[How I explore ... differential diagnosis of a red eye].

As a common reason for consultation, red eye can be a symptom of benign diseases, such as conjunctivitis, subconjunctival hemorrhage, dry eye syndrome,..., which can be managed by the general practitioner or internist. Conversely, more serious pathologies require a ophthalmologist management: these are keratitis, uveitis, acute glaucoma attack, or endophtalmitis. This article is intended to help practitioner to guide diagnosis when he's faced with a red eye.