A 27-year-old male presents to the emergency with severe pain behind his right eye for the last 30 minutes. He states that his right eye has also been 'watering excessively' for the last two hours. The man has had similar episodes over the last few weeks, but this time the pain is significantly worse which has prompted him to present to the ER. The vitals are normal and ophthalmic examination demonstrates conjunctival injection and miosis of the right pupil. A CT scan of the brain and ESR are unremarkable. Which is the initial treatment of this patient?