Practice question

A 60-year-old woman with hypertension presents to the Emergency Department reporting a sudden, painless, and profound loss of vision in her right eye, which occurred about an hour ago. She describes it like a 'curtain falling' over her vision. On examination, visual acuity is Counting Fingers in the right eye and 6/6 in the left. Fundoscopy of the right eye reveals a pale retina, attenuated arterioles, and a distinct 'cherry red spot' at the macula. What is the most likely diagnosis?