Which Carotid Artery Causes Left-Eye Amaurosis Fugax
The left (ipsilateral) carotid artery is responsible for your left-eye transient visual loss. Retinal ischemia occurs from emboli or stenosis in the carotid artery on the same side as the affected eye. 1
Anatomic Basis for Ipsilateral Causation
The internal carotid artery supplies the ophthalmic artery on the same side, which in turn perfuses the central retinal artery and posterior ciliary arteries that nourish the retina and optic nerve. 1
Embolic occlusion originates from the ipsilateral internal carotid artery in the vast majority of cases—85% of patients with nonarteritic central retinal artery occlusion have ipsilateral carotid plaque on vascular imaging. 1
71% of patients with retinal arterial occlusion have ipsilateral carotid plaque, though only 18% have >80% stenosis, indicating that embolization from atherosclerotic plaque (rather than hemodynamic insufficiency) is the primary mechanism. 1
Clinical Evidence Supporting Ipsilateral Disease
All patients with amaurosis fugax in one surgical series had 75% or greater stenosis of the internal carotid artery at the bifurcation on the symptomatic side, and all had unilateral visual symptoms that were relieved by ipsilateral carotid endarterectomy. 2
Retinal arterial emboli visible on fundoscopy indicate ipsilateral carotid disease—in three case presentations, patients with monocular vision loss and retinal emboli all had 50-79% stenosis of the ipsilateral internal carotid artery on duplex ultrasound. 3
60% of patients with acute ischemic eye syndromes have ipsilateral carotid artery disease on specialized vascular imaging, confirming the same-side relationship. 4
Critical Diagnostic Workup Required
Duplex ultrasound of the left carotid artery should be performed urgently to assess for stenosis or ulcerated plaque, as this is the most likely source of emboli causing your left-eye symptoms. 3, 5
Brain MRI with diffusion-weighted imaging identifies concurrent stroke in up to 24% of retinal vascular events, so neuroimaging should be obtained even if vision has returned to normal. 6
The stroke risk remains highest in the first 7 days even if vision improves—never assume that symptom resolution eliminates stroke risk, as retinal TIAs carry the same cardiovascular mortality risk as cerebral TIAs. 6, 1
Common Pitfall to Avoid
Do not assume bilateral carotid evaluation is unnecessary—while the left carotid is the culprit for left-eye symptoms, 50% of patients also have contralateral carotid disease that requires assessment for overall stroke risk stratification. 4
In patients over 50 years, always check ESR and CRP to exclude giant cell arteritis, which can cause arteritic retinal ischemia and requires immediate high-dose steroids to prevent blindness in the contralateral eye. 6, 7