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': 'Commonest cause of loss of vision in non- proliferative diabetic retinopathy is – \nSelect and explain. \nA. Vitreous heamorrhage, B. Macular edema, C. Detachment of retina, D. Subretinal haemorrhage', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Macular edema is the most common cause of loss of vision in NPDR.', 'role': 'assistant'}]