It is common for the macula to break down as one ages. Sometimes, the deterioration of the macula, as well as a predilection to risk factors such as heredity, race (whites are more susceptible than people of darker pigment), smoking, or a high-fat, low-antioxidant diet leads to age-related macular degeneration (AMD).
The wet, exudative form of AMD occurs when the pigment epithelial layer of the macula, located just behind the layer of cells responsible for central vision, sustains such damage that it breaks. Damage to this thin, mesh-like layer of capillaries may occur because of the presence of drusen or because of fluid accumulating in the sub-retinal space between the two layers.
When the pigment epithelial layer breaks, blood leaks into the photoreceptor layer. In most people, new but very fragile capillaries begin to grow back from the broken membrane, and the condition is further classified as neovascular AMD. Instead of forming in an organized fashion, these new blood vessels messily make their way into other layers of the macula like unruly tendrils of a vine. These new vessels often break as well, and along with the broken vascular layer, destroy the healthy macula.
Combined, wet AMD and neovascular AMD account for only 10% of all cases of AMD. Unfortunately, these cases also account for the most severe loss of vision.
For both groups, leakage of blood and other fluids into the macula causes extreme blurriness and even dark “blobs” in the center of vision. Over time, reading and other pastimes requiring detailed, straight-ahead vision will be affected. However, total blindness does not normally occur, since AMD does not affect peripheral vision.
The upside of wet and neovascularized AMD is that there are a number of very effective treatments available, mostly targeting the new blood vessels that form in response to the broken layer between the retina and the choroid. There are currently three anti-vegf agents, Macugen (pegaptanib), Lucentis (ranibizumab), and Avastin (bevacizumab), that are used to prevent new, fragile blood vessels from growing back. Additionally, laser photocoagulation and photodynamic therapy work in slightly different ways to seal off broken vessels or destroy new, unhealthy ones.