Assessing Preclinical Diabetic Retinopathy: The Role of Optical Coherence Tomography Angiography.

Objective The present study aimed to investigate the variations in retinal microvascular parameters among diabetic patients without diabetic retinopathy (No DR), those with nonproliferative diabetic retinopathy (NPDR), and healthy controls using spectral domain optical coherence tomography angiography (SD-OCTA). Methods An observational cross-sectional case-control study was conducted involving 68 eyes classified into three groups: 32 eyes with No DR, 16 eyes with NPDR, and 20 controls. The study assessed parameters such as perfused capillary vessel density, foveal avascular zone (FAZ) area, mean vessel diameter, number of capillary dropouts, and flow void areas. OCTA images were obtained using the SD-OCT system (Spectralis HRA, Heidelberg Engineering, Germany) and analyzed with custom MATLAB software. Statistical analysis was performed using SPSS Statistics (IBM Corp., Armonk, NY), with significance set at p<0.05. Results Significant differences were observed across the groups for perfused capillary density, FAZ area, number of capillary dropouts, and number of flow void areas. Specifically, NPDR patients exhibited a significantly lower perfused capillary density (36.50%) and No DR patients demonstrated a considerably higher perfused capillary density (43.98%) when compared with controls (42.71%; p<0.001). The FAZ area was significantly larger in NPDR patients (0.5981 mm²) compared to the No DR (0.3581 mm²) and controls (0.3550 mm; p<0.001). The number of capillary dropouts and flow void areas were significantly higher in NPDR patients but were also detected in the No DR group (p<0.001). No significant differences were found in mean vessel diameter among the groups (p=0.061). Conclusions The study confirms that NPDR is associated with distinct changes in retinal microvascular parameters compared to both No DR and control groups. These changes include reduced perfused capillary density, increased FAZ area, and elevated numbers of capillary dropouts and flow void areas. It also confirms that No DR can be associated with increased capillary vessel density as well as with capillary dropouts and void areas. OCTA proves to be a valuable instrument for evaluating retinal microvascular changes and could aid in the early detection and treatment of diabetic retinopathy (DR).