CHOROIDAL NEOVASCULAR MEMBRANE
Dr. Thomas Thachil, MS
Consultant Ophthalmologist
Giridhar Eye Institute, Cochin.
Choroidal neovascular membrane (CNVM) is an ingrowth of new vessels from the choriocapillaris through a break in the outer aspect of Bruch’s membrane into the sub-pigment epithelial space.
These new vessels are accompanied by fibroblasts, resulting in a fibrovascular complex that proliferates within the inner aspect of Bruch’s membrane. This fibrovascular complex can disrupt and destroy the normal architecture of the choriocapillaris, Bruch’s membrane, and the RPE. In addition, fibroglial and fibrovascular tissue can also disrupt and destroy the normal architecture of the photopreceptors and remaining outer retina leading to the formation of a disciform scar.
Within the subpigment epithelial space, the CNV can leak fluid and blood and may be accompanied by a serous or haemorrhagic detachment of the RPE.
CNVM that remains restricted to the sub-RPE space is Type1 CNVM and when it becomes sub-retinal it is Type 2 CNVM.
Symptoms of CNVM: Sudden onset of decreased vision
Metamorphopsia
Central scotoma
Signs of CNVM:
- Presence of subretinal fluid
- Subretinal or sub-RPE bleed
- Subretinal or intraretinal lipid
- Subretinal pigment ring
- Irregular elevation of RPE
- Subretinal grey-white lesion
- Cystoid macular edema
- Subretinal small vessels
Diagnosis of CNVM: Fundus fluorescein angiography(FFA) is the gold standard for diagnosis of CNVM. When there is overlying blood or occult CNVM, Indocyanine green angiography(ICGA) helps in decision making.
FFA patterns of CNVM: Two main patterns are seen---Classic and occult. Additionally there may be combinations of the two also.
Classic CNVM is seen as an area of bright, hyperfluorescence seen in the early phase of the angiogram which intensifies throughout the transit phase and leaks in the late phase showing fuzziness of borders in late phase. The early hyperfluorescence is often seen as a lacy pattern with well defined borders. Depending on its location with respect to the fovea, classic CNVM may be:
- Extrafoveal when the CNVM is more than 200microns from the centre of the foveal avascular zone(FAZ).
- Subfoveal when the centre of the FAZ is involved either by extension from an extrafoveal area or by originating directly under the centre of the fovea.
- Juxtafoveal when the CNVM is closer than 200microns from the centre of the FAZ but does not involve it.
Fig 1: Large Classic CNVM
Fig 2: Extrafoveal Classic CNVM
Fig 3: Subfoveal CNVM
Fig4: Juxtafoveal Classic CNVM
