Review Question - QID 214388

A 65-year-old man presents to the emergency department with a 1 hour history of vision loss. He states that he was gardening when he noticed hazy vision in his left eye with a sensation that he was seeing flashes. He has never had these symptoms before. He also has an ongoing headache. His history is notable for hypertension and diabetes. He states that he is still experiencing flashes in his left eye. His temperature is 97.0°F (36.1°C), blood pressure is 174/91 mmHg, pulse is 88/min, respirations are 13/min, and oxygen saturation is 98% on room air. Cranial nerves II-XII are grossly intact. An ocular ultrasound is performed as seen in Figure A. Which of the following is the most likely diagnosis?