Eye Redness (The Red Eye)

Introduction to Eye Redness for MCCQE1

Eye redness (hyperemia) is one of the most common ophthalmologic presentations in Canadian primary care and emergency departments. For the MCCQE1, candidates must demonstrate the Medical Expert CanMEDS role by efficiently distinguishing between benign, self-limiting conditions (e.g., viral conjunctivitis) and vision-threatening emergencies (e.g., acute angle-closure glaucoma, infectious keratitis).

This guide focuses on the clinical reasoning, differential diagnosis, and management of the red eye within the Canadian healthcare context.

Clinical Approach to the Red Eye

A systematic approach is essential to avoid missing critical pathology.

History Taking

When taking a history for a patient with a red eye, focus on the following “Red Flag” symptoms:

• Pain: Scratchy/gritty (surface) vs. deep/boring (scleritis/glaucoma).
• Photophobia: Suggests iritis/uveitis or keratitis.
• Visual Changes: Blurring, haloes around lights (glaucoma), or loss of vision.
• Discharge: Purulent (bacterial), watery (viral/allergic), or ropy (allergic).

Physical Examination

Differential Diagnosis

The differential diagnosis can be broadly categorized by the anatomy involved or the presence of pain.

Comparison of Conjunctivitis Types

A frequent MCCQE1 topic is distinguishing between types of conjunctivitis.

High-Yield MCCQE1 Topics

1. Acute Angle-Closure Glaucoma (AACG)

This is an ocular emergency.

• Risk Factors: Hyperopia (far-sighted), Inuit/Asian descent (shallow anterior chambers), medications (anticholinergics, sympathomimetics).
• Presentation: “Steamy” cornea, mid-dilated fixed pupil, rock-hard eye on palpation.
• Management:
  1. Lower IOP: Acetazolamide (IV/PO), topical beta-blockers (Timolol), alpha-agonists (Brimonidine).
  2. Constrict Pupil: Pilocarpine (once pressure drops).
  3. Definitive: Laser Peripheral Iridotomy (LPI).

2. Contact Lens Associated Red Eye

• Pathogen: Pseudomonas aeruginosa is the feared pathogen.
• Management: Never patch a contact lens wearer with a red eye. Requires fluoroquinolone drops (e.g., Moxifloxacin) and close follow-up.

3. Anterior Uveitis (Iritis)

• Associations: HLA-B27 spondyloarthropathies (Ankylosing Spondylitis, Reactive Arthritis, IBD, Psoriatic Arthritis).
• Treatment: Topical steroids (prednisolone) and cycloplegics (dilate pupil to prevent synechiae and reduce pain).

Canadian Guidelines and Stewardship

Choosing Wisely Canada

• Antibiotics for Conjunctivitis: Do not routinely prescribe antibiotics for acute mild-to-moderate conjunctivitis. Most cases are viral or allergic and self-limiting.
• Imaging: Do not order imaging (CT/MRI) for simple red eye unless orbital cellulitis or trauma is suspected.

Canadian Ophthalmological Society (COS)

• Herpes Zoster Ophthalmicus: Patients with shingles involving the tip of the nose (Hutchinson’s sign) must be seen by an ophthalmologist to rule out ocular involvement. Oral antivirals (Valacyclovir/Famciclovir) should be started within 72 hours.

Key Points to Remember for MCCQE1

• Neonatal Conjunctivitis:
  • Day 2–5: Neisseria gonorrhoeae (Hyperacute, purulent, emergency). Rx: IM Ceftriaxone.
  • Day 5–14: Chlamydia trachomatis. Rx: Oral Erythromycin.
• Glaucoma Drops Contraindications:
  • Beta-blockers (Timolol) $\rightarrow$ Avoid in asthma/COPD/heart block.
• Steroid Use: Never prescribe topical steroids (e.g., Pred Forte) without ruling out Herpes Simplex Keratitis (fluorescein stain). Steroids can cause “geographic ulcers” and corneal perforation in HSV.

// Mnemonic for Acute Angle Closure Glaucoma symptoms:
const AACG_Symptoms = {
  H: "Haloes around lights",
  A: "Aching eye (severe)",
  R: "Red eye (ciliary flush)",
  D: "Dilated pupil (mid-fixed)",
  S: "Steamy cornea (edema)"
};

Sample Question

Clinical Scenario

A 24-year-old female university student presents to the emergency department with a 1-day history of severe pain, redness, and photophobia in her right eye. She wears soft contact lenses and admits to sleeping in them occasionally. She reports her vision is blurred in the affected eye.

Physical Examination:

• Visual Acuity: OD 20/80, OS 20/20.
• Inspection: Significant conjunctival injection and ciliary flush OD.
• Slit Lamp: A 2mm round white opacity is visible on the central cornea.
• Fluorescein Staining: The opacity stains brilliantly green.

Question

Which one of the following is the most appropriate initial management step?

• A. Prescribe topical gentamicin drops and discharge with follow-up in 48 hours.
• B. Apply a pressure patch to the right eye and prescribe oral analgesia.
• C. Prescribe topical prednisolone acetate drops to reduce inflammation.
• D. Obtain corneal scrapings for culture and refer immediately to an ophthalmologist.
• E. Reassure the patient it is a viral infection and recommend artificial tears.

Explanation

The correct answer is:

• D. Obtain corneal scrapings for culture and refer immediately to an ophthalmologist.

Detailed Analysis

• Diagnosis: The clinical presentation (contact lens wearer, severe pain, white corneal opacity that stains) is classic for Bacterial Keratitis (Corneal Ulcer). The most causative organism in contact lens wearers is Pseudomonas aeruginosa.
• Why D is correct: Bacterial keratitis is a vision-threatening emergency. Pseudomonas can perforate the cornea rapidly (within 24–48 hours). The standard of care involves obtaining cultures (scraping) to guide antibiotic therapy and starting intensive topical antibiotics (often fortified tobramycin/cefazolin or monotherapy with a fluoroquinolone like moxifloxacin). This requires urgent ophthalmology management.
• Why A is incorrect: Gentamicin alone is often insufficient for severe ulcers, and 48-hour follow-up is too long; these patients need daily (or twice daily) assessment initially.
• Why B is incorrect: NEVER patch a contact lens wearer with a red eye or a suspected corneal ulcer. Patching creates a warm, dark environment that promotes bacterial growth (especially Pseudomonas).
• Why C is incorrect: Topical steroids are contraindicated in the initial management of infectious keratitis as they inhibit wound healing and immune response, potentially leading to perforation.
• Why E is incorrect: The presence of a corneal opacity (infiltrate) rules out simple viral conjunctivitis.

References

1. Medical Council of Canada. MCCQE Part I Objectives: Ophthalmology. Available at mcc.ca.
2. Choosing Wisely Canada. Ophthalmology: Five Things Physicians and Patients Should Question.
3. Canadian Ophthalmological Society. Clinical Practice Guidelines.
4. Hampton Roy, F., et al. (2023). Ocular Differential Diagnosis.
5. Toronto Notes 2024. Ophthalmology Chapter.