Macular Degeneration—Ag... Health Article

Diagnosis

A variety of tests is used to diagnose AMD. The visual acuity test measures the smallest letters an individual can read with one eye on a standardized chart at a distance of 20 ft (6 m). The refraction test involves the same standardized eye chart, but requires the patient to focus through a refraction lens to determine the amount of correction needed for optimum visual acuity. The pupillary reflex test examines the ability of the pupil to constrict or dilate in the presence or absence of bright light. The slit lamp examination is also known as biomicroscopy. A high-intensity light source is focused to shine as a slit on the anterior portion of the eye. The eyes are examined with a microscope designed for the eye called a biomicroscope. The eyes may be temporarily stained with an orange-colored dye called fluorescein to help visualize the structures of the eye. Examination of the posterior portion of the eye involves dilating the pupils with specialized eye drops before examination. Retinal photography can then be performed. Fluorescein angiography, or retinal photography, uses fluorescein dye injected into a vein of the arm and a special camera to analyze and photograph the retina, choroid, and associated blood vessels. This examination can be used to visualize the changes in vasculature associated with wet AMD. Tonometry

measures the pressure levels inside the eye. Color testing assesses the functioning of the cone cells in recognizing colors. Standardized pictures made up of dots of different colors are arranged in specific patterns and used to determine color recognition. The Amsler grid test uses a printed paper grid to test for decreased central vision, distorted vision, or blind spots.

As of 2005, genetic testing for genes associated with AMD is not recommended. The utility of such tests would be minimal at best, because there is no information available on how to interpret test results as applies to an individual's likelihood of developing AMD. Individuals with AMD are encouraged to monitor changes in their own vision through the use of an Amsler grid.

Treatment and management

There is no universal cure for either type of AMD. Some individuals with wet AMD can prevent further progression of damage with laser photocoagulation therapy. Light rays are focused by a thermal laser to burn off abnormal blood vessels forming beneath the macula, preventing further leakage of blood and fluid. Some normal tissue is also affected. Previously lost vision is not restored with this treatment. Only a small percentage of wet AMD cases can be treated with laser surgery. Laser surgery is most effective if the abnormal blood vessels have developed away from the fovea, the central part of the macula. Laser photocoagulation treatments do not prevent future abnormal blood vessels from forming, and are not effective for dry AMD. In 2000, the FDA approved the use of a light-activated drug called Visudyne (verteporfin). Visudyne is injected into the bloodstream via a vein in the arm. It circulates through the body to the eyes, specifically attaching to the abnormal AMD blood vessels present under the macula. When light rays from a non-thermal laser hit these blood vessels, the Visudyne is activated to produce a chemical reaction that destroys the abnormal vessels, causing very little damage to nearby healthy tissues. If the abnormal blood vessels re-grow, the procedure is repeated. While this therapy does not cure AMD, it is useful in managing specific problem areas and reducing further vision loss.

There is no specific treatment for dry macular degeneration; laser therapy is not useful. Once dry AMD reaches the advanced stage, no form of treatment can prevent vision loss. The National Eye Institute's Age-Related Eye Disease Study (AREDS) reported that taking a high-dose antioxidant and zinc supplement significantly reduced the risk of advanced AMD and vision loss. The specific daily quantities reported were 500 mg vitamin C, 400 I.U. vitamin E, 15 mg beta-carotene (equivalent to 25,000 I.U. vitamin A), and 80 mg zinc oxide. Two milligrams of copper in the form of cupric oxide was added to the formulation to prevent a condition called copper deficiency anemia, associated with high levels of zinc intake. Supplementation is indicated in individuals with intermediate AMD in one or both eyes, or advanced AMD in one, but not the other eye. The AREDS reported that supplementation did not keep individuals with early AMD from progressing to an intermediate stage.

In December 2004, the FDA approved Macugen drug treatment. This treatment attacks a growth factor protein involved in abnormal blood vessel growth in the eye. Macugen was developed by Eyetech Pharmaceuticals and Pfizer, and is administered through injections directly into the eye every six weeks. In previous clinical trials with Macugen, some patients experienced slower rates of vision loss, or restored vision. There are other drugs currently in clinical trials that have not yet been approved by the FDA. Avastin has a mechanism of action similar to Macugen, but is administered by intravenous injection into a vein in the arm. In 2005, Avastin had FDA approval for treatment of colorectal cancer, but not for macular degeneration. The FDA has issued a caution that Avastin has been shown to increase the risk of stroke and heart attack. Another drug in clinical trials is Retaane, which attacks enzymes involved in abnormal blood vessel growth. Retaane would not be administered with a needle and treatments would be every six months. In October 2000, it was reported that a medication called Iloprost, over a six-month time period, caused improvements in visual acuity, daily living activities, and overall quality of life for individuals with dry AMD. Follow-up research is being done to investigate the safety and usefulness of these medications.

In 2005, multiple future therapies are being investigated. Radiation treatment to destroy abnormal blood vessels and implantable telescopes to improve vision are being tested. Japan developed a method of blood filtration called rheopheresis to remove harmful proteins and fatty acids to treat the dry form of AMD. This technique has not been approved by the FDA in the United States, but is being used in Canada and Europe.

Low-vision devices are available to help improve AMD vision difficulties by using magnifying lenses and bright lights. Some low-vision aids shift images to the periphery for clearer vision. There are many different types of low-vision devices that can help to overcome vision impairment and live independently.