Red eye: diagnostic criteria, signs of alert and therapeutic approach.

"Red eye" is one of the main reasons of urgent consultation in Primary Care and in Ophthalmologic Emergencies. In many cases, the underlying cause is a benign condition that can be managed by the Primary Care Physician. However, not every red eye is a conjunctivitis, so it is important to recognize the warning signs and symptoms associated with potentially serious conditions. Causes of red eye include diseases of the ocular surface (conjunctivitis), which are generally benign; internal eye diseases (uveitis, glaucoma, scleritis, trauma) and extraocular diseases (cavernous sinus thrombosis, orbital cellulitis), which are generally ophthalmic and systemically severe, respectively. In this expert review, we aim to provide a practical approach to the differential diagnosis of red eye in general practice, defining the criteria of severity and urgency for referral to a specialized Ophthalmology consultation.