Age-related macular degeneration, or AMD, affects 10 million Americans and is the leading cause of blindness in people over age 60, the University of Maryland Medical Center says. AMD causes vision loss because it affects the macula, the central point of vision on the retina, the light-sensitive tissue that lines the back of the eye. One eye or both may develop the disease.
Types
AMD can be one of two types: dry or wet. Dry AMD, the more common type, occurring in 85 percent of people with the condition, is characterized by drusen, yellowish fatty deposits in the retina. Mild drusen doesn't interfere with vision, but advanced drusen can. Wet AMD, the more damaging type, occurs in 15 percent of people with the disease and disrupts central vision. Dry AMD precedes wet AMD in almost all cases of the disease, according to the Mayo Clinic.
Causes
Blood vessels known as choroids supply the macula with nutrients across the retinal pigment epithelium (RPE), a layer of tissue under the retina. Waste products are removed from the retina across the RPE. The RPE often thins as people age and loses effectiveness in removing waste and supplying nutrients, leading to cell damage in the macula. Drusen forms under the macula and may enlarge or increase in number. In wet macular degeneration, abnormal blood vessels form under the retina; the abnormal vessels swell and leak fluid.
Risk Factors
Macular degeneration occurs more frequently in people over age 60, with women and Caucasians at higher risk. A family history of the disease and obesity may also contribute to macular degeneration, the National Eye Institute says.
Diagnosis
Ophthalmologists diagnose AMD by dilating the eye and examining the retina through a lamp. Tests done to confirm the diagnosis include fluorescein angiography, a series of photos of the blood vessels in the retina taken after a fluorescent dye is injected into a vein, and optical coherence tomography (OCT), in which pictures of the layers of the retina are taken to look for fluid accumulation under the macula.
Symptoms
Mild dry AMD may have no symptoms. If drusen builds up, vision blurs. Colors may dim and difficulty adapting to low-level lighting may develop, the Mayo Clinic says. Wet AMD causes painless, but progressive central vision loss. People with wet AMD first complain of wavy lines, black spots or blurriness in the center of their vision. These symptoms make reading, driving and facial recognition very difficult. Peripheral vision is normally preserved. If serious vision loss occurs, a bizarre and unusual condition called Charles Bonnet syndrome may occur, with vivid visual hallucinations.
Treatment
Much research continues into treatments for wet AMD, and for treatments to prevent dry AMD from becoming wet. Current treatments for wet AMD include intravitreal injections of medications that attack VEGF, a protein that helps leaking blood vessels develop. Two commonly used medications, Avastin and Lucentis, are also used to treat cancer by destroying the blood vessels that feed tumors. Injections are usually given in a series until abnormal blood vessels stop developing, and leaking stops.
Laser treatment known as photodynamic therapy, or PDT, may also be done in place of or in conjunction with intravitreal injection. A drug that is activated by light, called Visudyne, is given intravenously. A laser beam is then aimed at the abnormal blood vessels, sealing them and stopping the leaking. A vitamin formulation called AREDS, which contains antioxidants and zinc, may decrease the chance of intermediate dry AMD turning wet in some cases.
