Wet AMD accounts for 10 percent of patients with AMID. It is also called choroidal neovascularisation, subretinal neovascularisation, exudative form, or disciform degeneration. In wet AMD, new abnormal blood vessels begin to grow beneath the macula, in a thin layer of tissue called the choroid. The choroid is the main source of oxygen and nutrients for the retinal photo receptors, and it is the only blood supply for the macula. New fragile blood vessels develop which may leak fluid and blood, and then cause the choroid and retina to deteriorate. This causes the retinal layer to blister under the macula, and the photo receptor cells to degenerate. At this stage, there is marked disturbance of vision in the affected eye.
Wet macular degeneration is the more advanced type of AMD. Although it affects only 10-15 percent of those who have the condition, it accounts for 90 percent of the severe vision loss caused by macular degeneration. With this type, the membrane underlying the retina thickens, then breaks. The oxygen supply to the macula is disrupted and the body responds by growing new, abnormal blood vessels. These begin to grow through the breaks of the membrane behind the retina towards the macula, often raising the retina. To visualize this, imagine the roots of a tree growing and spreading until they crack and grow through a sidewalk. Then imagine rainwater seeping up throughout the cracks. These abnormal blood vessels (the "roots") tend to be very fragile. They often grow and leak or bleed, causing scarring of the macula. This fluid is called exudate and wet AMD is sometimes called exudative macular degeneration. This damage to the macula results in rapid central vision loss. Once this vision is destroyed, it cannot be restored. However, there are several treatment options for wet AMD which can be very effective if applied early.
Wet macular degeneration may also be called neovascular, it is likely to cause severe visual loss over quite a short time - sometimes just months. Very occasionally, if there is a bleed from a new blood vessel, this visual loss can occur suddenly, within hours or days. In wet macular degeneration, in addition to the retinal pigment cells degenerating, new tiny blood vessels grow from the tiny blood vessels in the choroid. This is called choroidal neovascularisation. The new vessels break through Bruch's membrane and into the macular part of the retina. These vessels are not normal. They are fragile and tend to leak blood and fluid. This can damage the rods and cones, and cause scarring in the macula, causing further vision loss.