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 selective 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) and may allow these harmful elements from the blood to damage and scar the retina (the "wet" phase of macular degeneration).

This disorder results in the loss of central vision only -- peripheral fields are always maintained. Although loss of ability to read and drive may occur from macular degeneration, complete blindness never occurs from this disease.

The incidence increases with each decade over age 50 to almost 15% by the age of 75. Other risk factors are family history, cigarette smoking, and being Caucasian.

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