Eternal Mangekyo Sharingan

The Eternal Mangekyo Sharingan is a form of Sharingan that after the user goes blind from using Mangekyo Sharingan and steals a siblings Mangekyo Sharingan eye(s)(this is also the real reason that Itachi let Sasuke live).

The only know user of this "eternal Mangekyo Sharingan" is Madara Uchiha/Tobi,current member of the Akatsuki and sorta a part-time boss of the Akatsuki.

Thats all the info I have now and if you have more information plz tell me.