Also called classic, type 2 neovascularization refers to new blood vessels that penetrate the pigment epithelium and proliferate directly beneath the photoreceptor layer of the retina, in the sub-retinal space. 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. Neovascularization may occur secondary to any process that damages the pigment epithelium, including age-related macular degeneration and pathological myopia. 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. For example, laser photocoagulation can successfully destroy small, primarily classic (type 2) neovascular growth but is not effective in destroying blood vessel growth beneath the pigment epithelium.