Volumetric Measures of Capillary Nonperfusion on Optical Coherence Tomography Angiography Detect Early Ischemia in Diabetes Without Retinopathy.

Purpose: The purpose of this study was to compare volumetric 3-dimensional (3D) against standard 2-dimensional (2D) measurements of ischemia for distinguishing early stages of diabetic retinopathy (DR) using optical coherence tomography angiography (OCTA). Methods: This cross-sectional study considered 82 eyes of 82 patients (aged 51.0 ± 11.9 years) including 27 healthy controls, 31 patients with diabetes mellitus (DM) without DR, and 24 patients with mild nonproliferative DR (NPDR). Using OCTA, we obtained 2D scans and 3D volumes of the superficial capillary plexus (SCP), middle capillary plexus (MCP), and deep capillary plexus (DCP). We calculated geometric perfusion deficits (GPDs), which define ischemic regions as those located farther than a specified threshold distance from the nearest blood vessel. For the GPD parameter, we compared the performance of a 20 µm versus 30 µm cutoff. Results: On 2D scans, eyes with mild NPDR had significantly higher GPDs in all 3 retinal capillary layers, indicating worse ischemia, compared with both healthy controls and patients with DM without DR, using either threshold (20 µm or 30 µm) to define GPD (all P < 0.05). DM without DR showed no significant difference from healthy eyes in 2D images. Interestingly, however, using 3D volumes, DM without DR eyes had significantly greater DCP GPDs than healthy eyes using a GPD threshold of 20 µm (P = 0.012), but not with 30 µm (P = 0.057). Conclusions: Using a stringent threshold (20 µm), volumetric OCTA imaging detects significant DCP perfusion defects in diabetic eyes even before DR onset, whereas traditional 2D OCTA does not. Volumetric scans may therefore be more sensitive to early ischemia in diabetes.