Distance-thresholded intercapillary area analysis versus vessel-based approaches to quantify retinal ischemia in OCTA

Abstract

Purpose: To develop and compare different analytic approaches for quantifying ischemia in OCT-angiography (OCTA), including vessel-based approaches and intercapillary area analysis. Methods: En face OCTA (6 ☓ 6) images of the superficial plexus of 20 healthy eyes and 20 eyes with different ischemic retinal diseases were analyzed retrospectively. Included retinal diseases were diabetic retinopathy (n = 9), central (n = 5) and branch retinal vein occlusion (n = 4), hypertensive retinopathy (n = 1), and occlusive retinal vasculitis in sarcoidosis (n = 1). Vessel-based approaches consisted of the mean gray scale, perfusion density, and vessel density. Intercapillary areas (ICAs) were analyzed measuring the distance of each intercapillary pixel from the surrounding vessels. In particular, we applied a vector method to measure the shortest, the mean, and the longest distance in eight predefined directions. Size of ICAs was determined applying different global or local distance thresholds. Results: All approaches revealed significant differences between ischemic and healthy retinae (P < 0.001, with Bonferroni-Holm correction P = 0.001–0.025; Wilcoxon-Mann-Whitney test). Discrimination between the healthy and ischemic retinae based on ROC curves was best in the ICA analysis using a locally set threshold of the shortest distance. Conclusions: In the present study, ICA analysis was superior to vessel-based approaches in the quantification of retinal ischemia when defining a local or global distance threshold. Translational Relevance: In order to establish OCTA imaging in everyday clinical and scientific practice, standardized, device-independent image analysis methods are necessary.