Knowing signs of impending stroke is essential

Baltimore-Ophthalmologists must learn to recognize the signs and symptoms that indicate an impending stroke and initiate the appropriate evaluation for each patient, according to Preston C. Calvert, MD. He outlined a plan for ophthalmologists to implement to ensure a rapid neurologic consultation when patients present with risk factors for stroke.

"The ophthalmologist has a key role in diagnosing and managing stroke," said Dr. Calvert, assistant professor, department of neurology, Johns Hopkins University School of Medicine, Baltimore. "The prevention of stroke is really the main 'treatment' that we have available despite all our efforts with treatments such as tissue plasminogen activator. Many patients who will present to ophthalmologists' offices are at high risk of having a stroke in the immediate future. Ophthalmologists must take strong responsibility for what happens to these patients."

Dr. Calvert also underscored the importance of differentiating carotid disease from vertebrobasilar disease.

Speed is important in these cases. The most common form of cerebrovascular disease that ophthalmologists will see is atheromatous internal carotid artery disease with distal embolism into the retina, Dr. Calvert said.

"This can present as either amaurosis fugax or as a central or branch retinal artery occlusion. The risk of a completed stroke in those patients is immediate and severe," he said. The Oxfordshire Community Stroke Project, which looked at patients after a first transient ischemic attack of the retina or brain, found that there was a 5% risk of a completed stroke within 2 days of the first event, an 8.6% risk within 7 days, and 12% risk in the first month.

In patients who present to ophthalmologists, the risk of carotid stenosis, which is the most treatable cause of preventable stroke, is more frequent in those with amaurosis fugax or retinal artery occlusion than in patients who present with a stroke. Dr. Calvert noted that a recent study reported that 30% of patients who had amaurosis fugax had a lesion of 30% or greater in the ipsilateral carotid artery; that figure was 22% if they had a branch retinal artery occlusion or central retinal vein occlusion, and 15% with a cerebral infarct.

"These percentages show that patients who present to an ophthalmologist are at the highest risk," he said. "Those patients with a high-grade stenosis are walking time bombs, because the risk of stroke is about 5% per week before they undergo surgery."

Carotid syndromes Amaurosis fugax and the retinal artery occlusions are the primary signs that the patient has a carotid syndrome.

"The goal with these patients is to find any process that needs treatment other than by antiplatelet agents. Patients with greater than 70% stenosis are best treated by endarterectomy. Identify the patients with a dissection or a cardiac source who need anticoagulation therapy and identify those with giant cell arteritis," he said.

Dr. Calvert described the noninvasive evaluators of patients with carotid syndrome. Color duplex ultrasound has a very high sensitivity and specificity, is inexpensive, is performed rapidly, and is available in most places the day it is ordered. One of its limitations is that it is used to evaluate only the carotid bifurcation and the proximal internal carotid and not the distal carotid; in addition, carotid dissection can be missed. Another limitation is that a tight stenosis may be called an occlusion, which must be confirmed.

Magnetic resonance angiography (MRA) is another imaging option that uses several techniques to visualize the cervical and cranial carotid arteries and the vertebrobasilar circulation. The test is optimal with gadolinium contrast enhancement. For carotid stenosis exceeding 70%, the sensitivities range up to 95% and specificities up to 94%, Dr. Calvert pointed out. MRA can visualize the distal internal carotid to locate dissections, carotid siphon stenosis, fibromuscular dysplasia, and tandem stenoses. The limitations of MRA are that the test cannot be accessed the same day as ordered in many places, it is more expensive than ultrasound, and the procedure cannot be performed in patients with pacemakers.