It seems that your son is suffering from spring catarrh, which can cause keratitis and should get better as he grows older. This condition does not respond to treatment quickly and vision does not get affected either however chronic nature of this condition causes bother to patients. This is usually caused by allergy to something like grass or pollen and affects both eyes. He seems to be getting too much treatment. If it is peripheral keratitis just in one eye, find out what is causing this in the first place.