Nystagmus
Nystagmus
Nystagmus, or talantropia, is an involuntary, usually bilateral, oscillation of the eyeballs (very occasionally it is unilateral, e.g., in internuclear ophthalmoplegia), of which many varieties are described. This may be:
- Physiological:
Optokinetic nystagmus (OKN; e.g., looking out of a moving railway carriage)
Induced by vestibular stimuli (e.g., merry-go-round; caloric testing)
Nystagmoid jerks: in extremes of lateral or vertical gaze (end-point nystagmus, a form of gaze-evoked nystagmus)
- Pathological:
Nystagmus may be classified according to direction, waveform, anatomy/etiology, or clinical frequency (common, rare). When describing nystagmus, it is necessary to make observations in the nine cardinal positions of gaze for the direction, amplitude and beat frequency of nystagmus. Nystagmus may be abortive (transient) or sustained in duration. The intensity of jerk nystagmus may be classified by a scale of three degrees:
1st degree: present when looking in the direction of the fast phase; 2nd degree: present in the neutral position;
3rd degree: present when looking in the direction of the slow phase (i.e., present in all directions of gaze).
It is important to distinguish nystagmus from other involuntary eye movements, such as square-wave jerks, ocular flutter, and opsoclonus (q.v.).
- Directional classification of nystagmus: Horizontal (common)
Vertical (rare):
Downbeat: seen with structural lesions of the cervicomedullary junction, midline cerebellum and floor of the 4th ventricle, but also with more diffuse cerebellar disease. Upbeat: of less localizing value than downbeat, upbeat nystagmus may occur with pontomesencephalic, pontomedullary, and even caudal medullary lesions (infarct, inflammation); bow-tie nystagmus is probably a variant of upbeat nystagmus. Torsional: usually accompanies horizontal nystagmus of peripheral vestibular (labyrinthine) origin.
- Waveform classification of nystagmus: Jerk nystagmus:
characterized by a slow drift of the eyes in one direction (slow phase) followed by a rapid, corrective, saccadic movement in the opposite direction (fast phase); the direction of jerk nystagmus is named according to the direction of the fast phase, but it is the character of the slow phase, the pathological part of the process, which is more eloquent regarding anatomical correlation (vide infra).
Pendular or undulatory nystagmus:
in which the movements of the eyes are more or less equal in amplitude and velocity (sinusoidal oscillations) about a central (null) point. This is often congenital, may be conjugate or disconjugate (sometimes monocular), but is not related to concurrent internuclear ophthalmoplegia or asymmetry of visual acuity.
When studied using oculography, the slow phase of jerk nystagmus may show a uniform velocity ("saw-toothed"), indicative of imbalance in vestibulo-ocular reflex activity. A slow phase with exponentially decreasing velocity (negative exponential slow phase) is
ascribed to "leakiness" of a hypothetical neural integrator, a structure which converts eye or head velocity signals into approximations of eye or head position signals (thought to lie in the interstitial nucleus of Cajal in the midbrain for vertical eye movements, and in the nucleus propositus hypoglossi for horizontal eye movements). A slow phase with exponentially increasing velocity (high-gain instability, runaway movements) may be seen in congenital or acquired pendular nystagmus. The pathophysiology of acquired pendular nystagmus is thought to be deafferentation of the inferior olive by lesions of the red nucleus, central tegmental tract, or medial vestibular nucleus.
- Anatomical/etiological classification of nystagmus: Peripheral Vestibular:
unidirectional (directed to side opposite lesion), and more pronounced when looking in direction of the fast phase (i.e.,1st degree), usually with a rotatory component and associated with vertigo. Tends to fatigue, and usually transient (e.g.,in Hallpike maneuver). Nystagmus of peripheral vestibular origin is typically reduced by fixation (hence these patients hold their heads still) and enhanced by removal of visual fixation (in the dark, with Frenzel’s lenses).
Central Vestibular:
unidirectional or multidirectional, 1st, 2nd, or 3rd degree; typically sustained and persistent. There may be other signs of central pathology (e.g., cerebellar signs, upper motor neurone signs). Not affected by removal of visual fixation. Cerebellar/brainstem:
commonly gaze-evoked due to a failure of gaze-holding mechanisms. It may be unidirectional with a unilateral cerebellar lesion (e.g., vascular disease) in which case it typically occurs when the eyes are looking in the direction of the lesion (cf. peripheral vestibular nystagmus); multidirectional nystagmus of cerebellar origin may occur in multiple sclerosis, drug/toxin exposure, cerebellar degenerations.
Congenital:
usually horizontal, pendular type nystagmus; worse with fixation, attention, anxiety. It may appear with blindness of childhood onset, or be acquired with neurological disease (multiple sclerosis, mitochondrial disease, Whipple’s disease, Pelizaeus-Merzbacher disease).
Other forms of nystagmus include:
- Ataxic/Dissociated:
in abducting >> adducting eye, as in internuclear ophthalmoplegia and pseudo-internuclear ophthalmoplegia.
- Periodic Alternating:
primary position nystagmus, almost always in the horizontal plane, which stops and then reverses direction every minute or so; 4-5 minutes observation may be required to see the whole cycle; localizing value similar to downbeat nystagmus.
- Convergence-retraction (Körber-Salus-Elschnig syndrome):
adducting saccades (medial rectus contraction), occurring spontaneously or on attempted upgaze, often accompanied by retraction of the eyes into the orbits, associated with mesencephalic lesions of the pretectal region (e.g., pinealoma).
- See-saw:
a disconjugate cyclic movement of the eyes, comprising elevation and intorsion of one eye while the other eye falls and extorts, followed by reversal of these movements; may be congenital (e.g., with albinism, retinitis pigmentosa) or acquired (mesodiencephalic or lateral medullary lesions, e.g.,brainstem stroke, head trauma, syringobulbia).
Many pathologies may cause nystagmus, the most common being demyelination, vascular disease, tumor, neurodegenerative disorders of cerebellum and/or brainstem, metabolic causes (e.g., Wernicke-Korsakoff ’s syndrome), paraneoplasia, drugs (alcohol, phenytoin, barbiturates, sedative-hypnotic drugs), toxins, and epilepsy. Treatment of nystagmus is usually that of the underlying cause, where possible. Pendular nystagmus may respond to anticholinesterases, consistent with its being a result of cholinergic dysfunction. Periodic alternating nystagmus responds to baclofen, hence the importance of making this diagnosis. See-saw nystagmus may respond to baclofen, clonazepam, or alcohol.
References
Bertholon P, Bronstein AM, Davies RA et al. Positional down beating nystagmus in 50 patients: cerebellar disorders and possible anterior semicircular canalithiasis. Journal of Neurology, Neurosurgery and Psychiatry 2002; 72: 366-372
Janssen JC, Larner AJ, Morris H, Bronstein AM, Farmer SF. Upbeat nystagmus clinicoanatomical correlation. Journal of Neurology,Neurosurgery and Psychiatry 1998; 65: 380-381
Leigh RJ, Zee DS. The Neurology of Eye Movements (3rd edition). New York: OUP, 1999
Lopez LI, Bronstein AM, Gresty MA, Du Boulay EPG, Rudge P. Clinical and MRI correlates in 27 patients with acquired pendular nystagmus. Brain 1996; 119: 465-472
Lueck CJ. A simple guide to nystagmus. Hospital Medicine 2000; 61: 544-546, 548-549
Serra A, Leigh RJ. Diagnostic value of nystagmus: spontaneous and induced ocular oscillations. Journal of Neurology, Neurosurgery and Psychiatry 2002; 73: 615-618
Cross References
Caloric testing; Hallpike maneuver, Hallpike test; Internuclear ophthalmoplegia; Myorhythmia; Optokinetic nystagmus (OKN), Optokinetic response; Opsoclonus; Oscillopsia; Palatal myoclonus; Pseudo-Internuclear ophthalmoplegia; Spasmus nutans; Square-wave jerks; Vertigo
