Collateral Vessels in Branch Retinal Vein Occlusion: Anatomic and Functional Analyses by Optical Coherence Tomography Angiography

Abstract Purpose To anatomically and functionally analyze collateral vessels (CVs) associated with branch retinal vein occlusion (BRVO) using optical coherence tomography angiography (OCTA). Design Retrospective review Participants Twenty-nine consecutive cases with BRVO. Methods The distribution of the CVs 12 months after the onset of BRVO was studied using spectral-domain OCTA. En-face 3×3-mm OCTA images were acquired from nine locations centered on the fovea and used to create a montage image of an 8.1 × 8.1-mm square. The CVs were identified in three separate areas: the radial peripapillary capillary (RPC), superficial capillary plexus (SCP), and deep capillary plexus (DCP) layers. The numbers of CVs were evaluated in four regions: zone 1, the area within a 3-mm-diameter circle centered on the fovea; zone 2, the area between the 3-mm circle and its outer 6-mm-diameter circle; zone 3, the area beyond the 6-mm circle; and the temporal raphe. Main Outcome Measures The relationship between the number of CVs and vessel density (VD) in each layer, persistent macular edema (ME) at 12 months, and the number of injections of anti-vascular endothelial growth factor (VEGF) agents. Results The number of CVs in zone 1 was correlated negatively ( P =0.0079) with the VD in the SCP, and the numbers of CVs in zone 3 and the temporal raphe were correlated negatively ( P =0.0017 and P =0.036, respectively) with the VD in the DCP. The number of CVs in the RPC and the total number of CVs also were correlated negatively ( P =0.0034 and P =0.0113, respectively) with the VD in the DCP. In cases with persistent ME, the number of CVs in zone 1 was significantly ( P =0.0156) greater than in cases with non-persistent ME and correlated positively ( P =0.025) with the number of anti-VEGF injections. Conclusions The CVs in BRVO form as result of capillary dropout and are considered to represent remodeling of the retinal capillaries. The CVs around the fovea might be good indicators of persistent ME.