<prompt> Placido disc is useful for detecting:MicrocorneaMegalocorneaCorneal scarsKeratoconus  <response>: 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 