What is the most likely diagnosis and urgent management for a transient, sharply demarcated grey loss of vision in the lower half of the left visual field lasting 3–4 minutes?

Transient Monocular Vision Loss (Amaurosis Fugax) – Ocular TIA

This patient has experienced amaurosis fugax (transient monocular vision loss), which is a retinal transient ischemic attack and stroke equivalent requiring immediate emergency department referral to a certified stroke center without any delay for additional testing. 1

Most Likely Diagnosis

Amaurosis fugax – a transient retinal ischemic attack characterized by:

• Sudden, painless monocular vision loss lasting seconds to minutes (this patient: 3-4 minutes) 2
• Sharp demarcation (classic "curtain" or "shade" descending over visual field) 1
• Complete resolution 2
• Represents embolic material (fibrin, cholesterol crystals/Hollenhorst plaques) traveling from the ipsilateral internal carotid artery via the ophthalmic artery to retinal circulation 1

Urgent Management Protocol

Immediate Action (Within Minutes)

Transfer the patient directly to the nearest emergency department affiliated with a certified stroke center immediately, accompanied by a note stating "Ocular TIA." 3, 1

• Do NOT delay for ophthalmologic workup or additional testing – only one-third of ophthalmologists currently follow this guideline, but delay is dangerous 1
• Call ahead to warn the stroke center that "a stroke patient is on the way" 3
• The risk of stroke is maximum within the first 7 days after visual symptoms and remains elevated for 30 days 1

Critical Time-Sensitive Considerations

If presenting within 4.5 hours of symptom onset:

• Intravenous tissue plasminogen activator (tPA) may be considered after thorough benefit/risk discussion 1, 4

Antiplatelet therapy should be started without delay (aspirin 81 mg daily or clopidogrel 75 mg daily) 1, 4

Emergency Department Workup (Within 24 Hours)

Neuroimaging

• Brain MRI with diffusion-weighted imaging (DWI) to identify silent brain infarctions, which occur in 19-25% of patients with retinal artery occlusions 1, 2

Vascular Imaging

• Carotid artery imaging (duplex ultrasound, CTA, or MRA) is critical – clinically significant carotid stenosis is discovered in up to 70% of patients with symptomatic retinal artery occlusions 1, 2

Cardiac Evaluation

• ECG and echocardiography to evaluate for atrial fibrillation, valvular disease, and other cardioembolic sources 1, 4

Age-Specific Consideration

If patient is over 50 years old:

• Urgent ESR and CRP to rule out giant cell arteritis (GCA) 2, 4
• Inquire about jaw claudication (likelihood ratio 4.90 for GCA), scalp tenderness, proximal muscle pain 1, 5
• If GCA suspected, start high-dose IV corticosteroids immediately before biopsy confirmation to prevent bilateral blindness 1, 4

Risk Stratification and Prognosis

Stroke risk based on vascular risk factors (hypertension, hypercholesterolemia, diabetes, smoking): 1

• 0-1 risk factors: 1.8% 3-year stroke risk
• 2 risk factors: 12.3% 3-year stroke risk
• 3-4 risk factors: 24.2% 3-year stroke risk

Patients with amaurosis fugax carry the same cardiovascular risk as those with cerebral TIA and require identical intensity of secondary prevention 1

Definitive Treatment for High-Grade Carotid Stenosis

If carotid stenosis >70% is identified:

• Carotid endarterectomy (CEA) should be performed within 2 weeks of symptom onset to achieve maximal benefit 1, 4
• Surgical benefit declines sharply after 2 weeks and is greatly diminished beyond this period 1

Secondary Prevention

• Aggressive control of hypertension, diabetes, and hyperlipidemia 1
• Smoking cessation 1
• Statin therapy 4
• Long-term antiplatelet or anticoagulation (if atrial fibrillation detected) 4

Critical Pitfalls to Avoid

• Do not confuse with transient visual obscurations (TVOs) – TVOs last only seconds (not minutes), represent optic nerve head ischemia from raised intracranial pressure, and require papilledema evaluation rather than stroke workup 1
• Do not miss the 2-week window for carotid endarterectomy – surgical benefit is time-dependent 1
• Do not overlook giant cell arteritis in patients over 50 – requires immediate corticosteroids to prevent bilateral blindness 1, 4
• Do not attempt further ophthalmologic testing before emergency referral – this delays life-saving stroke evaluation 3, 1