Macular degeneration is a progressive disease that can cause a loss of central vision. It occurs when the small central portion of the retina, known as the macula, deteriorates. Because the disease develops as a person ages, it is often referred to as age-related macular degeneration (AMD). Although macular degeneration is almost never totally blinding, it can be a source of significant visual disability. There are two types of AMD: wet (neovascular/exudative) and dry (non-neovascular). Roughly 90% of patients with AMD experience the dry form of the disease. Dry AMD is caused when yellow deposits called drusen form in the macula, leading to loss of vision. Wet AMD occurs when abnormal blood vessels grow from beneath the retina, leaking blood and tissue fluids. Unless stopped, the process can result in severe loss of sight.