This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
[{'content': 'A 52 year old male with a history of hea disease presents with sudden painless loss of vision in one eye. Examination reveals cherry red spot. Diagnosis is: \nSelect and explain. \nA. Central retinal vein occlusion, B. Central retinal aery occlusion, C. Diabetic retinopathy, D. Acute ischemic optic neuritis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Central retinal aery occlusion: It occurs due to obstruction at the level of lamina cribrosa. Causes sudden painless loss of vision. Retina becomes white due to oedema & a cherry red spot is seen at the fovea. Aerioles become narrow & blood column within the retinal vessels is segmented. Resuscitation time of the human retina following retinal ischemia is 11/2 hours. Ref: Review of Ophthalmology by A.K. Khurana, 5th Edition, Page 113', 'role': 'assistant'}]