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
[{'content': 'Placido disc is used for \nSelect and explain. \nA. Uveitis, B. Keratoconus, C. Retinoblastoma, D. Retinal detachment', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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', 'role': 'assistant'}]