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
Placido disc is useful for detecting: 
Select and explain. 
A. Microcornea, B. Megalocornea, C. Corneal scars, D. Keratoconus
D: Keratoconus
Answer: D: Keratoconus 
Explanation: 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