 This study will enrol patients with diabetes who have already elected to undergo pars plana vitrectomy eye surgery to remove persistent vitreous haemorrhage a complication of severe diabetic eye disease in which blood fills the inner cavity of the eye, obscuring the vision and preventing treatment to stop the bleeding. Those in the treatment arm will have an intravitreal injection of ranibizumab Lucentis at the same dose used for the treatment of neovascular wet age-related macular degeneration a disease that has some features in common with diabetic eye disease. 