your present problem of dryness and foreign body sensation is not related to dilatation done by your doctor. for dryness the doctor has prescribed you systane eye drop which is a very good lubricating eye drop. the cause of foreign body sensation could be meibomitis (inflammation of meibomian glands). for that you can do hot fomentation and lid massage with index finger from up to down. you can also apply antibiotic steroid combination eye ointment over the lid margins. also keep using systane eye drop. for further information consult an eye care ophthalmologist online --> <link>
what could cause foreign body sensation in the eye?