Q. A 65-year-old man presents to the emergency room with a complaint of "walking into walls." He reports that yesterday, he walked into the side of the wall at work and hit his left shoulder against the door frame. When he was driving home, he didn't see a car at the intersection and almost got into an accident. His vital signs are normal and his general medical exam is normal. On neurological exam, visual field testing demonstrates a left hemianopia (loss of vision). Which of the following cranial nerves is primarily responsible for visual processing?