What should you know about one red eye?

A small surface blood vessel can break after rubbing, coughing or straining, producing a sharply defined red patch without pain or discharge. Irritation from dust, smoke, contact lenses or chemicals may cause watering and a gritty feeling. Allergic Conjunctivitis commonly causes itching and watering, while Conjunctivitis may cause discharge and eyelids that stick together. A painful red eye can involve deeper inflammation or pressure and cannot be diagnosed from colour alone.

Do not rub the eye. Remove contact lenses and avoid wearing them until symptoms have fully settled and a clinician says they are suitable. Rinse away loose irritants with clean water; after a chemical splash, flush continuously and seek emergency help. Use a clean cool compress for comfort, and do not share towels, cosmetics or eye drops. Arrange an examination if redness persists, worsens or comes with discharge, pain or light sensitivity.

Get urgent eye care for reduced or blurred vision, severe pain, marked light sensitivity, injury, a foreign body that will not wash out, swelling around the eye, or nausea with a painful red eye. Emergency help is needed after a chemical injury or if vision is suddenly affected. Contact-lens wearers with a painful red eye should seek same-day assessment.

Does the redness look like surface irritation, an infection or a deeper eye problem? Should I use any drops, and should I avoid contact lenses for now? Could the other eye become affected, and how can I reduce spread?