Characteristics of type 1 and 2 CNV in exudative AMD in OCT-Angiography

Background With FA and SD-OCT, different types of CNV in exudative AMD may be differentiated: type 1 CNV (within the sub-RPE space, typically corresponding to angiographically occult CNV), type 2 CNV (within the subretinal space, typically corresponding to angiographically classic CNV) and type 3 NV (intraretinal retinal angiomatous proliferation). OCT-angiography (OCT-A) is a new method to visualize vasculature based on flow characteristics. A correlation of type 1 and 2 CNV was performed. Methods Thirty-six eyes (17 type 1 CNV, 9 combined type 1 and 2 CNV, and 10 type 2 CNV) of 36 patients were examined by FA, SD-OCT and OCT-A. Standardized OCT-A segmentations were performed at the level of mid-choroid, choriocapillaris (CC), RPE and outer retina. On these images the size and demarcation of CNV lesions were classified: "not distinguishable", "minor" or "sharp" demarcation. Furthermore, the size of the different CNV sub-types was determined and compared. Results Both types of CNV were visible in OCT-A. They could be detected on the slabs "mid-choroid", "CC" and "RPE". While type 1 CNV showed most often a minor demarcation from the surrounding vasculature, type 2 CNV showed nearly always a sharp demarcation. In addition, type 2 CNV extended into the slab "outer retina" and were much smaller than type 1 CNV. Conclusions Different types of CNV in exudative AMD can be visualized and differentiated with OCT-A. Type 1 CNV were larger with minor demarcation from the surrounding vasculature and were visible on the slab "mid-choroid", "CC" and "RPE". In contrast, type 2 CNV demonstrated a sharp demarcation from the surrounding vasculature reaching the slab "outer retina".