OCT Angiography Biomarkers in Diabetic Retinopathy: Current Evidence and Future Perspectives for Personalized Ophthalmology

Optical coherence tomography angiography (OCT-A) enables noninvasive, depth-resolved assessment of retinal microvasculature and can reveal quantitative abnormalities before diabetic retinopathy (DR) is clinically visible. This review aims to synthesize evidence on the foveal avascular zone (FAZ), vessel density (VD), perfusion density (PD), vessel length density (VLD), and fractal dimension (FD), and to assess their
potential contribution to individualized DR evaluation. A narrative review of English language human studies published from January 2021 through December 2025 was conducted using PubMed/MEDLINE and reference-list screening. Original studies, systematic reviews, and meta-analyses reporting quantitative OCT-A outcomes in diabetes or DR were considered. VD and PD are consistently reduced as DR severity increases and may be abnormal in diabetes without clinically visible retinopathy. FAZ enlargement is more consistent after retinopathy develops, whereas evidence in preclinical disease is heterogeneous. VLD and FD capture capillary rarefaction and vascular-network simplification, but their values depend on scan size, segmentation, device, and image-processing method. Meta-analytic evidence supports good diagnostic and staging performance, while longitudinal data indicate that the most informative metric may vary by DR severity and retinal plexus. OCT-A biomarkers can complement clinical examination and structural OCT for detection, staging, and monitoring of diabetic retinal microvascular injury. Device-specific thresholds and limited cross-platform comparability currently prevent universal clinical cutoffs; standardized acquisition and analysis, as well as external validation, are required before individualized risk models can be adopted routinely.