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 Topics on this page include: |
| What is macular degeneration? | Types | Contributing factors | Symptoms | Testing for macular degeneration | Treatment | Preventing vision loss | Low vision aids |
The retina is located at the rear of the eye. It works like the film in a camera, recording light entering your eye and transforming it into electrical impulses transmitted to your brain, which interprets what the eye is seeing. In the middle of the retina we find the macula. Light entering the eye is focused onto the macula, which contains the highest concentration of cells that change light into nerve signals. The macula gives us our center vision and allows us to see fine details when looking straight at something. Center vision is needed for driving, reading, recognizing faces, and doing close work such as sewing. When macular degeneration occurs, the nerve cells in the macula are damaged or disrupted and can't process images properly. When this happens, the patient loses his or her center vision. Macular degeneration doesn't affect the patient's peripheral vision; therefore, they don't go completely blind.
Macular degeneration is the most common cause of severe vision loss in people over age sixty-five, affecting as many as fifteen million people over age fifty. Although it is possible for people to develop macular degeneration in their forties and fifties, it usually occurs after age sixty. People who are in their fifties have about a two percent chance of developing it, but after age seventy-five, the incidence rate reaches thirty percent. Around 300,000 new cases of age-related macular degeneration occur each year. Fifteen to twenty percent of age-related macular degeneration (AMD) patients have one or more close relatives who also have AMD. Japan has lowest incidence of AMD while Greenland has highest incidence rate.
The cause of macular degeneration is unknown. There is no cure for macular degeneration. The physician's goal is to help the patient to see better and to stabilize the condition.
There are two basic types of macular degeneration. The first is dry macular degeneration. This accounts for ninety percent of the cases of macular degeneration. It is produced by the aging and thinning of the retinal tissues, which causes light sensitive cells to break down. Dry macular degeneration develops slowly with mild vision loss occurring. The patient may experience a dimming of his or her vision.
No cure is available for dry macular degeneration. If the fovea, or center of the macula, is affected, vision may be reduced significantly. If not, vision may remain good for a long time. As dry macular degeneration progresses, new abnormal blood vessels may form and begin to leak causing wet macular degeneration.
Wet macular degeneration, which makes up ten percent of the cases of macular degeneration, is a much greater threat to a person's vision than dry macular degeneration. It affects six percent of people between the ages of sixty-five and seventy-four and twenty percent of those over age seventy-five. Wet macular degeneration is the cause of ninety percent of all cases of legal blindness or of vision less than 20/200.
In wet macular degeneration, fragile new blood vessels form in the back of the eye. If the blood vessels leak fluid and blood, they can damage the cells in the macula causing a large blind spot to occur.
When new blood vessels first grow under the retina, the effect is similar to tree roots growing under a sidewalk. The blood vessels force the retina away from the eyeball causing vision distortions such as straight lines appearing wavy. This is an early warning sign of macular degeneration. In most cases, the blood vessels will eventually leak and cause damage.
Leakage can develop under the retina causing a blister to form. The leakage may or may not be caused by abnormal blood vessels. If no blood vessels are present, the blister is usually left untreated. A blister may cause some vision impairment, but most of the patient's vision will remain. If the blister is invaded by blood vessels, it is called a neovascular membrane. In this case, if treatment doesn't take place, vision will deteriorate because of leaking blood vessels.
A number of factors contribute to macular degeneration. The first is heredity. It tends to run in families. Fifteen to twenty percent of age-related macular degeneration (AMD) patients have one or more close relatives who also have AMD.
Long-term exposure to light, especially blue or ultra-violet light, seems to be another contributing factor. People with light-colored eyes are at a greater risk than those with dark-colored eyes; Caucasians are more likely to develop AMD than African-Americans, and women are at a greater risk than men.
People with macular degeneration seem to have low blood levels of antioxidant vitamins such as A, C, and E as well as low levels of minerals such as zinc.
In addition, people with high cholesterol levels seem to be more likely to develop macular degeneration.
According to one study, people who smoke more than a pack of cigarettes per day are two and one-half times more likely to develop macular degeneration than non-smokers. The risk persists for fifteen to twenty years after quitting smoking. In 1995, the Beaver Dam Eye Study associated beer consumption with increased risk of wet macular degeneration. Another new study shows that consumption of moderate amounts of wine is associated with a decreased risk of developing macular degeneration.
One of the earliest signs of age-related macular degeneration that can be observed by a
physician is the development of drusen, which are small yellow deposits under macula. They are common in people over age fifty. Drusen don't usually cause a major decrease in a person's vision, but may indicate a future development of macular degeneration and loss of center vision.
Symptoms of dry macular degeneration include grayness, haziness, and a blind spot in the center of a person's vision. The patient may also notice blurred words when reading or sense that colors are dimmer. Some people notice a change in their vision only if macular degeneration affects both eyes.
One of the first symptoms people who develop wet macular degeneration notice is that straight lines such as sentences on a page, the side edges of building, or telephone poles appear wavy. Dark or empty areas called blind spots may appear in the center of the patient's vision. The blind spots are usually black or gray when the blood vessels first begin leaking. When they have stopped leaking and scar tissue forms, the spots are gray or white.
If you are experiencing some of the symptoms described here, it does not necessarily mean you have macular degeneration. However, if you experience one or more of these symptoms, you should contact your eye doctor for a complete exam. Click here for information on emergency or immediate care.
Testing for macular degeneration
There are a number of tests that can be done to check for macular degeneration. Using the Amsler grid, people can do one simple test at home. The Amsler grid has a pattern resembling a checkerboard with a dot in the center. The person covers one eye at a time and looks at the dot. If the straight lines appear wavy, or if they are missing, the person may be suffering from wet macular degeneration and should call an ophthalmologist immediately.
The ophthalmologist will do a simple visual acuity test to see how well the person sees at various distances. Next the doctor will dilate the patient's pupil and look at the retina for signs of macular degeneration. The presence of drusen in the retina indicates the eye may be at risk for developing macular degeneration. The ophthalmologist may also be able to see abnormal blood vessels in the eye and signs of leaking vessels.
A more definitive test is fluorescein angiography, which detects leaky blood vessels under the retina. In this test, fluorescent dye is injected into a vein in the arm. Photographs are taken as the dye passes through the blood vessels in the eye. This helps the eye professional evaluate leaking blood vessels to see how they should be treated.
The standard treatment for wet age-related macular degeneration is laser photocoagulation surgery. It is used in severe cases and works best when the blood vessels have not grown under the macula. When the new subretinal vessels lie beneath the macula, the laser destroys not only the abnormal vessels but also the overlying retina. A permanent dry scar is left, and the patient loses their vision in the scarred area.
Laser photocoagulation is not always successful and results may be temporary. Only about half the patients maintain the same vision or have improved vision. Abnormal blood vessels may reoccur causing further vision loss. If the abnormal blood vessel is located off-center in the retina, treatment may save some center vision although the laser damages the patient's sight. Laser treatment sacrifices less important vision to save center vision.
During surgery, the ophthalmologist will dilate the pupil and apply drops to numb the eye. They may also numb the area behind eye. To do the surgery, the doctor applies a special lens to eye. The patient may see flashes of light. Patients can go home soon after the surgery. Their vision may be a little blurry, and they may need some pain medication. The patient will need to follow up their laser surgery with additional visits to the doctor to make sure the leaky vessels are sealed. More fluorescein angiography may be required to make sure abnormal vessels aren't leaking, and additional laser treatments may be needed. Fifty percent of laser patients need repeat surgery within one year because new blood vessels grow. Laser photocoagulation is not a cure; it is just a treatment.
Another experimental treatment involves removing trouble-making vessels. However, the visual results have been disappointing.
In photodynamic therapy, the abnormal blood vessels are destroyed without damaging the overlying retinal tissue. The procedure is painless and is done on an outpatient basis in the ophthalmologist's office. Special photodynamic dye is injected into an arm vein. After five minutes, a "cold" laser light is aimed at the blood vessels which selectively absorb the dye. The laser light activates the dye and an active form of oxygen called singlet oxygen is produced to occlude the vessels.
Many people believe nutritional supplements will help slow the progress of dry macular degeneration, but at this point, there are no definitive conclusions. However, a large National Eye Institute research study on the issue is currently in progress.
Zinc is normally highly concentrated in the eye and is important for the health of the retina. Therefore, some doctors think zinc supplements may slow down the progress of macular degeneration. Antioxidant vitamins such as betacarotene and other caratenoids, vitamins C and E, and selenium may also slow the progress of dry macular degeneration.
The key to preventing vision loss from macular degeneration is early detection. Everyone should get regular eye checkups, especially if macular degeneration runs in their family. Patients at high risk can also use the Amsler grid on a regular basis to check for signs and symptoms of macular degeneration. If a person develops macular degeneration in one eye, the other eye has a sixty-percent chance of developing macular degeneration within five years. These people should be particularly vigilant about using the Amsler grid regularly and scheduling routine visits with their eye doctor.
Another thing people can do to prevent macular degeneration is to eat a balanced diet with plenty of green leafy vegetables to ensure they get the vitamins and minerals needed for healthy eyes. They can also wear sunglasses that block out harmful ultraviolet light. Finally, they should not smoke.
Low vision aids can help the macular degeneration patient perform daily activities. These aids usually involve a combination of magnification and bright lights. Different aids may be needed in different situations. The devices, which are stronger than regular eyeglasses, include telescopic glasses, lenses that filter light, and magnifying glasses. Electronic devices that can be held in the hand or put directly on reading material are also available.