Can you not summon up anything to take his attention away from you so that you can focus on the eye.
.... The Staff is not working on the eye....
~Cutscene doesn't load at the start.
~I have the Staff of Magnus (fully charged) but it has no affect on the eye at all.
~I have some other Mages with me who are attacking him too, but they can do no damage.
~The eye is actually closed to begin with so I can't use the staff on it, but Ancano is still protected by his barrier.
~I have reloaded an earlier save and the same thing happened.
~I have left the room, re-entered, left and completed other quests, came back and the same problem exists.