Acute Visual Disturbance/Loss

Introduction to MCCQE1 Objectives

Acute visual disturbance or loss is a critical presentation in the Ophthalmology and Surgery sections of the MCCQE1. As a Canadian medical graduate, you are expected to rapidly differentiate between benign, self-limiting conditions and sight-threatening or life-threatening emergencies.

The Medical Council of Canada (MCC) assesses your ability to:

1. Differentiate between painful and painless visual loss.
2. Recognize red flags requiring urgent ophthalmological referral.
3. Apply the CanMEDS roles, particularly Medical Expert (diagnosis) and Communicator (explaining prognosis and urgency).
4. Manage initial treatment steps in a Canadian resource context (e.g., rural vs. urban settings).

Anatomy and Pathophysiology Review

Understanding the location of the lesion is paramount. Visual loss can stem from pathology in the:

• Media: Cornea, Anterior Chamber, Lens, Vitreous.
• Retina: Macula, Peripheral Retina, Vessels.
• Neural Pathway: Optic Nerve, Chiasm, Optic Tract, Occipital Cortex.

Canadian Epidemiology Note

In Canada, Age-Related Macular Degeneration (AMD) is the leading cause of visual loss in the elderly, while Diabetic Retinopathy is the leading cause of blindness in working-age adults. However, for acute presentations, vascular events and detachments take precedence.

Differential Diagnosis

A strategic approach for the MCCQE1 is to categorize acute visual loss based on the presence of pain and the duration of symptoms.

Clinical Approach: The MCCQE1 Framework

When encountering a clinical scenario on the exam, follow these steps to maximize data acquisition scores.

High-Yield Conditions for MCCQE1

1. Central Retinal Artery Occlusion (CRAO)

• Etiology: Embolus (carotid or cardiac) lodging in the central retinal artery.
• Presentation: Sudden, profound, painless monocular vision loss.
• Exam Findings:
  • RAPD: Present.
  • Fundoscopy: Pale, opaque retina with a “Cherry Red Spot” at the fovea.
• Management: Ocular emergency (poor prognosis).
  • Digital ocular massage (attempt to dislodge embolus).
  • Anterior chamber paracentesis (Ophthalmology).
  • Stroke Workup: Carotid Doppler, Echocardiogram, ECG (to prevent CVA).

2. Central Retinal Vein Occlusion (CRVO)

• Risk Factors: Hypertension, Diabetes, Hyperviscosity syndromes.
• Presentation: Subacute, painless vision loss.
• Exam Findings:
  • Fundoscopy: “Blood and Thunder” appearance (diffuse retinal hemorrhages), dilated tortuous veins, cotton wool spots.
• Management: Treat underlying vascular risk factors. Monitor for neovascularization (glaucoma).

3. Acute Angle-Closure Glaucoma (AACG)

• Epidemiology: Hyperopic (farsighted) individuals, Inuit populations (highest prevalence globally - very high-yield Canadian fact), Asians, Elderly.
• Precipitating Factors: Pupillary dilation (dim light, sympathomimetics, anticholinergics).
• Presentation: Severe eye pain, headache, nausea/vomiting, haloes around lights.
• Exam Findings:
  • Red eye (ciliary injection).
  • Corneal edema (cloudy/steamy).
  • Mid-dilated, fixed pupil.
  • Elevated Intraocular Pressure (IOP) often >40-50 mmHg.
  • Eye feels “rock hard” on palpation.
• Immediate Management:
  • Medical: Acetazolamide (IV/PO), Topical Beta-blockers (Timolol), Alpha-2 agonists (Brimonidine), Pilocarpine (once pressure drops).
  • Definitive: Laser Peripheral Iridotomy (LPI).

4. Retinal Detachment (RD)

• Pathophysiology: Separation of neurosensory retina from retinal pigment epithelium (RPE). Usually rhegmatogenous (due to a tear).
• Risk Factors: Myopia (nearsightedness), cataract surgery, trauma.
• Presentation: 4 F’s:
  1. Flashes (Photopsia).
  2. Floaters (new onset).
  3. Field defect (dark curtain/shadow).
  4. Fall in acuity (if macula involved).
• Exam Findings: Gray, elevated retina.
• Management: Urgent Ophthalmology referral for surgical repair.

5. Giant Cell Arteritis (Temporal Arteritis)

• Epidemiology: Age >50 (usually >70).
• Presentation: Unilateral temporal headache, Jaw Claudication (highest specificity), scalp tenderness, polymyalgia rheumatica symptoms, sudden vision loss (Arteritic Anterior Ischemic Optic Neuropathy - AAION).
• Labs: Elevated ESR and CRP.
• Treatment: High-dose systemic corticosteroids (IV Methylprednisolone if visual loss present; Oral Prednisone if no visual loss). Temporal artery biopsy is the gold standard but should not delay treatment.

Summary of Key Diagnostic Findings

Canadian Guidelines & Health Systems

Referral Pathways

In Canada, primary care physicians often collaborate with Optometrists for initial triage of non-emergent visual disturbances. However, for acute visual loss (red flags), direct referral to an Ophthalmologist or transfer to an Emergency Department with ophthalmology coverage is required.

Rural and Remote Considerations

For patients in remote areas (e.g., Northern Canada), Tele-ophthalmology is increasingly used for retinal imaging. If AACG is suspected in a remote setting without immediate ophthalmology access, medical management must be started immediately while arranging Medevac.

Choosing Wisely Canada

• Don’t order imaging (CT/MRI) for uncomplicated headaches unless there are red flags (like papilledema or sudden visual loss).
• Don’t delay referral for suspected wet AMD; early anti-VEGF treatment preserves vision.

Key Points to Remember for MCCQE1

• RAPD is the most important objective sign of unilateral optic nerve or extensive retinal dysfunction.
• Amaurosis Fugax in a patient >50 requires a TIA/Stroke workup (Carotids, Cardiac).
• Contact lens wearers with a red, painful eye have a Pseudomonas corneal ulcer until proven otherwise.
• Inuit populations have a genetic predisposition to shallow anterior chambers, increasing the risk of Acute Angle-Closure Glaucoma.
• Optic Neuritis is often the first presentation of Multiple Sclerosis (young female, painful eye movement).

Sample Question

Case: A 72-year-old woman presents to the Emergency Department with a 2-day history of severe right-sided headache and scalp tenderness. She reports that her jaw feels tired when she chews her toast in the morning. Today, she experienced a sudden, transient blurring of vision in her right eye that lasted 5 minutes. Her blood pressure is 150/90 mmHg, and heart rate is 80 bpm. Visual acuity is 20/30 in both eyes. There is no RAPD. Fundoscopy is unremarkable.

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

• A. Order a temporal artery biopsy
• B. Prescribe oral prednisone 60 mg daily
• C. Order an Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP)
• D. Prescribe aspirin 81 mg and discharge with neurology follow-up
• E. Order a CT head to rule out intracranial hemorrhage

Explanation

The correct answer is:

• B. Prescribe oral prednisone 60 mg daily

Detailed Analysis: This patient presents with classic symptoms of Giant Cell Arteritis (GCA): elderly age, new headache, scalp tenderness, and jaw claudication (the most specific symptom). The transient visual blurring represents a warning sign of impending permanent visual loss (Arteritic Anterior Ischemic Optic Neuropathy).

• Option B is correct: In the context of high clinical suspicion for GCA, particularly with visual symptoms (transient or permanent), immediate systemic corticosteroids are required to prevent permanent blindness in the affected eye and protect the contralateral eye. You treat before confirming the diagnosis.
• Option A is incorrect: While temporal artery biopsy is the gold standard for diagnosis, arranging it takes time. Delaying steroids to wait for a biopsy places the patient at high risk of permanent blindness. The biopsy remains positive for weeks after starting steroids.
• Option C is incorrect: While ESR and CRP are essential diagnostic tests to support the diagnosis, waiting for the results in a patient with transient visual symptoms should not delay the administration of steroids if the clinical suspicion is high. In practice, you might draw the blood and give the pill immediately, but “Prescribe prednisone” is the critical management action.
• Option D is incorrect: This treats a potential TIA but ignores the inflammatory etiology. GCA requires immunosuppression.
• Option E is incorrect: The clinical picture points to an inflammatory vascular process, not an intracranial bleed.

References

1. Medical Council of Canada. (n.d.). Objectives for the Qualifying Examination Part I. Retrieved from mcc.ca 
2. Canadian Ophthalmological Society. (2023). Clinical Practice Guidelines.
3. Choosing Wisely Canada. (2023). Ophthalmology: Five Things Physicians and Patients Should Question.
4. Bagheri, N., & Wajda, B. (2017). The Wills Eye Manual: Office and Emergency Room Diagnosis and Treatment of Eye Disease. 7th Edition. Wolters Kluwer.
5. Royal College of Physicians and Surgeons of Canada. CanMEDS 2015 Physician Competency Framework.