Timothy C. Hain, MD
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Nystagmus is defined as involuntary movement of the eyes. Most frequently it is composed of a mixture of slow and fast movements of the eyes. Nystagmus can occur normally, such as when tracking a visual pattern. Nystagmus may also be abnormal, usually in situations where one would want the eyes to be still, but they are in motion. Vertigo (a sensation of spinning), is often accompanied by nystagmus. The following material attempts to illustrate and describe nystagmus subtypes.
|Typical appearance of vestibular type spontaneous nystagmus.|
Spontaneous nystagmus denotes movement of the eyes without a cognitive, visual or vestibular stimulus. Most commonly spontaneous nystagmus is caused by a vestibular imbalance. Normally, both vestibular nerves fire at a tonic rate. The two nerves input is subtracted centrally. When the head is still, this results in a signal of 0 spikes/sec, and no nystagmus. When one vestibular nerve has decreased firing relative to the other, this provides an offset which produces a constant nystagmus. Vestibular nystagmus is "jerk" nystagmus" -- the eye moves slowly towards the side of decreased firing, and then "jerks" back towards the center.
Vestibular nystagmus is typically inhibited by visual fixation and also typically follows Alexander's law (it becomes greater on gaze in direction of the fast phases). If the nystagmus does not follow these characteristics, it is likely not peripheral vestibular, or there may also be other problems superimposed with the oculomotor system or central pathways. Processes that increase gaze-evoked nystagmus, such as ingestion of sedating medications, increase the effects of Alexander's law. In very high velocity vestibular nystagmus, or in persons with poor vision, fixation may be ineffective also.
Normal individuals are able to null out spontaneous nystagmus from minor fluctuations in vestibular tone over a period of days-weeks through a combination of low level automatic processes perhaps related to denervation hypersensitivity, and peripheral and central adaptation. This nulling out process is rapid, with the great majority being done in a few weeks. For complete unilateral lesions, a small residual nystagmus may persist for years.
With this in mind, spontaneous nystagmus is abnormal, but its significance may not always be apparent (Kumar, 1982). A spontaneous nystagmus today might be related to a recent, relatively minor vestibular imbalance or an ancient, complete unilateral vestibular loss. Spontaneous nystagmus must also be considered in the context of the recording method that one has available. Using highly sensitive recording methods such as video-ENG, or infrared, small amounts (e.g. 2 deg/sec) may be significant. Using the more common electronystagmographic recording, which is prone to drift, the upper limit of normal is 5 deg/sec.
In Meniere's Disease, vestibular imbalance type nystagmus is typically seen during an acute attack. Attacks typically last 2 hours only, but usually the next day or two there will be some nystagmus also. In about 85% of the cases, the nystagmus is horizontal with the fast component directed towards the healthy hearing ear, suggesting a vestibular paresis on the side to which the slow phases are directed. The nystagmus slow-phase velocity can reach as high as 40 deg/s. Occasionally nystagmus is also seen directed in the opposite direction. This may occur early on, reflecting a temporary excitation, or later, reflecting a recovery nystagmus (known as Bechterew's phenomena).
Most frequently, pendular nystagmus is caused by central lesions involving the central tegmental tract. The concept is that there is a feedback loop controlling eye position or velocity. Lesions add delays, causing instability and nystagmus. Multiple sclerosis is the most common cause of this sort of nystagmus. Dysmyelinating disorders such as Pelizaeus-Merzbacher is another example (Hobson et al, 2000). Ashoff et al concluded that this type of nystagmus was caused by damage to the cerebellar nuclei, and Gresty et al suggested that the lesion was near the oculomotor nuclei. Gabapentin has been reported as a potential treatment, used in doses of 600-1500 mg/day (Stahl et al, 1995).
Visual disorders, particularly present during early life, can also produce a pendular nystagmus. Spasmus nutans is a transient pendular nystagmus that occurs in children, accompanied by a head tremor and torticollus. It usually resolves spontaneously in 1-4 years. Occasionally individuals with acquired blindness develop a pendular nystagmus, the so-called "nystagmus of the blind".
|Pendular nystagmus of Spasmus Nutans.|
The most common cause of vertical pendular nystagmus is the vertical nystagmus that frequently appears after pontine hemorrhage. The PPRF is damaged which makes horizontal saccades difficult, and a vertical pendular nystagmus emerges, possibly related to damage to the central tegmental tract. Treatment is difficult. Herishanu and Louzoun reported a single patient who improved after chronic trihexyphenidyl treatment. The doses are relatively massive (1 mg-60 mg), precluding use in most cases because of anticholinergic side effects. The so-called "ocular myoclonus" associated with the oculo-palatal myoclonus syndrome, may respond to valproic acid (Lefkowitz and Harpold, 1985). It has also been reported to be successfully treated with INH (200 mg BID to QID, with pyridoxine) combined with converging prisms.
Toluene sniffing, usually associated with glue sniffing, also can manifest as a vertical pendular nystagmus, usually in accompaniment with cognitive and cerebellar deficits (Maas et al, 1991).
Sometimes a horizontal and vertical nystagmus will occur together. They are usually of the same frequency, but their relative phase may different. Depending on the mutual phase, the eyes may take on an oblique direction, form an ellipse. So far, I know of no report of a nystagmus that changes relative phases (causing a pattern where the ellipse was changing). This seems possible however, as in a nystagmus called "windmill nystagmus", the vector of the horizontal nystagmus changes from right-left to up-down and back again, constantly.
Pelizaeus-Merzbacher disease is a cause of elliptical nystagmus. It is an inherited disorder, X-linked recessive in children and autosomal dominant in adults. It affects of central white matter, with neonatal, childhood and adult onset forms. Among the leukodystrophies, PMD can be largely distinguished by its binocular pendular nystagmus and head tremor that usually begin at onset. Of the other leukodystrophies, only Cockayne's syndrome has a similar nystagmus. In Cockayne's syndrome, in addition to the findings of PMD, there are also basal ganglia calcifications. In the connatal form of PMD, death usually occurs within a few years of life. In the infantile (classical) onset form, death usually occurs in the second or third decade of life.
Trobe JD, Sharpe JA, Hirsch DK, Gebarski SS. Nystagmus of Pelizaeus-Merzbacher Disease. Arch Neurol, 48, 1991. 87-91
Seesaw nystagmus is a rare binocular disorder characterized by alternating vertical skew deviation and conjugate ocular torsion. Jerk seesaw consists of torsional slow phases in one direction and quick phases in the opposite. In Pendular SSN, there are slow, smooth eye oscillations. Pendular SSn has frequently been found associated with visual disorders and may also be of congenital origin.
Reference: Rambold and others. Seesaw nystagmus associated with involuntary torsional head oscillations. Neurology 1998:51:831-837
DN is a nystagmus where oscillations are present only in one eye. It has been described in spasmus nutans, congenital nystagmus, and various brainstem disorders, as well as disorders where there has been monocular visual loss from an early age, or acquired later in life. The nystagmus is generally primarily vertical, has a pendular waveform, is of low frequency and small amplitude.
Asymmetrical nystagmus can also be seen when the vergence system is involved in a nystagmus. For example, this can occur after a pontine hemorrhage.
Congenital nystagmus is a term which is applied a diverse group of abnormal eye movements which are noted at birth or shortly thereafter. Congenital nystagmus is included under the category of disorders of fixation because it can frequently present as a severe gaze-evoked nystagmus, and because it is often increased by attempts at fixation. Congenital nystagmus is universal in albinism and also occurs in achromatopsia. Such patients usually show rounding of slow-phases, with convexity in the direction of gaze. Such "increasing exponential velocity profiles" are typical of congenital nystagmus. No special procedure is required to elicit congenital nystagmus, other than that described for registration of gaze-evoked nystagmus.
There are several types of acquired nystagmus that appear similar to congenital nystagmus. These have been discussed earlier in this monograph. Nystagmus of the blind is a constantly present nystagmus which may undergo periodic changes in direction.
Spasmus nutans consists of a pendular, dysconjugate nystagmus accompanied by head-nodding, which occurs in children. Ocular recordings in patients with spasmus nutans may show a phase difference between oscillations in each eye, or in other words, may dissociated. Spasmus nutans usually remits within 1-2 years of onset although it may persist for eight years or more.
Similar acquired pendular nystagmus in adults can be caused by multiple sclerosis, and follow brainstem infarcts. Acquired pendular nystagmus may have components about any axis - -horizontal, vertical or torsional. Differences in phase or amplitude between eyes is often seen in acquired pendular nystagmus. Acquired pendular nystagmus may be temporarily suppressed by saccades.
Occasional central nystagmus patterns, such as those related to Wernicke's encephalopathy, may have increasing-exponential velocity profiles similar to those seen in some forms of congenital nystagmus. An autosomal dominant pedigree linked to chromosome 6p12 was recently described (Kerrison JB et al, 1998).
One must be cautious when using infrared oculography for registration of congenital nystagmus and gaze-evoked nystagmus because artifact due to transducer nonlinearity can cause an ordinary gaze-evoked nystagmus to resemble the increasing exponential pattern described above. Care must be also taken that an unusually intense gaze-evoked nystagmus is not mistaken for congenital nystagmus.
Latent Nystagmus is a variant of congenital nystagmus although some authors prefer to reserve the term congenital nystagmus for other variants. It is mainly encountered in persons with strabismus and amblyopia. In the most common form, the nystagmus appears only when one eye is covered. When both eyes are viewing, no nystagmus is seen. This is the reason why it is called "latent" nystagmus. It can be recognized because the eyes always move with their slow-phase towards the nose for the viewing eye. In other words, the direction of the nystagmus in both eyes changes with the viewing eye. The figure below shows a right beating nystagmus, associated with left eye viewing. Recording method is infrared.
There are a few variants of latent nystagmus. Manifest latent nystagmus is latent nystagmus that can be seen even with both eyes viewing. Dissociated vertical deviation or DVD is a vertical strabismus characterized by a slow upward rotation of one eye without movement of the other.
This type of nystagmus is classically due to a dorsal midbrain lesion.
This type of nystagmus is rare, and is classically due to the Arnold Chiari malformation.
This rare oculomotor disorder may occur congenitally or as a result of injuries to the cerebellar nodulus. It can sometimes be effectively treated with the drug Baclofen. It is typified by a nystagmus that first goes one way, then reverses, and then repeats. A typical period is 200 seconds, or about 3 to 4 minutes.
The author has observed that some normal persons appear to have minor amounts of PAN. In order to record this, one must use a sensitive method (i.e. IR) and record for several minutes. He has also seen PAN provoked by an attack of Meniere's disease (Chiu, 2002). Recently it has been reported that PAN can be provoked by lithium (Lee and Lessell, 2003). This is unsurprising as lithium toxicity can induce other types of central nystagmus and is also a cerebellar toxin. It seems likely that other disorders that affect vision or cerebellar function may also be associated with PAN in the future.
Strong primary position upbeat nystagmus has been described in lesions of the medulla, the ventral tegmentum, the anterior vermis of the cerebellum, and the adjacent brachium conjunctivum and midbrain. Upbeat nystagmus also is found in smokers as a side effect of nicotine, and as a side effect of other medications. UBN has been reported in association with Wernicke's encephalopathy, multiple sclerosis, brainstem infarction and other lesions. While UBN is generally caused by midline lesions, cases have been reported in unilateral medial midbrain lesions. Hirose and others (1998) have proposed that in this instance, UBN may be caused by a lesion in the nucleus intercalatus of Staderini, one of the three subnuclei of the perihypoglossal nucleus (others include the nucleus of Roller, the nucleus prepositus hypoglossi which performs neural integration for the horizontal oculomotor system). Ranalli and Sharpe (1988) suggested that some forms of UBN were explained by disruption of the ventral tegmental pathway for the upward VOR (vestibulo-ocular reflex), causing imbalance in the vertical VOR.
Upbeat nystagmus can be modulated by convergence, changing into downbeat, when it occurs congenitally as well as when associated with Wernicke's. This has been reported by Cox and others (1981).
DBN is classically attributed to the Chiari malformation. Numerous large studies have been published, largely concluding that while the Chiari may contribute as many as 1/3 of cases, cerebellar degenerations, demyelinating disease, drug toxicity, neoplasia, and "idiopathic" are other common causes.
In a review of 91 patients by Yee (1989), the most frequent causes were infarction, cerebellar and spinocerebellar degeneration syndromes, MS and developmental anomalies affecting the pons and cerebellum. Toxicity from anticonvulsant drugs probably causes nystagmus in a few patients and the author of this review has seen this more frequently than the other etiologies listed above. Clinical examinations, excluding eye movement recordings, were used to localize lesions. Localizations included the cerebellum in 88% of the patients. However, localizations to structures outside of the cerebellum were made in several patients.
Downbeating nystagmus is reported to often increase on supine positioning (Leigh and Zee, 1991), but the author has not confirmed this in his own practice. Small amounts of downbeating nystagmus are seen in many normal subjects when using sensitive recording methods (i.e. video ENG in the dark). If downbeating nystagmus cannot be seen during fixation, it is unlikely to reflect a serious pathology. In older people, a DBN may be seen on supine positioning. This is probably a anterior canal BPPV variant as it does not seem to be accompanied by progression or disability. A small literature exists about this called "matitutional vertigo".
Downbeating nystagmus can be elicited by the head-shaking test. In this instance it may reflect an underlying mechanism of migraine or cerebro-vascular disease (this is the authors opinion).
Torsional nystagmus in primary position (the eyes centered, person sitting upright) is very rare. The most useful technique for seeing it is fundoscopy. It is seen in disorders of the medulla such as syringomyelia, in degenerative disorders of the nervous system, in persons with palatal myoclonus, in multiple sclerosis, and in persons with midbrain lesions (Helmchen et al, 2002). In midbrain lesions, small amounts of torsional nystagmus may last for years. In midbrain lesions, vertical saccades are often slowed. Torsional nystagmus is more commonly elicited by positional maneuvers such as the Dix-Hallpike test. In that context, torsional nystagmus is generally attributed to benign paroxysmal positional vertigo (BPPV).
Gaze-evoked nystagmus is the nystagmus that is provoked by particular directions of gaze. See this page for more information.
Head-shaking nystagmus is the nystagmus evoked by moving the head sinusoidally, typically for 20 cycles. See this page for more information.
Hyperventilation Induced Nystagmus
Hyperventilation induced nystagmus has been reported in patients with acoustic neuroma and other CP angle tumors, in microvascular compression, in perilymph fistula, and in patients with MS and patients with cerebellar dysfunction.
- Minor LB, Haslwanter T, Straumann D, Zee DS. Hyperventilation-induced nystagmus in patients with vestibular schwannoma. Neurology 1999:53:2158-2168
Vibration Induced Nystagmus
Under video Frenzel goggles, it is common to see nystagmus provoked by vibration over the ears, over the front or back of the neck. This nystagmus is presently under investigation by several groups. In persons with unilateral vestibular loss, a nystagmus occurs nearly 100% of the time on vibration over the SCM muscles, with slow-phases directed toward the side of lesion. While the slow-phase velocity may not be very high, the nystagmus can easily be seen as being different from normal fixation behavior. In many normal individuals nystagmus is produced that beats to the left on stimulation of the left side and to the right on the right side. This is not associated with any known pathology.
Hamman KF, Schuster EM. Vibration-induced nystagmus -- A sign of unilateral vestibular deficit. ORL J. 1999 Mar-Apr 61(2) 74-9
Please see the BPPV page system for information about positional nystagmus, especially the benign paroxysmal positional vertigo variant. About 85% of positional nystagmus is due to BPPV. In the remainder, most are "idiopathic". A small number of persons has an identifiable brainstem or cerebellar disorder. In general, in the author's opinion, if positional nystagmus is the only physical abnormality, it is best to initially assume the patient has BPPV and proceed accordingly. If treatment for BPPV fails, then one may wish to explore other possibilities.