One hypothesis is that, in the setting of decreased systemic blood pressure, PDE5 inhibitors induces retinal vein engorgement, and since they share a common adventitia with central retinal artery at the level of lamina cribrosa, they compress central retinal artery that eventually leads to retinal ischemia, endothelial injury, vasospasm, and even central retinal artery occlusion [24]. This evidence concerns the gene PDE5A and retinal ischemia.