Board Thread:Theories and Speculation/@comment-5273810-20150207055437/@comment-5407586-20150207112442

Who knows. Kakashi did suffer the blindness that comes along with the Mangekyō Sharingan, so it can't be simply due to Obito's eyes being "special". I guess it was Hashirama's cells that somehow kept the blindness at bay, though I believe that without Susanoo (aka, without the Double Mangekyō) the eye goes blind way slower.