CXCL16 and proliferative diabetic retinopathy: Comparisons of vascular endothelial growth factor (VEGF), CXCL16, CX3CL1, ADAM10 and ADAM17 levels in proliferative diabetic retinopathy (PDR) patients with or without active neovascularization and nondiabetic patients with rhegmatogenous retinal detachment (RD).