Occult CNVM is a poorly defined membrane. It may present in two forms:
Fibrovascular pigment epithelial detachment(PED)which is an irregular elevation of RPE with stippled or granular irregular fluorescence seen in early phase usually by 1-2 minutes after dye injection. There is progressive leakage from these regions with a stippled hyperfluorescent pattern that is not as diffuse as seen in classic CNVM.
Fig 5: Fibrovascular PED
Fig 6: OCT image of Fibrovascular PED
Late leakage of an undetermined source when regions of hyperfluorescence are seen at the level of RPE which are best appreciated in the late phase of the angiogram.
Fig 7: Diffuse Hyperflourescence of undetermined source
When looking at the size of a CNVM, all areas of classic and occult CNVM as well as areas with obscured features such as blood in contiguity with the CNVM, pigment, scar tissue as well as serous PED ,must be taken into account.
The terms predominantly classic, minimally classic, and occult with no classic are used to determine who will benefit from photodynamic therapy. Predominantly classic lesions are those where the CNVM occupies more than 50% of the lesion,(including contiguous blood, pigment, scar and staining) and the proportion of classic CNVM also occupies more than 50% of the entire lesion. Minimally classic CNVM is one where the proportion of classic CNVM occupies between 1% and 49% of the entire lesion. Occult with no classic CNVM is when there is no classic CNVM in the lesion and the whole lesion is only occult CNVM.
Causes of CNVM:
- Neovascular age related macular degeneration
- Ocular Histoplasmosis Syndrome
- Angioid Streaks
- Pathologic Myopia
- Idiopathic CNVM
- Choroidal rupture from trauma
- Intense photocoagulation(iatrogenic)
Fig 8: Angioid streak with CNVM
Fig 9: Myopia with CNVM
Fig 10: Choroidal rupture
