Is the vision affected?
Headache and change in pupil size could be due to glaucoma(pupil dialted when eye pressure is raised) or uveitis(pupil may be constricted). A refreactive error can also cause a headache but it does not cause change in pupil size. In the initial stages in glaucoma and uveitis vision may not be affected. He needs to be seen by an ophthalmologist to rule out these conditions. Another possibility could be papilledema in which the intracranial pressure may be raised which can cause headache. You should see an ophthalmologist early. Thanks and best wishes.
Please, click the ACCEPT BUTTON so that I can get my dues. BONUS and a POSITIVE FEEDBACK will be appreciated.