Also called occult, type 1 neovascularization refers to new blood vessels that proliferate underneath the pigment epithelium. The new capillaries originate from the choroid and form in response to damage at the pigment epithelium, the layer between the choroid and the retina. Their growth sometimes causes the pigment epithelium to detach.
Neovascularization may occur secondary to any process that damages the pigment epithelium, including age-related macular degeneration (AMD), pathological myopia, and other conditions. When new blood vessel growth occurs as a result of AMD, the condition is then called neovascular AMD. Most people with neovascular AMD have a combination of type 1 and type 2 neovascularization. When new blood vessel growth occurs without a known cause, it is called idiopathic choroidal neovascularization. Regardless of the cause of new vessel growth, it is that growth that is responsible for nearly all of the vision loss associated with these conditions.
Physicians can determine the type of neovascularization through different technologies. This is important because certain treatments can successfully destroy new blood vessel growth at some locations but not others.