Aims To quantify retinal vascular bed area (RVBA) in square millimetres on stereographically projected ultra-wide field (UWF) fluorescein angiography (FA) in eyes with diabetic retinopathy (DR).

Methods A prospective, observational study. Baseline Optos 200Tx UWF FA images of 80 eyes with DR from the DAVE (NCT01552408) and RECOVERY (NCT02863354) studies were stereographically projected at the Doheny Image Reading Center to adjust for peripheral distortion. The early-phase FA frame was used to extract the retinal vasculature as a mask for calculating RVBA. The pixels of the retinal vasculature were automatically computed in square millimetres using manufacturer-provided software.

Results Eighteen of 80 diabetic eyes were excluded because image quality and contrast were insufficient for automatic extraction of the retinal vasculature from the background fluorescence. The remaining 62 eyes were included in the final analysis. In comparison with age-matched and sex-matched normal controls, eyes with DR had a higher global RVBA for the entire retina (p<0.001), and RVBA correlated with DR severity (p<0.001), with a higher RVBA in eyes with proliferative DR (66.1±16.2 mm²) than in those with non-proliferative DR (56.2±16.6 mm²) or in normal controls (37.2±9.9 mm²). This tendency was also present in the posterior retina and mid-periphery but absent in the far-periphery. RVBA did not correlate with retinal ischaemia (p>0.05).

Conclusions Eyes with DR harboured a larger global RVBA for the entire retina than normal controls, and RVBA appeared to indicate DR severity. However, this biomarker was not observed to be a good indicator of retinal ischaemia.