Question category: Ophthalmology
A 60 year old man presents with sudden painless sight loss in his left eye when he woke that morning. On examination, visual acuity is normal in the right eye and decreased in the left. A marked afferent papillary defect is seen. Fundoscopy shows retinal haemorrhages globally, dilated tortuous retinal veins, cotton wool spots and macular oedema. The right eye is normal. The patient has no history to note, is not on any medication, but his blood pressure at examination was 190/110 and a blood sugar of 13.1 mmol/L. What has caused the sight loss?