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
Commonest cause of loss of vision in non- proliferative diabetic retinopathy is – 
Select and explain. 
A. Vitreous heamorrhage, B. Macular edema, C. Detachment of retina, D. Subretinal haemorrhage
B: Macular edema
Answer: B: Macular edema 
Explanation: Macular edema is the most common cause of loss of vision in NPDR.