Wet AMD is caused by an overgrowth of new blood vessels in the macula, which is part of the retina and enables fine detailed vision. When these vessels leak blood or fluid, the macula bulges. That causes distorted vision and a decrease in central vision, often leading to legal blindness if the disease attacks both eyes. (There is another type of age-related macular degeneration called dry AMD. It affects about 13.4 million Americans and is less severe than wet AMD. However, there is no treatment for dry AMD, and Macugen isn't approved for this disease.) Macugen is the first in a new class of eye care drugs to inhibit the activity of vascular endothelial growth factor, or VEGF, a protein that plays a key role in developing the unwanted blood vessels. By blocking VEGF, the drug can stop the growth of runaway blood vessels before they can spread and leak. Macugen must be injected into the eye every six weeks. Macugen also is the first therapy indicated for the treatment of all types of wet AMD. Until now, the only FDA-approved drug treatment was designed for one type of wet AMD that accounts for perhaps one-fourth of the affected patients. This other treatment requires the intravenous injection of Visudyne, a drug made by QLT ( QLTI) and Novartis ( NVS).The drug is administered every six months. Visudyne chemically sensitizes the eye, which is then exposed to infrared light, also known as a cold laser. This therapy stops unwanted blood vessels from leaking. It doesn't restore lost vision and it doesn't stop the development of new blood vessels. Called photodynamic therapy, this treatment must be repeated every three to four months. Another treatment involves using a thermal laser to cauterize the unwanted blood vessels in the eye. This laser leaves a permanent blind spot where AMD has already damaged the eye. Thermal lasers don't stop new blood vessels from developing; they don't restore lost sight. Visudyne and Macugen don't cause blind spots.