Proliferative diabetic retinopathy (PDR) is the most common causes of irreversible blindness in diabetic retinopathy (DR).Although pars plana vitrectomy (PPV) is the cornerstone for treatment of advanced PDR, related postoperative complications such as recurrent VH, NVG, and postoperative fibrovascular proliferation progression may still cause serious visual impairment. Preoperative intravitreal injections of anti-VEGF drugs may represent a new strategy for making vitrectomy safer and more effective for severe PDR.

Proliferative diabetic retinopathy (PDR) is the most common causes of irreversible blindness in diabetic retinopathy (DR).It is characterized by progressive loss of vision, retinal edema, vitreous hemorrhage (VH), retinal neovascularization, fibrovascular proliferation, tractional retinal detachment (TRD) and neovascular glaucoma (NVG).Although pars plana vitrectomy (PPV) is the cornerstone for treatment of advanced PDR, related postoperative complications such as recurrent VH, NVG, and postoperative fibrovascular proliferation progression may still cause serious visual impairment. It is well known that vascular endothelial growth factor (VEGF) is a leading role of the neovascularization, vascular permeability, and diabetic macular edema.preoperative intravitreal injections of anti-VEGF drugs may represent a new strategy for making vitrectomy safer and more effective for severe PDR.Until now, there are two kinds of anti-VEGF drugs in China, including monoclonal antibodies, like imported drug Ranibizumab, militating by block VEGF-A, and fusion proteins, like domectic drug Conbercept, competitively inhibiting the binding of VEGF with its receptor by blocking multiple targets, VEGF-A, VEGF-B, and placental insulin-like growth factor (PlGF). Studies focusing on the comparison of efficacy between preoperative intravitreal injections of the two drugs for patients with severe PDR undergoing vitrectomy is still limited. Thus, in this study, we aim to carry out a more comprehensive comparison in intraoperative and postoperative aspects on the efficacy and safety between intravitreal ranibizumab injection (IVR) and intravitreal conbercept injection (IVC) before vitrectomy of PDR.

Inclusion Criteria:

• patients aged 18 years or more with type 1 or 2 diabetes who were clinically diagnosed with diabetic retinopathy (DR); hemoglobin A1c (HbA1c) ≤ 12%;
• persistent VH for more than 1 month or recurrent vitreous hemorrhage (VH) with or without panretinal photocoagulation (PRP);
• TRD detected by indirect ophthalmoscope or B-scan ultrasonography.

Exclusion Criteria:

• previous vitreoretinal surgeries (including vitrectomy, intravitreal drug injection) in the study eyes;
• eyes with any ocular disease that may hinder visual improvement other than PDR, such as optic atrophy or macular hole;
• history of thromboembolic events (including cerebral vascular infarctions or myocardial infarctions) or coagulation system disorders or receiving anticoagulant or antiplatelet therapy;
• eyes given gas tamponade or additional treatment like ranibizumab injection again or supplementary retinal photocoagulation during follow-up periods.