A patient has a right homonymous hemianopia with saccadic pursuit movements and defective optokinetic nystagmus. The lesion is most likely to be in the
Right nomonymous hemianopia with saccadic pursuit movements and detective optokinetic nystagmus confirms the diagnosis of perietal lobe lesion.
Optokinetic Nystagmus: - It can be elicited in all normal individuals.
Defect in optokinetic nystagmus and lesions of brain associated with it.
In a case of hemianopia due to lesions of the parietal lobe optokinetic nystagmus is absent.
Other lesions where optokinetic Nystagmus is defective:-

Frontal lobe lesions - it inhibits this response only temporarily.
Brainstem lesions - it results in asymmetry of this response in vertical plane.
Frontal lobe
Occipital lobe
Parietal lobe
Temporal lobe