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
The most characteristic visual field change in primary open-angle glaucoma is: 
Select and explain. 
A. Nerve fibre bundle defect, B. Enlargement of blind spot, C. Generalised constriction of field, D. Sector-shaped defects
A: Nerve fibre bundle defect
Answer: A: Nerve fibre bundle defect 
Explanation: Ans. Nerve fibre bundle defect