What Is Macular Degeneration?

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Age-related macular degeneration (AMD) is a progressive disease of the retina wherein the light-sensing cells in the central area of vision (the macula) stop working and eventually die. The disease is thought to be caused by a combination of genetic and environmental factors, and it is most common in people who are age sixty and over. AMD is the leading cause of visual impairment in senior citizens. An estimated fifteen million people in the United States have it, and approximately two million new cases are diagnosed annually.

Other less common types of macular degeneration, which are hereditary and can affect younger people, are Best's disease, Stargardt's disease, and Sorsby's disease. Collectively, these types are called juvenile macular degeneration. For definitions of each, see the MD Support Glossary with accompanying links.

Other diseases of the retina and extreme myopia (near-sightedness) can also result in degeneration of the macula. These conditions are not to be confused with AMD, but the end result, loss of central vision, can be the same. For more information about them, see "Eye Diseases and Conditions" on this site.

Most cases of macular degeneration are the "dry," or "atrophic", form, distinguished by yellowish deposits of debris in the retina. Called "drusen," the material comprising these deposits is usually carried away by the same blood vessels which bring nutrients to the retina. But for reasons yet unknown, this process is diminished in macular degeneration. Some of the potential causes being studied are inflammation, inadequate blood circulation in the retina, and premature aging of the sight cells due to genetic deficiencies. In addition, environmental, behavioral, and dietary factors are thought to contribute to the progress of the disease in those who are susceptible to it.

Dry AMD may occur in three stages in one or both eyes:

1. "Early." Identified by several small drusen or a few medium-sized drusen. No obvious symptoms or vision loss.

2. "Intermediate." Identified by many medium-sized drusen or one or more large, irregular-shaped drusen (called "soft" drusen). Symptoms may include a blurred or blind spot ("scotoma") or distortion of images in the central field of vision. Also, more light and higher contrast may be needed for seeing.

3. "Advanced Dry." Identified by drusen as described above, plus a breakdown of light-sensing "photoreceptor cells" and surrounding tissue in the macula. Blind spots may become larger and distortion more severe, and may eventually encompass the entire center field, making detail vision impossible, and causing the patient to rely upon the peripheral field for sight.

Treatments and cures for dry AMD and the juvenile forms of MD will likely come from the fields of genetic replacement therapy and stem cell transplantation. A good amount of research is being done in these areas, and we can reasonably expect a cure to be found within a decade.

There is yet no way to actually prevent the dry form of macular degeneration, but studies have shown that a person can take certain steps to help slow its progress: (1) eat a diet rich in leafy green vegetables; (2) take daily doses of antioxidants and zinc as recommended by the Age-Related Eye Disease Study (AREDS); (3) supplement this healthy diet with lutein and zeaxanthin; (4) avoid excessively bright sunlight by wearing a wide-brimmed hat and wrap-around sunglasses that are protective against both ultraviolet (UV) rays and blue light; (5) don't smoke, and (6) contact a low vision specialist if vision worsens. More details on these recommendations may be found in the MD Support Library or by contacting the organizations and foundations listed in the resource links.

About 10-15% of macular degeneration cases are the "wet" (or "exudative") form, in which newly-formed, immature blood vessels grow from the choroid ("choroidal neovascularization") and leak into the spaces above and below the photoreceptor cells. This process can damage the photoreceptor cells and cause permanent central vision loss. For illustrations, definitions, and more information about the parts of the eye mentioned in this article, see Anatomy of the Eye" on this site.

Nearly 90% of wet MD cases are of the subfoveal type. This means that the offending vessels are beneath the fovea, or very center of the macula. Other types are called "juxtafoveal" and "extrafoveal." The main subtypes of subfoveal wet AMD are:

1. "Predominantly classic." Seen in about 25% of cases, the leaking vessels are well-defined. This is usually the most aggressive form of subfoveal wet MD, leading to quicker vision loss than the other subtypes.

2. "Occult." Seen in about 40% of the cases, all of the offending blood vessels are "hidden" beneath the fovea and not readily defined. Results in the slowest rate of vision loss of the three sub-types.

3. "Minimally classic" (also called "mixed.") Seen in about 35% of the cases, it has a slower rate of vision loss than "predominantly classic," but faster than "occult."

Two laser treatments have been shown to temporarily stop the leakage. One is laser photocoagulation, in which a hot laser beam cauterizes the vessel. The other is photodynamic therapy (PDT), which involves a light-sensitive drug, called Visudyne, injected into the patient's veins. The light from a low-voltage laser is then used to coagulate the vessel.

Surgical procedures that have had some success are macular translocation, which involves rotating the macula to a healthier part of the retina, and submacular surgery, which involves removing the leaking membrane.

Pharmaceutical treatments are also showing success in the treatment of wet AMD. Several antiangiogenic drugs now in clinical trials are stopping the development of blood vessels in the retina. One of these, called Macugen, was approved for public use in February of 2005. The most recent is Lucentis, approved in June of 2006. A third antiangiogenic drug now in use off-label is Avastin, a drug originally developed for treatment of cancer. For information about all of these drugs, including those still in trials, read "Antiangiogenic Drugs Are Stopping Neovascularization in Wet Macular Degeneration" to be found in the MD Support library.

At its worst, macular degeneration will damage only central vision, which arises from the macular area, comprising less than 5% of the total retina, but responsible for about 35% of the visual field. This means that an affected person will find it difficult or impossible to read, drive, or recognize faces. The peripheral vision, however, is left untouched, so macular degeneration does not, by itself, lead to total blindness. (See "Age-related Macular Degeneration Does Not Cause Blindness." Many affected people move about with no assistance at all and lead independent, productive lives. The most successful of them have also learned to use a wide variety of visual aids such as magnifiers, closed circuit TV readers, special bioptic glasses, etc., all of which are readily available and can be found by contacting the distributors listed on this web site at: Low Vision Aids. It is highly recommended that a person with advanced macular degeneration enroll in a program of low vision rehabilitation. This program will provide evaluation of visual needs, assistance with environmental adaptations, and training in the use of appropriate low vision devices and computer software. For more information on low vision rehabilitation and coping with visual impairment, see the photo essays, "Learning to Live With Low Vision" and "The T.A.S.K. of Living With Central Vision Loss" at this link.

The risk of developing macular degeneration depends upon a person's age and whether soft drusen and/or changes in retinal pigment (color) are present. A person with these conditions who is 80 or older has a 42% chance of developing AMD within five years (Arch Ophthalmol 2003;121:519-26). A person who is less than 60 with a healthy retina has a 0.7% chance, and that risk gradually increases to 22.5% as the person reaches 80. Studies have shown that, for people with AMD in one eye, the chance of eventually developing the disease in the partner eye is between 38.7% and 55% (reported by the Rotterdam and Age-Related Eye Disease studies respectively.)

Understanding and treatment of macular degeneration in all of its forms is progressing steadily. Meanwhile, education helps people to become discriminating consumers of therapies and services. It also keeps them aware of progress in the continuing battle to slow macular degeneration and improve the quality of life of those who have it.