Placido disc is used for diagnosing which of the following condition?

Placido disc examination is used to diagnose keratoconus. In a case of keratoconus, placido disc examination shows irregularities of the circles. Placido's keratoscopic disc: It is a disc painted with alternating black and white circles. It may be used to assess the smoothness and curvature of corneal surface. Normally, on looking through the hole in the center of disc a uniform sharp image of the circle is seen on the cornea. Distoion of the circles occur when irregularities are present on the corneal surface. Ref: Comprehensive Ophthalmology By AK Khurana, 4th edn, page 119