abnormalities, except perhaps strabismus and amblyopia. Typically, the abnormal eye and head movements disappear after several years (usually by the end of the first decade of life).

Kiblinger GD, Wallace BS, Hines M, Siatkowski RM. Spasmus nutans-like nystagmus is often associated with underlying ocular, intracranial, or systemic abnormalities. J Neuroophthalmol. 2007:27(2):118–122.

Gaze-Evoked Nystagmus

Gaze-evoked nystagmus develops because of an inability to maintain fixation in eccentric gaze. The eyes drift back to the midline owing to the elastic properties of the orbit, and a corrective saccade is generated to reposition the eyes on the eccentric target. Hence, the fast phase is always in the direction of gaze. The amplitude of the nystagmus increases as the eyes are moved in the direction of the fast phase. This pattern is in accordance with Alexander’s law, which states that nystagmus increases in intensity (amplitude and frequency) as the eyes are moved in the direction of the fast phase.

Gaze-evoked nystagmus is caused by dysfunction of the neural integrator (see Chapter 1). For horizontal gaze, the neural integrator includes the nucleus prepositus hypoglossi and the medial vestibular nuclei. For vertical gaze, the interstitial nucleus of Cajal serves as the neural integrator. The flocculus and nodulus of the cerebellum also play a role in maintaining an eccentric position of gaze. The neural integrator receives a velocity signal (the “pulse”) from the appropriate gaze center and, through the mathematical process of integration, generates a “step” signal to maintain the eccentric position of the eyes (see Chapter 7, Fig 7-1). Thus, the neural integrator ensures a level of neural activity adequate to maintain the eyes in an eccentric position of gaze against the elastic forces of the orbit. If the neural integrator fails to function properly (becomes “leaky”), eccentric eye position cannot be maintained.

A few beats of symmetric jerk nystagmus at the extremes of far horizontal gaze without other features (eg, rebound nystagmus, saccadic dysmetria) is physiologic and of no clinical significance. However, sustained or asymmetric gaze-evoked nystagmus should prompt further evaluation. Metabolic and toxic etiologies include ethanol and a variety of medications, such as anticonvulsants, sedatives, and hypnotics. Whenever gaze-evoked nystagmus is asymmetric, it can be presumed that an ipsilateral lesion of the brainstem or cerebellum—typically stroke, demyelination, or tumor—is present. Such a finding should prompt appropriate patient evaluation, including targeted neuroimaging. End-organ disease such as extraocular myopathies and myasthenia can also cause gazeevoked nystagmus, with a pattern similar to that observed with lesions of the central nervous system.

Rebound Nystagmus

Prolonged eccentric viewing may induce rebound nystagmus, which is a jerk nystagmus in the opposite direction after an attempted return to primary gaze. Such eccentric viewing may produce a directional bias in ocular motor control in an attempt to counteract the centripetal tendency of the eyes to return to primary position (primarily due to elastic forces within the orbit). This induced bias becomes evident when the eyes return to primary position and then show a tendency to return to the prior eccentric direction of gaze. The bias induces corrective saccadic movement in the direction opposite to the initial eccentric position of gaze. Rebound nystagmus is often a manifestation of