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': 'Which of the following instrument is not required to calculate the power of IOL? \nSelect and explain. \nA. Amplitude scan, B. Keratometer, C. Pachymetry, D. Biometer', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Amplitude scan gives Axial length.\nKeratometer gives corneal curvature.\nBiometer is used to\xa0calculate the power of IOL.\nAxial length and corneal curvature are substituted in SRK formula for calculation of IOL.\nPachymetry is used to calculate thickness of Cornea which is not used in SRK formula for calculation of IOL.', 'role': 'assistant'}]