A 50-year-old truck driver presents to your office for a routine physical examination. He denies any medical problems; he has never had surgery; he takes no medications or over-the-counter supplements. He has smoked 1 pack of cigarettes daily for 30 years. He does not use alcohol or illicit drugs. His family history is remarkable for hypertension and stroke. On physical examination you notice that one pupil is larger than the other by 0.4 mm; everything else is normal. What is the most likely diagnosis?