Board Thread:Naruto Discussions/@comment-24824148-20160724215526/@comment-732150-20160724221535

The first time MS-induced blindness was mentioned, was when Kakashi himself asked Itachi (or rather, Sasori's underling who was shapeshifted into Itachi) how bad his eye-sight was. Considering a few chapters later Kakashi himself was revealed to have MS, it stands to reason he would know about the deteriorating eye-sight because he himself was experiencing it. Kakashi's simply wasn't as bad because he hardly ever used MS.