This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuro-ophthalmology, Subject name: Ophthalmology
[{'content': 'Optic neuritis causes - \nSelect and explain. \nA. Gradual painless loss of vision, B. Sudden painless loss of vision, C. Gradual painful loss of vision, D. Sudden painful loss of vision', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Visual loss in optic neuritis : Sudden, progressive and profound visual loss. Patients may complain of dull eye ache. Ref:AK Khurana 6thE pg 318', 'role': 'assistant'}]