From WoWWiki
The Eye of Sargeras as seen in Warcraft 3: The Frozen Throne
An artifact found in the
Tomb of Sargeras by
Illidan Stormrage. The artifact was sought by both Illidan and
Gul'dan, the former gaining it only through the aid of the
Naga, the latter being torn apart by crazed demons. We don't know if the Eye was Sargeras's actual eye, or simply an artifact which held a portion of his power after the battle with
Aegwynn. (Illidan after all claims that the power of Sargeras is beyond his grasp)
The Eye of Sargeras was used by Illidan in an attempt to destroy the Frozen Throne, but the intervention of Malfurion and Maiev destroyed the Eye instead.
