Quote Originally Posted by GreatLimmick
And maybe that's how Kakashi knows Itachi's eyesight is deteriorating? After all, Kakashi's Sharingan is always on as well. (Sure, he keeps that eye closed and covered most of the time, but it's still on.
it's deteriorating from the usage of MS, not the normal sharingan.

maybe he has to keep it on all the time because his eye sight has gotten so bad from the use of the MS... otherwise he'd be a blind mofo.