A-Z of Posterior Eye Conditions
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Amaurosis fugax derives from the Latin and is a descriptive term for temporary, monocular, visual loss. The most common cause is temporary retinal ischaemia caused by embolism from the carotid artery, heart or aorta. Less commonly, when stenotic atherosclerotic disease is present in vessels along the course from the heart to the globe, amaurosis fugax may be precipitated by postural changes or cardiac arrhythmias. In temporal arteritis, transient visual loss may be a harbinger of impending permanent visual loss - urgent treatment is therefore essential.
Other causes of amaurosis fugax include impending central retinal vein occlusion, glaucoma, retinal migraine, intermittent ocular haemorrhage and optic nerve head drusen. Very rarely, an intraorbital tumour may cause amaurosis fugax by compressing the optic nerve or a blood vessel in certain positions of gaze.
SYMPTOMS
The visual loss usually lasts for seconds to minutes, but may extend for 1-2 hours. As the symptoms have usually resolved prior to presentation, careful history-taking is crucial. The patient should be asked questions to differentiate true monocular visual loss from homonymous hemianopia. For example, did the patient cover one eye to test vision during the episode?
The potential range of previous or accompanying symptoms reflects the diverse causality of amaurosis fugax. For example, the patient may have experienced other symptoms of cerebrovascular or cardiovascular disease (such as palpitations, transient ischaemic attacks or claudication). Temporal arteritis may be manifested by jaw claudication, temporal headache, scalp tenderness or muscle aches.
SIGNS
Although ocular examination is often normal, a variety of signs may aid diagnosis. An embolus may be visible within a retinal arteriole. There may be signs of the ophthalmic artery hypoperfusion (dilated veins, mid-peripheral retinal haemorrhages, iris neovascularisation). Evidence of an old branch retinal vein occlusion may be present. Systemic medical examination may reveal signs of cerebrovascular or cardiovascular disease.
SIGNIFICANCE
Depending on the cause, prompt assessment and treatment may prevent permanent loss of vision. Amaurosis fugax may be the presenting symptom of vascular disease affecting multiple organ systems.
DIFFERENTIAL DIAGNOSIS
Arteritic ischaemic optic neuropathy; central retinal artery occlusion; central retinal vein occlusion; ophthalmic artery hypoperfusion.
MANAGEMENT
Blood tests and pathology
Blood tests included in the assessment of systemic vascular causes of amaurosis fugax include full blood examination and fasting blood glucose and lipid studies.
If temporal arteritis is suspected, urgent erythrocyte sedimentation rate and C-reactive protein measurement are performed.
Imaging investigations
Fluorescein angiography may show focal arterial staining at the site of an embolus.
Ultrasonographic evaluation of the heart and carotid vessels may reveal lesions amenable to medical or surgical treatment. Other imaging investigations (cerebral tomography, magnetic resonance imaging) may also be indicated when cerebrovascular or neoplastic disease is suspected.
Medications and advice
Essential to the management of atherosclerotic disease is risk factor modification incorporating diet and exercise, smoking cessation and diabetic control. Anti-platelet agents, antihypertensive drugs and lipid-lowering agents may be beneficial. Temporal arteritis is treated initially with intravenous corticosteroids. Other causes are treated differently (for example, calcium channel blockers for retinal migraine).
Surgery
Carotid endarterectomy for carotid stenosis; cardiac surgery for valvular lesions; surgery and/or chemoradiotherapy for mass lesions.