[From conjunctivitis to glaucoma. When is a red eye an alarm signal?]

A red eye is mostly a relatively harmless sign of simple conjunctivitis. Viral conjunctivitis may be extremely contagious. If no improvement is seen after ten days of treatment, referral to an ophthalmologist is indicated. Local corticosteroids and local anesthetics must not be prescribed. The patient should also be referred to an ophthalmologist when the red eye is chronic or recurrent, and when a unilateral red eye is associated with severe pain and vomiting (suspicious for acute glaucoma!), or generally when severe pain or impairment of sight, indicative of corneal infiltration or a hypopyon, presents. The diagnostic use of fluorescein to stain the cornea and any alteration of corneal transparency also belong in the hands of the ophthalmologist.