Mrs Straw is a 27 year old nursery school teacher who is concerned about her eyes. She reports a three day history of red and itchy eyes, which intermittently have a watery discharge. Her vision is normal and she has had no pain. Systems review is normal apart from a recent upper respiratory tract infection which she thinks she caught from a child at work. Mrs Straw is normally fit and well, she drinks 14 units of alcohol a week and does not smoke. Examination reveals moderate erythema of the palpebral conjunctiva and small follicles seen on eyelid eversion. Eye movements are normal and visual acuity is 6/6 with glasses.
Based on the likely diagnosis, what is the most appropriate treatment?