Board Thread:Naruto Discussions/@comment-26104388-20140919031519/@comment-24808887-20140921102702

@JOA20, of course because Uchiha didn`t have Rinnegan nor "Sages body"(Yang part here), they used degenerated version(Izanag) which costed them(due lack or Yang part i presume) 1 eye per one use.