Amaurosis Fugax (Transient Vision Loss)
Amaurosis Fugax (transient vision loss)
Amaurosis fugax (AF) refers to transient vision loss (TVL). AF can either be monocular (TMVL) or binocular (TBVL). It most commonly occurs monocularly, secondary to ischemia in the retina, choroid, or optic nerve. The most common cause of TMVL is an ipsilateral carotid artery disease (e.g., internal carotid artery dissection or atherosclerosis) with secondary thromboemboli, but it can also be a symptom of vasculitis (e.g., giant cell arteritis). AF can be a harbringer of impending stroke and thus merits urgent evaluation. TBVL is less common than TMVL and may be due to cortical lesions (e.g. migraine, seizure, or vertebrobasilar ischemia). AF caused by ischemia is considered a form of transient ischemic attack (TIA) and usually lasts from seconds to minutes, followed by full visual recovery. AF should be differentiated from structural optic disc and intraocular causes of TMVL (e.g., impending central retinal vein occlusion, optic disc drusen, or papilledema).
Causes of TMVL can be divided into vascular (e.g. carotid pathology, cardioembolic source, GCA, vasospasm), neurologic (e.g. retinal migraine), or ophthalmic (e.g. papilledema, optic disc drusen, intermittent angle-closure glaucoma). Causes of TBVL can be divided into the same categories. Vascular (e.g. TIA, bilateral carotid pathology), neurologic (e.g., migraine, occipital seizure, posterior reversible encephalopathy syndrome), or ophthalmic (e.g. papilledema) etiologies must be considered.
Risk factors for AF depend on the etiology, but for classic ischemic TMVL, the most important risk factor is carotid artery stenosis. Other risk factors include atrial fibrillation, hypertension, diabetes, hyperlipidemia, hypercoagulable state, and myeloproliferative disorders.
TMVL can be caused by a number of etiologies as described above, but the common unifying mechanism is hypoperfusion of the retina or optic nerve. This hypoperfusion could be due to hypotension, thrombus, embolus, arteritis, or vasospasm. Most commonly, an embolus from the carotid artery breaks free and transiently occludes the central or branch retinal arteries or the ophthalmic artery. If the ischemia targets the optic nerve, it is usually due to decreased perfusion through one or more posterior ciliary arteries. TBVL can also occur due to the same hypoperfusion mechanism if it is bilateral (e.g., vertebrobasilar ischemia), as well as secondary to the other neurologic or ophthalmic etiologies described above. It also implies that the lesion is either bilateral anteriorly, chiasmal, or retrochiasmal.
An accurate history is important as it will heavily guide the differential diagnosis for AF. The age of the patient and the past medical history (e.g., vasculopathic risk factors, history of migraines, cardiac or valvular disease, vasculitis) are important predisposing considerations. The patient should be asked whether the visual loss was unilateral or bilateral (e.g. visual loss with one or the other eye covered during the episode). Other features of the event including any triggering or precipitating factor, the duration of the episode, whether the resolution was complete vs. incomplete, and any symptoms that lingered afterwards all contribute heavily to the clinical picture. Special concern should also be taken to inquire for any prior symptoms of GCA in elderly patients (e.g., jaw claudication, headache, scalp tenderness)
A complete ophthalmologic exam is mandatory (e.g., Hollenhorst plaque, angle closure glaucoma). Additionally, special attention should be given to the temporal artery region, examining for tenderness or erosions. A complete cardiovascular exam may also be performed with an emphasis on the presence of arrhythmias or a carotid bruit. Most patients with AF, however, have normal eye exams.
Patients usually report negative visual symptoms, typically lasting from seconds to minutes; however, longer episodes have been reported, and positive visual symptoms (though more rare) do not rule out an ischemic etiology. Transient visual loss precipitated by gaze (i.e., gaze evoked AF) may suggest an orbital lesion.
After ophthalmologic evaluation, laboratory tests include inflammatory markers like erythrocytes sedimentation rate (ESR) and C-reactive protein (CRP) to evaluate for GCA in elderly patients. Imaging of the carotid arteries and cardiac evaluation are generally recommended. Neuroimaging (e.g., magnetic resonance imaging (MRI) of the brain) and vascular imaging (e.g., CTA or MRA of head and neck) may show intracranial vascular occlusive disease, brain ischemia, or prior stroke. Electroencephalogram (EEG) may be indicated if the TVL was bilateral or if the history suggests a seizure.
Management of TMVL or TBVL depends on suspected etiology, but pertinently, if TIA is suspected, the patient should undergo an expedited stroke work-up. If GCA is suspected then the patient could be started on empiric steroid therapy, have laboratory testing (e.g., ESR and CRP) and undergo a temporal artery biopsy. Antiplatelet (e.g., aspirin) or anticoagulation (e.g., for atrial fibrillation) may be indicated depending on etiology.
Prognosis varies with age and etiology.
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- Syndee Givre, MD, PhD, Gregory P Van Stavern, MD, ed. UpToDate. Waltham, MA: UpToDate Inc. https://www.uptodate.com/contents/amaurosis-fugax-transient-monocular-or-binocular-visual-loss/print?search=amaurosis-fugax&source=search_result&selectedTitle=1~42&usage_type=default&display_rank=1 (Accessed on July 8, 2019.)