Correct! In order to get the correct answer here, you must be aware that pursuit is mediated by a pathway that starts in the parietal lobe and generates pursuit eye movements ipsilaterally. When you move the optokinetic drum, you generate an obligatory pursuit movement in the direction of the moving stripes (the patient must be paying attention!). Each pursuit movement is met by an oppositely-directed reflex conjugate saccadic movement that restores the eye position to straight ahead. This obligatory reaction is called “optokinetic nystagmus” (OKN). If you see a discrepancy in nystagmus amplitude between rightwardly and leftwardly directed stripes, you must conclude that there is a unidirectional pursuit deficit caused by a lesion in the ipsilateral parietal lobe. By the way, the patient will not notice this pursuit deficit.

This maneuver is also diagnostically useful in the following settings: 1) you suspect a subtle sixth nerve palsy in a patient with full ductions; the stripes will elicit reduced OKN in the affected abducting eye; 2) you suspect a subtle internuclear ophthalmoplegia; the stripes will elicit reduced OKN in the affected adducting eye; 3) you suspect a subtle dorsal midbrain syndrome; the downwardly moving stripes will elicit convergence-retraction of both eyes; 4) you suspect factitious blindness; the stripes will elicit normal OKN in all directions.