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

Abstract

<b><i>Introduction:</i></b> 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). <b><i>Methods:</i></b> 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. <b><i>Results:</i></b> 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 (<i>p</i> &#x3c; 0.001) and the peripapillary (<i>p</i> &#x3c; 0.001) regions was significantly different in different groups, whereas the pRNFL was not statistically significant (<i>p</i> = 0.764). Compared with that in healthy subjects, the RPC vessel densities in 4, 5, and 8 peripapillary sectors in NDR (all <i>p</i> &#x3c; 0.05), NPDR (all <i>p</i> &#x3c; 0.05), and PDR (all <i>p</i> &#x3c; 0.05) groups, respectively, were reduced. Compared with that in healthy subjects, the pRNFL thickness significantly decreased in the inferior nasal sector (<i>p</i> = 0.001) in NDR but significantly increased in the 2 sectors (all <i>p</i> &#x3c; 0.01) in PDR. The DR severity was negatively correlated with the peripapillary RPC vessel density (<i>r</i> = −0.583, <i>p</i> &#x3c; 0.001) but had no correlation with the pRNFL thickness (<i>r</i> = −0.045, <i>p</i> = 0.648). The positive correlation between the peripapillary RPC vessel density and the pRNFL thickness was statistically significant in the control (<i>r</i> = 0.531, <i>p</i> = 0.004), NDR (<i>r</i> = 0.528, <i>p</i> = 0.004), and NPDR (<i>r</i> = 0.405, <i>p</i> = 0.040) groups but not in the PDR group (<i>r</i> = 0.394, <i>p</i> = 0.05). <b><i>Conclusions:</i></b> 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.