← All articles
Clinical Resources
The Red Eye: Conjunctivitis or Something Serious?
How to distinguish benign conjunctivitis from sight-threatening acute glaucoma, uveitis, or keratitis, and when to refer patients urgently.
Why this matters
Community pharmacists are often the first point of contact for patients seeking over-the-counter treatment for a red or irritated eye. Most presentations are benign, such as bacterial or allergic conjunctivitis. A small proportion, however, represent genuine ophthalmic emergencies that can lead to permanent sight loss within hours if left untreated.
The key conditions to recognise are acute angle-closure glaucoma, anterior uveitis, microbial keratitis, and chemical or traumatic injury. Important warning features include pain, photophobia, reduced visual acuity, or a cloudy cornea. Bilateral itchy eyes with normal vision are usually benign. A unilateral red eye with pain, photophobia, or any visual disturbance requires same-day eye casualty assessment.
Chemical eye injuries are a separate emergency. Any acid, alkali, or cleaning product splash to the eye requires immediate irrigation with clean water or saline before assessment. Irrigation should not be delayed while waiting for professional advice. After initial irrigation, the patient must attend Eye Casualty or Accident and Emergency (A&E) without delay.
Red flags vs more likely benign
| Feature | More likely benign | Red flag ⚠ |
|---|---|---|
| Laterality | Bilateral involvement | Unilateral, especially with pain, photophobia, or vision change |
| Pain | None or mild gritty sensation | Deep aching, sharp, or severe pain |
| Vision | Normal | Reduced, blurred, or altered vision |
| Photophobia | None or mild | Marked photophobia or inability to tolerate normal light |
| Pupil | Round and reactive | Irregular, fixed, or mid-dilated |
| Cornea | Clear | Hazy, cloudy, or visible corneal infiltrate |
| Discharge | Purulent in bacterial conjunctivitis, watery and itchy in allergic conjunctivitis | Little or no discharge despite pain: consider glaucoma, uveitis, or keratitis |
| Contact lenses | Not worn or occasional use without problems | Regular wearer with painful red eye: possible keratitis including Acanthamoeba keratitis |
What to do in pharmacy
Chemical eye injury: if a patient describes an acid, alkali, or cleaning product splash to the eye, advise immediate irrigation with clean water or saline and refer without delay to Eye Casualty or A&E. Do not wait until irrigation is complete before calling for help. Chemical injury can cause irreversible corneal damage within minutes, with alkali injuries (such as bleach or oven cleaner) penetrating more deeply than acid.
Penetrating eye injury or suspected embedded foreign body: advise the patient not to rub or irrigate the eye. Attend Eye Casualty immediately. Do not attempt to remove an embedded object.
Suspected acute angle-closure glaucoma: this is a clinical emergency. Features include severe unilateral eye pain, markedly reduced vision, halos around lights, a fixed mid-dilated pupil, a hazy or steamy-looking cornea, and associated nausea or vomiting. The condition may be mistaken for migraine. Emergency same-day ophthalmology assessment is required: direct the patient to Eye Casualty, an Ophthalmology Emergency Department, or A&E according to local provision. Call 999 if transport is not available or the patient is deteriorating rapidly. Do not refer to a GP or optician in the first instance.
Penetrating eye injury or suspected embedded foreign body: advise the patient not to rub or irrigate the eye. Attend Eye Casualty immediately. Do not attempt to remove an embedded object.
Suspected acute angle-closure glaucoma: this is a clinical emergency. Features include severe unilateral eye pain, markedly reduced vision, halos around lights, a fixed mid-dilated pupil, a hazy or steamy-looking cornea, and associated nausea or vomiting. The condition may be mistaken for migraine. Emergency same-day ophthalmology assessment is required: direct the patient to Eye Casualty, an Ophthalmology Emergency Department, or A&E according to local provision. Call 999 if transport is not available or the patient is deteriorating rapidly. Do not refer to a GP or optician in the first instance.
Send the patient to eye casualty the same day for: any unilateral red eye with deep aching pain, photophobia, or reduced visual acuity (suggesting anterior uveitis or keratitis); a visible corneal infiltrate or any corneal clouding; an irregular or poorly reactive pupil; a contact lens wearer with a painful red eye (ask them to remove lenses immediately, as microbial keratitis including Acanthamoeba keratitis can progress rapidly and cause permanent corneal damage); suspected herpes simplex keratitis (unilateral painful red eye with photophobia, watery discharge, or a history of recurrent episodes on the same eye; this is frequently misidentified as conjunctivitis and should not receive an over-the-counter recommendation without assessment). Also refer to a GP or optometrist for a persistent unilateral red eye without an obvious benign cause, or recurrent episodes without a clear trigger.
Over-the-counter treatment is appropriate only when symptoms strongly suggest benign conjunctivitis: bilateral itchy or gritty eyes with no pain, no photophobia, and normal vision.
Bacterial conjunctivitis (purulent discharge, sticky lids): chloramphenicol 0.5 percent drops or 1 percent ointment, available over the counter for patients aged 2 years and older; use according to the licensed product instructions.
Allergic conjunctivitis (bilateral itch, watering, often seasonal): sodium cromoglicate, ketotifen, or olopatadine eye drops.
Viral conjunctivitis (watery discharge and mild discomfort): usually self-limiting; offer lubricating drops and hygiene advice.
When supplying contact lens solutions, remind patients never to rinse lenses or cases with tap water. Acanthamoeba is found in tap water and can cause preventable, sight-threatening keratitis.
Bacterial conjunctivitis (purulent discharge, sticky lids): chloramphenicol 0.5 percent drops or 1 percent ointment, available over the counter for patients aged 2 years and older; use according to the licensed product instructions.
Allergic conjunctivitis (bilateral itch, watering, often seasonal): sodium cromoglicate, ketotifen, or olopatadine eye drops.
Viral conjunctivitis (watery discharge and mild discomfort): usually self-limiting; offer lubricating drops and hygiene advice.
When supplying contact lens solutions, remind patients never to rinse lenses or cases with tap water. Acanthamoeba is found in tap water and can cause preventable, sight-threatening keratitis.
Key takeaways
- A red eye with deep pain, photophobia, or reduced visual acuity requires urgent eye casualty assessment. Do not attribute these features to simple conjunctivitis.
- A painful red eye in a contact lens wearer is keratitis until proven otherwise. Remove lenses, refer urgently, and reinforce that lenses and cases must never be rinsed with tap water.
- Acute angle-closure glaucoma can mimic migraine. If a patient presents with a unilateral red eye, severe headache, and vomiting, treat as an emergency and direct them to Eye Casualty, an Ophthalmology Emergency Department, or A&E according to local pathways. Call 999 if transport is unavailable or the patient is deteriorating.
Download the checklist
Professional disclaimer: This article is for educational purposes
to support healthcare professionals' clinical decision-making. It does not replace
independent professional judgement, local pathways, NICE guidance, or standard
medical literature. Members of the public must not use this resource for
self-diagnosis and should seek prompt advice from a qualified healthcare
professional if experiencing chest pain, palpitations, fainting, or breathlessness.