This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
Astigmatism is due to – 
Select and explain. 
A. Irregularity of curvature of cornea, B. Irregularity of curvature of lens, C. Forward displacement of the lens, D. Backward displacement of lens
A: Irregularity of curvature of cornea
Answer: A: Irregularity of curvature of cornea 
Explanation: Most common cause of astigmatism is abnormalities of curvature of cornea.