This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Glaucoma, Subject name: Ophthalmology
Which of the following is not a source of error in the applanation tonometry: 
Select and explain. 
A. High Pressure on the globe, B. Tear film, C. Astigmatism, D. Wide pulse pressure
B: Tear film
Answer: B: Tear film 
Explanation: Tear film is required for accurate measurement , is not a source of error. Sources of error in tonometry: Inappropriate fluorescein pattern. Pressure on the globe. Central Corneal thickness. Corneal edema. Pulse pressure. Astigmatism. Incorrect calibration. Wide pulse pressure.