Dr. Paul Sieving, Director of the National Eye Institute, stated, "Now that we know antioxidants and zinc are helpful in reducing the risk of severe disease, it is even more important for older-age Americans to have regular eye exams. Intervening in at-risk individuals could help reducesevere disease and vision loss in millions of Americans."
Specifically, the AREDS study found that AMD patients with advanced cases of dry AMD or vision loss due to wet AMD in one eye, who took daily supplements containing vitamin C, vitamin E, beta carotene, and zinc, had a 20% chance of developing wet macular degeneration over a five-year period. By comparison, the control group taking a placebo pill lacking any nutrients had a 28% chance of developing wet macular degeneration over a five-year period. This finding is important because delaying the onset of wet AMD and its accompanying vision loss by several years can prolong the independence and mobility of seniors and preserve their quality of life.
What is Macular Degeneration?
Macular degeneration is so named because it causes the degeneration of the macula, the central portion of the retina that helps us perceive fine visual detail. Dry macular degeneration is first diagnosed by the appearance of fatty deposits called drusen in a layer of cells beneath the retina called the retinal pigment epithelium (RPE). As drusen deposits accumulate and become larger, they interfere with the function of photoreceptor cells in the macula, causing a gradual loss of central vision. In the later
stages of dry AMD, drusen deposits can also cause the death of cells in the RPE, a condition called geographic atrophy.
Researchers have found that patients with
extensive intermediate and large size drusen deposits are at a higher risk
of developing the more severe wet form of AMD than patients with fewer or
smaller drusen. In wet AMD, abnormal, leaky blood vessels grow beneath the
retina, allowing plasma and blood to seep into the macula. Because wet AMD
usually results in a rapid and devastating loss of central vision,
researchers are searching for treatments that prevent or delay this form of the disease from developing. Antioxidants and zinc, in the doses administered in the AREDS study, provide the first therapy for
patients with advanced cases of dry AMD, who are at increased risk of developing wet AMD.
Vitamin companies are not yet manufacturing a supplement of antioxidants and zinc containing the dosages used in the AREDS study. Until such a formulation becomes available, patients can purchase each nutrient separately. The daily therapeutic dosages of each of the nutrients used in the AREDS study are as follows: vitamin C, 500 mg; vitamin E, 400 IU; beta carotene, 15 mg; and zinc, 80 mg
Cancer prevention studies have found that high doses of beta carotene increase the risk of developing lung cancer in cigarette smokers. These studies strongly suggest that cigarette smokers, or those with
smoking histories, should avoid taking beta carotene to prevent advanced macular degeneration.
The AREDS study findings are specific
to patients with advanced cases of dry macular degeneration or vision loss
from wet AMD in one eye. Thestudy did not evaluate patients with early onset
forms of macular degeneration such as Stargardt and Best disease. Due to the
nature of the severe genetic defects that cause these early onset forms of
macular degeneration, there is no evidence to support the use of high doses
of antioxidants and zinc. There is also no evidence that antioxidants
and zinc would offer benefit to patients with other retinal degenerative diseases such as retinitis pigmentosa. To the contrary, a well-designed clinical trial found that a daily dose of
400 IU of vitamin E resulted in a faster progression of vision loss for patients with common forms of retinitis pigmentosa.
Lutein and Zeaxanthin
Lutein and zeaxanthin are two antioxidant nutrients found highly concentrated in the macula. They give the macula its characteristic yellow appearance. Lutein and zeaxanthin are thought to protect the
macula from oxidative stress due to light exposure. Because lutein and zeaxanthin supplements were not available at the start of the AREDS study, these nutrients could not be included. Future clinical trials will need to evaluate these antioxidants in AMD.
Am I Candidate For This Treatment?
Only a trained ophthalmologist can determine whether you have AMD and would be a candidate to begin antioxidant and zinc therapy. The Foundation Fighting Blindness and the National Eye Institute strongly urge adults over age 55 to have regular eye exams.
AREDS is a prime example of the importance of clinical trials in determining the safety and efficacy of treatments. With this therapy, patients can hopefully delay severe vision loss as researchers work
to develop even more effective therapies for AMD. For example, researchers recently submitted an application to the FDA to begin clinical trials testing the safety of a gene therapy treatment that
inhibits blood vessel growth. Drug treatments that block blood vessel growth are already in clinical trials. Still other clinical trials are testing the effectiveness of low-intensity laser
treatment in dry AMD to delay or prevent severe vision loss. The Foundation is collaborating with a biotech company called Oculex to test the use of a drug delivery device that slow-releases a steroid
to prevent immune complications after retinal cell transplantation. Such a device could help elevate transplantation therapies to clinical trials. As with all retinal degenerative diseases,
researchers are at last able to develop and test promising therapies.
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Date last modified November 4, 2001