H.W.
I second the idea of a pediatric opthalmologist. You need a doctor who will test for eye function and not just acuity.
Likely, they will be able to give him some exercises or do therapy to help strengthen the eye. My son is five and has some vision issues; for him, we've found the therapy to be very helpful. He has 20/20 acuity, but will have a diagnosis for other eye issues when he's 11 and his eyes are fully developed, to determine if glasses are needed.