eMedicine Specialties > Ophthalmology > Extraocular Muscles

Nystagmus, Acquired

Christopher M Bardorf, MD, MS, Ophthalmology, Children's Eye Physicians, Denver, CO
Gregory P Van Stavern, MD, FACP, Assistant Professor, Departments of Ophthalmology and Neurology, Wayne State University; Enrique Garcia-Valenzuela, MD, PhD, Clinical Assistant Professor, Department of Ophthalmology, University of Illinois Eye and Ear Infirmary; Consulting Staff, Vitreo-Retinal Surgery, Midwest Retina Consultants, SC, Parkside Center
Contributor Information and Disclosures

Updated: Apr 5, 2006

Introduction

Background

Nystagmus may be defined as a periodic rhythmic ocular oscillation of the eyes. The oscillations may be sinusoidal and of approximately equal amplitude and velocity (pendular nystagmus) or, more commonly, with a slow initiating phase and a fast corrective phase (jerk nystagmus).

Nystagmus may be unilateral or bilateral, but, when the nystagmus appears unilateral, it is more often asymmetric rather than truly unilateral. Nystagmus may be conjugate or disconjugate (dissociated). It may be horizontal, vertical, torsional (rotary), or any combination of these movements superimposed upon each other.

Nystagmus may be congenital or acquired. When acquired, it most often is caused by abnormalities of vestibular input. Congenital forms may be associated with afferent visual pathway abnormalities (sensory nystagmus).

To understand the mechanisms by which nystagmus may occur, it is important to discuss the means by which the nervous system maintains position of the eyes. Foveal centration of an object of regard is necessary to obtain the highest level of visual acuity. Three mechanisms are involved in maintaining foveal centration of an object of interest: fixation, the vestibulo-ocular reflex, and the neural integrator.

Fixation in the primary position involves the visual system's ability to detect drift of a foveating image and signal an appropriate corrective eye movement to refoveate the image of regard. The vestibular system is intimately and complexly involved with the oculomotor system.

The vestibulo-ocular reflex is a complex system of neural interconnections that maintains foveation of an object during changes in head position. The proprioceptors of the vestibular system are the semicircular canals of the inner ear. Three semicircular canals are present on each side, anterior, posterior, and horizontal. The semicircular canals respond to changes in angular acceleration due to head rotation.

The third mechanism is the neural integrator. When the eye is turned in an extreme position in the orbit, the fascia and ligaments that suspend the eye exert an elastic force to return toward the primary position. To overcome this force, a tonic contraction of the extraocular muscles is required. A gaze-holding network called the neural integrator generates the signal. The cerebellum, ascending vestibular pathways, and oculomotor nuclei are important components of the neural integrator.

Pathophysiology

A disorder affecting any of the 3 mechanisms that control eye movements may result in nystagmus. Both focal and diffuse disorders may cause nystagmus. The characteristics of the nystagmus, as well as associated signs and symptoms help to localize the lesion and suggest possible etiologies.

Vestibular nystagmus

Vestibular nystagmus may be central or peripheral. Important differentiating features between central and peripheral nystagmus include the following: peripheral nystagmus is unidirectional with the fast phase opposite the lesion; central nystagmus may be unidirectional or bidirectional; purely vertical or torsional nystagmus suggests a central location; central vestibular nystagmus is not dampened or inhibited by visual fixation; tinnitus or deafness often is present in peripheral vestibular nystagmus, but it usually is absent in central vestibular nystagmus. According to Alexander's law, the nystagmus associated with peripheral lesions becomes more pronounced with gaze toward the side of the fast-beating component; with central nystagmus, the direction of the fast component is directed toward the side of gaze (eg, left-beating in left gaze, right-beating in right gaze, up-beating in upgaze).

Downbeat nystagmus

Downbeat nystagmus is defined as nystagmus with the fast phase beating in a downward direction. The nystagmus usually is of maximal intensity when the eyes are deviated temporally and slightly inferiorly. With the eyes in this position, the nystagmus is directed obliquely downward.In most patients, removal of fixation (eg, by Frenzel goggles) does not influence slow phase velocity to a considerable extent; however, the frequency of saccades may diminish.

The presence of downbeat nystagmus is highly suggestive of disorders of the craniocervical junction (eg, Arnold-Chiari malformation). This condition also may occur with bilateral lesions of the cerebellar flocculus and bilateral lesions of the medial longitudinal fasciculus, which carries optokinetic input from the posterior semicircular canals to the third nerve nuclei. It may also occur when the tone within pathways from the anterior semicircular canals is relatively higher than the tone within the posterior semicircular canals. Under such circumstances, the relatively unopposed neural activity from the anterior semicircular canals causes a slow upward pursuit movement of the eyes with a fast, corrective downward saccade.

Upbeat nystagmus

Upbeat nystagmus is defined as nystagmus with the fast phase beating in an upward direction. Daroff and Troost described 2 distinct types. The first type consists of a large amplitude nystagmus that increases in intensity with upward gaze. This type is suggestive of a lesion of the anterior vermis of the cerebellum. The second type consists of a small amplitude nystagmus that decreases in intensity with upward gaze and increases in intensity with downward gaze. This type is suggestive of lesions of the medulla.

This condition may occur when the tone within the pathways of the posterior semicircular canals is relatively higher than the tone within the anterior semicircular canals, and it can occur from lesions of the ventral tegmental tract or the brachium conjunctivum, which carry optokinetic input from the anterior semicircular canals to the third nerve nuclei.

Torsional (rotary) nystagmus

Torsional (rotary) nystagmus refers to a rotary movement of the globe about its anteroposterior axis. Torsional nystagmus is accentuated on lateral gaze. Most nystagmus resulting from dysfunction of the vestibular system has a torsional component superimposed on a horizontal or vertical nystagmus.

This condition occurs with lesions of the anterior and posterior semicircular canals on the same side (eg, lateral medullary syndrome). Lesions of the lateral medulla may produce a torsional nystagmus with the fast phase directed away from the side of the lesion. This type of nystagmus can be accentuated by otolithic stimulation by placing the patient on their side with the intact side down (eg, if the lesion is on the left, the nystagmus is accentuated when the patient is placed on his right side).

Pendular nystagmus

Pendular nystagmus is a multivectorial nystagmus (ie, horizontal, vertical, circular, elliptical) with an equal velocity in each direction that may reflect brain stem or cerebellar dysfunction. Often, there is marked asymmetry and dissociation between the eyes. The amplitude of the nystagmus may vary in different positions of gaze.

Horizontal nystagmus

Horizontal nystagmus is a well-recognized finding in patients with a unilateral disease of the cerebral hemispheres, especially with large, posterior lesions. It often is of low amplitude. Such patients show a constant velocity drift of the eyes toward the intact hemisphere with fast saccade directed toward the side of the lesion.

Seesaw nystagmus

Seesaw nystagmus is a pendular oscillation that consists of elevation and intorsion of one eye and depression and extorsion of the fellow eye that alternates every half cycle. This striking and unusual form of nystagmus may be seen in patients with chiasmal lesions, suggesting loss of the crossed visual inputs from the decussating fibers of the optic nerve at the level of the chiasm as the cause or lesions in the rostral midbrain. This type of nystagmus is not affected by otolithic stimulation.

Gaze-evoked nystagmus

Gaze-evoked nystagmus is produced by the attempted maintenance of an extreme eye position. It is the most common form of nystagmus. Gaze-evoked nystagmus is due to a deficient eye position signal in the neural integrator network. Thus, the eyes cannot be maintained at an eccentric orbital position and are pulled back toward primary position by the elastic forces of the orbital fascia. Then, corrective saccade moves the eyes back toward the eccentric position in the orbit.

Gaze-evoked nystagmus may be caused by structural lesions that involve the neural integrator network, which is dispersed between the vestibulocerebellum, the medulla (region of the nucleus prepositus hypoglossi and adjacent medial vestibular nucleus [NPH/MVN]), and the interstitial nucleus of Cajal (INC). Patients recovering from a gaze palsy go through a period where they are able to gaze in the direction of the previous palsy, but they are unable to sustain gaze in that direction; therefore, the eyes drift slowly back toward primary position followed by a corrective saccade. When this is repeated, a gaze-evoked or gaze-paretic nystagmus results.

Gaze-evoked nystagmus often is encountered in healthy patients; in which case, it is called end-point nystagmus. End-point nystagmus usually can be differentiated from gaze-evoked nystagmus caused by disease, in that the former has lower intensity and, more importantly, is not associated with other ocular motor abnormalities.

Spasmus nutans

Spasmus nutans is a rare condition with the clinical triad of nystagmus, head nodding, and torticollis. Onset is from age 3-15 months with disappearance by 3 or 4 years. Rarely, it may be present to age 5-6 years. The nystagmus typically consists of small-amplitude, high frequency oscillations and usually is bilateral, but it can be monocular, asymmetric, and variable in different positions of gaze.

Periodic alternating nystagmus

Periodic alternating nystagmus is a conjugate, horizontal jerk nystagmus with the fast phase beating in one direction for a period of approximately 1-2 minutes. The nystagmus has an intervening neutral phase lasting 10-20 seconds; the nystagmus begins to beat in the opposite direction for 1-2 minutes; then, the process repeats itself. The presumed mechanism is disruption of the vestibulo-ocular tracts at the pontomedullary junction.

Abducting nystagmus of internuclear ophthalmoplegia

Abducting nystagmus of internuclear ophthalmoplegia (INO) is, as the name implies, nystagmus in the abducting eye contralateral to a medial longitudinal fasciculus (MLF) lesion.

Mortality/Morbidity

Dependent upon etiology

Age

Onset of spasmus nutans is in infants aged 3-15 months with disappearance by age 3 or 4 years. Rarely, it may be present until children are aged 5-6 years.

Clinical

History

A thorough history is important to help determine the etiology of the nystagmus. Important aspects of the history include the following:

• Age of onset of the nystagmus, whether it is constant or intermittent, the presence of any aggravating or alleviating factors (eg, head position)
• Presence or absence of vertigo, oscillopsia (an illusory motion of the seen world), and sensation of disequilibration suggest a lesion of the vestibular system.
• Deafness or tinnitus is present with peripheral lesions of the vestibular system.
• Presence of diplopia, particularly in certain positions of gaze: Patients with INO may report diplopia only on lateral gaze or intermittent blurring of vision.
• Ask questions regarding the presence of any associated symptoms, such as symptoms related to demyelinating disease (eg, a history of loss of vision, eye pain, or numbness or weakness of the extremities), symptoms related to cerebrovascular accident (eg, hemiplegia).

Physical

A complete neuro-ophthalmic examination is imperative in patients with nystagmus. Aside from a complete ophthalmic examination, including visual acuity, measurement and reactivity of the pupils to light and accommodation, measurement of intraocular pressure, testing the function of extraocular muscles, and anterior and dilated posterior segment examination, other important aspects of the examination include the following:

• Observing the nystagmus with regard to type (eg, horizontal, vertical), frequency, amplitude, direction, and conjugate/disconjugate is important. Pure vertical, pure horizontal, or pure rotary nystagmus almost always represents central vestibular dysfunction.
• Note whether the character of the nystagmus changes in certain directions of gaze.
  • Nystagmus due to vestibular disease increases in intensity when the eyes are turned in the direction of the saccade (fast phase), ie, Alexander law.
  • A horizontal nystagmus due to peripheral vestibular imbalance remains horizontal on upward and downward gaze.
• Note the presence or absence of head nodding or torticollis (spasmus nutans).
• Note whether the nystagmus dampens with fixation. Fixation inhibits nystagmus and vertigo due to peripheral lesions of the vestibular system.
• Optokinetic nystagmus (OKN) drum: The optokinetic reflex allows us to follow objects in motion when the head remains stationary (eg, observing individual telephone poles on the side of the road as one travels by them in a car). The reflex develops at about age 6 months. The normal eye movements that one observes depend upon the orientation of the drum in front of the patient. If the drum is held in front of the patient with the bars directed vertically and is spun to the left (the patient's right), one would observe a slow pursuit movement of the eyes to the patient's right as a moving bar is followed, then a quick saccade to the patient's left as the patient searches for the next moving bar to fixate on and again follows that bar with a slow pursuit movement to the patient's right.
  • This reflex is abnormal in patients with congenital nystagmus. One may observe a paradoxical reversal of the optokinetic nystagmus response.
  • Patients with horizontal nystagmus with unilateral hemispheric lesions, especially parietal or parietal-occipital lesions, show impaired optokinetic nystagmus when the drum is rotated toward the side of the lesion.
  • The OKN drum may be used as an estimate of visual acuity. The striped drum is equivalent to a vision of counting fingers when held at a distance of 3-5 feet from the patient. The further the drum is from the patient, the better the visual acuity must be to respond normally to the moving drum.
• Confrontational visual field testing may reveal gross field defects that may help determine the presence and/or location of an intracranial lesion.
• For Romberg testing have the patient stand with eyes closed and feet together. If a defect in the vestibular system is present, the patient tends to fall toward the side of the lesion.
• Oculocephalic reflex (doll's head phenomenon)
  • The oculocephalic reflex develops within the first week of life and essentially represents a vestibulo-ocular reflex normally suppressed in a conscious individual that attempts to turn the head to fixate on an object.
  • This test consists of the rapid rotation of the patient's head in a horizontal or vertical direction. With intact vestibular nuclei and medial longitudinal fasciculi, the eyes move conjugately in the opposite direction of the head turn. Alternatively, the test may be performed by having the patient extend the arm out in front of the body and fixate on the outstretched thumb. Patients should be instructed to rotate their torso back and forth about their longitudinal axis such that the thumb remains in front of the body at all times.
  • Patients with the ability to suppress the oculocephalic reflex should be able to maintain fixation on their thumb while rotating. An abnormal test result would show the patient continuously losing fixation of the thumb.
  • Inability to suppress the oculocephalic reflex is common in patients with vestibular imbalance.
• Caloric testing
  • Instilling cold or warm water into the external auditory canal can reproduce the same movement of endolymph in the semicircular canals produced by rotations of the head. Instillation of water into the external auditory canal causes endolymph convection currents that in turn induce nystagmus.
  • While sitting erect, the patient tilts the head back 60°. While in supine, the patient elevates the head 30°; this brings the horizontal semicircular canals into the vertical plane.
  • The external auditory canal is irrigated with cold or hot water. Cold water instilled into the right ear causes the endolymph in the right semicircular canal to cool and sink. This movement of endolymph is the same movement induced by a rotation of the head to the left, inducing a horizontal nystagmus directed to the left (ie, to the opposite side the water was placed). Warm water in the same ear produces the opposite effect (ie, a horizontal nystagmus directed to the right or toward the same side the water was placed); ie, cold-opposite, warm-same (COWS).
• Note whether the character of the nystagmus changes with otolithic stimulation. Failure to respond to otolithic stimuli implies peripheral vestibular disease.

Causes

• Seesaw nystagmus
  • Rostral midbrain lesions
  • Parasellar lesions (eg, pituitary tumors)
  • Visual loss secondary to retinitis pigmentosa
• Downbeat nystagmus
  • Lesions of the vestibulocerebellum and underlying medulla, including the following:
    • Arnold-Chiari malformation
    • Demyelination (eg, multiple sclerosis)
    • Microvascular disease with vertebrobasilar insufficiency
    • Brain stem encephalitis
    • Tumors at the foramen magnum (eg, meningioma, cerebellar hemangioma)
    • Trauma
    • Drugs (eg, alcohol, lithium, antiseizure medications)
    • Nutritional (eg, Wernicke encephalopathy, parenteral feeding, magnesium deficiency)
  • Heat stroke
  • Approximately 50% have no identifiable cause.
• Upbeat nystagmus
  • Medullary lesions, including perihypoglossal nuclei, the adjacent medial vestibular nucleus, and the nucleus intercalatus (structures important in gaze holding)
  • Lesions of the anterior vermis of the cerebellum
  • Benign paroxysmal positional vertigo
• Periodic alternating nystagmus
  • Arnold-Chiari malformation
  • Demyelinating disease
  • Spinocerebellar degeneration
  • Lesions of the vestibular nuclei
  • Head trauma
  • Encephalitis
  • Syphilis
  • Posterior fossa tumors
  • Binocular visual deprivation (eg, ocular media opacities)
• Pendular nystagmus
  • Demyelinating disease
  • Monocular or binocular visual deprivation
  • Oculopalatal myoclonus
  • Internuclear ophthalmoplegia
  • Brain stem or cerebellar dysfunction
• Spasmus nutans
  • Usually occurs in otherwise healthy children
  • Chiasmal, suprachiasmal, or third ventricle gliomas may cause a condition that mimics spasmus nutans.
• Torsional - Lateral medullary syndrome (Wallenberg syndrome)
• Abducting nystagmus of internuclear ophthalmoplegia
  • Demyelinating disease
  • Brain stem stroke
• Gaze evoked
  • Drugs - Anticonvulsants (eg, phenobarbital, phenytoin, carbamazepine) at therapeutic dosages
  • Alcohol

References

• Nystagmus, Congenital