This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Uveal tract, Subject name: Ophthalmology
Placido disc is used for 
Select and explain. 
A. Uveitis, B. Keratoconus, C. Retinoblastoma, D. Retinal detachment
B: Keratoconus
Answer: B: Keratoconus 
Explanation: It is a disc painted with alternating black and white circles. Used to assess the smoothness and curvature of corneal surface. It shows irregularity of circles in keratoconus. Ref khurana page no.126