Purpose: To quantify changes of the retinal vascular bed area (RVBA) in mm(2) on stereographically projected ultrawide field fluorescein angiography images in eyes with proliferative diabetic retinopathy after antivascular endothelial growth factor injection. Methods: This is a prospective, observational study. The early-phase ultrawide field fluorescein angiography images (Optos 200Tx) of 40 eyes with proliferative diabetic retinopathy and significant nonperfusion obtained at baseline and after six months (NCT02863354) were stereographically projected by correcting peripheral distortion. The global retinal vasculature on ultrawide field fluorescein angiography was extracted for calculating RVBA by summing the real size (mm(2)) of all the pixels automatically. Results: For the entire cohort, the global RVBA for the entire retina decreased from 67.1 +/- 15.5 to 43.6 +/- 18.8 mm(2) after anti-VEGF treatment at six months (P < 0.001). In the subgroup receiving monthly anti-VEGF injections, the global RVBA decreased from 68.7 +/- 16.2 to 33.9 +/- 13.3 mm(2) (P < 0.001). In the subgroup receiving anti-VEGF every three months, the global RVBA decreased from 65.6 +/- 15.1 to 50.8 +/- 19.3 mm(2) (P = 0.004). Conclusion: RVBA seems to be a new biomarker to indicate efficiency of retinal vascular changes after anti-VEGF injection. Eyes with proliferative diabetic retinopathy and significant nonperfusion demonstrate reduced RVBA after anti-VEGF treatment.