The purpose of this study is to determine the effect of pre and intra-operative bevacizumab injection on postoperative vitreous hemorrhage after diabetic vitrectomy in comparison to vitrectomy without bevacizumab injection.

Postoperative vitreous hemorrhage is a common complication after vitrectomy for proliferative diabetic retinopathy. Bevacizumab (Avastin) is a potent inhibitor of angiogenesis and has been shown to decrease retinal and iris neovascularization in proliferative diabetic retinopathy. We believe that preoperative bevacizumab injection could reduce postoperative vitreous hemorrhage by decreasing the amount of abnormal vessels and intraoperative injection could also reduce postoperative vitreous hemorrhage by inhibiting the vessel formation after surgery

Inclusion Criteria:

• patients undergoing first vitrectomy for vitreous hemorrhage secondary to proliferative diabetic retinopathy

Exclusion Criteria:

• follow-up period of less than 3 months
• not first vitrectomy
• abnormal blood coagulation
• uncontrolled hypertension