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': 'For tonometry is : \nSelect and explain. \nA. 4% xylocaine, B. 3% xylocaine, C. 2% xylocaine, D. 1% xylocaine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Tonometry is the method of measuring intraocular pressure using calibrated instruments. The normal range is 10 to 21 mm Hg.Schiotz tonometry, a drop of surface anaesthetic solution like 4%xylocaine is used. Ref :Greenberg R.D., Daniel K.J. (2011). Chapter 31. Eye Emergencies. In R.L. Humphries, C. Stone (Eds), CURRENT Diagnosis & Treatment Emergency Medicine, 7e.', 'role': 'assistant'}]