Why isn't Tobi blind yet? There is a Naruto character named Tobi who maintains his eyesight though his special ability should have caused a great amount of macular degeneration. The following includes extensive spoilers.


   By my math, Tobi possesses his Mangekyo for quite some years. It is his Mangekyo, he stated it himself. So in that case, how come he hadn't gone blind yet? Itachi went almost completely blind in under 10 years. Sasuke got half blind in less than 1 year (because he abused it freely).


So how come Tobi hasn't gone blind? As far as I can figure:


   He obviously replaced his other eye, but it was kept behind his one-eyed mask for a long period of time, he didn't use it for vision.
This answer contains lots of spoilers so I might as well make one block, edit if you will


   When Madara rescued Obito from the collapsed cave he used Hashirama
 Senju's living clone to heal Obito's crushed body. Not only did this
 heal Obito's body but it also gave him access to Hashirama Senju's
 abilities, the wood release ability, as seen when he defeated the
 ninjas who wanted to steal Rin's body.
 Now Hashirama Senju had unique medical ninjutsu which healed himself without forming any
 seals whatsoever. So if Obito gained access to the wood release ninjutsu he may also gained 
 this medical ninjutsu, which in turn healed his eye throughout the years.