ive thought this too. i suspect madara's eyes weren't losing their light like itachi, but rather lost their light forever like danzo's and tobi's eyes after izanagi. because in the flashback madara's eyes were bandaged. but izuna definatly died because the clan later resented madara for taking his bros eyes and called him powerhungry, or greedy, or vengeful or w/e. in the end he left or was forced out of the clan only to return to battle hashirama for the title of hokage. i mention izuna's death because some ppl think he's tobi. i do not.