An 80-year-old man is evaluated for a 2-year history of sudden-onset episodes of flashing lights in the right visual field that typically last 10 to 20 seconds. He does not believe that he loses awareness during these events, but his daughter, who accompanied him, reports that he stared and smacked his lips during the two recent episodes she witnessed. Symptoms started 6 months after he had a cryptogenic stroke of the left occipital lobe. The patient also has hypertension. Medications are aspirin, atorvastatin, and lisinopril.
On physical examination, temperature is 36.7 °C (98.0 °F), blood pressure is 140/90 mm Hg, and pulse rate is 67/min and irregular. Visual field testing reveals right homonymous hemianopia. All other findings from the general physical and neurologic examinations are within normal limits.
An MRI reveals a chronic infarct in the territory of the left posterior cerebral artery.
Which of the following is the most appropriate treatment?