Q. A 70-year-old woman is brought to the emergency department 30-minutes after a sudden onset of visual problems and numbness on the left side of her body. She has a history of hypertension and coronary artery disease. Her current medications are enalapril, simvastatin, aspirin, and propranolol. Her BP is 160/88 mmHg, but her remaining vital signs are normal. On clinical examination, she has loss of vision in the temporal field in the left eye and the nasal field in the Right eye with macular sparing. Sensations decreased on the left side of her body, but deep tendon reflexes are intact. Which of the following is the cause of this patient’s presentation?