Red Eye: What It Means and When to Worry

The harmless causes

• Viral conjunctivitis: watery, gritty, often starting in one eye and spreading to the other, with a cold; clears in one to three weeks
• Bacterial conjunctivitis: sticky discharge, lids stuck on waking; treated with antibiotic drops
• Allergic conjunctivitis: itching above all, both eyes, with sneezing; antihistamine drops
• Dry eye and blepharitis: chronic, mild redness with grittiness, worse later in the day
• Subconjunctival hemorrhage: a bright red patch on the white of the eye, painless, alarming to look at, harmless; clears in one to two weeks
• Irritation from smoke, chlorine, wind, screens or a contact lens worn too long

The causes that need same-day care

• Corneal infection or ulcer, especially in a contact lens wearer: pain, light sensitivity, a white spot on the cornea
• Iritis or uveitis, inflammation inside the eye: deep ache, light sensitivity, redness concentrated around the cornea, sometimes with a small pupil
• Acute angle-closure glaucoma: severe pain, headache, nausea, halos, a hazy cornea
• Scleritis: deep, severe, boring pain in a violet-red eye, often with autoimmune disease
• Herpes simplex or zoster keratitis: pain, light sensitivity, sometimes a rash
• Injury or a chemical splash

How to tell them apart at home

Ask three questions. Does it hurt, beyond grittiness? Is light uncomfortable? Is vision reduced? A yes to any means the eye should be examined the same day. Also ask: do you wear contact lenses? If so, remove them and be seen the same day whatever the answers. Redness with discharge, itch or a cold and none of the above is almost always conjunctivitis.

What to avoid

Redness-relief drops constrict the surface vessels and whiten the eye temporarily; with repeated use the vessels rebound and the eye becomes redder, and the drops hide the signs an examination needs. Use preservative-free lubricants instead. Do not use leftover prescription drops, particularly steroids, which can worsen an infection. Do not wear contact lenses in a red eye.

The examination

The slit lamp shows the pattern of redness, the state of the cornea with dye, the front chamber of the eye for inflammation, and the lids and lashes. Eye pressure is checked. Most diagnoses are made in minutes and treatment starts the same visit.