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
For tonometry is : 
Select and explain. 
A. 4% xylocaine, B. 3% xylocaine, C. 2% xylocaine, D. 1% xylocaine
A: 4% xylocaine
Answer: A: 4% xylocaine 
Explanation: 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.