Excerpt from Neovascularization, Choroidal

Synonyms, Key Words, and Related Terms: choroidal neovascularization, choroidal NV, CNV, subretinal neovascularization, Bruch's membrane, subretinal space, retinal pigment epithelium, RPE, visual loss, vision loss, vascular endothelium growth factor, VEGF, pigment epithelium derived factor, PEDF

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Background: This disorder describes the growth of new blood vessels that originate from the choroid through a break in the Bruch membrane into the sub–retinal pigment epithelium (sub-RPE) or subretinal space. Choroidal neovascularization (CNV) is a major cause of visual loss.

Pathophysiology: Mechanisms of CNV are not understood. Virtually any pathologic process that involves the RPE and damages the Bruch membrane can be complicated by CNV. Recently, a protein derived from the RPE, pigment epithelium derived factor (PEDF), was found to have an inhibitory effect on ocular neovascularization. Another peptide vascular endothelium growth factor (VEGF) is a well-known ocular angiogenic factor.

The balance between antiangiogenic factors (eg, PEDF) and angiogenic factors (eg, VEGF) is speculated to determine the growth of CNV. VEGF has been temporally and spatially correlated with the development of CNV. Histopathologic specimens obtained from submacular surgery reveal the presence of VEGF in CNV. In addition, several researchers have induced CNV formation in animal models by overexpressing VEGF. Once secreted, VEGF binds to its receptors in endothelial cells activating several signal transduction pathways that end with the formation of a network of new vessels. As new choroidal blood vessels grow, they may extend into the sub-RPE space (Gass type 1) or into the subretinal space (Gass type 2). The location, growth pattern, and type (1 or 2) of CNV depend on the patient's age and the underlying disease. Bleeding and exudation occur with further growth, accounting for the visual symptoms.

Frequency:

In the US: In the Wisconsin Beaver Dam Study, prevalence of CNV associated with age-related macular degeneration (ARMD) was 1.2% in adults aged 43-86 years. Myopia is the second most common cause of CNV in the US and Europe. CNV is estimated to occur in 5-10% of myopes; 60-75% of these are subfoveal.
Disciform scars secondary to CNV from presumed ocular histoplasmosis syndrome (POHS) were present in 0.1% of people living in endemic areas. In multiple evanescent white dot syndrome (MEWDS), development of CNV is rare. In multifocal choroiditis, estimates of CNV range from 25-40% of patients. In punctate inner choroidopathy (PIC), 33% of patients develop CNV. Of these, 50% are subfoveal and result in visual acuities between 20/80 and 20/200.
CNV occurs in 5% of patients with birdshot chorioretinopathy. CNV occurs in virtually all choroidal ruptures during the healing phase; most involute spontaneously. In 15-30% of patients, CNV may recur and lead to a hemorrhagic or serous macular detachment with concomitant visual loss.

Mortality/Morbidity:

ARMD is the most common cause of visual loss in people older than 50 years in the developed world. Up to 90% of visual loss in ARMD is secondary to CNV.

Myopia is the seventh greatest cause of registered blindness in the US and Europe. CNV is responsible for most of this visual loss.

POHS is an uncommon cause of visual loss. Incidence and prevalence in the blind of Tennessee, an area endemic for histoplasmosis, were reported to be 2.8% and 0.5%, respectively.

Sex: No gender predilection exists. Certain diseases that may be complicated by CNV, ie, choroidal ruptures, angioid streaks, myopic macular degeneration, multifocal choroiditis, punctate inner choroidopathy, and MEWDS, have gender proclivity.

Age: CNV is associated with multiple ocular conditions, so the age distribution of CNV reflects the underlying condition.

For instance, younger patients are affected with POHS, multifocal choroiditis, MEWDS, PIC.

Older patients will be affected by CNV secondary to ARMD.