The choroidal layer of the eye lies behind the retina and contains blood vessels that nourish the retina. In some patients, choroidal neovascularization (CNV), the growth of new blood vessels in the choroidal layer, occurs with no apparent cause, a disorder known as idiopathic CNV. The abnormal, newly formed blood vessels tend to be fragile and leakage from these vessels can damage vision. Although the incidence of idiopathic CNV is not known, it tends to occur in patients younger than 50 years of age and it often progresses and damages vision more slowly than other types of CNV. CNV can be treated with laser photocoagulation; however, this treatment may be highly damaging, particularly when the CNV occurs directly behind or close to the fovea, a small dimple in the retina responsible for the eye's sharpest vision and strongest color perception. There is no clear consensus on the best treatment for idiopathic subfoveal CNV.