I wouldn't rule out vision. But, I can also add that, in my experience as a parent and as a teacher, kids can get frustrated when their intellectual interests do not match up with what is at a comfortable reading level. If he is able to think abstractly, deeply, and quickly, then even if he has a high reading level, the books that he can read on his own aren't rewarding enough intellectually. I would highly suggest reading aloud to him. Or, allow him to do puzzles or move around while listening to audio-books. I think that you will find that he will like it more. I also think that you will find that he will retain the information and that the positive attitude toward "books" will then transfer to printed text after a while.
