Age-related macular degeneration (AMD) is the leading cause of poor vision in people over 60. When the macula degenerates, central vision is gradually lost. Peripheral (side) vision normally remains so AMD does not lead to total blindness. The degeneration usually involves both eyes, though it may start in one eye and not affect the other eye until much later.
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The macula is the tiny area in the retina that provides sharp central vision. Though the macular area is no larger than a pinhead, it contains the visual cells for seeing straight ahead, fine detail, and color. If the macula is damaged -- or degenerates, as from AMD -- central vision is interfered with. So when you look at an object, part of it may seem distorted, blotted out, or shrouded in a dark haze.
What Causes AMD?
Scientists have not yet learned why a macula that has functioned well for most of your life begins to degenerate. Heredity is likely to play a role, as well as years of exposure to bright sunlight. It is also possible that tissue changes accompanying the normal aging process somehow interfere with the macula's getting enough oxygen. Smokers and former smokers have been found to have a much higher risk of AMD, though stopping smoking does not reverse the degeneration or even slow it down. Other risk factors are hypertension and heart disease. Some studies have found a relationship to a high intake of saturated fat, but those findings are not conclusive. AMD is not caused by using your eyes too much.
Types of AMD
There are two types: "dry" and "wet." Most patients have the dry form, which tends to develop slowly as the tissue beneath the macula gradually deteriorates. With wet AMD, tissue deterioration is accompanied by tiny abnormal blood vessels called "subretinal neovascular membranes" that form under the retina. Because they're fragile they leak fluid or bleed. If the fluid or blood reaches the macula and lifts it out of position, vision becomes hazy, distorted, and visual sharpness can be lost.
The typical first symptom (with either form) is blurring of vision. When the blurring is gradual, you may think you need new eyeglasses. But a new prescription is not likely to improve your vision because the problem is not with the optical parts of the eye. As time goes on, you may notice a hazy or dark zone in the center of objects you look at directly. Colors may begin to look different or lose richness. With wet AMD especially, straight lines, such as the edges of doorways, may start to look bent or crooked as vision becomes distorted, and you may see brief flashes of lights, like a sunburst. Symptoms may be gradual or sudden -- suddenness is more likely with wet AMD. When the loss of vision is in one eye only, you can't always tell how long it has existed, since it is "hidden" when both eyes are used together. It may only become apparent when the good eye is covered.
What You Can Do
In addition to having regular eye exams, there is an easy and important test you can do yourself. Take a few seconds every day to check your vision with an Amsler grid, a card printed with crossing lines that form small squares. Test each eye separately, with the other eye covered. The lines should look straight and solid. If any lines suddenly start looking wavy or having missing segments, it could indicate the beginning of wet changes that might be treatable, and you should make an appointment to have your eyes examined within the next few days.