Red Eye

A red eye is one of the commonest things people worry about, and most of the time the cause is minor — conjunctivitis, dryness, an irritated eyelid, or a burst surface blood vessel that looks dramatic and means nothing.

Three features separate the harmless from the sight-threatening, and they are worth memorising: significant pain in the eye itself, sensitivity to light, and any change in vision. A red eye with none of those is very rarely serious. A red eye with any of them needs assessing in person, usually the same day.

The fourth thing that changes the calculation is contact lenses. A painful red eye in a lens wearer is treated as a corneal ulcer until proven otherwise, because sight can be lost within days.

Usually harmless

• Conjunctivitis — gritty and sticky rather than painful, often both eyes, vision unaffected. Most cases are viral and clear without antibiotics
• Subconjunctival haemorrhage — a bright red patch of blood on the white of the eye, from a cough, sneeze or nothing at all. Alarming to look at, painless, and resolves over two to three weeks without treatment
• Blepharitis — red, sore lid margins with crusting
• Dry eye, which causes redness and paradoxical watering
• Allergic conjunctivitis — itchy, watery, both eyes, seasonal
• Stye or chalazion causing localised lid redness

Needs urgent in-person assessment

• Keratitis or corneal ulcer — painful, light-sensitive, and strongly associated with contact lens wear
• Iritis (uveitis) — a deep ache, light sensitivity, blurring, often recurrent and sometimes linked to inflammatory conditions
• Acute angle-closure glaucoma — severe pain, haloes around lights, vomiting, a hard eye
• Scleritis — severe boring pain that wakes you at night
• Orbital cellulitis — spreading lid swelling with fever and painful eye movement

Send clear, well-lit photographs before your appointment — one wide, one close-up, and one with the lower lid gently pulled down. Eyes photograph well and the images add a great deal.

The honest limit

We cannot examine your eye with a slit lamp, stain the cornea with fluorescein, or measure the pressure inside the eye. Those are what confirm or exclude the serious causes. What a consultation does reliably is sort a red eye into "this needs seeing today" or "this is minor and here is how to treat it" — and it does that quickly, which for a painful eye is exactly what you need.

What the consultation covers

• Screening for the three sight-threatening features — pain, photophobia, changed vision — and for contact lens use
• Distinguishing conjunctivitis from lid disease from dry eye, which have different treatments
• Whether antibiotic drops are actually needed. Most conjunctivitis is viral and self-limiting; antibiotic drops are handed out far more often than the evidence supports
• Treatment for allergic eye disease, dry eye and blepharitis, prescribed where appropriate
• Advice on hygiene and avoiding spread, and when to stay off work or school
• Immediate direction to eye casualty where the picture is not benign — with the reasoning set out so you are not starting from scratch

How do I know if it's just conjunctivitis?

Three features distinguish it, and they are easy to check yourself:

• Conjunctivitis: gritty or itchy rather than painful, discharge or crusting, redness spread diffusely across the white, vision unaffected, and bright light merely irritating
• Something more serious: deep aching pain, reduced vision, genuine light sensitivity, redness concentrated in a ring around the iris, an abnormal pupil, or only one eye affected with severe symptoms

The three that matter are pain, vision and light sensitivity. Any of them means same-day assessment.

Do I need antibiotic drops?

Usually not. Most conjunctivitis is viral, and antibiotic drops do nothing for it. Even bacterial conjunctivitis largely resolves on its own within a week or two — drops shorten it slightly and are worth it in some circumstances, but the reflex prescription is not necessary and contributes to resistance.

Where they are appropriate: heavily purulent discharge that reglues the lids within minutes, symptoms not settling after a week, contact lens wearers under supervision, or anyone immunosuppressed.

I wear contact lenses. Is that different?

Yes, categorically. Lens wearers can develop microbial keratitis — an infection of the cornea itself — which threatens sight and progresses quickly. It presents as a red, painful eye with light sensitivity and sometimes blurred vision, and early on it can be indistinguishable from conjunctivitis.

Remove the lenses, keep them, and get the eye examined the same day. Do not resume lens wear until you are told it is safe.

What's wrong with redness-relief drops?

They constrict the blood vessels in the eye, which makes it look white without treating anything. When they wear off the vessels dilate more than before, so the eye looks worse, so more drops go in — a genuine dependency loop. They also mask a red eye that may need assessing. Lubricating drops are the right choice for comfort.

Can I go to work or send my child to school?

Yes. Conjunctivitis is not a reason to keep a child off school — that is current national guidance, and exclusion policies asking otherwise are out of date. Sensible hygiene is what matters: separate towels, frequent handwashing, and not sharing pillows or flannels. The same applies to adults at work.

When is a red eye acute glaucoma?

The picture is distinctive and dramatic: a severely painful red eye, blurred vision, coloured halos around lights, a hazy-looking cornea, an oval mid-sized pupil, and often severe headache with nausea and vomiting. It typically affects one eye, comes on over hours, and is more common in older and long-sighted people.

It is an emergency — A&E, not an appointment. Pressure in the eye damages the optic nerve within hours. It is not uncommonly first treated as a migraine or a stomach bug because of the headache and vomiting.

Can an eye really be assessed over video?

Partly, and it is worth being straight about where the line falls. We can take the history — which distinguishes most causes — look at good photographs, ask you to test each eye's vision separately against text, check for light sensitivity, prescribe where appropriate, and decide urgency.

What we cannot do is examine the eye with a slit lamp, stain the cornea with fluorescein, or measure the pressure inside the eye — and those are what settle the serious causes.

Where should I go if I need an eye examined today?

Two good options, and the first surprises people: most high street optometrists offer acute eye assessments — often at no charge under NHS minor eye conditions schemes — and they have exactly the equipment needed. They are frequently the fastest route to a proper eye examination in the UK, faster than any GP and far faster than A&E.

For an injury, chemical splash, sudden vision loss or suspected acute glaucoma, go to A&E or a dedicated eye casualty.