Purpose: To perform a quantitative analysis of retinal and choroid capillary ischaemia in diabetic patients by using optical coherence tomography angiography (OCTA). Methods: A total of 97 type 2 diabetic patients and 48 controls were included in this cross-sectional study. Diabetic patients without diabetic retinopathy (DR) were categorized as no DR (NDR) group; DR was classified into mild nonproliferative diabetic retinopathy (NPDR), moderate NPDR, severe NPDR and proliferative diabetic retinopathy (PDR). Quantitative parameters included foveal and parafoveal vascular density (VD) in superficial, deep and choroid capillary plexus (SCP, DCP and CCP), and foveal flow area in CCP. Stepwise comparisons between groups were performed in the adjacent stages. Results: Diabetic patients had significantly lower flow area in CCP and VD in all three layers compared with controls. In NDR group, foveal flow area in CCP significantly decreased compared with controls. In mild NPDR, parafoveal VD significantly decreased in all three layers compared with NDR, especially in temporal and nasal areas. In moderate NPDR, VD reduction extended to the inferior area in SCP and DCP compared with mild NPDR. In severe NPDR, progressive losses of VD were presented in all layers compared with moderate NDPR. In PDR, the superior VD in SCP significantly increased compared with severe NPDR. Conclusion: In diabetic patients, the microvascular ischaemia originated in choroid layer and extended inward affecting the deep and superficial layer. OCTA can serve as a reliable method for early detection and to monitor progressions in diabetic retinopathy.

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