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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.1
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 often benign, but bilaterality does not exclude serious disease: any pain, photophobia, corneal change, trauma, contact lens-related symptoms, or reduced vision overrides the pattern and requires further assessment. A unilateral red eye with pain, photophobia, or any visual disturbance requires same-day eye casualty assessment.1
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.2
Red flags vs more likely benign
| Feature | More likely benign | Red flag ⚠ |
|---|---|---|
| Laterality | Bilateral involvement | Unilateral, especially with pain, photophobia, or vision change; bilateral symptoms do not exclude serious disease if other red flags are present |
| 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; remove lenses immediately |
What to do in pharmacy
In every red-eye consultation, ask about contact lens use, trauma, chemical exposure, vision change, pain, and photophobia.
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.2 Do not wait until irrigation is complete before calling for help. Advise the patient to continue irrigating while waiting for transport or medical assessment. If there is significant pain, reduced vision, alkali exposure (such as bleach or oven cleaner), or the patient is unable to irrigate safely, call 999. Chemical injury can cause irreversible corneal damage within minutes, with alkali injuries penetrating more deeply than acid.2
Penetrating eye injury or suspected embedded foreign body: advise the patient not to rub or irrigate the eye.4 Cover the eye lightly with a clean shield or pad without applying pressure; do not pad firmly. Advise them to avoid eating or drinking in case surgery is needed. Attend Eye Casualty immediately. Do not attempt to remove an embedded object.4
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.1 Direct the patient immediately to Eye Casualty, an Ophthalmology Emergency Department, or A&E. If severe headache, vomiting, marked visual reduction, or systemic distress is present, call 999. Do not delay emergency ophthalmic or A&E assessment by routine GP or non-urgent optometry referral.
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.2 Do not wait until irrigation is complete before calling for help. Advise the patient to continue irrigating while waiting for transport or medical assessment. If there is significant pain, reduced vision, alkali exposure (such as bleach or oven cleaner), or the patient is unable to irrigate safely, call 999. Chemical injury can cause irreversible corneal damage within minutes, with alkali injuries penetrating more deeply than acid.2
Penetrating eye injury or suspected embedded foreign body: advise the patient not to rub or irrigate the eye.4 Cover the eye lightly with a clean shield or pad without applying pressure; do not pad firmly. Advise them to avoid eating or drinking in case surgery is needed. Attend Eye Casualty immediately. Do not attempt to remove an embedded object.4
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.1 Direct the patient immediately to Eye Casualty, an Ophthalmology Emergency Department, or A&E. If severe headache, vomiting, marked visual reduction, or systemic distress is present, call 999. Do not delay emergency ophthalmic or A&E assessment by routine GP or non-urgent optometry referral.
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)1; 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 and advise them not to restart lens wear until fully assessed and symptoms have resolved; do not patch the eye)3; suspected herpes simplex keratitis (unilateral painful red eye with photophobia, watery discharge, or a history of recurrent episodes on the same eye; frequently misidentified as conjunctivitis)1; vesicular rash around the eye, eyelid, forehead, tip, side, or root of the nose may indicate herpes zoster ophthalmicus: if there is red eye, eye pain, photophobia, eyelid involvement, or visual symptoms, arrange same-day ophthalmology or eye casualty assessment; do not supply OTC eye treatment.1
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. For access pathways, follow local eye casualty, urgent optometry, MECS/CUES, or A&E commissioning arrangements.
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. For access pathways, follow local eye casualty, urgent optometry, MECS/CUES, or A&E commissioning arrangements.
Over-the-counter treatment is appropriate only when symptoms strongly suggest benign conjunctivitis: bilateral itchy or gritty eyes with no pain, no photophobia, normal vision, and no other red flags. Do not supply or recommend steroid-containing eye preparations, topical anaesthetic drops, cosmetic redness-relief vasoconstrictor drops, or leftover antibiotic or steroid eye drops for any painful or red-flag presentation.
Bacterial conjunctivitis (purulent discharge, sticky lids): chloramphenicol 0.5 percent drops or 1 percent ointment may be supplied over the counter for appropriate patients aged 2 years and older, following the licensed product instructions and pharmacy suitability checks.1, 5 Advise reassessment if symptoms worsen at any time or fail to improve within 48 hours. Note that this age limit applies to OTC supply; chloramphenicol may be used in younger children when prescribed.
Allergic conjunctivitis (bilateral itch, watering, often seasonal): sodium cromoglicate or ketotifen eye drops are the most widely available OTC options. Olopatadine may be supplied where licensed and appropriate for the patient.
Viral conjunctivitis (watery discharge and mild discomfort): usually self-limiting; offer lubricating drops and hygiene advice.6
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.3
Bacterial conjunctivitis (purulent discharge, sticky lids): chloramphenicol 0.5 percent drops or 1 percent ointment may be supplied over the counter for appropriate patients aged 2 years and older, following the licensed product instructions and pharmacy suitability checks.1, 5 Advise reassessment if symptoms worsen at any time or fail to improve within 48 hours. Note that this age limit applies to OTC supply; chloramphenicol may be used in younger children when prescribed.
Allergic conjunctivitis (bilateral itch, watering, often seasonal): sodium cromoglicate or ketotifen eye drops are the most widely available OTC options. Olopatadine may be supplied where licensed and appropriate for the patient.
Viral conjunctivitis (watery discharge and mild discomfort): usually self-limiting; offer lubricating drops and hygiene advice.6
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.3
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, do not patch the eye, 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. Call 999 if transport is unavailable or the patient is deteriorating.
📚 References
- NICE. Red eye. Clinical Knowledge Summaries. 2023. Available from: https://cks.nice.org.uk/topics/red-eye/
- College of Optometrists. Clinical Management Guidelines: Chemical eye injury. College of Optometrists; 2023. Available from: https://www.college-optometrists.org/clinical-guidance/clinical-management-guidelines/anterior-eye-and-adnexa/chemical-injury
- College of Optometrists. Clinical Management Guidelines: Microbial keratitis (including Acanthamoeba keratitis). College of Optometrists; 2023. Available from: https://www.college-optometrists.org/clinical-guidance/clinical-management-guidelines/anterior-eye-and-adnexa/microbial-keratitis
- NHS. Eye injuries. NHS; 2023. Available from: https://www.nhs.uk/conditions/eye-injuries/
- Joint Formulary Committee. Chloramphenicol. British National Formulary. London: BMJ Group and Pharmaceutical Press. Available from: https://bnf.nice.org.uk/drugs/chloramphenicol/
- NHS. Red eye. NHS; 2023. Available from: https://www.nhs.uk/conditions/red-eye/