Amaurosis fugax pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Prior to 1990, amaurosis fugax could, "clinically, be divided into four identifiable symptom complexes, each with its underlying pathoetiology: embolic, hypoperfusion, angiospasm, and unknown."[1] In 1990, the causes of amaurosis fugax were better refined by Amaurosis Fugax Study Group, which has defined five distinct causes of transient monocular blindness: embolic, hemodynamic, ocular, neurologic, and idiopathic.[2] Concerning the pathology underlying these causes (stay idiopathic), "some of the more frequent causes include atheromatous disease of the internal carotid or ophthalmic artery, vasospasm, optic neuropathy, giant cell arteritis, angle-closure glaucoma, increased intracranial pressure, orbital compressive disease, a steal phenomenon, and blood hyperviscosity or hypercoagulability."[3]


Embolic and Hemodynamic Origin

With respect to embolic and hemodynamic causes, this transient monocular visual loss ultimately occurs due to a temporary reduction in retinal artery, ophthalmic artery, or ciliary artery blood flow, leading to a decrease in retinal circulation which, in turn, causes retinal hypoxia.[4] Also, it must be noted that while, classically and most commonly, emboli causing amaurosis fugax are described as coming from an atherosclerotic carotid artery, any emboli arising from vasculature preceding the retinal artery, ophthalmic artery, or ciliary arteries may cause this transient monocular blindness.

  • Atherosclerotic carotid artery: Amaurosis fugax may present as a type of transient ischemic attack (TIA), during which an embolus unilaterally obstructs the lumen of the retinal artery or ophthalmic artery, causing a decrease in blood flow to the ipsilateral retina. The most common source of these thromboemboli is an atherosclerotic carotid artery.[5]
    However, a severely atherosclerotic carotid artery may also cause amaurosis fugax due to its stenosis of blood flow, leading to ischemia when the retina is exposed to bright light.[6] "Unilateral visual loss in bright light may indicate ipsilateral carotid artery occlusive disease and may reflect the inability of borderline circulation to sustain the increased retinal metabolic activity associated with exposure to bright light."[7]
  • Atherosclerotic ophthalmic artery: Will present similarly to an atherosclerotic internal carotid artery.
  • Temporary vasospasm leading to decreased blood flow can be a cause of amaurosis fugax.[8][9] Generally, these episodes are brief, lasting no longer that five minutes,[10] and have been associated with exercise.[4][11] These vasospastic episodes are not restricted to young and healthy individuals. "Observations suggest that a systemic hemodynamic challenge provoke[s] the release of vasospastic substance in the rentinal vasculature of one eye."[10]
  • Giant cell arteritis: Giant cell arteritis can result in granulomatous inflammation within the central retinal artery and posterior ciliary arteries of eye, resulting in partial or complete occlusion, leading to decreased blood flow manifesting as amaurosis fugax. Commonly, amaurosis fugax caused by giant cell arteritis may be associated with jaw claudication and headache. However, it is also not uncommon for these patients to have no other symptoms.[12] One comprehensive review found a two to nineteen percent incidence of amaurosis fugax among these patients.[13]
  • Drug abuse-related intravascular emboli[2]

Ocular origin

Ocular causes include:

Neurologic origin

Neurological causes include:

  • Papilledema: "The underlying mechanism for visual obscurations in all of these patients appear to be transient ischemia of the optic nerve head consequent to increased tissue pressure. Axonal swelling, intraneural masses, and increased influx of interstitial fluid may all contribute to increases in tissue pressure in the optic nerve head. The consequent reduction in perfusion pressure renders the small, low-pressure vessels that supply the optic nerve head vulnerable to compromise. Brief fluctuations in intracranial or systemic blood pressure may then result in transient loss of function in the eyes."[31] Generally, this transient visual loss is also associated with a headache and optic disk swelling.
  • Multiple Sclerosis can cause amaurosis fugax due to a unilateral conduction block, which is a result of demyelination and inflammation of the optic nerve, and "...possibly by defects in synaptic transmission and putative circulating blocking factors."[32]


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