How does Obito not lose his eyesight after excessive use of the mangekyo? I've been thinking about his Mangekyo and how it seems to have had no impact on his eye sight and how he could have escaped the effects. After much thought on the topic I think I might have the solution and am wondering if this is a valid theory or not. My theory is you need both Mangekyo to hurt your vision. Since he had only 1 eye this effectively allows him to use part of its power for no effect compared to people like Itachi and Sasuke who do have both and had issues with this. Basically if I didn't make it clear enough with only 1 eye he couldn't get Susanoo or the other great abilities but also didn't have the downside of losing his sight. So do you think this is a valid theory? I know its unprovable either way just trying to see if I'm the only one who thinks this is a possible solution.
Considering he have hundreds of spare Sharingan and half body of white zetsu. It is quite easy for him to maintain Mangekyu Sharingan (can never actually use eternal mangekyu).

We can see that in the scene when he transplanted Itachi's eyes to Sasuke.