Description, Causes and Risk Factors:
Def: A transient blindness that may result from a transient ischemia due to carotid artery insufficiency, retinal artery embolus, or to centrifugal force (visual blackout in flight).
Amaurosis fugax is loss of vision in one eye due to a temporary lack of blood flow to the retina. The symptom usually develops suddenly, and many individuals describe the event as “it was as if a shade or curtain came over my eye.”
It is caused by a blockage or low blood flow within the main blood vessel supplying the eye. Blockages are usually due to a blood clot or plaque (small piece of cholesterol) that breaks off from a larger artery and travels upward to the brain or eye, becoming lodged in the main artery supplying the eye. Low blood flow to the eye may also result from a critical narrowing of one of the main blood vessels supplying blood to the brain and eye.
This condition can also occur in ruminants suffering from a vitamin B1 deficiency due to thiamine related cerebrocortical necrosis.
Vision loss occurs as long as the blood supply to the artery is blocked. Atherosclerosis of the arteries in the neck is the main risk factor for this condition.
Other risk factors may include:
Ocular: Dry eye syndrome, blepharitis, keratitis, intermittent angle closure glaucoma, optic disc drusen, vitreous detachment, retinal break, orbital tumor, intraocular hemorrhage, and angiospasm.
Neurologic: Optic neuritis, papilledema, multiple sclerosis, intracranial tumor, and lupus.
Circulatory: Carotid emboli, hypoperfusion, coagulation disorder, carotid stenosis, arrhythmia, increased blood viscosity, and migraine.
Symptoms include the sudden loss of vision in one eye. This usually only lasts seconds but may last several minutes. Some patients describe the loss of vision as a gray or black shade coming down over their eye.
The experience of amaurosis fugax is classically described as a transitory monocular imagination departure that appears as a "drape coming downward vertically into the area of imagination in one heart;" however, this altitudinal visual departure is comparatively rare.Other descriptions of this experience include a monocular blindness, dimming, fogging, or blurring. Total or sectorial imagination departure typically lasts simply a few seconds, but may live minutes or still hours. Duration depends on the etiology of the imagination departure.
Certainly, extra symptoms may be existing with the amaurosis fugax, and those findings will bet on the etiology of the transitory monocular imagination departure.
When interviewing a patient with amaurosis fugax, it is important to pay special attention to the medical history. The clinician should attempt to uncover the presence of hypertension, diabetes, previous myocardial infarction, prior cerebrovascular accidents, hypercholesterolemia, long standing migraine history, or peripheral vascular disease (PVD).
The eye care provider should perform biomicroscopy paying special attention to the lid margins, tear film, cornea, and anterior chamber. Conditions such as dry eyes, blepharitis, and iritis can all be ruled out from the differential diagnosis if the biomicroscopy is normal. Gonioscopy permits direct observation of the anterior chamber angle of the eye under high magnification. This clinician observation can rule out micro hemorrhage in the anterior chamber or evidence of angle closure glaucoma. Therefore, it should be performed for patient experiencing transient visual disturbance.
A dilated retinal examination is mandatory for patients presenting with amaurosis fugax. The retina, retinal vasculature, optic nerve and vitreous will all provide additional information forming a clinical diagnosis. A vitreous detachment, retinal tear, or retinal detachment should be observable once the patient's eyes are dilated.
Other tests may include an ultrasound of the carotid arteries in the neck, a study of the electrical system of the heart, a magnetic resonance angiography (MRA) scan of the blood vessels in the head and neck, an echocardiogram of the heart, or an angiogram (dye imaging of the blood vessels). If these studies reveal the source of the problem, medication and/or surgery may be necessary.
The treatment of amaurosis fugax depends upon identifying the source of the blood clots or cholesterol that have caused low blood flow or blocked the main artery to the eye. Blood clots may come from arteries inside the head, arteries in the neck, or from the heart. If there is evidence of blockage of more than 70% of the carotid artery, the patient may be considered for surgery to remove the blockage.
Surgery options include: Balloon angioplasty, stenting. Both techniques are used to open up the area of the carotid artery that is blocked by plaque. These methods are promising, especially for patients who are not well enough to undergo major surgery.
The decision to perform surgery will also be based on the severity and the patient's general health. If the patient does not need surgery, doctors usually recommend aspirin or blood thinners.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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