A 65-year-old man with transient monocular vision loss.

What are the possible causes of the vision loss in this patient? Transient monocular vision loss, previously known as amaurosis fugax, has numerous causes. These include thromboembolic events (e.g., valvular heart disease and atherosclerosis of the carotid artery), hypoperfusion (e.g., stenosis of the carotid artery and ocular ischemic syndrome), ocular causes (e.g., impending or partial occlusion of the retinal artery or vein, intermittent angle-closure glaucoma and optic disc edema or anomaly) and vasospasm (e.g., ophthalmic migraine) (Box 1). What clinical clues help determine the cause of the vision loss? Transient monocular vision loss typically lasts from a few seconds to minutes, followed by a complete recovery. The amount of vision loss can range from mild blurriness to, less commonly, total blindness and can affect either a portion or all of the visual field. Although the cause cannot be determined solely from the patient’s history, transient monocular vision loss due to papilledema typically lasts only a few seconds, whereas the duration is minutes or longer when caused by thromboembolic events. In most patients (> 50%), the vision loss is secondary to ischemia induced by stenosis or embolism of the carotid artery or its tributaries. These patients usually have major risk factors for cardiovascular disease, such as smoking and dyslipidemia, and a carotid bruit may be heard on auscultation. Neck pain or ipsilateral Horner syndrome is suggestive of carotid dissection. In younger patients, ophthalmic migraine is the most common cause of transient monocular vision loss. In these patients, the vision loss is typically associated with positive phenomena, such as scintillations. It is important to consider a diagnosis of giant cell arteritis, particularly in older patients. Although the clinical presentation is highly variable, patients with giant cell arteritis may have temporal headache, jaw claudication, scalp tenderness, fever, weight loss and anorexia. Patients with carotid artery disease do not experi ence these symptoms.