MIF and proliferative diabetic retinopathy: Comparisons of migration inhibitory factor (MIF), vascular endothelial growth factor (VEGF) and soluble intercellular adhesion molecule-1 (sICAM-1) in vitreous samples from patients with proliferative diabetic retinopathy (PDR) and nondiabetic patients with rhegmatogenous retinal detachment (RD).