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': 'Thickness of cornea is best measured by: \nSelect and explain. \nA. Keratometer, B. Pachymeter, C. Optometer, D. Pentoscope', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Pachymeter', 'role': 'assistant'}]