Facts:
You can hit the eye with the staff of magnus with just one tap, holding and discharging the staff is a waste and yields nothing more than just one tap
Ancano has several surpassing healing potions, he can heal himself to full - not a bug
Every time either player or Ancano hits the eye there is a 10 seconds cooldown during which hitting the eye (for both Ancano or the player) has no effect (vanilla mechanic)
Ancano has a death laser spell that instantly vaporizes anyone with less than 75% magic resistance.
The fight is centered around mechanic of hitting the eye. Either player can hit the eye with the staff of magnus or Ancano with his special spark spell.
Bested all the hardest main bosses and still looking for a challenge? There are still two more fights you can take, but beware, for only the strongest will survive...
In certain areas of the game, you will find the item "Strange Scroll". There is one in Dimhollow Crypt, as well as Mzulft. Enthir also sells them. Use the scroll at the Throat of the World, in the same location where you read the Elder Scroll at the Time Wound. You will need to survive the effect.
After defeating the first secret boss, you can loot it for a teleport scroll that will take you to the second boss.