Those glowing green eyes underneath his blindfold? They're not eyes - they're green orbs of fel magic that replaced his eyes after Sargeras burned them out. They essentially give Illidan magical x-ray vision. This was a "gift" in return for his allegiance to the Burning Legion. This was actually a ruse, as Illidan intended to betray the Legion later - though having your eyes burned out to stick to your bluff is pretty hardcore.