Certain percent of the eyes with proliferative diabetic retinopathymay require pars plana vitrectomy (PPV) due to vitreous haemorrhage, proliferative membrane, and tractional retinal detachment. This study will compare intravitreal injection of anti-vascular endothelial growth factor (ranibizumab) versus sham injection before vitrectomy for PDR. The main focus is to see if pre-operative injection of ranibizuman can reduce peri-operative hemorrahge related complications.

Eyes responding to panretinal photocoagulation can remain stable for decades, but incomplete responses and relapses can occur in a certain percent of diabetic patients showing as proliferative diabetic retinopathy. At present vitrectomy is the main intervention for those eyes with vitreous hemorrhage, proliferative membrane, and tractional retinal detachment. And the surgical procedure might be complicated because of intraoperative bleeding. And post-operative complications might be also involved. Perioperative use of intraocular anti-VEGF might be associated with less hemorrhage related complications and better visula acuity. This study will compare intravitreal injection of anti-vascular endothelial growth factor (ranibizumab) versus sham injection one week before surgery. The investigators tried to make sure whether pre-operative injection of ranibizuman can reduce reduce intra-operative bleeding, reduce the frequency of using endodiathermy, decrease surgical time, improve microcurculation of retina, and elevte best-corrected visual acuity.

Inclusion Criteria:

• type I or type II diabetes
• there is clear indications for vitrectomy due to proliferative membrane in the vitreoretinal interface, mild hemorrhage, or tractional retinal detachment
• retinal large vessels could be detected within one PD away from the edge of optic disc by OCT
• microcurculation could be detected by FFA in at least one quadrant
• the patient could tolerant FFA examination

Exclusion Criteria:

• a history of vitrectomy or scleral bucke in the included eye
• retinal laser photocoagulation treatment within 90 days in the included eye
• anti-VEGF treatment with 90 days in either eye
• there is cocurrent neovascular glaucoma in the included eye
• any reason that might hinde the procedure of vitrectomy, FFA OCT or the observation of ocular fudus
• a history of cere-brovascular accident or heart stroke
• renal failure
• could not attend follow up regularly