RBP3 and Hyperglycemia: Conversely a growing body of evidence indicates that hyperglycemia-induced downregulation of a number of important neurotrophic factors, such as NGF, Pigment epithelium-derived factor (PEDF), CNTF, interphotoreceptor retinoid-binding protein (IRBP) and somatostatin, the loss of which may have a direct impact on neuronal survival [188].