Unilateral reversal of smooth pursuit and optokinetic nystagmus

A patient is presented who has had three six-month episodes of oscillopsia over the last eight years. During the episodes, abnormal smooth pursuit and optokinetic nystagmus were noted, but there were no other abnormalities. Oculography during the most recent episode demonstrated that when tracking from right to left, the patient's smooth pursuit was reversed. There are several features of the case which suggest that the aetiology may be a form of congenital nystagmus. A possible alternative mechanism whereby such an abnormality might arise as an acquired lesion is discussed.