Purpose: A projection-resolved optical coherence tomography angiography (PR-OCTA) algorithm with slab-specific strategy was applied in polypoidal choroidal vasculopathy (PCV) to differentiate between polyp and branching vascular network (BVN) and improve polyp detection by en face OCTA.
Methods: Twenty-nine participants diagnosed with PCV by indocyanine green angiography (ICGA) and 30 participants diagnosed with typical neovascular age-related macular degeneration (nAMD) were enrolled. Polyps were classified into three categories after using the slab-specific PR algorithm. Type 1 polyps were considered in high-elevated pigment epithelial detachment (PED) and displayed in green. Type 2 polyps were considered in low-elevated PED and encoded in yellow, similar to BVN structures. Type 3 polyps were not able to be detected on OCTA. The algorithms were tested in the nAMD group to differentiate PCV and typical nAMD.
Results: With the algorithm, type 1 polyps were readily differentiated from BVN on en face OCTA. Polyp detection rate on en face OCTA only (type 1) was 68%, which was significantly improved from 30% when the algorithm was not used (P = 0.0001). To identify type 2 polyps, a combination of en face and cross-sectional OCTA images was needed and this resulted in a 91% polyp detection rate (types 1 and 2). The absence of luminal structure on OCT at the polyp site, small polyp size, and absence of halo on ICGA appeared to influence the polyp detection rate. When applying the algorithm to the nAMD group, 83% were correctly classified as typical nAMD (absence of type 1 polyps), whereas 17% showed false detection of polyps due to flow signals at the apices of large PEDs.
Conclusions: The slab-specific PR-OCTA with different color coding provides significant improvement in detecting polyp structures on en face OCTA, leading to rapid coronal visualization and diagnosis of PCV without the risk of dye injection.