About This Page
This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
The Bottom Line
- Red eye with pain, photophobia, reduced visual acuity, corneal staining/opacity, abnormal pupil, or contact lens use needs urgent assessment
- Visual acuity is the vital sign of the eye — document it before treatment whenever possible
- Benign conjunctivitis usually causes gritty discomfort and discharge but not severe pain, photophobia, or reduced vision
- Fluorescein staining and intraocular pressure measurement help separate corneal disease and acute angle-closure glaucoma
- Topical steroids should not be started for undifferentiated red eye without ophthalmology direction
Approach to the Presentation
The MCCQE1 approach to red eye starts by separating benign external inflammation from sight-threatening ocular disease. Ask about pain severity, photophobia, vision change, discharge, contact lens use, trauma/foreign body, chemical exposure, headache, nausea, autoimmune disease, and immunosuppression. Examine visual acuity, pupils, extraocular movements, conjunctival pattern, cornea, anterior chamber, fluorescein staining, and intraocular pressure when available. A painless red eye with normal vision is often conjunctivitis or subconjunctival haemorrhage; a painful red eye with photophobia or reduced vision is keratitis, uveitis, scleritis, acute angle-closure glaucoma, or trauma until proven otherwise.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Acute Angle-Closure Glaucoma | must-not-miss | Severe eye pain, headache, halos, nausea/vomiting, reduced vision, mid-dilated fixed pupil, cloudy cornea, hard eye | Markedly elevated intraocular pressure; urgent ophthalmology |
| Infectious Keratitis / Corneal Ulcer | must-not-miss | Pain, photophobia, reduced vision, corneal opacity/infiltrate, fluorescein uptake; contact lens use is major risk, especially Pseudomonas | Slit lamp + fluorescein; corneal culture if severe; urgent ophthalmology |
| Anterior Uveitis / Iritis | must-not-miss | Painful red eye, consensual photophobia, ciliary flush, small/irregular pupil, blurred vision; associated with HLA-B27 disease, IBD, psoriasis, sarcoid | Slit lamp: cells and flare in anterior chamber |
| Scleritis | must-not-miss | Severe deep boring pain, pain with eye movement, violaceous hue, tenderness, often autoimmune association | Does not blanch with phenylephrine; urgent ophthalmology and systemic work-up |
| Chemical Eye Injury | must-not-miss | Exposure to alkali/acid, severe pain, blepharospasm, reduced vision, conjunctival blanching in severe burns | Immediate irrigation before full history/exam; check ocular pH repeatedly |
| Conjunctivitis — Viral | common | Watery discharge, gritty sensation, follicular conjunctiva, preauricular node, often bilateral sequential, URTI symptoms | Clinical; normal vision and no corneal opacity |
| Conjunctivitis — Bacterial | common | Purulent discharge, eyelids stuck shut, diffuse injection; usually mild discomfort and normal vision | Clinical; culture if neonatal, severe, recurrent, or gonococcal concern |
| Allergic Conjunctivitis | common | Bilateral itching, watery/stringy discharge, chemosis, allergic rhinitis, seasonal trigger | Clinical; itching is dominant symptom |
| Subconjunctival Haemorrhage | common | Painless sharply demarcated red patch, normal vision, no discharge; associated with cough, Valsalva, anticoagulation, hypertension | Clinical; check BP and bleeding history if recurrent |
| Corneal Abrasion / Foreign Body | common | Foreign body sensation, tearing, photophobia after trauma or contact lens; fluorescein linear/geographic staining | Fluorescein staining; evert lids for retained foreign body |
| Episcleritis | less common | Mild discomfort, sectoral redness, normal vision, recurrent, may be idiopathic or autoimmune | Blanches with phenylephrine; mild compared with scleritis |
Red Flags & Key History
Symptoms
Reduced visual acuity — sight-threatening until proven otherwise
Severe pain or photophobia, especially consensual photophobia — keratitis, uveitis, scleritis, glaucoma
Contact lens use with red painful eye — infectious keratitis risk
Chemical exposure — immediate irrigation before detailed examination
Headache, halos, nausea/vomiting — acute angle-closure glaucoma
Trauma, high-velocity foreign body, or hammering/grinding — penetrating injury risk
Itching with bilateral watery symptoms — allergic conjunctivitis
Painless sharply demarcated redness — subconjunctival haemorrhage
Signs
Corneal opacity, infiltrate, or fluorescein uptake over infiltrate — keratitis/corneal ulcer
Mid-dilated fixed pupil and cloudy cornea — acute angle-closure glaucoma
Irregular pupil, ciliary flush, or cells/flare — uveitis
Positive Seidel test — globe penetration
Pain with eye movement, violaceous hue, or scleral tenderness — scleritis
Diffuse conjunctival injection with normal vision and discharge — conjunctivitis
Approach to Investigation
First-line
Visual acuityDocument in each eye separately before drops if possible. Reduced vision is a red flag and changes disposition
Pupil examination and extraocular movementsLook for irregular pupil, relative afferent pupillary defect, painful ophthalmoplegia, or orbital involvement
Fluorescein stainingDetect abrasion, dendritic lesion, corneal ulcer, or Seidel sign. Contact lens wearers require particular caution
Intraocular pressureMeasure if acute angle-closure glaucoma suspected and globe rupture is not suspected
Second-line
Slit lamp examinationAssess corneal infiltrate, anterior chamber cells/flare, hypopyon, foreign body, and subtle trauma
Culture / swabFor severe purulent conjunctivitis, neonatal conjunctivitis, suspected gonococcal/chlamydial infection, or corneal ulcer as directed by ophthalmology
Systemic work-upFor recurrent uveitis/scleritis or autoimmune features: guided testing rather than broad screening in uncomplicated first episodes
Specialist
Urgent ophthalmologyReduced vision, severe pain, photophobia, corneal opacity/ulcer, contact lens keratitis, uveitis, scleritis, acute glaucoma, chemical injury, or globe injury
Orbital imagingCT orbit if penetrating injury, intraocular foreign body, orbital cellulitis, fracture, or severe trauma suspected
Management Principles
MCC Objective 30 + Canadian Ophthalmological Society learning objectives + CMAJ red eye guidance1
Immediate emergencies
- Chemical injury: irrigate immediately with copious saline/Ringer’s lactate; do not wait for ophthalmology before irrigation; check pH until neutral
- Suspected globe rupture: shield the eye, keep NPO, antiemetics/analgesia, avoid pressure/tonometry, urgent ophthalmology
- Acute angle-closure glaucoma: urgent ophthalmology; start IOP-lowering therapy per local protocol while arranging definitive treatment
2
Keratitis, uveitis, and scleritis
- Contact lens-related painful red eye: stop lenses and refer urgently; avoid patching; antipseudomonal topical therapy usually required under local guidance
- Anterior uveitis: ophthalmology-directed topical steroid/cycloplegic; do not start steroids blindly in undifferentiated red eye
- Scleritis: urgent ophthalmology; investigate systemic inflammatory disease when indicated
3
Conjunctivitis and benign causes
- Viral conjunctivitis: supportive care, hygiene, avoid sharing towels, work/school advice based on local policy
- Bacterial conjunctivitis: topical antibiotics may shorten course; urgent care for severe pain, vision loss, contact lens use, or gonococcal concern
- Allergic conjunctivitis: allergen avoidance, lubricants, topical antihistamine/mast-cell stabilizer; treat associated rhinitis
- Subconjunctival haemorrhage: reassurance if isolated; check BP and review anticoagulation/bleeding history if recurrent
4
Corneal abrasion / foreign body
- Remove superficial foreign body if competent; evert lids; topical antibiotic prophylaxis depending on risk
- Avoid contact lens use until healed and symptoms resolved
- Refer if central abrasion, large defect, rust ring, contact lens-related injury, persistent symptoms, or reduced vision
Complications & Pitfalls
- Forgetting visual acuity: It is the vital sign of the eye and should be documented in red eye presentations.
- Calling keratitis conjunctivitis: Contact lens use plus pain/photophobia is high risk for corneal ulcer.
- Using topical steroids casually: Steroids can worsen herpes keratitis and corneal infection if used without ophthalmology input.
- Delaying chemical burn irrigation: Irrigation is treatment and must start immediately.
- Missing acute glaucoma: Headache, halos, nausea, cloudy cornea, and mid-dilated pupil are the classic cluster.
MCCQE1 Exam Tips
- 1Every red eye question: first ask whether vision is reduced, pain is severe, photophobia is present, or contact lenses are involved
- 2Benign conjunctivitis should not reduce visual acuity or cause severe photophobia
- 3Consensual photophobia is a classic uveitis clue
- 4Contact lens wearer + painful red eye = infectious keratitis, not routine conjunctivitis
- 5Acute angle closure: painful red eye + headache + halos + nausea/vomiting + mid-dilated fixed pupil
- 6Chemical exposure: immediate irrigation is the next best step, before detailed history or referral
- 7Do not patch a contact lens-related corneal abrasion because of infection risk
- 8Topical steroids are not a primary care answer for undifferentiated red eye unless ophthalmology directs them
practicetest your knowledge on red eye (painful & painless)Apply what you've learnt with MCCQE1-style questions from the iatroX Q-Bank — ent & ophthalmologic and beyond.
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