MSFinals-3823

A 30-year-old woman comes to the clinic with asymmetrical pupils. Upon shining light into her eyes, the right pupil is 3 mm larger than the left. In a darkened room, the right pupil remains larger, but by only 1mm. Both pupils are regular in shape. She reports no discomfort, her sclerae appear normal, and a slit-lamp examination reveals no abnormalities. Her eye movements are also unaffected. The patient’s father died from a brain tumor, and she is concerned that she may have the same condition. What is the most probable underlying cause?