Macular degeneration occurs when the aging eye is unable to remove waste products efficiently and fat-like deposits called drusen form under the center of the retina, called the macula. Drusen are found in dry macular degeneration, the more common, less damaging form of the disease. Fifteen percent of people with dry macular degeneration develop the more damaging wet form, according to the Mayo Clinic. There are several factors commonly associated with macular degeneration.
Age
Changes related to aging are the most common cause of age-related macular degeneration, often called AMD. The retinal pigment epithelium, a layer of cells behind the retina, removes waste created by the rods and cones in the macula. As the eye ages, it's less able to remove the waste products, which form drusen under the macula. Drusen can cause blurred vision over time. New abnormal blood vessels grow under the macula in an effort to supply more oxygen to the eye; these fragile vessels leak fluid that causes distorted, wavy vision. Eventually, a dark spot forms in the center of the vision as fluid accumulates under the macula; scarring in the area results in permanent central vision loss.
According to the Ohio State University Medical Center, only 2 percent of people under age 60 have the disease; the percentage rises to 30 percent of those over age 75. Wet AMD occurs in less than 1 percent of people under age 60 and 15 percent of those 90 and older, All About Vision notes.
Heredity
Recent studies at Duke University and Columbia University indicate that variants of two genes, complement factor H and complement factor C, were found in 50 and 75 percent of patients with macular degeneration, respectively, All About vision reports. Macular degeneration has long been noted to occur more frequently in people whose close relatives have the disease. People of Caucasian background in general are more likely to develop macular degeneration, as are people who inherit light-colored eyes.
Other Factors
Smoking increases the risk of developing age-related macular degeneration. All About Vision cites a British study reported in the 2006 "British Journal of Ophthalmology" that found 25 percent of severe cases of AMD could be related to smoking. Inactivity and obesity can double the risk of developing advanced AMD, according to a study reported in the June 2003 "Archives of Ophthalmology." High cholesterol levels and high blood pressure also have been implicated in increasing the risk of macular degeneration. Certain drugs are known to increase the risk of macular degeneration, including anti-malarial drugs and anti-psychotic medications.
