Ziv-aflibercept (Zaltrap, Regeneron) is a recombinant fusion protein that acts as a soluble decoy receptor and binds to VEGF-A, VEGF-B, and placental growth factor, similar to aflibercept (Eylea, Regeneron, Tarrytown, NY), which is FDA approved for intravitreal administration to treat various retinal diseases. At the dose of 1.25 mg/0.05 mL, ziv-aflibercept has been reported to safely and effectively treat neovascular macular degeneration and diabetic macular edema, similar in efficacy to bevacizumab. Presently, there are no reports regarding the effectiveness of preoperative ziv-aflibercept administration prior to PPV for PDR. In this randomized clinical trial, we also evaluate the effectiveness of ziv-aflibercept to bevacizumab, and attempt to elucidate the most appropriate interval for the administration of preoperative ziv-aflibercept in patients with PDR undergoing PPV for non-clearing vitreous hemorrhaging, TRD or extensive fibrovascular proliferation.