PurposeImprovement in best corrected visual acuity (BCVA) and central subfield thickness (CST) have been well documented after intravitreal injection of anti-VEGF medications in diabetic macular edema (DME), however their effect on the vasculature of the macula in diabetic retinopathy (DR) remains poorly understood. Our aim was to explore the effect of intravitreal injection of anti-VEGF on parameters of retinal vascular microstructure in DR with optical-coherence tomography angiography (OCT-A). DesignRetrospective study of adult patients with DME that were treated with anti-VEGF intravitreal injections at the University of Illinois at Chicago between 2017-2022. Subjects, Participants, and/or Controls41 eyes from 30 patients with non-proliferative or proliferative DR with a mean age of 58.83 ± 11.71years, mean number of intravitreal injections of 2.8 ± 1.4, and mean follow up of 6.5 ± 1.7 months. Methods, Intervention, or TestingImageJ was employed to measure parameters of retinal vascular microstructure in OCT-A images, which included perfusion density, vessel length-density (VLD), vessel diameter, and FAZ characteristics (area, perimeter, circularity). Student’s T-tests and ANOVA were used to determine statistical significance. Main Outcome MeasuresA primary analysis was performed comparing the mean of each parameter of all patients as a single group at the beginning and end of the study period. A subgroup analysis was then performed after stratifying patients based on visual improvement, change in CST, prior injection history, and number of injections. ResultsEyes demonstrated statistical improvement in BCVA logMAR score and CST after anti-VEGF treatment. Primary analysis showed a reduction in the vessel diameter of the superficial and deep retinal vasculature as well as an increase in the circularity of the FAZ within the superficial retinal vasculature after anti-VEGF treatment. Subgroup analysis revealed that eyes with improvement in BCVA exhibited reduced vessel diameter in the superficial retinal vasculature and that eyes with the largest decrease in CST displayed increased perfusion density and VLD in the deep retinal vasculature. ConclusionsIntravitreal injection of anti-VEGF agents to treat DME improved parameters of retinal vascular microstructure on OCT-A over a period of 3-9 months, and this effect was most pronounced in eyes that experienced improvement in BCVA and CST.