 NAION produces an ischemic insult in the optic nerve head presumably due to the hypoperfusion of the short ciliary arteries that supply it. This leads to the release of vascular endothelial growth factor VEGF and swelling of the affected area of the nerve. Vascular endothelial growth factor VEGF causes a rapid and reversible increase in vascular permeability and thus vasogenic edema of the affected area of the optic nerve head. Subsequently, increased pressure from the swelling of the affected segment causes compression and infarction of the previously not affected parts of the optic nerve by creating a sort-of compartment syndrome. 