Peripapillary RNFL/vessel density ratio in patients with type2 diabetes without clinical diabetic retinopathy

To identify how diabetic retinal neurodegeneration (DRN) and microvascular impairment are affected differently by various factors in type 2 diabetes (T2DM) patients without diabetic retinopathy via the ratio of RNFL thickness/vessel density (RNFL/VD) ratio. In this retrospective cross-sectional study, subjects were divided into two groups: controls (control group) and patients with T2DM (DM group). The RNFL thickness, VD, and RNDL/VD ratio were compared between two groups, and correlation analyses were performed to identify the relationship between the RNFL/VD ratio and various factors. A total of 411 eyes were enrolled: 195 eyes in the control group and 216 eyes in the DM group. The mean RNFL thickness was 95.9 ± 8.6 and 93.7 ± 8.7 μm (P = 0.016), the VD was 18.2 ± 0.7 and 17.6 ± 1.1 mm^-1 (P < 0.001), and the RNFL/VD ratio was 5.11 ± 0.47 and 5.22 ± 0.53 (P = 0.033) in the control group and DM group, respectively. In the DM group, age (coefficient = - 0.139, P = 0.041), axial length (coefficient = 0.163, P = 0.017), and T2DM duration (coefficient = - 0.180, P = 0.008) were significantly correlated with the RNFL/VD ratio. The RNFL/VD ratio of T2DM patients was higher than that of normal control, which would indicate that the impairment of microvasculature precedes DRN. Additionally, age and T2DM duration were negatively correlated with the RNFL/VD ratio, which suggests that inner retinal damage by DRN becomes more prominent over time than microvascular impairment in T2DM.