This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lens, Subject name: Ophthalmology
[{'content': 'Power of Intraocular lens is determined by? \nSelect and explain. \nA. Keratometry, B. Retinoscopy, C. Ophthalmoscopy, D. Gonioscopy\\/Biometry', 'role': 'user'}, {'content': "Answer: A \nExplanation: The most common method of determining IOL power uses a regression formula called 'SRK (Sanders, Retzlaff and Kraff) formula'. The formula is P = A - 2.5L - 0.9K, where: P is the power of IOL, \x01 A is a constant which is specific for each lens type. \x01 L is the axial length of the eyeball in mm, which is determined by A-scan ultrasonography. \x01 K is average corneal curvature, which is determined by keratometry.", 'role': 'assistant'}]