Acute Red Eye OSCE — History, Assessment & Differentials Guide

Why Acute Red Eye Is Tested in OSCEs

Acute red eye is a high-stakes OSCE topic because candidates must distinguish sight-threatening emergencies (acute angle-closure glaucoma, anterior uveitis with complications) from benign self-limiting conditions (episcleritis, subconjunctival haemorrhage). The station tests history-taking breadth, targeted examination knowledge, and appropriate referral urgency. Missing acute angle-closure glaucoma is a significant patient safety failure.

Opening the Consultation

Open with: "Can you tell me what's been happening with your eye?" Then apply structured history-taking. The six key discriminating features are: pain, visual disturbance, discharge, photophobia, timing/onset, and associated symptoms.

The Six Discriminating Features

Differential Diagnosis Table

History for Each Key Differential

Acute Angle-Closure Glaucoma (Emergency)

The most dangerous differential. Typically older, hypermetropic (long-sighted) patients. Presents with sudden onset severe unilateral eye pain, headache, nausea and vomiting (often misdiagnosed as migraine), blurred vision, and haloes around lights. The pupil is fixed and mid-dilated. Ask: "Did the pain come on suddenly? Did you see coloured rings around lights? Did you feel sick with it?" This is an ophthalmic emergency — refer immediately for intraocular pressure measurement.

Anterior Uveitis (Iritis)

Associated with systemic inflammatory conditions: ankylosing spondylitis, reactive arthritis, Crohn's, sarcoidosis, psoriatic arthritis, TB, herpes. Presents with dull aching eye pain, photophobia, blurred vision, and circumcorneal (ciliary) flush. Ask about HLA-B27-associated conditions: "Do you have any joint problems, back pain, or bowel problems?" Refer same-day to ophthalmology. Pupil may be small and irregular if posterior synechiae have formed.

Conjunctivitis

Bacterial: purulent discharge, bilateral (often starts unilateral), gritty sensation — no pain, normal vision. Viral: watery discharge, associated with URTI, follicles, preauricular lymphadenopathy. Allergic: bilateral, watery, itching, seasonal or allergen-related. Treatment depends on type: bacterial → topical chloramphenicol; viral → supportive; allergic → antihistamine drops.

Scleritis

Deep, boring, severe eye pain radiating to the face, often nocturnal, associated with systemic vasculitic/connective tissue disease (RA, SLE, GPA). Unlike episcleritis, the pain is severe, the vessels cannot be blanched with phenylephrine, and the eye is tender to touch. Urgent ophthalmology referral required.

Past Ocular and Medical History

• Previous episodes (anterior uveitis is recurrent in 50% of cases)
• Glasses or contact lens use (contact lens → pseudomonal corneal ulcer risk)
• Previous eye surgery or trauma
• Systemic disease: autoimmune conditions, HLA-B27-related diseases, herpes simplex, chickenpox, TB, sarcoidosis
• Immunosuppression (herpes zoster ophthalmicus risk)

Drug History

Topical or systemic steroids (mask infection, cause herpes zoster reactivation), anticoagulants (increase subconjunctival haemorrhage risk), medications causing dry eyes (antihistamines, antidepressants).

Examination Points to Mention

Visual acuity (always first), pupil size and reactivity, corneal clarity (slit lamp: fluorescein staining for abrasion/ulcer), intraocular pressure measurement, fundoscopy.

Mark-Scheme Checklist

Frequently Asked Questions

"How do I differentiate acute angle-closure glaucoma from other causes of acute red eye in the history?"

Acute angle-closure glaucoma presents with a very specific triad: sudden onset severe unilateral eye pain (often described as excruciating), blurred vision with coloured haloes around lights, and associated nausea and vomiting. The headache can be so severe it is initially attributed to migraine — a common and dangerous misdiagnosis. Risk factors include older age, female sex, hypermetropia (long-sightedness), and a positive family history. The fixed, mid-dilated oval pupil is the pathognomonic examination finding. In the history, the haloes around lights are the most distinctive and discriminating symptom — no other acute red eye cause produces them reliably. Immediate emergency referral is required as permanent vision loss occurs within hours.

"What systemic conditions are associated with anterior uveitis and how do I ask about them?"

Anterior uveitis is associated with HLA-B27-related conditions in ~50% of cases. These include ankylosing spondylitis (ask: lower back pain, morning stiffness, worse with rest, better with exercise), reactive arthritis (ask: recent urethritis or diarrhoeal illness, joint swelling), psoriatic arthritis (ask: skin plaques, nail changes), and inflammatory bowel disease (ask: diarrhoea, rectal bleeding, weight loss). Non-HLA-B27 causes include sarcoidosis (ask: breathlessness, skin lumps, bilateral parotid swelling), TB (ask: TB exposure, night sweats, weight loss), herpes simplex or zoster (ask: previous cold sores, shingles), and Behçet's disease (ask: oral ulcers, genital ulcers, skin lesions). Completing a systematic screen of these in an uveitis history demonstrates excellent clinical knowledge.

"What is the difference between scleritis and episcleritis and why does it matter clinically?"

Episcleritis is a benign, self-limiting inflammation of the superficial episcleral tissue. It causes mild redness and discomfort but no significant pain, no photophobia, and normal vision. It is often idiopathic or associated with mild systemic inflammatory disease. It responds to topical NSAIDs and resolves spontaneously. Scleritis, by contrast, is a severe sight-threatening inflammation of the sclera itself. It causes deep, boring, severe pain that is often worse at night and may radiate to the face. It is associated with systemic vasculitic disease (rheumatoid arthritis, granulomatosis with polyangiitis, SLE) and can lead to scleral thinning (scleromalacia), perforation, and vision loss. Episcleritis vessels blanch with topical phenylephrine; scleritis vessels do not. The clinical distinction matters because scleritis requires urgent systemic investigation and treatment.

"When should I refer a patient with a red eye urgently vs. as an emergency?"

Emergency same-day referral to ophthalmology or A&E: acute angle-closure glaucoma (intraocular pressure can be >60 mmHg and permanent vision loss occurs within hours), corneal perforation or chemical injury. Urgent same-day or next-day referral: anterior uveitis (to prevent synechiae, secondary glaucoma, and cataract), scleritis, suspected corneal ulcer especially in contact lens wearers (pseudomonas risk — can perforate rapidly), and herpes zoster ophthalmicus (hutchinson's sign — rash on the tip of the nose — predicts ocular involvement). Routine referral or GP management: episcleritis, subconjunctival haemorrhage (no treatment, reassurance), and bacterial conjunctivitis. In the OSCE, correctly identifying the appropriate urgency is often worth two to three marks.

"How does contact lens wear change my assessment of a red eye?"

Contact lens wear is a significant risk factor for microbial keratitis (corneal ulcer), particularly Pseudomonas aeruginosa infection, which can progress to corneal perforation within 24–48 hours. Any contact lens wearer with a painful red eye, reduced vision, or photophobia must be treated as an ophthalmic emergency. Ask specifically: "Do you wear contact lenses? Have you slept in your lenses? How long have you been wearing the same pair? Have you been swimming in them?" In the history, also ask about lens hygiene (tap water rinsing — acanthamoeba risk) and the timing of symptoms relative to lens wear. Contact lens-related red eye with any of these features requires same-day ophthalmology assessment, fluorescein staining, and usually empirical broad-spectrum topical antibiotics.

"What is subconjunctival haemorrhage and what does it need investigation for?"

A subconjunctival haemorrhage is a collection of blood under the conjunctiva due to rupture of small conjunctival vessels. It appears as a dramatic, well-demarcated bright red area over the sclera, but causes no pain, no visual disturbance, no discharge, and no photophobia. It requires no treatment and resolves spontaneously over 2–3 weeks. However, investigation is warranted if: it is recurrent (consider hypertension, coagulopathy, anticoagulant therapy), bilateral (consider leukaemia, coagulopathy), preceded by trauma (rule out open globe injury — urgent ophthalmology), or associated with a Valsalva manoeuvre (coughing, vomiting, weightlifting — no action required). Blood pressure should be checked in all patients. If the patient is on anticoagulants, check INR. Most cases are idiopathic and the patient needs reassurance, not referral.

Related guides: Ophthalmology History OSCE · Fundoscopy and Eye Examination OSCE · Cranial Nerve Examination OSCE · Headache History OSCE