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Amaurosis Fugax

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Title: Amaurosis Fugax

Author: Alexzandra Douglass, MSII, University of Utah School of Medicine

Overview

Amaurosis fugax (AF), stemming from Greek amaurosis meaning dark and latin fugax meaning fleeting, refers to the transient loss of vision in one or both eyes.^1,2  AF is defined as a sudden, transient visual loss or transient blurring or obscuration of vision with normal recovery after the episode. AF is considered a transient ischemic attack (TIA) and must be considered an ophthalmologic emergency.^1–5

Semiology

Patients typically present to the physician after the episode has resolved, in which case ophthalmologic and neurologic exams are normal. Reliance is then placed on the patient’s description of the transient visual loss (TVL). Important distinctions include monocular or binocular localization, onset, duration, description of the visual symptoms, associated features, and precipitating factors.^1–5 Relevant medical and family history may also provide essential information for the diagnosis.

AF can cause monocular or binocular TVL. Generally, monocular lesions localize anterior to the optic chiasm, affecting the optic nerve or structures within the eye. Binocular lesions suggest a more posterior process, localizing to the optic chiasm, optic tract, optic radiations or to visual cortex.^2,4,5 The onset is typically sudden and painless and lasts 1-15 minutes. ^1–5 Painful vision loss suggests a different entity than AF. TVL from any etiology can be described as mild blurring to complete blackness, which involves part or all of the visual field. One specific description to note is the “altitudinal” pattern, resembling a curtain or shade ascending or descending over the patient’s visual field. This type of TVL is considered to be strongly suggestive of a vascular etiology.^1–3

Differential diagnosis

TVL, whether monocular or binocular, represents a heterogeneous group of disorders ranging from benign conditions to those with serious ophthalmologic and neurologic sequelae. Giant cell arteritis and severe carotid stenosis are among two of the disorders with grave consequences and should not be missed. A few of the most common underlying conditions are described below:

• Carotid artery disease: consider in a patient with vascular risk factors that describes an abrupt onset of monocular altitudinal TVL that affects the entire visual field of one eye. This type of TVL is most commonly due to small emboli from a severely stenosed (greater than 70%) ipsilateral internal carotid artery. Emboli from any vascular origin can cause transient impaction of any vessel in the ophthalmic circulation.^2,3,5
• Giant cell arteritis: consider in an elderly patient that presents with accompanying symptoms of jaw claudication, scalp tenderness, headache and muscle weakness. TVL is not a common presentation of giant cell arteritis; however, when present is a grave prognostic factor.
• Ocular Migraine or Migraine with Aura: should be considered in patients of any age describing monocular or binocular TVL with or without positive visual symptoms that last for a relatively longer duration of time, such as greater than 20 minutes.^2–4
• Retinal vasospasm and/or retinal migraine: consider retinal vasospasm in a young patient with positive visual symptoms such as scintillation, that have several episodes in one day.^1,2
• Optic neuritis (multiple sclerosis): suspect this in patients describing transient loss of vision or blurring of vision associated with elevated body temperature after a hot shower or exercise (Uhthoff’s symptom). Uhthoff’s symptom is classically associated with multiple sclerosis and should prompt a corresponding workup, including an MRI of the brain with and without contrast.^1,2 Optic neuritis also is typically accompanied by pain with eye movements.
• Papilledema: TVL is a relatively uncommon presenting symptom of papilledema and is suspected to be due to fluctuations of optic nerve head perfusion associated with changes in position or posture; thus a detailed funduscopic exam is critical. Papilledema can cause monocular or binocular TVL.^1–3
• Cardiogenic embolism: emboli from the heart may lodge in the ophthalmic circulation and cause TVL; however, is more likely to cause a cerebral TIA.^2,3
• Vertebro-basilar ischemia: consider in patients experiencing homonymous TVL. The vision loss may be isolated or accompanied by brainstem symptoms such as dysarthria, dysphagia, diplopia or cerebral symptoms such as hemiparesis, hemi-sensory loss or aphasia.^2,3,5 This can cause monocular or binocular TVL.

Diagnostic workup

Diagnostic workup should be tailored to the most likely underlying condition based on the patient’s age, pertinent medical history, description of the TVL and the physical examination. To minimize the possibility of missing potential diagnoses with serious sequelae, certain diagnostic procedures should be performed on most patients over 50 years old with vascular risk factors. These procedures include a careful dilated eye exam, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to rule out giant cell arteritis and carotid imaging to assess for carotid artery disease.^1,2,4,5 The diagnostic workup can be more selective in young patients without vascular risk factors with a normal physical and ophthalmologic examinations or symptoms of migraine. However, the more that symptoms deviate from classic migraine, the broader the workup should become. ^1,2,4,5 Below is an outline of indication for each diagnostic test:

• Ophthalmologic evaluation: all patients should receive a detailed, dilated eye exam.
• ESR and CRP: should be performed on all patients older than 50 years old and any time giant cell arteritis is suspected.
• Carotid imaging: should be performed on all patients older than 50 years old and younger patients with vascular risk factors.
• Cardiac evaluation: baseline ECG should consider in patients older than 50 years old if giant cell arteritis and carotid artery disease have been excluded.
• Brain MRI: Diffusion-weighted imaging (DWI) should be consider in patients over 50 years old with binocular symptoms to rule out vertebro-basilar ischemia or if multiple sclerosis is the suspected underlying etiology.
• Hypercoagulable testing: should be performed in patients with personal or family histories suggestive of hypercoagulable disorders and an otherwise negative workup.

Treatment

Treatment for TVL is determined by the underlying cause. Two notable diagnoses to discuss include critical carotid artery stenosis (greater than 70%) and giant cell arteritis. Investigators recommend carotid endarterectomy (CEA) be performed on patients with internal carotid artery stenosis greater than 70%.^2,3,5 Referral to neurosurgery or vascular surgery would be indicated at this time. If an elderly patient presents with jaw claudication, TVL and temporal tenderness and giant cell arteritis is suspected, start high dose corticosteroid therapy immediately, do not await inflammatory marker results. Patients with giant cell arteritis are at high risk of permanent vision loss and thus time to corticosteroid treatment should be minimized.^2,3,5 These patients are then scheduled for an outpatient temporal artery biopsy to confirm the diagnosis.

References

1. Lavalle PC, Cabrejo L, Labreuche J, et al. Spectrum of transient visual symptoms in a transient ischemic attack cohort. Stroke. 2013;44(12):3312-3317.
2. Petzold A, Islam N, Hu HH, Plant GT. Embolic and Nonembolic Transient Monocular Visual Field Loss: A Clinicopathologic Review. Surv Ophthalmol. 2013;58(1):42-62.
3. Hayreh SS, Bridget Zimmerman M. Amaurosis fugax in ocular vascular occlusive disorders: Prevalence and pathogeneses. Retina. 2014;34(1):115-122.
4. Petzold A, Islam N, Plant GT. Patterns of non-embolic transient monocular visual field loss. J Neurol. 2013;260(7):1889-1900.
5. Kvickström P, Lindblom B, Bergström G, Zetterberg M. Amaurosis fugax: Risk factors and prevalence of significant carotid stenosis. Clin Ophthalmol. 2016;10:2165-2170.