Physiologic End Point Nystagmus

This is a normal subject with end point nystagmus in lateral gaze. Features that favor physiologic (normal) end point nystagmus (EPN) rather than pathologic gaze-evoked nystagmus include: only present in far lateral gaze (at close to 100% of the normal range of ocular movements); resolves when the visual target is brought back so that the adducting eye can see the target (at ~75% of the normal range of ocular movements); abates with prolonged lateral gaze; can have a torsional component (top poles beating in the same direction as the horizontal component); absence of rebound or centripetal nystagmus; an otherwise normal ocular motor examination (including fixation in primary gaze, saccades, smooth pursuit). Very mild upbeat nystagmus (UBN) in far upgaze can sometimes be due to EPN as well, although a comprehensive ocular motor and neurologic examination is essential in these patients to look for evidence of posterior fossa disease. Vertical gaze-evoked nystagmus including UBN in upgaze as well as downbeat in downgaze commonly accompany horizontal gaze-evoked nystagmus in cerebellar (or its connections) disease.