Painful red eye

A man in his early 30s comes to the emergency room (ED) to assess a painful red eye that has been present for the last ten days but has no significant medical history. The patient does not use contact lenses and claims that the right eye pain is unrelated to any discharge or change in vision. He claims that while he has experienced pink eye, it often goes away more quickly and is not as severe. The left eye of the patient remains unaffected. The vital signs of the patient are normal. Except for the right eye, which is red, the physical examination is normal (Figure). Conjunctiva, eyelids, sclera, cornea, pupil, anterior uvea, and other structures are examined.