Acute Visual Disturbance Loss

Introduction

Acute visual disturbance and loss is a critical topic for MCCQE1 preparation, particularly in the Ophthalmology section under Surgery. This comprehensive guide will help Canadian medical students understand the key concepts, diagnostic approaches, and management strategies essential for success in the MCCQE1 exam.

Classification of Acute Visual Disturbances

Understanding the classification of acute visual disturbances is crucial for MCCQE1 success. Here's a breakdown of the main categories:

Key Causes of Acute Visual Disturbance Loss

For MCCQE1 preparation, focus on these common causes of acute visual disturbance and loss in the Canadian population:

1. Vascular Occlusions

   • Central Retinal Artery Occlusion (CRAO)
   • Central Retinal Vein Occlusion (CRVO)
   • Giant Cell Arteritis (GCA)

2. Retinal Detachment

3. Acute Angle-Closure Glaucoma

4. Optic Neuritis

5. Vitreous Hemorrhage

6. Temporal Arteritis

7. Ischemic Optic Neuropathy

Diagnostic Approach for MCCQE1

When approaching a case of acute visual disturbance on the MCCQE1, remember the following steps:

Canadian Guidelines for Acute Visual Disturbance

The Canadian Ophthalmological Society provides guidelines for managing acute visual disturbances. Key points to remember for MCCQE1 include:

1. CRAO Management: Immediate referral to a stroke center for thrombolysis consideration within 4.5 hours of symptom onset.

2. Acute Angle-Closure Glaucoma: Urgent ophthalmological consultation and immediate initiation of IOP-lowering medications.

3. Giant Cell Arteritis: Start high-dose corticosteroids immediately if suspected, even before confirming diagnosis.

4. Retinal Detachment: Urgent referral to a retinal specialist for surgical evaluation.

MCCQE1 High-Yield Content: Acute Visual Disturbance Loss

For MCCQE1 success, focus on these key points:

1. CRAO vs. CRVO:

   • CRAO: Pale retina with cherry-red spot at macula
   • CRVO: Dilated, tortuous veins with flame-shaped hemorrhages

2. Acute Angle-Closure Glaucoma:

   • Symptoms: Severe eye pain, headache, nausea/vomiting
   • Signs: Red eye, mid-dilated pupil, cloudy cornea

3. Retinal Detachment:

   • Classic triad: Flashes, floaters, and visual field defect

4. Giant Cell Arteritis:

   • Remember the mnemonic "HEAD":
     • Headache
     • ESR elevation
     • Age >50
     • Dental pain or jaw claudication

5. Optic Neuritis:

   • Associated with multiple sclerosis
   • Painful eye movements and color desaturation

Canadian Epidemiology and Population Health Considerations

Understanding the Canadian context is crucial for MCCQE1 preparation:

• Diabetic Retinopathy: Affects approximately 500,000 Canadians, with higher prevalence in Indigenous populations.
• Age-Related Macular Degeneration: Leading cause of vision loss in Canadians over 50, affecting 1 in 4 Canadians over 75.
• Glaucoma: Affects 1-2% of Canadians over 40, with higher rates in Black and Asian populations.

Sample MCCQE1-Style Question

Sample Question

A 65-year-old woman presents to the emergency department with sudden, painless vision loss in her right eye that began 2 hours ago. She has a history of hypertension and hyperlipidemia. On examination, her visual acuity is hand motion in the right eye and 20/20 in the left eye. The right pupil is sluggishly reactive to light. Fundoscopic examination of the right eye reveals a pale retina with a cherry-red spot at the macula. Which one of the following is the most appropriate next step in management?

• A. Administer intravenous acetazolamide
• B. Perform urgent laser photocoagulation
• C. Refer for immediate thrombolysis evaluation
• D. Start oral prednisone therapy
• E. Arrange for outpatient carotid doppler ultrasound

Explanation

The correct answer is:

• C. Refer for immediate thrombolysis evaluation

This patient's presentation is consistent with Central Retinal Artery Occlusion (CRAO). The sudden, painless vision loss, pale retina with a cherry-red spot at the macula, and the patient's vascular risk factors (hypertension and hyperlipidemia) all point to this diagnosis.

In Canada, current guidelines recommend immediate referral to a stroke center for thrombolysis evaluation in patients with CRAO presenting within 4.5 hours of symptom onset. This approach is based on the understanding that CRAO is essentially a "stroke of the eye" and may benefit from acute stroke interventions.

• Option A (Acetazolamide) is incorrect as it's used in glaucoma management, not CRAO.
• Option B (Laser photocoagulation) is not indicated for acute CRAO.
• Option D (Prednisone) would be appropriate if giant cell arteritis was suspected, which is not the case here.
• Option E (Carotid doppler) is important for follow-up but not the most urgent next step.

Remember, for MCCQE1 preparation, it's crucial to understand the time-sensitive nature of CRAO management and the current Canadian guidelines emphasizing rapid referral for potential thrombolysis.

Key Points to Remember for MCCQE1

1. Time is crucial: Many acute visual disturbances require urgent intervention.
2. Systemic associations: Always consider systemic diseases (e.g., diabetes, hypertension) in ocular emergencies.
3. Canadian guidelines: Familiarize yourself with Canadian-specific management approaches, especially for conditions like CRAO and GCA.
4. Referral patterns: Understand when and how to refer within the Canadian healthcare system.
5. Population health: Be aware of demographic variations in ocular disease prevalence in Canada.

References

1. Canadian Ophthalmological Society. (2021). Clinical Practice Guidelines. Retrieved from https://www.cos-sco.ca/clinical-practice-guidelines/ (opens in a new tab)

2. Biousse, V., & Newman, N. J. (2015). Ischemic Optic Neuropathies. New England Journal of Medicine, 372(25), 2428-2436.

3. CNIB Foundation. (2021). Eye Conditions. Retrieved from https://cnib.ca/en/sight-loss-info/eye-conditions (opens in a new tab)

4. Flaxel, C. J., et al. (2020). Retinal and Ophthalmic Artery Occlusions Preferred Practice Pattern®. Ophthalmology, 127(2), P259-P287.

5. Health Canada. (2020). Vision Health in Canada: A Federal Report. Retrieved from https://www.canada.ca/en/public-health/services/publications/healthy-living/vision-health-canada-federal-report.html (opens in a new tab)