Conjunctivitis: red eye, three very different causes

What it is, in plain words

Conjunctivitis is inflammation of the thin membrane covering the white of the eye and the inside of the eyelids. The vessels dilate and the eye looks pink. The important task is not to treat every red eye the same, because a viral, bacterial, allergic or dangerous inner-eye cause each behaves differently.

Signs to look out for

• Viral: watery discharge, often starting in one eye then the other, gritty feeling, recent cold, swollen preauricular gland
• Bacterial: thick yellow or green discharge, lids stuck together in the morning
• Allergic: both eyes, intense itching, swelling, sneezing and a runny nose
• Vision remains normal in all three, apart from transient blurring cleared by blinking
• Pain, photophobia or reduced vision indicate a different, more serious problem

Why it happens

Viral conjunctivitis, usually adenovirus, is highly contagious and spreads by hands and shared towels. Bacterial forms are commoner in children. Allergic forms follow pollen, dust mites or animal dander.

How doctors confirm it

Diagnosis is clinical. Swabs are reserved for severe, recurrent or newborn cases, or for suspected chlamydia or gonorrhoea, which need urgent specific treatment.

Treatments and solutions

• Viral: cool compresses, artificial tears, strict handwashing, own towel, no shared pillow, resolves in one to two weeks
• Bacterial: often self-limiting, with antibiotic drops shortening the course in more purulent cases or contact lens wearers
• Allergic: antihistamine or mast cell stabiliser drops, cold compresses, allergen avoidance
• Stop wearing contact lenses until fully recovered, and replace the lens case
• Avoid corticosteroid drops unless prescribed by an ophthalmologist, as they worsen herpes infections

Living with it day to day

Return to school or work is guided by symptoms and hygiene rather than by a fixed number of days; the discharge is contagious as long as it persists.

When to seek medical help

See an eye specialist urgently for eye pain, sensitivity to light, reduced vision, a corneal white spot, contact lens use with severe redness, or a newborn with a discharging eye.

This article explains general health information in simple language. It does not replace advice from your own doctor.