CCN2 and vitreous hemorrhage: BACKGROUND: The study aimed to investigate the changes of vascular endothelial growth factor (VEGF) and connective tissue growth factor (CTGF) concentrations in proliferative diabetic retinopathy (PDR) combined with vitreous hemorrhage (VH) patients after panretinal photocoagulation (PRP), and to explore the risk factors associated with the occurrence of VH.