Deterioration of vision with advancing age is a phenomenon as old as human civilization. Today the most common cause of severe visual loss among people over 65 is age-related macular degeneration (formerly known as senile macular degeneration). For people 52 to 64 years of age, this eye disease affects 1 in 50; for people aged 65 to 74, the prevalence increases to 1 in 10; and for those between 75 and 85, 1 in 3 has the disease. As life expectancy increases, age-related macular degeneration is becoming an increasingly important public health problem – especially since it most often affects both eyes.
Macular degeneration affects the macula, the tiny central area of the retina. The macula provides central vision, which is essential for seeing fine detail, looking straight at an object, reading, and driving. Although patients with macular degeneration retain their peripheral, or side, vision, the absence of central vision can be a severe handicap. Age-related macular degeneration is a leading cause of legal blindness, one of the criteria being central vision of 20/200 or worse in the better eye with corrective eyeglasses.
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Symptoms and diagnosis
Patients with macular degeneration are frequently aware of a problem early in the course of the disease. They may complain that their vision has become blurry or distorted or that their reading ability has decreased and words seem to crowd together. Many then consult an eye doctor for new eyeglasses but find that glasses do not help.
A simple test for macular degeneration is the Amster grid, a visual target resembling ordinary graph paper. The patient covers one eye and stares at a central dot on the grid while viewing the pattern of lines. If the disease is present, the person often reports blurring or absence of some areas of the grid or distortion of some of the straight lines. Once a diagnosis is made, the patient should use the Amster grid every day to check for changes in vision. An ophthalmologist is able to diagnose macular degeneration by looking through the patient’s pupil to the back of the eye with a lighted instrument called an ophthalmoscope. In the early stage of macular degeneration, whitish deposits known as drusen, visible through the ophthalmoscope, form beneath the retina. If the disease progresses, it develops into one of two major forms.
Atrophic macular degeneration
The atrophic or dry form of macular degeneration is the most common. There is a gradual withering of the visual cells and the blood vessels of the choroid (the vascular layer of tissue behind the retina). Usually the atrophic form results in only moderate loss of central vision. Although there is no medical or surgical treatment for the dry form of macular degeneration, eyesight may be helped somewhat by low-vision aids. These devices include magnifying lenses, brighter light for reading, or an electronic magnifier using a TV screen. Specialists in the Low-Vision Service at the University of Illinois at Chicago work with low-vision patients to help improve their visual performance.
In about 10% of the patients with macular degeneration, the dry form develops into the more serious wet form, called neovascular or exudative macular degeneration.
Neovascular macular degeneration
In neovascular degeneration new choroidal blood vessels leak fluid and grow into the retina. Later the vessels bleed and scars form, permanently damaging the macula. The earlier new vessels are discovered, the more likely vision may be saved. Some patients with this form of macular degeneration may benefit from laser treatment, which can be used to destroy the abnormal blood vessels.
A common way to treat wet macular degeneration targets a specific chemical in your body that causes abnormal blood vessels to grow under the retina. That chemical is called vascular endothelial growth factor, or VEGF. Several new drug treatments (called anti-VEGF drugs) have been developed for wet AMD that can block the trouble-causing VEGF. Blocking VEGF reduces the growth of abnormal blood vessels, slows their leakage, helps to slow vision loss, and in some cases improves vision.
The only ideal treatment of age-related macular degeneration would be to prevent the development of the disease. This is not yet possible, as its causes are not clearly known. Many contributing factors other than age have been implicated, including heredity, nutritional deficiency, high blood pressure, preexisting eye diseases, and smoking. A balanced diet and stopping smoking may be beneficial. In addition, investigators at the University of Illinois at Chicago have found that injury to the eye caused by light produces abnormalities resembling age-related macular degeneration. A special kind of dark sunglasses that prevent excessive exposure to bright sunlight may prevent macular degeneration and slow deterioration of vision.
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