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': 'Following are the causes of painless sudden onset of loss of vision except ? \nSelect and explain. \nA. Acute congestive glaucoma, B. Vitreous hemorrhage, C. CRAO, D. Central serous retinopathy', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Acute congestive glaucoma Acute congestive glaucoma causes sudden painful loss of vision.", 'role': 'assistant'}]