Definition of Macular degeneration:

Macular degeneration is a disorder that affects the macula (the central part of the retina of the eye) causing decreased vision and possible loss of central vision.

Causes, incidence, and risk factors:

The macula is the part of the retina that allows the eye to see fine details at the center of the field of vision. Degeneration results from a partial breakdown of the retinal pigment epithelium (RPE).

The RPE is the insulating layer between the retina and the choroid (the layer of blood vessels behind the retina). The RPE acts as a filter to determine what nutrients reach the retina from the choroid. Many components of blood are harmful to the retina and are kept away from the retina by normal RPE.

Breakdown of the RPE interferes with the metabolism of the retina, causing thinning of the retina (the "dry" phase of macular degeneration). These harmful elements may also cause new blood vessel to form and fluid to leak (the "wet" phase of macular degeneration).

This disorder results in the loss of central vision only -- peripheral fields usually stay normal. Although loss of ability to read and drive may be caused by macular degeneration, the disease does not lead to complete blindness.

The disease becomes increasingly common as people age over 50. By age 75, almost 15% of people have this condition. Other risk factors are family history, cigarette smoking, and being Caucasian.