to place the grid in an area where you can conveniently notice it each day. The lines of the grid appear straight if the macula is normal, and distorted or missing if there is a problem (i.e., abnormal blood vessels or fluid). If any changes are noted in the grid in either eye, the patient should contact his ophthalmologist immediately. The grid is positioned 14″ from the eye on a flat surface which is well-lighted. The eye focuses on the dark spot in the center of the grid. The horizontal and vertical lines should appear straight, and the squares formed by these lines should not be distorted. The Amsler grid should be placed in a convenient spot where it can be easily viewed on a daily basis (i.e., the back of a cabinet door in the bathroom or in the kitchen).
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