Proliferative diabetic retinopathy (PDR) is the most common causes of irreversible blindness in diabetic retinopathy (DR).Intravitreal injection of anti-VEGF drugs is a good adjunct to vitreous surgery for severe PDR. Some studies have confirmed that the application of anti-VEGF drugs before vitrectomy for PDR patients can reduce the difficulty of surgery and improve postoperative best corrected visual acuity (BCVA), but very few researches focused on the injections of anti-VEGF during surgery.Therefore, investigators carry out this clinical trial to compare the effects of preoperative and intraoperative intravitreal injections of ranibizumab (IVR) on vitrectomy outcomes for PDR patients.One group receive ranibizumab injection (0.5mg/0.05ml) 3-5 days before vitrectomy. Another group receive ranibizumab injection (0.5mg/0.05ml) at the end of vitrectomy. Intraoperative and postoperative indices are collected for further comparison.Investigators enroll PDR patients whose baseline characteristics including age, sex, BMI, type of diabetes, HbA1c level, duration of DM, hypertension, previous history of laser photocoagulation, status of lens, indication for surgery, baseline BCVA, IOP, baseline CRT and extent of VAG are comparable.The enrolled eyes are randomly assigned according to the Central Randomization System with a ratio of 1:1 to preoperative IVR group and intraoperative IVR group. Intraoperative including surgery time, intraoperative bleeding, intraocular electrocoagulation use, iatrogenic retinal breaks, relaxing retinotomy and silicone oil tamponade, and postoperative indices including postoperative best-corrected visual acuity (BCVA), central retinal thickness (CRT), postoperative vitreous hemorrhage (VH), neovascular glaucoma (NVG), recurrent retinal detachment, postoperative fibrovascular proliferation progression and reoperationare collected for further comparison.

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 progressive fibrovascular proliferation 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.Intravitreal injection of anti-VEGF drugs before or during PPV maybe a good adjunct to vitreous surgery for severe PDR. Some studies have confirmed that the application of anti-VEGF drugs before vitrectomy for PDR patients can reduce the difficulty of surgery and improve postoperative best corrected visual acuity (BCVA),but very few researches focused on the injections of anti-VEGF during surgery.Therefore, investigators carried out this study to compare the effects of preoperative and intraoperative intravitreal injections of ranibizumab (IVR) on vitrectomy outcomes for PDR patients.Investigators enroll PDR patients whose baseline characteristics including age, sex, BMI, type of diabetes, HbA1c level, duration of DM, hypertension, previous history of laser photocoagulation, status of lens, indication for surgery, baseline BCVA, IOP, baseline CRT and extent of VAG are comparable.The enrolled eyes are randomly assigned according to the Central Randomization System with a ratio of 1:1 to preoperative IVR group and intraoperative IVR group. Intraoperative and postoperative indices are collected for further comparison. Intraoperative indices including surgery time, intraoperative bleeding, intraocular electrocoagulation use, iatrogenic retinal breaks, relaxing retinotomy and silicone oil tamponade. Investigators compare whether there are statistical differences in the above indicators between the two groups. Meanwhile, postoperative indices are collected during 1week, 1 month, 3 month follow-up, including best-corrected visual acuity (BCVA), central retinal thickness (CRT), postoperative vitreous hemorrhage (VH), neovascular glaucoma (NVG), recurrent retinal detachment, postoperative fibrovascular proliferation progression and reoperation. Investigators compare whether there are statistical differences in the above indicators between the two groups at different visit time.

Inclusion Criteria:

• patients aged 18 years or more with type 1 or 2 diabetes who were clinically diagnosed with PDR;
• persistent VH for more than 1 month or recurrent VH with or without panretinal photocoagulation (PRP);
• TRD detected by indirect ophthalmoscope or B-scan ultrasonography.

Exclusion Criteria:

• previous vitrectomy or intravitreal 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;
• poor control of diabetes mellitus (DM) with hemoglobin A1c (HbA1c) > 12%;
• 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 during follow-up periods.