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Involuntary rhythmic oscillation of the eyeballs, either pendular or with a slow and fast component. [G. nystagmos, a nodding, fr. nystazo, to be sleepy, nod]

- after-n. n. occurring after the abrupt cessation of rotation in the opposite direction of the rotatory n..

- amaurotic n. SYN: ocular n..

- Bruns n. a fine, jerking (vestibular) n. on horizontal gaze in one direction, together with a slower, larger amplitude (gaze, paretic) n. on looking in the opposite direction; due to lateral brainstem compression, usually by a cerebellar-pontine angle mass such as an acoustic neuroma.

- caloric n. n. with slow and fast components induced by labyrinthine stimulation with warm or cool water in the ear. SEE ALSO: Bárány sign.

- cervical n. n. arising from a lesion of the proprioceptive mechanism of the neck.

- compressive n. a jerky n. resulting from unilateral changes of pressure in semicircular canals.

- congenital n. 1. n. present at birth or caused by lesions sustained in utero or at the time of birth; 2. inherited n., usually X-linked, without associated neurologic lesions and nonprogressive; all three patterns of mendelian inheritance may occur: autosomal dominant [MIM*164100, *164150], autosomal recessive [MIM*257400], or X-linked recessive [MIM*310800, *310700]; 3. the n. associated with albinism, achromatopsia, and hypoplasia of the macula.

- conjugate n. a n. in which the two eyes move simultaneously in the same direction.

- convergence-retraction n. irregular, jerky n. combining convergence and retraction of the eye into the orbit, especially on attempting an upward gaze. SYN: Koerber-Salus-Elschnig syndrome.

- deviational n. SYN: end- point n..

- dissociated n. a n. in which the movements of the two eyes are dissimilar in direction, amplitude, and periodicity. SYN: dysjunctive n., incongruent n., irregular n..

- downbeat n. a vertical n. with a rapid component downward, occurring in lesions of the lower part of the brainstem or cerebellum.

- dysjunctive n. SYN: dissociated n..

- end- point n. a jerky, physiologic n. occurring in a normal individual when attempts are made to fixate a point at the limits of the field of fixation. SYN: deviational n..

- fast component of n. compensatory movement of the eyes in the vestibuloocular reflex.

- fixation n. n. aggravated or induced by ocular fixation, arising as optokinetic n., or resulting from midbrain lesions.

- galvanic n. n. involving galvanic stimulation of the labyrinth.

- gaze paretic n. a n. occurring in partial gaze paralysis when an attempt is made to look in the direction of the gaze paresis.

- incongruent n. SYN: dissociated n..

- irregular n. SYN: dissociated n..

- jerky n. n. in which there is a slow drift of the eyes in one direction, followed by a rapid recovery movement, always described in the direction of the recovery movement; it usually arises from labyrinthine or neurologic lesions or stimuli.

- labyrinthine n. SYN: vestibular n..

- latent n. jerky n. that is brought out by covering one eye. The fast phase is always away from the covered eye.

- miner's n. n. occurring in 19th century coal miners and thought at the time to be related to lack of illumination as well as other factors. SYN: miner's disease (1).

- minimal amplitude n. SYN: micronystagmus.

- ocular n. the pendular or, rarely, jerky n. seen in severely reduced vision. SYN: amaurotic n..

- opticokinetic n. SYN: optokinetic n..

- optokinetic n. n. induced by looking at moving visual stimuli. SYN: opticokinetic n., railroad n..

- palatal n. a clonic spasm of the levator palati muscle, causing an audible click. SEE ALSO: palatal myoclonus.

- pendular n. a n. that, in most positions of gaze, has oscillations equal in speed and amplitude, usually arising from a visual disturbance.

- positional n. n. occurring only when the head is in a particular position.

- railroad n. SYN: optokinetic n..

- rotational n. jerky n. arising from stimulation of the labyrinth by rotation of the head around any axis and induced by change of motion.

- rotatory n. a movement of the eyes around the visual axis.

- seesaw n. a n. in which one eye moves upward as the other moves downward, often combined with a torsional rotation (down and out, up and in—as in a see-saw).

- slow component of n. the fundamental movement of the eyes in the vestibuloocular reflex.

- upbeat n. a vertical jerky n. with a rapid component upward, occurring with brainstem lesions.

- vertical n. an up-and-down oscillation of the eyes.

- vestibular n. n. resulting from physiological stimuli to the labyrinth that may be rotatory, linear, caloric, compressive, or galvanic, or due to labyrinthal lesions. SEE ALSO: Bárány sign. SYN: labyrinthine n..

- voluntary n. pendular n. in which the individual causes an extremely fine and rapid horizontal oscillation of the eyes. The nystagamus consists of back-to-back saccades and is seldom done for more than a few seconds at a time.

nys·tag·mus nis-'tag-məs n involuntary usu. rapid movement of the eyeballs (as from side to side) occurring normally with dizziness during and after bodily rotation or abnormally following head injury or as a symptom of disease

rapid involuntary movements of the eyes that may be from side to side, up and down, or rotatory. Nystagmus may be congenital and associated with poor sight; it also occurs in disorders of the part of the brain responsible for eye movements and their coordination and in disorders of the organ of balance in the ear or the associated parts of the brain. Optokinetic nystagmus occurs in normal people when they try to look at a succession of objects moving quickly across their line of sight. Jerking eye movements sometimes occur in normal people when tired, on concentrating their gaze in any direction. These are called nystagmoid jerks and they do not imply disease.