Board Thread:Theories and Speculation/@comment-27916438-20170329044844/@comment-734582-20170411201914

Ravenlot 27 wrote: In fact, this is the main lie he told, all the other stories were more or less true, though again, limited by his own intel. The Mangekyou losing it's light story is also "more or less" true. Like i said, Obito's case shows that the Mangekyou losing it's light is simply damage, damage that can be healed. Use of the Mangekyou causes damage to it, which is more or less what Itachi said. But it's not that the eye loses light just by existing as some feature. We've seen Sasuke clearly losing light after every use.

So unlike what Itachi made it sound like (a feature), Obito's case shows it's not. Since other eyes exist with greater power and no blindness, it suggests that the Mangekyou is not supposed to go blind.