Signaling events regulated by stabilized HIF-1a contribute to the pathogenesis of ROP: Avascular retina and Vasoproliferation. (HIF1α, Hypoxia-inducible factor-1 ALPHA; VEGF, vascular endothelial growth factor; STAT3, signaling transducer and activator of transcription 3; EPO, erythropoietin; PRVD, physiologic retinal vascular development)