Vascular Density of Deep, Intermediate and Superficial Vascular Plexuses Are Differentially Affected by Diabetic Retinopathy Severity.

Purpose: The purpose of this study was to evaluate differences in optical coherence tomography angiography (OCTA) metrics in the superficial (SCP), intermediate (ICP), and deep (DCP) vascular plexuses across diabetic retinopathy (DR) severity levels.
Methods: This was a cross sectional observational retrospective chart review study. Eligible patients with diabetes who underwent same day RTVue XR Avanti OCTA, spectral-domain optical coherence tomography (SD-OCT), and 200-degree Optos ultrawide field color imaging. SCP, ICP, and DCP vessel density (VD) and vessel length density (VLD) were assessed using 3-D projection artifact removal software (PAROCTA) software.
Results: Of 396 eyes (237 patients), 16.1% had no DR, 26.9% mild nonproliferative DR (NPDR), 21.1% moderate NPDR, 12.1% severe NPDR, 10.1% proliferative DR (PDR) without panretinal photocoagulation (PRP), and 13.4% PDR with PRP. When comparing mild NPDR to no DR eyes, ICP and DCP VD and VLD were significantly lower, but there was no difference for SCP metrics. In eyes with more severe DR, there were significant differences in SCP VD and VLD between DR severity levels (mild versus moderate NPDR: VD 35.45 ± 3.31 vs. 34.14 ± 3.38, P = 0.008 and VLD 17.59 ± 1.83 vs. 16.80 ± 1.83, P = 0.003; moderate versus severe NPDR: VLD 16.80 ± 1.83 vs. 15.79 ± 1.84, P = 0.019), but no significant differences in ICP or DCP. Conclusions: Although VD of each of the three individual layers decreases with increasing DR severity, DR severity has a substantially different effect on OCTA parameters within each layer. Vascular changes in eyes with no to early DR were present primarily in the deeper vascular layers, whereas in eyes with advanced DR the opposite was observed. This study highlights the effects of ICP and the importance of assessing SCP and DCP changes independently across each DR severity level.