Timothy C. Hain, MD Page last modified: November 21, 2009
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 (for example it may be due to congenital nystagmus), 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).
Following unilateral vestibular lesions (such as vestibular neuritis, transtympanic gentamicin, acoustic neuroma surgery, or vestibular nerve section), spontaneous nystagmus gradually fades away over months.
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.
Vertical pendular nystagmus associated with oculopalatal myoclonus syndome. Recording method: infrared video
(c) 2003 Timothy C. Hain, M.D. Educational use is permitted.
The so-called "ocular myoclonus" associated with the oculo-palatal myoclonus syndrome, an example of which shown above, 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. In spite of these sporadic reports of success, we have not had much success ourselves.
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).
We have seen one case of vertical pendular nystagmus due to superior canal dehiscence. Here the presumed mechanism is pulsations in CSF pressure stimulating the superior canal via the dehiscenct bone.
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 (PMD) 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.
Torsional pendular nystagmus.
The author has seen several cases of torsional pendular nystagmus, sometimes associated with palatal myoclonus, mainly in the context of atrial fibrillation and treatment with antiarrythmic medications. Torsional pendular is generally seen in the upright position. Pendular SSn has been found associated with visual disorders and may also be of congenital origin.
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.
DN is a nystagmus where oscillations are present only in one eye. It has been described in spasmus nutans, congenital nystagmus (see below), 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.
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 be acquired 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.
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).
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