To investigate ranibizumab's benefit on prevention of early postoperative vitreous haemorrhage in PDR-DME patients receiving vitrectomy.

Primary Objective: To investigate ranibizumab's benefit on prevention of early postoperative vitreous haemorrhage in PDR-DME patients receiving vitrectomy.

Secondary Objective:To investigate ranibizumab's additional benefit on visual improvement, facilitation of surgery and postoperative outcomes in PDR-DME patients receiving vitrectomy.

Study design: This study is a prospective, randomized, single-blinded, blank-controlled, multi-center clinical trial that requires vitrectomy for PDR-DME patients.

Inclusion Criteria:

1. Age≥18 years old;
2. Type I or II diabetes mellitus, clinically diagnosed as diabetic macular edema
3. Diagnosed as proliferative diabetic retinopathy and pas plana vitrectomy (PPV) is required to undergo due to non-absorbent vitreous hemorrhage (VH), fibrovascular proliferation with vitreoretinal adhesions or tractional retinal detachment (TRD); or active severe proliferative retinopathy not responding to previous panretinal laser photocoagulation; as well as other indications of PPV at the investigator's discretion
4. Ability to provide written informed consent and comply with study assessments for the full duration of the study.

Exclusion Criteria:

1. Pregnancy or lactation;
2. History of stroke, peripheral vascular disease, angina or myocardial infarction within six months
3. Intraocular treatment with corticosteroids, anti-vascular endothelium growth factor or intraocular surgery within 45 days preceding baseline;
4. Clinically confirmed intraocular pressure (IOP) >=21 mmHg, uncontrolled glaucoma or iris neovascularization in either eye