OCT angiography analysis in acute non-arteritic anterior ischemic optic neuropathy: The importance of segmentation.

Background: In non-arteritic anterior ischemic optic neuropathy (NAION), optical coherence tomography angiography (OCTA) shows changes in peripapillary vascularization. However, the presence of an optic disc edema may induce artifacts that prevent visualizing the peripapillary network. The aim of this study was to evaluate the peripapillary vascularization in acute NAION using swept-source OCTA algorithms allowing segmenting only the retinal nerve fiber layer (RNFL).

Methods: Retrospective analysis of 15 eyes with acute NAION of 15 patients. The optic nerve head was imaged using swept-source OCTA. Morphological and quantitative analyzes were performed. The capillary flux index (CFI), defined as the total weighted area of perfused vasculature per unit area, and the capillary perfusion density (CPD), defined as the total area of perfused microvasculature per unit area, were quantified. Each NAION eye was compared to the unaffected fellow eye using a Wilcoxon test for matched samples.

Results: After segmentation at the RNFL, the morphological analysis showed less vascular dropout and more vascular tortuosity than the analysis of a larger segmentation. The quantitative analysis showed that the mean CFI and the CFI in the four quadrants were significantly higher in NAION eyes compared to healthy eyes ( = 0.0002 and  < 0.01). The mean CPD and the CFD in the inferior quadrant were lower in NAION eyes ( = 0.03 and  = 0.0054, respectively).

Discussion: The RNFL segmentation allowed better visualizing the peripapillary network because the edema related darkening was reduced. The increased CFI suggests an autoregulatory phenomenon to compensate the ischemic process at the ciliary vasculature.