Macular Diseases

AMD is caused by the loss of photoreceptor cells in the centre of the retina (the macula) where the vision is sharpest. The loss of the cells is the leading cause of permanent blindness among people over the age of 50 in most countries. The underlying causes of macular degeneration are not known.

There are two types of AMD. Dry AMD is the most common type and begins with loss of photoreceptor cells from small areas of the retina. The result is mild aberrations in central vision. Dry AMD progresses slowly and most people are able to maintain vision in at least one eye even after being afflicted with it for years. There is no treatment or cure for dry AMD.

In the second type called wet AMD, abnormal blood vessels develop underneath the retina. These deviant blood vessels bleed and leak fluid, which leads to vision loss. Gradually a scar forms under the macula which affects central vision. Treatments are available for wet macular degeneration; they can prevent formation of the scar so that central vision is not impaired and all round vision can be preserved and even improved (see below).

The National Eye Institute, part of the National Institutes of Health in the United States sponsored an important clinical trial called the Age-Related Eye Disease Study (AREDS). The results, published in the 2001 issue of Archives of Ophthalmology, revealed that high levels if zinc and antioxidants could reduce the risk of losing vision in patients with AMD.

The AREDS trial clearly demonstrated that vitamin supplements slow down the progression of AMD. But questions remained whether the optimal dosage was used in the study and whether other antioxidants could still improve outcomes. As a result a new trial known as AREDS2 was conducted, which tested different doses of the vitamins as well as other antioxidants like lutein, zeaxanthin and omega-3 fatty acids. The results are awaited.