Choroidal Neovascular Membrane Definition
A choroidal neovascular membrane (CNV) consists of abnormal blood vessels originating from the choriocapillaris that perforate and grow through Bruch's membrane, entering the subretinal pigment epithelial and/or subretinal spaces 1.
Anatomical Pathophysiology
The defining characteristic of CNV is the breach of Bruch's membrane by choroidal vessels. This anatomical violation allows vessels from the underlying choriocapillaris to extend into spaces where they do not normally exist:
- Sub-RPE space (between Bruch's membrane and retinal pigment epithelium)
- Subretinal space (between the RPE and neurosensory retina)
This process is synonymous with the terms "subretinal neovascular membrane" or "choroidal neovascular membrane" 1.
Clinical Classification
CNV can be categorized based on angiographic appearance and anatomical location:
By Angiographic Pattern:
Classic CNV (Type 2): Appears as bright, well-demarcated hyperfluorescence in early-phase fluorescein angiography, with progressive dye pooling in late phases in the overlying subsensory retinal space 1
Occult CNV (Type 1): Characterized by fibrovascular RPE detachment and/or late leakage of undetermined source, with indistinct or poorly demarcated boundaries on fluorescein angiography 1
By Location Relative to Fovea:
- Subfoveal: Underlies the center of the foveal avascular zone 1
- Juxtafoveal: Between 1-199 μm from the foveal avascular zone center 1
- Extrafoveal: No closer than 200 μm from the foveal avascular zone center 1
- Peripapillary: Any portion lies within one disc diameter of the optic nerve head 2
Clinical Significance
CNV represents a vision-threatening complication that manifests clinically through:
- Subretinal serous fluid accumulation
- Exudation within the macula
- Subretinal hemorrhage
- Progressive metamorphopsia and vision loss
If left untreated, CNV typically progresses to a disciform scar—subretinal fibrovascular tissue that becomes increasingly fibrous over several years 1.
Common Pitfalls
The term "neovascular macular degeneration" specifically refers to manifestations of CNV and/or RPE detachment associated with subretinal serous fluid, exudates, and/or blood 1. While CNV is most commonly associated with age-related macular degeneration, it can occur in diverse conditions including post-inflammatory states, trauma, high myopia, and even idiopathic intracranial hypertension 3, 4.