Don't have any direct experience with dyslexia but was wondering whether you've tried throwing your son a few pitches. Not only for practice, but to determine whether your son is unable to see in three dimensions at all, or whether his ability to perceive or 'place' a moving object in three dimensions is affected by distance, speed and/or duration of visually tracking the object. It could be that he has [or recently acquired] a visual or visual/spatial condition unrelated to his dyslexia.
Tried a search for online dyslexia support groups. No success; only useful item was this article on learning disabilities which lists several support groups. [They may have Web sites - didn't check.]
Suggest you also try the neuroscience and ophthamology branches of the NIH - depth perception, parallax, etc.