The purpose of this study is to determine the effect of pre- and intra-operative bevacizumab injection on postoperative vitreous hemorrhage after diabetic vitrectomy.

Postoperative vitreous hemorrhage(VH) is a common complication after vitrectomy for proliferative diabetic retinopathy. Persistent or recurrent VH can delay visual rehabilitation and give patients much trouble. There have been efforts to lower the incidence of postoperative VH such as using intraoperative gas tamponade and preoperative bevacizumab injection. Bevacizumab(Avastin) is a potent inhibitor of angiogenesis and has been shown to decrease retinal and iris neovascularization in proliferative diabetic retinopathy. Recently there have been reports showing that preoperative intravitreal bevacizumab (IVB) injection could reduce intraoperative bleeding from abnormal vessels and could make surgery easier and more successful.Our hypothesis is that preoperative bevacizumab injection could reduce postoperative VH by way of decreasing the amount of abnormal vessels and intraoperative injection could also reduce postoperative VH by inhibiting the vessel formation after surgery.

To prove our hypothesis, we started the prospective randomized comparative study to determine the effect of pre- and intra-operative IVB injection on postoperative vitreous hemorrhage after diabetic vitrectomy.

Inclusion Criteria:

• Patients undergoing first vitrectomy for complications of proliferative diabetic retinopathy such as vitreous hemorrhage, tractional fibrovascular membrane proliferation, tractional or combined retinal detachment)

Exclusion Criteria:

• Follow-up period of less than 6 months
• Intraoperative use of long-acting gas or silicone oil
• Repeat vitrectomy after first vitrectomy for diseases other than vitreous hemorrhage
• Not first vitrectomy
• Uncontrolled hypertension
• Medical history of abnormal blood coagulation
• Time interval between IVB injection and PPV longer than 2 weeks and recent history (within 3 months) of IVB treatment