VEGFA and retinal ischemia: Microangiopathy leads to retinal ischemia, visual impairment, activation of the polyol pathway, accumulation of late glycosylation end products (AGEs), oxidative stress, activation of protein kinase C, inflammation, upregulation of the renin-angiotensin system and vascular endothelial growth factor (VEGF), and ultimately disruption of the blood-retinal barrier (BRB)