The face contains countless vessels, and it is practically impossible to inject fillers without damaging the vessels at all. The reason why we should know the vessel structure and positioning relationship of the arteries is to avoid these complications which can lead to skin necrosis and visual complications. Figure 3.1 shows the facial supraorbital and supratrochlear arteries which most likely to cause such complications. Of course, if the filler is injected into the superficial temporal artery, it can reach the ophthalmic artery via the supraorbital or supratrochlear artery, both able to cause eventually visual complications.