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
Incidence of primary open-angle glaucoma in population over 40 years of age is about: 
Select and explain. 
A. 1 in 100, B. 1 in 200, C. 1 in 500, D. 1 in 1000
A: 1 in 100
Answer: A: 1 in 100 
Explanation: Ans. 1 in 100