EPO and retinopathy of prematurity: Hypoxia induces secretion of pro-angiogenic growth factors, including vascular endothelial growth factor (VEGF) as well as erythropoietin (EPO), which can stimulate uncontrolled retinal vascular growth towards the vitreous at the border between avascular and vascular zones, leading to the second hypoxia-induced proliferative phase of ROP.