This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Elementary Optics, Subject name: Ophthalmology
[{'content': "What is Sturm's Conoid? \nSelect and explain. \nA. Distance between two focal points created by differential refractive power of lens or cornea in different meridians., B. Pattern of alignment of rays due to a cylindrical lens, C. Method of calculating IOL power, D. Tool in Diagnosis of Myopia", 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Distance between two focal points created by differential refractive power of lens or cornea in different meridians o Sturm's Conoid:# It is an optical condition in which the refractive power of lens or cornea is not the same in all meridians, hence two focal points separated by a focal interval are formed which is called the Sturm's Conoid.o Etiology:A) Corneal Causes:# Astigmatism# KeratoconusB) Lenticular Causes:# Lenticonus# Congenital tilting of lens# Index astigmatism", 'role': 'assistant'}]