Instant Eye for an Eye deals X damage to the controller of the source of your choice that dealt damage to you this turn, where X is the damage dealt to you by that source this turn.1
Cannot be used on spells and abilities that cause loss of life. It can only be used on damage. [bethmo 1994/06/01]
This spell is played after damage is dealt to you, so if you lost due to the original damage, you cannot use this spell to get in a final shot at your opponent. [D'Angelo 2000/02/25]
If the damage is prevented, it was never dealt and this spell won't let you choose a source that didn't damage you. [D'Angelo 2000/02/25]
Does white damage to your opponent. [D'Angelo 1994/06/01]