Flow patterns on spectral‐domain optical coherence tomography reveal flow directions at retinal vessel bifurcations

Purpose:  To study intravascular characteristics of flowing blood in retinal vessels using spectral‐domain optical coherence tomography (SD‐OCT). Methods:  Examination of selected arterial bifurcations and venous sites of confluence in 25 healthy 11‐year‐old children recruited as an ad hoc subsample from the population‐based, observational Copenhagen Child Cohort 2000 study. Results:  The blood stream in retinal arteries maintains a figure‐of‐8 SD‐OCT profile consistent with a laminar flow in concentric sheets and a parabolic velocity distribution up to the point of divergence at arterial bifurcations. In contrast, the blood stream at the site of confluence of two retinal veins remains divided into two parallel sets of sheets with separate velocity distribution for a downstream distance of at least four trunk vessel diameters. Consequently, retinal trunk vessels near bifurcations/confluences have distinctly different internal SD‐OCT profiles, a figure‐of‐8 pattern in arteries and a figure figure‐of‐88 in veins that can be used to distinguish between the two vessel types. Conclusion:  This study verified the hypothesis that directions of blood flow at dichotomous vascular branchings can be determined using SD‐OCT. This feature may assist the identification of flow reversal near sites of vascular occlusion, the analysis of blood flow near vascular malformations and the segmentation of retinal SD‐OCT images.