Red Eye in Primary Care: When to Treat, Refer or Send Today
Published Oct 11, 2026 · Updated Oct 12, 2026
A red eye is one of the most common eye complaints in family practice, and most cases are safe to treat in the office. The skill is spotting the few that can cost a patient their sight. This guide walks through a simple triage: four questions, a five-step exam and three outcomes, with the slides from our TopMedCast episode on red eye. Red eye is one of the CFPC’s priority topics for the family medicine certification exam, and the same red flags come up in other licensing exams.
Start with four questions
Before the exam, ask four things: has vision changed, is there significant pain, is there photophobia, and does the patient wear contact lenses?
No to all four: carry on with a routine primary care exam. Yes to any: treat it as urgent until you have ruled out keratitis, acute angle-closure glaucoma and uveitis.
The exception: chemical injury
A chemical in the eye skips the triage. Irrigate straight away with saline or water, before taking a full history or examining the eye. Remove contact lenses when you can, check the pH, and keep irrigating until the pH is normal and stays normal after a pause. Then arrange emergency assessment.
Never try to neutralise a chemical: no alkali for an acid, and no acid for an alkali. Irrigation is the only priority.
The five-step exam
Check visual acuity in each eye separately, then the pupils (size and reaction), the lids and cornea (clarity, crusting, swelling) and eye movements. Use fluorescein staining when you need to look for an epithelial defect.
Ask about recent trauma or chemical exposure, recent eye surgery or injections, the type of discharge, and previous episodes.
Two paths after the exam
Safe for the office: normal pupil, clear cornea, preserved vision and simple surface disease. Treat locally, arrange follow-up and give clear advice on when to come back.
Urgent specialist care: reduced vision, an abnormal pupil, a cloudy cornea or severe pain. Escalate now, and don’t hold the patient back for office tests first.
Whichever path you choose, new vision loss, more pain, photophobia or worsening swelling means an urgent reassessment.
Office path: conjunctivitis
Viral: a watery, gritty eye, often after a cold. It is very contagious and often starts in one eye before spreading to the other. Cool compresses, artificial tears and careful hand hygiene (no shared towels or cosmetics). Stop contact lenses. Antibiotics don’t treat viral conjunctivitis.
Bacterial: mucopurulent discharge and lids stuck together on waking, although the symptoms overlap with viral. Mild cases can be watched or given a delayed prescription. If you treat, use a topical antibiotic from your local formulary, and reassess if it lasts beyond 48 hours.
Allergic: itch in both eyes is the strongest clue, often with sneezing, watery discharge and a seasonal pattern. Allergen avoidance, cool compresses and a topical antihistamine or combined mast-cell stabiliser such as olopatadine or ketotifen. Avoid routine steroid drops.
Office path: other surface problems
Dry eye: burning, grittiness and blur that improves with blinking. Preservative-free artificial tears, a lubricating gel at night, screen breaks, and a review of medicines that can dry the eye.
Blepharitis: crusting around the lashes and irritated lid margins, often recurrent. Warm compresses, gentle lid massage and regular lid cleaning, with artificial tears. Refer if it doesn’t settle.
Subconjunctival haemorrhage: a sharply defined red patch with normal vision and no real pain. Reassure the patient that it fades in one to two weeks, check the blood pressure and ask about trauma and bleeding. Don’t stop a prescribed anticoagulant for an isolated haemorrhage alone.
Episcleritis: localised redness with mild discomfort and normal vision. Reassurance and cool compresses. Refer if you are unsure, if it keeps coming back or if real pain develops, since that suggests scleritis.
Urgent path: the contact lens wearer
A painful red eye in a contact lens wearer needs the cornea assessed before anyone calls it conjunctivitis.
Infectious keratitis or corneal ulcer: pain, photophobia, reduced vision and a white corneal infiltrate. Stop the lenses and arrange same-day ophthalmology for corneal sampling and intensive antimicrobial drops. Don’t use a routine conjunctivitis treatment, don’t patch and don’t use steroids.
Corneal abrasion: sudden pain, tearing and a foreign-body feeling after minor trauma, with a defect that stains with fluorescein. Stop lenses and don’t patch. An abrasion in a contact lens wearer needs antibiotic cover against Pseudomonas and a review within 24 hours.
Urgent path: deep inflammation
Anterior uveitis: deep aching pain, photophobia, redness concentrated in a ring around the cornea (ciliary flush), a small or irregular pupil and little discharge. Refer to ophthalmology within 24 hours, and ask about linked conditions such as inflammatory back pain, psoriasis and inflammatory bowel disease. Steroid or cycloplegic drops are started only after a specialist has excluded corneal infection.
Scleritis: severe, deep, boring pain, often worse at night or with eye movement, with deep violet redness. It needs same-day ophthalmology and an assessment for systemic autoimmune or infectious disease. Don’t start systemic steroids before talking to the specialist.
Emergencies that threaten sight
Acute angle-closure glaucoma: severe eye pain, blurred vision, halos, headache, nausea and vomiting, with a hazy cornea and a mid-dilated, poorly reactive pupil. Transfer immediately. Coordinate pressure-lowering treatment with ophthalmology and give pain relief and an antiemetic, but don’t delay transfer to finish an office workup. Laser peripheral iridotomy is the definitive treatment.
Endophthalmitis: a red, painful eye with reduced vision after recent eye surgery or an injection into the eye. Contact ophthalmology immediately: it usually needs intravitreal antibiotics, sometimes surgery. Topical antibiotics alone are not enough.
Suspected penetrating injury: high-velocity trauma or an irregular pupil. Put on a rigid shield with no pressure on the eye. No tonometry, no manipulation, and don’t remove an embedded object. Arrange emergency care.
Herpes simplex keratitis: a branching (dendritic) ulcer with terminal bulbs on fluorescein. Urgent ophthalmology for antivirals. Steroid drops are contraindicated because they make the epithelial infection worse.
Hyperacute conjunctivitis, including in newborns: copious pus that quickly comes back after wiping. Think of gonococcal or chlamydial infection. It needs urgent specimens and systemic treatment; drops alone are not enough.
Superficial foreign body: pain and tearing after minor trauma. Remove it only if you have the right equipment and experience, and give pain relief, lubrication and prophylactic antibiotic drops, especially if it was contaminated.
Preseptal or orbital cellulitis?
The orbital septum divides the two. Preseptal cellulitis stays in front of it: eyelid redness and swelling with normal vision, normal eye movements and no proptosis. A well patient can have oral antibiotics with a review in 24 to 48 hours; infants and unwell patients need hospital assessment.
Orbital cellulitis spreads behind it: painful or limited eye movements, double vision, proptosis and reduced vision. It is an emergency that needs hospital admission for IV antibiotics, imaging and specialist care.
Six things not to do
Don’t use steroid eye drops in a red eye that hasn’t been diagnosed. They can make herpes or other infectious keratitis worse.
Don’t patch an eye with suspected keratitis or an abrasion linked to contact lenses.
Don’t try to neutralise a chemical injury with an acid or an alkali. Irrigate.
Don’t delay transfer for acute angle-closure glaucoma to finish an office workup.
Don’t apply pressure, measure eye pressure or remove an embedded object when the globe may be penetrated.
Don’t stop a prescribed anticoagulant only because of an uncomplicated subconjunctival haemorrhage.
Listen to the case, then practise
Hear the full discussion in the TopMedCast episode Primary Care Guide to Managing Red Eye Diagnoses. Then test yourself with exam-style questions in the CCFP SAMP question bank or the MCCQE Part I question bank.
Study takeaway: Document the vision in each eye, look at the cornea, take contact lens use seriously, avoid steroid drops until a specialist has seen the eye, and always tell the patient when to come back.