Eyes, Ears, Nose and Throatcommon
A 66-year-old man with atrial fibrillation presents 40 minutes after the sight in his left eye "went out like a light" while reading; there was no pain. He can now only perceive hand movements with that eye. The left pupil reacts sluggishly to direct light but briskly when light is shone into the right eye. Fundoscopy of the left eye shows a pale, milky retina with markedly narrowed arterioles and a small bright red spot at the centre of the macula. The right eye is normal. There is no history of headache, scalp tenderness or jaw pain.
Which one of the following is the most likely diagnosis?