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': "First sign seen in open-angle glaucoma is: \nSelect and explain. \nA. Arcuate scotoma, B. Extension above blind spot, C. Roene's nasal step, D. Siedel's scotoma", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Extension above blind spot', 'role': 'assistant'}]