This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and Errors of Refraction, Subject name: Ophthalmology
[{'content': 'Placido disc is useful for detecting: \nSelect and explain. \nA. Microcornea, B. Megalocornea, C. Corneal scars, D. Keratoconus', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Placido disc Placido disc is a type of video-keratoscopy which helps understand details about the corneal surface and anterior curvature -In normal cornea , there is no distoion of reflected pattern - In keratoconus , there is distoion of reflected pattern', 'role': 'assistant'}]