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': "The earliest clinically significant field defect in primary open-angle glaucoma is: \nSelect and explain. \nA. Paracentral scotoma, B. Baring of blind spot, C. Seidel's scotoma, D. Isopter contraction", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Paracentral scotoma', 'role': 'assistant'}]