Retinal neurodegeneration, macular circulation and morphology of the foveal avascular zone in diabetic patients: quantitative cross-sectional study using OCT-A

Purpose Using OCT-A to investigate the association between neurodegeneration and vascular morphology in diabetic retinopathy (DR). Methods Cross-sectional study. One hundred and sixty-two patients were enrolled and following fundoscopy were assigned to two groups according to DR severity: 54 patients to the group of no clinical signs of DR (noDR) and 54 to the non-proliferative DR (NPDR) group. Fifty-four age-matched patients without known diabetes were recruited as the control group. Patients underwent full ophthalmic examination followed by OCT-A. Central retinal thickness (CRT), vessel density (VD) in the superficial and deep retinal layers and foveal avascular zone (FAZ) area were measured. Additionally, ganglion cell complex (GCC) layer thickness along with global loss volume (GLV) and focal loss volume (FLV) indices was measured. Results In total, 85 men with mean age of 51.93 +/- 9.03 and 77 women with age of 50.14 +/- 10.35 were examined. Mean diabetes duration was 4.62 +/- 2.16 years in the noDR group and 11.34 +/- 2.73 years in the NPDR group (p < 0.001). Superficial VD (sVD) and deep VD (dVD) were significantly different only between noDR and NPDR groups (p < 0.001 for both comparisons), but no statistically significant difference was observed between the controls and the DR groups. Global loss volume was significantly higher in the NPDR (4.38 +/- 2.22) compared to the noDR group (3.24 +/- 1.76; p < 0.03). Focal loss volume was significantly higher in both noDR (1.22 +/- 1.03) and NPDR (2.09 +/- 1.72) groups compared to controls (0.95 +/- 0.83; p < 0.001 between noDR and NPDR and p = 0.02 between control and noDR groups). Significant associations were found between GLV and deep VD (p < 0.01, r = -0.48), FLV and superficial VD (p < 0.01, r = -0.42) and FLV with deep VD (p < 0.01, r = -0.64). Conclusion In this study, we evaluated the impact of DR in both the vascular layers and neural components of the retina as expressed by FAZ, sVD, dVD and GCC thickness, FLV and GLV using OCT-A. We found that FLV was significantly higher in both noDR and NPDR groups indicating that in progressive DR stages FLV values might be increased, which might serve as an early index of neuronal damage in patients with diabetes even in the absence of overt DR signs.