Cursed Vision of Sargeras

Cursed Vision of Sargeras is an epic leather helm for physical DPS classes.

Source
This item drops from Illidan Stormrage in the Black Temple.

Origin
When Illidan joined forces with the Burning Legion in the War of the Ancients trilogy, Sargeras "gifted" him with new vision. He did this by burning his eyes from his skull and replacing them with an ability to see the magic in existence all throughout Kalimdor. Because the sight of his empty eye sockets was unnerving and displeasing to Azshara and her Highborne, and because it did not impede his magical vision, Illidan was given an amber cloth which he tied around his head over his eyes.

As it's the new eyes given by Sargeras that granted him a new vision, it seems to be a mistake that Illidan's bandana allows players to see demons. See : Illidan's Bandana Retcon