Board Thread:Naruto Discussions/@comment-1872728-20160329033053/@comment-5407586-20160501201140

Thekillman wrote: As to why this even fixes it, i would say that the donor's chakra stays in the eye, and is reinforced with the acceptor's chakra. This mixture is strong enough to resist wear. On the other hand, Obito's zetsu body was already strong enough to resist wear on it's own. Itachi's Mangekyō did last for quite some time as well, though not as long as Obito's. I agree on the Zetsu part (though I'd say it was Hashirama's cells which helped) slowing down/stopping the blindness induced from the dōjutsu's overusage.

Even the theory about Susanoo being the main reason for inducing blindness is good.