Hm. So he appears to read well, which suggests that he uses some method that works (perhaps only one of his eyes at a time) while reading, but then struggles with physical written output, despite apparently good oral expression. That would be in line with the act of writing being the problem, whether because of visual, fine-motor, or eye-hand coordination reasons, or perhaps inattention. (In an older child, I would throw in automaticity, too, but most children of this age don't have automaticity for handwriting, so that wouldn't distinguish him from age-peers.) It's possible the absence of binocular vision, or even switching back and forth between the two eyes, may interfere with his ability to coordinate what he sees on the page with his motions. I would echo following up on this with the developmental opto. Vision needs to be ruled out as the principal cause, before you move on to an occupational therapist eval, let alone ADHD. (Just about everything looks like distractibility in small children.)
