Peter Jackson's movie adaptation depicts the Eye of Sauron as the all-seeing eye with the prequel adaption revealing it to be an extending aura with Sauron's spiritual essence serving as the iris.
Peter Jackson's movie adaptation depicts the Eye of Sauron as both an actual ball of flame atop Barad-dûr (which Sauron can actually use to see). The prequel adaption depicts it as an extended aura with Sauron's spiritual essence serving as the iris.