Quantitative Analysis of the RPC Vessel Density and the RNFL Thickness in Patients with Type 2 Diabetes Mellitus by Using OCT Angiography

Abstract

Introduction: This study aims to compare the structural differences in the optic disc blood perfusion and the peripapillary retinal nerve fibre layer (pRNFL) thickness in age-matched healthy subjects and patients with type 2 diabetes mellitus (DM) by using quantitative analysis with optical coherence tomography angiography (OCTA). Methods: A cross-sectional cohort study on patients with type 2 DM with or without diabetic retinopathy (DR) and healthy subjects was conducted. The 4.5-mm scanning angio-disc pattern of the OCTA system was used to assess the optic disc. The analysed indices included radial peripapillary capillary (RPC) vessel density and pRNFL thickness. Results: A total of 78 eyes from 78 patients with type 2 DM, including 27 without clinical DR (NDR), 26 with non-proliferative DR (NPDR), and 25 with proliferative DR (PDR), and 28 age-matched healthy subjects were enrolled. The average RPC vessel density of the whole (p < 0.001) and the peripapillary (p < 0.001) regions was significantly different in different groups, whereas the pRNFL was not statistically significant (p = 0.764). Compared with that in healthy subjects, the RPC vessel densities in 4, 5, and 8 peripapillary sectors in NDR (all p < 0.05), NPDR (all p < 0.05), and PDR (all p < 0.05) groups, respectively, were reduced. Compared with that in healthy subjects, the pRNFL thickness significantly decreased in the inferior nasal sector (p = 0.001) in NDR but significantly increased in the 2 sectors (all p < 0.01) in PDR. The DR severity was negatively correlated with the peripapillary RPC vessel density (r = -0.583, p < 0.001) but had no correlation with the pRNFL thickness (r = -0.045, p = 0.648). The positive correlation between the peripapillary RPC vessel density and the pRNFL thickness was statistically significant in the control (r = 0.531, p = 0.004), NDR (r = 0.528, p = 0.004), and NPDR (r = 0.405, p = 0.040) groups but not in the PDR group (r = 0.394, p = 0.05). Conclusions: The peripapillary RPC perfusion decreased with DR aggravation, which may be considered as a useful indicator of DR severity. However, the pRNFL thickness had little diagnostic power in differentiating healthy and DM eyes.