Your son might be suffering from amblyopia ,be careful for his  vision recovery otherwise you will repent later on. Diminition of vision without any pathology is known as amblyopia & in common language called lazy eye. Amblyopic eye can only be treated upto 10 yrs with the help of occlusion &,pleoptic treatment which is not available every where, you will have consult eye hospital with well equipped orthopedics & pleoptic department with well trained paramedical staff.Parents  with amblyopic child will have to search such hospital .I have experience of minimum 2000 children getting 6/6 or 6/9 from less than 6/60 vision but diagnosis of amblyopia before 10 yrs is must because there is not much improvement even after dedicated pleoptic for 2-3 months. Lazy eye ultimately to divergent squint because it takes anatomical position, our eyes are straight because vision keeps eye straight. Eyes with no Vision or very less vision will always lead to divergent squint, so eyes with divergent squint even after squint surgery again results into divergent squint. Most important point to note here is if amblyopic child vision is restored normal with the help of pleoptic treatment & the operated for Squint surgery it will remain straight & have binocular single Vision through out life & child will never face the problem of divergent squint again in life.