Eye for an Eye

The next time a source of your choice would deal damage to you this turn, instead that source deals that much damage to you and Eye for an Eye deals that much damage to that source's controller.

Masters Edition IV

Fifth Edition

Play only when a creature, spell, or effect assigns damage to you. Eye for an Eye deals an equal amount of damage to that source's controller.

Fourth Edition Foreign Black Border

Fourth Edition

You may cast Eye for an Eye only when a creature, spell, or effect deals damage to you. Eye for an Eye deals an equal amount of damage to the controller of that creature, spell, or effect. If another spell or effect reduces the amount of damage you receive, it does not reduce the damage dealt by Eye for an Eye.

Summer Magic / Edgar

Eye for an Eye must resolve before damage would be dealt to you in order to affect that damage.

The damage dealt to you is still being dealt by the original source. The damage dealt to the other player is being dealt by Eye for an Eye.