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Transient monocular vision loss is an important warning sign that should not be ignored because this complaint may predict risk for a major cerebrovascular or cardiovascular event.
"Transient monocular vision loss is often associated with widespread atherosclerosis. Therefore, optometrists have a critical role in evaluating patients for possible causes of transient vision loss and identifying those who should be referred to an internist, cardiologist, or radiologist for evaluation and treatment of an underlying medical condition," said Dr. Krumholz, associate professor, SUNY College of Optometry, New York.
"Our goal is to make sure our patients receive an appropriate work-up and intervention that may have lifesaving potential," he said.
Cholesterol emboli arising from an atheromatous plaque in the carotid artery represents a cause of TMVL known as amaurosis fugax. This condition is manifested by its sudden onset and monocular, painless presentation.
The vision loss usually persists for minutes as opposed to seconds, hours, or days, may be sectoral or have an altitudinal pattern, and the patient is more likely to describe negative versus positive visual phenomena. After the episode, the patient regains the previous state of vision.
Dr. Krumholz explained that a cholesterol embolus from an atheromatous plaque in the carotid artery may travel to the brain and cause a hemispheric transient ischemic attack, commonly known as a mini-stroke. Alternatively, the embolus can occlude a retinal artery, causing transient vision loss.
"So, amaurosis fugax arising from carotid artery disease can be thought of as a transient ischemic attack of the eye," he said.
In addition to hypercholesterolemia and carotid artery disease, affected patients often also have hypertension and coronary artery disease and are at risk for myocardial infarction. TMVL may also be a marker of cardiac disease because an embolus arising from a calcified cardiac valve may also be the culprit.
Clinical significance and evaluation
Evidence from clinical trials underscores that amaurosis fugax is not a benign event. Available data show that it is associated with a 2% to 8% annual risk of ipsilateral stroke, as well as an increased rate of mortality, with heart disease being the leading cause of death. Understanding these associations and their diagnosis and management will assure the optometrist can identify these patients and make the appropriate referrals, Dr. Krumholz said.
The diagnostic work-up of patients with TMVL suspected to be caused by carotid artery disease includes carotid duplex scanning, which is a noninvasive test providing both anatomic and functional information about the blood flow in the carotid artery.
Since the duplex scanning generally only identifies vessels that are not completely occluded, CT or X-ray angiography may also be performed to differentiate partial from complete occlusions for which the treatment differs. Visualization of blood flow in vessels within the head that are surrounded by dense bone can be studied with magnetic resonance angiography.
Cardiac evaluation with electrocardiography and echocardiography is indicated if the patient's history and examination suggests cardiogenic emboli as the source of the amaurosis fugax. Electrocardiography identifies dysrhythmias associated with blood turbulence within the heart that can precipitate an embolus; whereas echocardiography detects the presence of valve calcification.