Pendular nystagmus

INTRODUCTION — Pendular nystagmus is a sinusoidal oscillation. The waveform of pendular nystagmus may occur in any direction; it can be torsional, horizontal, vertical, or a combination of these, resulting in circular, oblique, or elliptical trajectories. It may be different in the two eyes, sometimes even monocular. Diagnosis is an exercise in pattern recognition since pendular nystagmus is subdivided into a number of types, some characterized by specific trajectories:

●Acquired pendular nystagmus

●Pendular nystagmus from visual loss

●Specific variants: spasmus nutans, oculopalatal myoclonus, see-saw nystagmus, oculomasticatory myorhythmia (Whipple's)

●Congenital nystagmus

ACQUIRED PENDULAR NYSTAGMUS

Causes and pathophysiology — Most patients with acquired pendular nystagmus have multiple sclerosis [1,2]; the incidence of pendular nystagmus in this population is approximately 2 to 4 percent [3,4]. Less commonly it follows strokes, encephalitis, or vascular malformations in the cerebellum or brainstem [1,5,6] and only very occasionally tumors [7]. Rare causes include chronic toluene encephalopathy [8], Pelizaeus-Merzbacher and other leukodystrophies [9,10], unusual familial syndromes [11], and orbital myositis [12]. One unique case with monocular nystagmus had a chiasmal glioma [13]. There is also one report of transient pendular nystagmus after fosphenytoin use [14].

The pathophysiology of acquired pendular nystagmus is unclear. It is associated with cerebellar signs, so it may be a "cerebellar tremor" [3]. The association with internuclear ophthalmoplegia suggests a brainstem site [1]; dysfunction of the vergence system is a possibility in some patients [15].

Pendular nystagmus can be asymmetric or even monocular. How this arises is an interesting problem. It may reflect asymmetric brainstem disease [1]; however, asymmetries in nystagmus do not correlate with asymmetries in other brainstem signs [4,16]. It may be related to optic nerve function since larger oscillations correlate with greater optic neuropathy [4]. Taking all this together, pendular nystagmus is most likely caused by abnormal brainstem feedback circuits for eye position [17], which are calibrated by visual factors [18,19].

Imaging studies have revealed lesions in the pontine tegmentum and cerebellar nodulus [4,6,16]. A requirement for multiple lesions in visual and cerebellar systems may explain why it tends to be a less common, late, and unremitting sign in multiple sclerosis.

While pendular nystagmus is almost always due to cerebral dysfunction, there is one reported case of a conjugate horizontal pendular nystagmus that was synchronous with the pulse, and proved on computed tomography (CT) scan of the temporal bones to be due to a perilymph fistula that complicated surgery for a cholesteatoma [20].

Clinical features and diagnosis — Most patients complain of constant oscillopsia that interferes with tasks such as reading, although patients with poor vision may not notice oscillopsia [3,4]. Poor vision is due partly to blurring from constant eye motion, but many patients with multiple sclerosis also have optic neuropathy [2,4].

Acquired pendular nystagmus is usually present in primary position and seldom varies with gaze direction [21], with exceptions [22]. The nystagmus often differs in size and direction between the two eyes, and can even be monocular [3,4,21,23,24].

Many patients also have jerk nystagmus, including gaze-evoked, rebound, and upbeat nystagmus [4]. Most have cerebellar dysfunction of gait, limb coordination, or speech, and tremor or head titubation [3,4]. Some have internuclear ophthalmoplegia [1,4]. (See "Internuclear ophthalmoparesis".)

A video example of acquired pendular nystagmus in the setting of multiple sclerosis is available at http://www.neuroophthalmology.ca/case-of-the-month/eye-movements/monocular-blurry-vision-in-multiple-sclerosis.

The direction of nystagmus should be observed to see if it fits a specific variant, such as see-saw nystagmus, oculomasticatory myorhythmia, and spasmus nutans in children. These require different evaluations. (See 'Specific variants' below.)

Otherwise, the investigation of choice is magnetic resonance imaging (MRI) with focus on the cerebellum and brainstem, and sequences designed to detect demyelination. Other investigations for multiple sclerosis can include cerebrospinal fluid (CSF) studies and brainstem, somatosensory, and visual evoked potentials; these are unnecessary if the MRI, history, and examination point strongly to multiple sclerosis.

Prognosis and treatment — As previously mentioned, pendular nystagmus is seldom a presenting sign of multiple sclerosis. It tends to develop later in the course and persists indefinitely, resolving in only 5 percent [3,4].

Controlled trials show transient benefit with intravenous anticholinergic drugs [25]; oral or transcutaneous forms are not helpful [26,27]. Memantine, a glutamate antagonist [27], and gabapentin, 300 mg three times daily [28], may be effective. Two small crossover trials have compared gabapentin and memantine in patients with acquired pendular nystagmus [29-31]. Both drugs appeared to have efficacy in regard to measures of reduced median eye speed and amplitude as well as improved visual acuity and the symptom of oscillopsia [32]. There also are anecdotal reports of benefit with clonazepam [33], isoniazid [34], and valproate [35].

There are ongoing investigations of devices that have electronically servo-controlled prisms, much like the gaze stabilization features in modern cameras. These use a sensor that detects eye movements to adjust prisms to shift the image in the direction opposite to the eye oscillation [36-38]. Other devices use eye movement sensors to trigger a filter that gates vision, eliminating periods with excessive motion [38]. Experiments with surgery and botulinum toxin injections to weaken extraocular muscles have been somewhat disappointing [39,40], although some successes have been reported [41]. One unusual case report describes symptom improvement and transient cessation of nystagmus with vibration applied to the skull with a handheld muscle massager [42].

SPECIFIC VARIANTS

Spasmus nutans — Spasmus nutans is a pediatric disorder that consists of the triad of ocular oscillations, head-nodding, and head-turning (torticollis). All three are not required for the diagnosis; head-nodding and nystagmus are most common, with head turn in only 30 percent. The age at onset is usually 6 to 12 months, but can be up to several years [43].

●Epidemiology and pathogenesis – Spasmus nutans was more common at the turn of the century [44]; it was attributed to poor socioeconomic conditions, inadequate diet, and light deprivation since it seemed to occur in winter and resolve in the spring [45]. A case-control study in 2002 found that spasmus nutans was associated with Hispanic and African-American ethnicity, lower gestational age at birth, lower household income, and higher incidence of psychiatric and substance abuse problems in parents, compared with a control group of congenital nystagmus [46]. A hereditary component is suggested by its occurrence in monozygotic twins [47].

Delayed maturation of eye movement circuits with prolonged time delays are hypothesized to underlie this disorder, possibly involving the saccadic system [45]. However, saccades are normal in most [45].

●Clinical features – The nystagmus is a small, fast oscillation, usually horizontal, sometimes oblique [4]. A key feature is dysconjugacy: spasmus nutans can be unilateral or bilateral with asymmetric size, and when bilateral it is not synchronized between the two eyes [45,48]. The nystagmus can even change within a session [45]. It is often intermittent, with bursts of 5 to 30 seconds.

The head motion is often oblique, with both nodding and shaking [23]. It is slower and larger than nystagmus [49,50]. Head nodding is a compensatory act that suppresses nystagmus [49-51].

Strabismus and amblyopia are seen in 60 percent of children [43,48,52]. These in turn can be associated with latent nystagmus and dissociated vertical divergence [52]. Refractive errors such as anisometropia and astigmatism are more frequent [43]. (See "Amblyopia in children: Classification, screening, and evaluation".)

●Evaluation and diagnosis – Criteria for distinguishing spasmus nutans from congenital nystagmus have been derived (table 1) [48,53]. Head-nodding is not specific for spasmus nutans since it occurs in approximately 10 percent of children with congenital nystagmus [44].

Some cases are associated with underlying retinal or neurologic problems, with a small series finding these in 6 of 22 patients [53]. The features of nystagmus do not differentiate more benign spasmus nutans from that with these other problems [48,54,55]. Even spontaneous resolution of spasmus nutans has been reported with a chiasmal glioma [56].

•Retinal conditions include achromatopsia [54], congenital stationary night blindness [55,57], and cone or cone-rod dystrophies [53].

•Neurologic problems consist of underlying tumors in approximately 1 percent of cases [58]. These are usually gliomas of the intracranial visual system [59-62], but sometimes can be ependymomas of the fourth ventricle [23] and posterior thalamic tumors [63]. A vertical or see-saw nystagmus should raise the suspicion of tumor [58]. Other rarely reported neurologic associations include Leigh encephalopathy [64], arachnoid cysts, and porencephalic cysts [49,65].

Clinical features distinguish spasmus nutans from congenital nystagmus. A positive family history and infantile myopia are clues to congenital stationary night blindness; the diagnosis is made with electroretinogram (ERG) [57]. Associated signs that suggest tumors [58,65] include optic atrophy, visual loss, failure to thrive [60,66], and hydrocephalus. Magnetic resonance imaging (MRI) of the brain or orbits is required if such features are present.

Unlike congenital nystagmus, spasmus nutans is considered transient, lasting a few months to years [43,45]. However, clinical resolution does not always occur; even when it does, residual oscillations are seen on eye movement recordings [52].

●Prognosis – In the long term, visual acuity is good, 20/50 or better in most [52]. Slight reductions in acuity may reflect strabismic amblyopia [52] and are not correlated with the nystagmus [43]. Developmental delay is seen in a few children [43,48].

Oculopalatal myoclonus — One of two variants of palatal myoclonus or tremor is associated with nystagmus [67]. Symptomatic palatal tremor follows brainstem infarction or cerebellar degeneration, and the palatal motion results from contraction of the levator veli palatini [67]. Other muscle groups also are frequently involved, such as the tongue and pharynx; oscillations can be shown in the limbs on electromyography (EMG) [68]. This group frequently has nystagmus. By contrast, essential palatal tremor presents with symptoms of ear-clicking from motion of the tensor veli palatini; no other muscles are involved, and there is no nystagmus. (See "Etiology and diagnosis of tinnitus", section on 'Neurologic disorders'.)

In most cases of symptomatic palatal tremor, the abnormal movements develop months to years after a brainstem infarction [18,69,70]. On occasion it has been described in multiple sclerosis [70,71] and progressive supranuclear palsy [72]. Palatal tremor has also been described in adult-onset Alexander disease [73,74].

●Pathophysiology – The damage affects components of the dentato-rubro-olivary circuit, "Mollaret's triangle." This denervates the inferior olive, which subsequently hypertrophies [75]. The mechanism by which this leads to nystagmus is unclear; one hypothesis is that cerebellar control of the vestibulo-ocular reflex is impaired due to failure of visuo-vestibular adaptive mechanisms mediated by the inferior olive [18]. One model proposes that the hypertrophied inferior olive develops increased conductance through gap junctions, causing it to become a generator of synchronized spike trains, which are passed on to the cerebellum; cerebellar learning processes for timing adjustments then transform into outputs that cause ocular oscillations [76].

●Clinical features – Oscillopsia is a frequent complaint. Patients may or may not be aware of the noise from the palatal motion. Other oscillations are not often a problem.

The ocular oscillations are a distinct subset of acquired pendular nystagmus. The trajectory is stereotyped, with one of two forms [18]:

•A vertical-torsional form, which is conjugate, except that the vertical component is much larger in one eye. In these cases the palatal myoclonus is unilateral, involving the side with the eye that has the larger vertical nystagmus.

•A pure symmetric vertical pendular oscillation, associated with bilateral palatal myoclonus.

The nystagmus is slow (approximately 2 to 3 Hz), regular, and synchronous with the palatal motion [2,69,70]. It is larger in amplitude, slower, and more irregular than acquired pendular nystagmus [2]. Like the palatal movements, pendular nystagmus persists in a more irregular form during sleep.

Associated signs of brainstem damage are common, including horizontal gaze paresis, palsies of cranial nerves V to XII, cerebellar dysarthria and ataxia, and damage to spinothalamic and pyramidal tracts [67,69,70]. In some patients with pontine strokes, similar nystagmus results without the palatal tremor, although rhythmic motions may be seen in other muscles such as the tongue, mentalis, or arm; most of this group have severe lesions, causing coma or the locked-in state, and have horizontal gaze palsies [1].

MRI shows increased signal and size of the inferior olive in the lateral medulla [67,77]. This pseudohypertrophy is considered essential to the genesis of oculopalatal myoclonus. With the lateralized or dissociated form, there is cerebellar atrophy on the side with larger nystagmus and olivary hyperintensity on that side [18,67,78]. The symmetric form of nystagmus can be seen with unilateral or bilateral signal change in the inferior olivary nucleus.

●Treatment – There is no proven therapy. There are small reports of benefit with valproate [35] and trihexyphenidyl [79]. Gabapentin and memantine may reduce the amplitude and frequency variability of the oscillation and improve symptoms [29,31,72].

See-saw nystagmus

●Causes – The most frequent cause of see-saw nystagmus is a parasellar mass, usually a craniopharyngioma [80-82] or pituitary adenoma (figure 1) [83,84]. Vascular disease such as lateral medullary infarcts, mesodiencephalic infarcts, or hemorrhages can cause jerk-type see-saw nystagmus [85,86].

Head trauma can also cause see-saw nystagmus [19,87-89]. In rare cases, see-saw nystagmus is described in Arnold-Chiari malformation [90], multiple sclerosis [91], and spinocerebellar ataxia type 2 [92]. It has been reported with myoclonus in the Lance-Adams syndrome following hypoxic-ischemic encephalopathy [93].

See-saw nystagmus is also associated with visual disorders, including cone-rod dystrophy [94], retinitis pigmentosa [95], septo-optic dysplasia, and toxoplasma chorioretinitis [96]. Congenital forms exist [81,97,98], including patients born without an optic chiasm (the "nondecussating retinal-fugal fiber syndrome") [99,100].

●Pathophysiology – The pathophysiology of see-saw nystagmus is controversial. Large masses that compress the optic chiasm could also damage midbrain structures that control vertical and torsional eye movements [83,101]. This "midbrain theory" is supported by cases with midbrain lesions and no bitemporal hemianopia [83,102], and cases in which see-saw nystagmus resolved but bitemporal hemianopia remained [80,82]. This is the likely mechanism in cases of see-saw nystagmus from medullary or midbrain infarction, particularly jerk forms [85]. The experimental evidence from monkeys is mixed: using muscimol to inactivate neurons, one group failed to find an effect of injection into the interstitial nucleus of Cajal [103], whereas another group produced hemi-see-saw nystagmus with injections just caudal to this midbrain nucleus [104].

However, there are cases with visual loss and no midbrain damage [94,95]. Suggestions that bitemporal hemianopia may cause see-saw nystagmus [80,83] have received support from reports of nystagmus in humans and sheepdogs with congenital absence of the optic chiasm [99]. The optic chiasm may contain visual fibers that send a corrective visual signal for the vestibular system to the brainstem [19].

●Clinical features and diagnosis – See-saw nystagmus manifests as a combination of a conjugate torsional motion and a dysconjugate but synchronized vertical component: as one eye goes up, the other descends; the elevating eye intorts while the descending eye extorts. Both components are pendular.

Acquired see-saw nystagmus causes oscillopsia; patients with the congenital version do not have this symptom. See-saw nystagmus is usually present in all positions of gaze, although maximal in downgaze [83,97,101]. It is usually constant, and rarely intermittent [23]. The frequency varies from 2 to 5 Hz [80,81,105]. A jerk type of see-saw nystagmus occurs with unilateral midbrain or medullary lesions [85,106].

Bitemporal hemianopia is frequent with sellar masses or head trauma [19,87,88]. Among cases without bitemporal hemianopia, mainly from brainstem infarction, there is often internuclear ophthalmoplegia, exotropia [81-83,102], and skew deviation [17,21]. Congenital see-saw nystagmus is mixed with other more typical features of horizontal congenital nystagmus [81,97,99].

A fundus examination and possibly ERG are indicated if there is suspicion of visual loss that does not fit with bitemporal hemianopia. If bitemporal hemianopia is present, MRI of the sella with contrast is required. Without hemianopia, MRI should be directed at the brainstem.

●Prognosis and treatment – The prognosis of see-saw nystagmus is variable. Cases with brainstem infarction may resolve [83,102]. With sellar masses, see-saw may resolve postoperatively as visual loss improves, but it may also resolve even if bitemporal hemianopia does not [80,82].

There is no agreed-upon treatment. Some patients benefit from contact lenses [97] or ethanol [88,95]. One patient is said to have improved with memantine [29], and another with clonazepam [89].

Oculomasticatory myorhythmia — The finding of oculomasticatory or oculo-facial-skeletal myorhythmia (continuous rhythmic movements of eye convergence with concurrent contractions of the masticatory or other muscles) is present in approximately 20 percent of patients with Whipple's disease and is considered pathognomonic of the disease [107].

Whipple's disease is a rare systemic infection, affecting the central nervous system (CNS) in 4 percent of cases [107]. Cognitive dysfunction is the most common abnormality among those with CNS disease. CNS Whipple's disease can be associated with other systemic or ocular features [108-110]. Oculomasticatory myorhythmia can also occur without them as an initial presentation [111], or during a relapse of previously systemic disease, sometimes many years later [112,113]. (See "Whipple's disease".)

The mechanism of oculomasticatory myorhythmia is unknown. It may derive from dysfunction in control of the vergence system, but it is difficult to speculate how that would lead to synchronized oscillation with other muscles.

●Clinical features – The nystagmus is usually asymptomatic, although other people may note the abnormal movements. Patients with CNS disease usually present with other complaints, especially dementia and arousal disturbances.

Ocular myorhythmia is a slow convergent-divergent nystagmus, in that the eyes oscillate horizontally towards and away from each other [114]. The nystagmus is synchronous with diffuse muscle contractions elsewhere, particularly the masticatory and facial muscles, including lids, mouth, tongue, and neck [110,114-116], and sometimes the palate, arms, and legs [110,113,117].

There is almost always an associated supranuclear gaze palsy affecting vertical then horizontal eye movements, with eventual loss of all eye movements [108-110,112,114,118]. Bilateral ptosis can occur [1,9]. Hypersomnolence with sleep disorders can be present [119,120].

●Diagnostic testing – MRI is normal [110,117,118] or shows multifocal enhancing lesions [107,109]. Cerebrospinal fluid (CSF) can be normal [109,110,117] or contain periodic acid-Schiff (PAS)-positive cells [107]. A mild lymphocytosis and elevated protein is seen in some cases [108].

Intestinal biopsy shows PAS-positive cells and bacilli on electron microscopy [117,118], but may be normal in patients with isolated CNS disease [114]. PAS-positive cells also can be found in brain tissue [107,116].

A polymerase chain reaction assay for the 16s ribosomal RNA sequence can diagnose active Whipple's disease in intestinal biopsies [121]. However, the value of the intestinal test in CNS Whipple's is uncertain: it has been positive in two cases [122] but negative in three who developed CNS relapses after treatment [121].

The approach to the diagnosis of Whipple's disease is discussed separately. (See "Whipple's disease", section on 'Diagnosis'.)

●Treatment – The treatment of CNS Whipple's disease is discussed separately. (See "Whipple's disease", section on 'Initial management'.)

The myorhythmia may symptomatically respond to valproate [110], although the effect can fade after a few months [113]. Clonazepam and baclofen are ineffective [112].

Pendular nystagmus from visual loss — Monocular pendular nystagmus occurs in children with congenital optic atrophy, strabismic amblyopia, and acquired visual loss, including chiasmal glioma [1,123,124]. Bilateral visual impairment in infants with optic nerve hypoplasia or optic atrophy can cause intermittent vertical pendular nystagmus [125]. Infantile esotropia is not uncommonly associated with a fine torsional pendular nystagmus that may be seen only with funduscopy [126]; it occurs alone or with latent nystagmus.

Adults may develop vertical pendular oscillations years after visual loss [127,128]. The nystagmus is usually, but not always, small and slow [127-129]. The nystagmus can resolve if the visual loss is correctable [129].

A video example of pendular nystagmus with visual loss in the setting of an optic nerve meningioma is available at http://www.neuroophthalmology.ca/case-of-the-month/eye-movements/video-disc-and-mri-puzzle.

Pendular nystagmus mimics — Pendular pseudonystagmus is seen in patients with two unrelated conditions: essential head tremor and bilateral vestibular loss [130,131]. Funduscopy reveals a fine pendular motion of the eyes, which is reduced by firm support of the head. The oscillopsia from vestibular insufficiency improves if the head tremor is treated with propranolol.

CONGENITAL NYSTAGMUS (INFANTILE NYSTAGMUS SYNDROME)

Symptoms — Most patients are not aware of oscillopsia. Decreased visual acuity is the rule. In part, this is caused by degradation of the visual image by continual eye motion, but it may also reflect associated visual abnormalities, which are frequent.

Signs — Most congenital nystagmus is horizontal and conjugate, with rare vertical hereditary variants [132,133]. A small torsional component is apparent in many [134]. Initially, congenital nystagmus was divided into two broad types, jerk and pendular [135], but detailed analyses show a wide variety of patterns of oscillation [136,137]. Most patients have a mix of jerk and pendular waveforms, varying from moment to moment with direction of gaze, and with age [137-139]. With jerk forms, there is often a gaze position to the side where nystagmus is minimal (the null point), and beyond which the nystagmus reverses direction.

Head turn may be present to place the eyes at the null point when looking straight ahead. Other signs are generally related to the associated visual problems. (See 'Etiology/differential diagnosis' below.)

Pathophysiology — The origins of congenital nystagmus remain obscure. Infantile nystagmus is broadly divided into those with and those without sensory abnormalities. However, in those with underlying visual abnormalities, the actual waveform does not correlate with any specific condition [138]. Abnormal feedback to eye movement control systems is probably responsible [140]. Failure in sensorimotor integration, perhaps secondary to reduced contrast sensitivity at high spatial frequencies, may explain the association of congenital nystagmus with conditions like foveal hypoplasia or congenital cataracts [141]. Monkeys raised in a strobe-lit environment also develop a pendular nystagmus, suggesting that impaired motion processing in early life may also lead to congenital nystagmus [142].

Etiology/differential diagnosis — Among children, the main differential is spasmus nutans. Differentiation from spasmus nutans can be made by close attention to the features of nystagmus (table 1). Most adults with congenital nystagmus have known about their problem since childhood. Rarely, cases with purported congenital nystagmus have been reported to have onset in adulthood, with symptomatic oscillopsia [143].

The visual disorders associated with congenital nystagmus encompass a wide range of conditions:

●Structural ocular lesions such as corneal scars, cataracts, and vitreous hemorrhages

●Retinal dystrophies such as Leber congenital amaurosis, achromatopsia, congenital stationary night blindness, cone-rod dystrophies, albinism, Aland Island eye disease, and Alstrom syndrome [144,145]

●Optic neuropathy and optic nerve hypoplasia

Genetic studies have revealed some associations with congenital nystagmus, particularly those with an X-linked pattern of inheritance, which have been linked to mutations of the FRMD7 gene [146,147] or with the GPR143 gene in the case of ocular albinism type 1 [148]. PAX6 mutations can cause aniridia, cataracts, and infantile nystagmus [149].

Diagnostic evaluation — In most cases the diagnosis is straightforward. Ophthalmologic examination is required. Electroretinogram (ERG) is useful if a retinal dystrophy is suspected. With optic nerve disease, visual evoked potentials or magnetic resonance imaging (MRI) of orbits and sella are sometimes helpful.

Prognosis and treatment — Congenital nystagmus is a lifelong condition.

Symptomatic treatment is attempted occasionally to reduce head turn or improve motion-degraded visual acuity. Soft contact lenses can dampen the oscillations [150]. Some suggest that this benefit can be predicted in those who show dampening of nystagmus with stimulation of the first branch of the trigeminal nerve, as with forehead vibration [151].

As with acquired pendular nystagmus, medical treatment may be helpful in managing symptoms. In a clinical trial, 48 patients with congenital nystagmus were randomly assigned to treatment with memantine (20 to 40 mg daily), gabapentin (1200 to 2400 mg daily), or placebo [152]. Both treatments were associated with improved visual acuity and reduced intensity of nystagmus.

There is no high-quality evidence for benefit of surgery and no randomized controlled trials comparing surgery with no intervention [153]. Prisms or surgery can be used to shift the null point to coincide with gaze straight ahead, as well as to increase convergent tone in far gaze, in those patients whose nystagmus decreases in near gaze [151]. Four-muscle tenotomy has also been advocated as a treatment, but more studies are required [151].

SUMMARY

●Definition – Pendular nystagmus consists of slow, sinusoidal, "pendular" oscillations to and fro.

●Acquired pendular nystagmus – Acquired pendular nystagmus is most often seen in the setting of multiple sclerosis.

Patients complain of oscillopsia and/or blurred vision. Nystagmus is present in the primary position and does not change with gaze direction, it may affect either eye asymmetrically. Other forms of nystagmus may co-occur along with other findings of cerebellar or brainstem dysfunction.

Medication trials may provide symptomatic benefit. (See 'Acquired pendular nystagmus' above.)

●Spasmus nutans – Spasmus nutans is pediatric disorder that consists of the triad of nystagmus, head-nodding, and torticollis. The nystagmus is a small, fast oscillation, usually horizontal, sometimes oblique. The age at onset is usually 6 to 12 months, but can be up to several years. The condition is generally benign and self-limited; some cases are associated with retinal or neurologic problems. (See 'Spasmus nutans' above.)

●Oculomotor myoclonus – An acquired pendular nystagmus can occur along with symptomatic palatal tremor that usually results from brainstem infarction. The oscillations can be vertical-torsional and asymmetric or purely vertical and symmetric. Associated brainstem signs are common. (See 'Oculopalatal myoclonus' above.)

●See-saw nystagmus – See-saw nystagmus is a combination of a conjugate torsional motion and a dysconjugate but synchronized vertical component: as one eye goes up, the other descends. There are many potential causes; the most frequent is a parasellar mass. (See 'See-saw nystagmus' above.)

●Oculomasticatory myorhythmia – Characterized by continuous rhythmic movements of eye convergence with concurrent contractions of the masticatory or other muscles, oculomasticatory nystagmus is present in approximately 20 percent of patients with Whipple's disease and is considered pathognomonic. (See 'Oculomasticatory myorhythmia' above.)

●Congenital pendular nystagmus – Although patients frequently have impaired vision either as a consequence of the nystagmus or because of associated visual abnormalities, the nystagmus itself is generally asymptomatic. Most congenital nystagmus is horizontal and conjugate. (See 'Congenital nystagmus (infantile nystagmus syndrome)' above.)