Age-related macular degeneration
Age-related macular degeneration (AMD) is caused by the loss of retinal photoreceptor cells in the center of the retina where vision is the sharpest (the macula). It is the leading cause of irreversible blindness among people 50 years of age and older in most industrialized countries. The underlying cause of macular degeneration is still unknown.
There are two forms of age-related macular degeneration. The first, called dry AMD, is the most common form of macular degeneration. It begins with small areas of retinal photoreceptor cell loss, leading to mild defects in central vision. This disease progresses slowly, with most people maintaining some vision in at least one eye.
The second form, called wet AMD, occurs when abnormal blood vessels form underneath the retina. These blood vessels bleed and leak fluid, leading to significant vision loss. Eventually, a scar forms under the macula and central vision is lost. There are several treatments for “wet” macular degeneration that can prevent scar formation and preserve or improve vision (see below). The treatments do not stop the progression of dry AMD, however.
Vitamins and the development of macular degeneration
The National Eye Institute, a branch of the National Institutes of Health, sponsored a major clinical trial called the Age-Related Eye Disease Study (AREDS). The results were published in the October 2001 issue of Archives of Ophthalmology. Scientists found that high levels of antioxidants and zinc may reduce the risk of losing vision in patients with obvious AMD. Patients with a very early stage of AMD showed no benefit from the AREDS supplement, and this supplement was never tested in people without clear evidence of AMD
Even though the AREDS trial showed that vitamin supplementation slowed the progression of AMD, questions were raised about whether the best dosing regimen was used in the study and if other anti-oxidants could improve the outcomes. For these reasons, a new trial known as AREDS2 is underway. AREDS2 will test different doses of the supplements as well as lutein, zeaxanthin, and omega-3-fatty acids.
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