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Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of poor vision in people over 60. (Some patients are younger, but that is rare.) 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.

The macula is the tiny area in the retina that provides sharp central vision. (The retina is the light-sensitive nerve tissue at the back of the eye: like the film in a camera, it is the "screen" that images are focused on.) 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.

People who develop AMD are typically in good health. The condition does not appear to be caused by diabetes or by drinking alcoholic beverages. In fact, drinking a moderate amount of wine has been shown to decrease the odds of developing AMD.

Drusen

As the normal eye ages, tiny yellowish deposits called "drusen" sometimes build up under the macula. One form of drusen (called "hard") may be a normal, harmless sign of getting older, but "soft" drusen can be a sign that degenerative macular changes are starting to develop. Yet AMD sometimes develops without any detectable drusen at all.

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.

Symptoms

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.

Some people whose vision has been very poor from AMD (or from other causes) sometimes have visual hallucinations; they see things (objects or patterns) that are not really there. These phantom visions last from a few seconds to a minute or so and then disappear. Such hallucinations are fairly common and they are not serious.

Examination

Your vision will be checked and you will have a refraction (test for glasses) along with a complete eye exam. Your pupils will be dilated (enlarged) with eyedrops so that the interior of your eyes can be evaluated with an ophthalmoscope. A special type of contact lens may be placed on your eyes while your retinas and maculas are examined under the high magnification of a slit lamp microscope.

Photographs may be taken of the retina at each visit to determine the extent of the problem and evaluate its progression. If you have a test called fluorescein angiography, an orange colored dye called fluorescein will be injected into a vein in your arm, and then a series of retinal photographs taken as the dye travels through the eye's blood vessels. The angiogram (photograph showing blood vessels) helps identify the position and extent of any abnormal blood vessels or leakages. If more information is needed, a dye called indocyanine green (ICG) may be used to make another type of angiogram. Angiograms provide important guidance for treatment.

Treatment

Dry AMD has long been thought to be untreatable. A recent national study, however, has indicated that patients who have moderate AMD, either dry or wet, can lower their risk (by 25%) of the condition advancing by taking high doses of antioxidants (combination of vitamin C, vitamin E, beta carotine) and zinc. These same supplements did not seem to offer any benefit to those with early AMD, nor were they helpful in preventing AMD from developing in the first place.

Wet AMD -- in the early stages only -- can sometimes benefit from treatment with a surgical laser, to seal the leaks or destroy the abnormal blood vessels under the macula. (The laser cannot help the dry type of AMD, or even most stages of the wet type.)

Laser surgery is never undertaken lightly. No matter how accurately performed, it involves some risk to vision because the laser can destroy normal neighboring tissue along with abnormal tissue. So the procedure will be recommended only if the risk to your vision is small and there is a reasonable chance for success -- that means that the degeneration is not too extensive, too advanced, or too near the center of the macula.

A newer type of laser surgery, called photodynamic therapy (PDT), is sometimes useful. (In several national studies, PDT appeared to be safer and was proven to be modestly effective for about two-thirds of those participating.) In this surgery, a light sensitive dye called verteporphin (Visudyne) is injected into the arm, travels to the retina, and concentrates in the abnormal blood vessels. A low intensity red laser is used to activate the dye. The objective is to destroy the abnormal blood vessels with the laser without damaging the normal retinal cells in the area. PDT has been approved by the FDA but further evaluation is still needed to determine its long term effectiveness.

PDT usually needs to be repeated three to five times over a year or more. Regular laser surgery may also require several re-treatments. With either standard laser or PDT, a result that is successful does not always mean that your vision will be better; only occasionally does vision actually improve. The goal of laser treatment is to prevent further leakage and stabilize vision. It is also possible that any beneficial effect will be only temporary, or there could be an actual worsening. So please be realistic and don't expect miracles from the laser.