There are several types of nystagmus, which is involuntary rhythmic eye movements. Optokinetic nystagmus occurs when watching a moving object, while jerky nystagmus alternates between slow and fast phases in different directions. Pendular nystagmus oscillations are equal in both directions. Nystagmus can also be caused by problems in the inner ear, brainstem, or cerebellum. Infantile nystagmus is seen in conditions causing early vision loss and remains horizontal in all gazes.

1. NYSTAGMUS
Involuntary, rhythmic movements of the eyes.
TYPES:
Optokinetic Nystagmus
A rhythmic jerk nystagmus which normally appears when one is watching a moving object (e.g., the passing landscape from a train window,
rotating drum with vertical stripes, or a strip of cloth with similar stripes).
Jerky nystagmus:
 The movements alternate between a slow component and a fast corrective component (jerk) in the opposite direction.
 The direction is named in the direction of the fast phase namely:
• Downbeat
• Upbeat
• Horizontal
• Torsional
• Mixed
Pendular nystagmus:
 The oscillations are roughly equal in rate in both directions, although on lateral gaze the pendular type may be converted to the jerk type
with the fast component to the side of gaze. Some examples are:
• Congenital nystagmus
• Acquired pendular nystagmus- Adult leukodystrophies, multiple sclerosis, toluene intoxication
• Pendular nystagmus with visual loss
• Specific variants: spasmus nutans; oculopalatal myoclonus; see-saw nystagmus; oculomasticatory myorhythmia (Whipple’s)
Nystagmus of labyrinthine origin
 Predominantly unidirectional (horizontal or vertical) jerky nystagmus
 Often with a slight torsional component, evident when the eyes are close to the central position and does not change with the direction
of the gaze.
 Fast component away from the side of the lesion
Nystagmus caused by Brainstem and Cerebellar disease
 Brainstem lesions often cause a unidirectional, gaze evoked nystagmus, which may be horizontal or vertical.
 Most apparent on visual fixation and follows a moving target
 Direction of nystagmus changes with the direction of gaze.
Upbeat nystagmus- Demyelinating/ vascular disease, tumors, phenytoin or Wernicke disease.
Downbeat nystagmus - Always of central origin, CV junction anomalies (Chiari malformation, basilar invagination), syringobulbia, and
demyelinating plaques.
- may be an initial sign of either paraneoplastic brainstem encephalitis or cerebellar degeneration with opsoclonus
- Downbeat nystagmus with oscillopsia- Lithium intoxication or profound Magnesium depletion
Dissociated nystagmus (ataxic nystagmus) - Seen in inter nuclear ophthalmoplegia; Occurs only in the abducting eye.
See saw Nystagmus - upbeat in one eye & downbeat in another ; craniopharyngioma, sellar or parasellar masses
Infantile (Congenital) Nystagmus
 Seen in conditions of early central vision loss, like albinism and diseases of the retina and refractive media.

2.  Remains horizontal in all directions of gaze
 suppressed during convergence
 May be associated with odd head positions or with head oscillations and with strabismus