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
Landolt's broken ring test is used for testing: 
Select and explain. 
A. Form sense, B. Contrast sense, C. Central field, D. Scotopic vision
A: Form sense
Answer: A: Form sense 
Explanation: Ans. Form sense