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
Optokinetic nystagmus is due to defect in 
Select and explain. 
A. Frontal lobe, B. Occipital lobe, C. Temporal lobe, D. Parietal lobe
D: Parietal lobe
Answer: D: Parietal lobe 
Explanation: Optokinetic nystagmus constitutes of saccadic and pursuit movements.
Defect in OKN indicates parietal lobe lesion.