Distinctive analysis of macular superficial capillaries and large vessels using optical coherence tomographic angiography in healthy and diabetic eyes

PURPOSE. To quantify and evaluate macular superficial capillaries and large vessels separately using an optical coherence tomographic angiography (OCTA)-based automatic segmentation algorithm. METHODS. In this cross-sectional study, all eyes were scanned using an OCTA device with 3 × 3 mm cube centered on the fovea. Retinal large vessels (arterioles/venules) were automatically segmented from superficial vasculature en-face images. All images were normalized, binarized, and skeletonized for quantification. Metrics of retinal capillaries were calculated by subtracting the measurements of large vessels from total vasculature. Perfusion density (PD), vessel length density (VLD), and vessel diameter index (VDI) within Early Treatment Diabetic Retinopathy Study (ETDRS) 3-mm ring were calculated for total superficial vasculature, large vessels (PD_large, VLD_large, and VDI_large) and capillaries (PD_cap, VLD_cap, and VDI_cap), respectively. RESULTS. Fifty-nine eyes from 59 healthy participants (mean age, 45 ± 14 years, 36 females) and 118 eyes from 67 patients with diabetes mellitus (mean age, 57 ± 10 years, 28 females) were included. The diabetic cohort included four subgroups (35 eyes without diabetic retinopathy, 30 eyes with mild to moderate nonproliferative diabetic retinopathy [NPDR], 27 eyes with severe NPDR, and 26 eyes with PDR). Linear regression showed that all above metrics were correlated with the disease stage (from healthy state to PDR), and the b value was -0.76, 0.24, -0.78, 0.80, 0.30, 0.77, -0.81, 0.16, and -0.82 for VD, VD_large, VD_cap, VDI, VDI_large, VDI_cap, VLD, VLD_large, and VLD_cap, respectively. CONCLUSIONS. Retinal capillaries and large vessels responded differently in the context of diabetes. VLD of capillary is a potentially reliable metric in diabetic retinopathy staging.