Age-Related Macular degeneration (AMD) is caused by the deterioration of the central portion of the retina (inside back layer of the eye.) AMD is the leading cause of legal blindness in the elderly Caucasian population, but is relatively rare in other races. AMD affects approximately 30% of the Caucasian population over age 75. The exact cause of AMD is not known but genetics seems to play a significant role.

The retina records the images we see and sends them, via the optic nerve, to the brain. The retina's central portion, known as the macula, is responsible for central vision and our ability to read, drive a car, recognize faces, colors and see objects in fine detail. If macular degeneration develops in one eye, it will generally develop in the other eye as well. In AMD, deposits called drusen occur beneath the central retina. Drusen are thought to be metabolic by-products of the retina itself.

The photograph: The image above is an actual photograph of the inside of an eye affected by AMD. The circular structure on the left is the head of the round optic nerve where it enters the eye. Blood vessels can be seen spreading across the retina after
exiting from the center of the optic nerve. Drusen are the yellowish spots visible beneath the transparent retina.

 

"Dry" Macular Degeneration There are two types of Macular Degeneration: dry and wet. The dry form accounts for about 90 percent of all cases. Vision loss from dry macular degeneration occurs very gradually over the course of many years. Individuals with dry macular degeneration do not usually experience a total loss of central vision. However, it can become difficult to perform tasks that require fine-detail vision. Until recently, it was said that there was no treatment available for the dry form of AMD. A good deal of research is underway and a potential treatment for dry AMD is discussed later in this article. "Wet" Macular Degeneration Wet macular degeneration accounts for about 10 percent of all cases. Wet macular degeneration may be referred to as "choroidal" or "subretinal" neovascularization. It can also be called "exudative" or "disciform" degeneration. In wet macular degeneration, abnormal blood vessels grow beneath the macula. These vessels leak blood and fluid into the macula, which damages the retina's light receptor cells. The wet form of macular degeneration tends to progress rapidly and can cause severe damage to central vision.  Photodynamic Therapy In Wet AMD when the abnormal blood vessels are growing under the central macula, photodynamic therapy is often employed. In Photodynamic Therapy a medication is injected into an arm vein. The injected medicine collects and binds to the abnormal blood vessels beneath the macula. A low-power laser beam is then used to activate the medication, which closes the abnormal blood vessels and decreases fluid leakage. PDT is usually combined with injection of drugs into the vitreous gel of the eye to decrease the need for future retreatment.

Test Yourself The square box at the left is called an Amsler Grid. It is one of the tests used to check for macular degeneration. Cover one eye and note the dot in the center. While keeping your eye trained on the dot, notice the lines which cross over the rest of the box. These lines should be straight with no gaps or missing areas. Repeat the test in your other eye. If there is any question about your result, you should schedule a eye examination for a more thorough test.

Drug Therapy

Several drugs are currently being studied for potential benefit in the treatment of
macular degeneration. An anti-cancer drug called Avastin that targets a particular
protein believed to be involved in the development of AMD is being studied. Avastin can be given via normal intravenous (IV) injection, rather than injection directly into the eye. Several companies are working on drugs that function by inhibiting growth of the abnormal blood vessels associated with AMD. A drug called Retaane recently received FDA approval. This drug works by attacking enzymes that weaken the walls of blood vessels and allow abnormal vessel growth. An advantage of Retaane is that it does not require administration via injection.


Prevention

According to Johanne M. Seddon, M.D., and colleagues at Harvard Medical School, "Increasing intake of foods that are rich in antioxidants, particularly certain carotenoids, may reduce the risk of developing advanced AMD." The carotenoids lutein and zeaxanthin show the strongest protective effect against this degenerative disease."

Some scientists have suggested an association between macular degeneration and high saturated fat, low carotenoid pigments, and other substances in the diet. There is evidence that eating fresh fruits and dark green, leafy vegetables (such as spinach and collard greens) may delay or reduce the severity of age-related macular degeneration. Taking anti-oxidants like Vitamins C and E may also have positive effects. Zinc, however, has shown mixed results. In some people, the long-term use of zinc causes digestive problems and anemia. Selenium is sometimes recommended, but you should always consult your doctor to determine appropriate dosages. 


A Final Word

1. All patients should wear lenses in their glasses which absorb ultraviolet light. These include high index UV-blocking plastic lenses. Protect your eyes whenever you are outdoors during daylight hours, even on cloudy days, since short-wavelength light is not filtered by the clouds. Sunglasses which filter out both ultraviolet and near-blue light are particularly recommended for patients with AMD.

2. If you have been told that you have deposits in your retina called "drusen", realize
that most people with drusen develop no symptoms and do not progress to AMD.

3. It is important to be followed closely by your eye doctor if drusen are present. Persons with drusen should also perform a self test (Amsler grid) on a routine basis to monitor for the presence of visual distortions.

4. Even in advanced cases of the more severe "wet" AMD, peripheral vision is normally unaffected and mobility is good. "White-cane" blindness is rare.

5. Always consult with an eye doctor at the first sign of any blurred or distorted central vision.