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396 Theory and Practice of Squint and Orthoptics
a. Oblique trajectory occurs when vertical and
horizontal components are of equal
frequency and amplitude and in phase with
each other.
b. Circular trajectory occurs when vertical and
horizontal components are of equal
frequency and amplitude and are 90°, out of
phase with each other.
c. Elliptical trajectory occurs when vertical and
horizontal components are of equal
frequency but unequal amplitudes and are
90° out of phase with each other.
PATHOPHYSIOLOGY OF NYSTAGMUS
Nystagmus and other related conditions in
essence disrupt steady fixation and thereby
degrade vision. To understand the pathophysiology of nystagmus, we must, therefore,
first look at what are the mechanisms that
maintain steady fixation.
Mechanisms that work together to
maintain a steady gaze
1. Fixation, which has two distinct components:
a. The visual system’s ability to detect retinal
image drift and program corrective eye
movements; and
b. The suppression of unwanted saccades that
take the eye off target.
2. Vestibulo-ocular reflex (VOR), by which eye
movements compensate for head movements at
short latency during natural activities, especially
locomotion. The proprioceptors of the vestibular
system are the semicircular canals of the inner
ear, which respond to changes in angular
acceleration due to head rotation4.
3. Neural integrator, ability of the brain to hold
the eye at an eccentric position in the orbit
against the elastic pull of the suspensory
ligaments and extraocular muscles. A gazeholding network called the neural integrator
generates this signal. The cerebellum, ascending
vestibular pathways, and oculomotor nuclei are
important components of the neural integrator.
For effective working of the performance,
three gaze-holding mechanisms are tuned by
adaptive mechanisms (recalibration) that monitor
the visual consequences of eye movements.
Nystagmus is caused by defect in any of above
mechanisms or their adaptive tuning. In other
words, nystagmus occurs due to disturbances
in the sensory or motor systems responsible for
neuromuscular coordination of the extraocular
muscles, which in turn provides a steady
fixation under normal circumstances.
• Sensory system consists of the retina, the
vestibular system and the proprioceptive end
organs of the cervical musculature.
• Motor system is formed by the extrinsic ocular
muscles innervated by the oculomotor cranial
nerves. The cerebellum controls the muscle tone
and facilitates the smooth operation of the
reflex responses involved.
CLASSIFICATION
Many classifications have been proposed for the
nystagmus, and so, the reader will find different
classifications in different books. It is important
to note here that the terms motor and sensory
nystagmus are no longer being considered.
National Eye Institute Workshop has developed
a new classification in 2001 called the
classification of eye movement abnormalities
and strabismus (CEMAS). In this volume, a
simple classification has been adopted by
slightly modifying CEMAS as below:
A. Physiological nystagmus
1. Optokinetic nystagmus
2. Endpoint nystagmus (eccentric gaze
nystagmus)
3. Physiological vestibular (caloric or rotational)
nystagmus
4. Voluntary nystagmus
B. Pathological nystagmus
I. Early onset (childhood) nystagmus
1. Infantile nystagmus syndrome (includes old
names such as ‘congenital’, ‘motor’, ‘sensory’,
idiopathic and nystagmus blockage)
2. Fusion maldevelopment nystagmus syndrome
(old names “latent, manifest latent,”
nystagmus blockage)
3. Spasmus nutans syndrome
• Without optic pathway glioma
• With optic pathway glioma
II. Late overset or acquired nystagmus. This group
includes various forms of nystagmus acquired
Nystagmus and Related Oscillations
397
after infancy, which can be further classified as
follows:
1. Nystagmus associated with diseases of visual
system
• Ocular jerk nystagmus
• Vertical nystagmus
• See-saw nystagmus
• Acquired pendular nystagmus
2. Vestibular nystagmus
i. Peripheral vestibular nystagmus, e.g.
Menière and drug toxicity nystagmus
ii. Central vestibular nystagmus
• Downbeat
• Upbeat
• Torsional
• Horizontal
iii. Periodic alternating nystagmus
3. Nystagmus due to disorders of gaze holding
• Gaze-evoked nystagmus
• Dissociated nystagmus (ataxic
nystagmus)
• Bruns’ nystagmus
• Convergence-retraction nystagmus
• Centripetal and rebound nystagmus
Note. Only a very brief account of the various
types of nystagmus is given here just as a
passing reference. For detailed accounts, the
readers should consult certain standard
textbooks on neuro-ophthalmology.
PHYSIOLOGICAL NYSTAGMUS
1. Optokinetic nystagmus. It is a physiological
jerk nystagmus induced by presenting to gaze
the objects moving serially in one direction; such
as strips of a spinning optokinetic drum. The
eyes will follow a fixed strip momentarily and
then jerk back to reposition centrally to fix up a
new strip. Similar condition occurs while
looking at outside things from a moving train.
OKN is used for:
• Assessment of vision in young infants and
uncooperative adults.
• Reversal of OKN is seen in infantile esotropia
syndrome and congenital nystagmus (now
called infantile nystagmus syndrome).
• Asymmetry/absent vertical OKN is diagnostic
of neurological/neurometabolic lesions and
warrants neuroimaging in children with
nystagmus.
2. End-point nystagmus. It is a gaze-evoked
nystagmus encountered in normal subjects. It
typically occurs on looking far laterally and is
poorly sustained. The nystagmus is primarily
horizontal. It is usually symmetric. Differentiating features from a pathological nystagmus
are that this nystagmus has lower intensity (i.e.
slower drift) and is not accompanied by other
ocular motor abnormalities.
3. Physiological vestibular nystagmus. It is a jerk
nystagmus which can be elicited by stimulating
the tympanic membrane with hot or cold water.
It forms the basis of caloric test. If cold water is
poured into right ear, the patient develops left
jerk nystagmus (rapid phase towards left) while
the reverse happens with warm water, i.e. patient
develops right jerk nystagmus. It can be
remembered by the mnemonic 'COWS’ (ColdOpposite, Warm-Same).
Physiological vestibular nystagmus can also be
elicited with head rotation (which is utilized for
vision assessment in young infants). Dampening
of physiological nystagmus should occur in 5–
10 seconds after stopping the rotation. If it does
not, it means that there exists significant visual
impairment.
PATHOLOGICAL NYSTAGMUS
A. EARLY ONSET (CHILDHOOD) NYSTAGMUS
The three most common forms of nystagmus
seen in childhood begin in infancy and are,
therefore, not congenital. These include:
1. Infantile nystagmus syndrome
2. Fusion maldevelopment nystagmus syndrome
3. Spasmus nutans syndrome
1. Infantile nystagmus syndrome
Infantile nystagmus syndrome (INS) is the new
name given in the CEMAS system for the old
‘congenital nystagmus, motor and sensory
nystagmus.’
Etiology. It may be:
I. Idiopathic. This type of nystagmus is present
from birth or develops during early infancy.
It typically appears without an identifiable
structural or neurological cause.
398 Theory and Practice of Squint and Orthoptics
II. Associated with sensory deprivation due to any
of the following causes:
• Retinal diseases, such as retinoblastism,
retinopathy of prematurity (ROP), persistant
hyperplastic primary vitreous (PHPV)
• Ocular albinism, characterized by iris transillu-
mination defects and foveal hypoplasia.
• Aniridia, i.e. bilateral near total congenital iris
absence.
• Leber's congenital amaurosis, characterized by
markedly abnormal or flat electroretinogram
bilateral congenital toxoplasmosis and bilateral
macular hypoplasia.
• Other causes include, bilateral congenital
cataract, achromatopsia, congenital stationary
night blindness, bilateral optic nerve hypoplasia.
Characteristic features. It is characterized by
erratic waveform with or without roving eye
movement associated with reduced visual
acuity due to above mentioned conditions.
CEMAS criteria for INS is summarized below:
• Infantile onset
• Ocular motor recordings show diagnostic
(accelerating) slow phases (Fig. 14.4A)
• Wave forms may change in early infancy,
• Head posture usually evident by 4 years of
age.
• Vision prognosis dependent on integrity of
sensory system.
Symbolic recording of an idiopathic case of INS is
shown in Fig. 14.4B.
Common associated findings
• Conjugate, horizontal-torsional, increases
with fixation attempt
Fig. 14.4B Symbolic recording of a case of idiopathic
infantile nystagmus syndrome (INS) depecting left beating
horizontal jerk nystagmus of medium amplitude and
moderate frequency in primary position. Intensity of
nystagmus increases in left gaze and decreases in right
gaze. There is null zone in right gaze with pendular waveform.
• Progression from pendular to jerk
• Family history often positive
• With or without normal visual acuity due to
associated sensory system deficits (e.g.
albinism, achromatopsia) associated
strabismus or refractive error
• Null and neutral zones present,
• Associated head posture or head shaking may
exhibit a “latent” component, “reversal” with
OKN stimulus or (a) periodicity to the
oscillation.
• May decrease with induced convergence,
increased fusion, extraocular muscle surgery,
contact lenses, and sedation.
Fig. 14.4A Left jerk nystagmus. Electronystagmographic
evaluation of infantile nystagmus syndrome (INS) sows an
exponential increase in velocity during the slow phase.
2. Fusion maldevelopment nystagmus syndrome
Fusion maldevelopment nystagmus syndrome
(FMNS) is the new name for the old term—
latent/latent manifest nystagmus as described in
CEMAS.
Characteristic features CEMAS criteria for
FMNS are summarized below:
• Infantile onset
• High frequency, low-amplitude pendular
nystagmus (dual-jerk waveform), jerk in
direction of fixing eye (Fig. 14.5A).
Fig. 14.5A An exponential decrease in velocity during the
slow phase is the waveform characteristic of fusion
maldevelopment nystagmus syndrome.
• Intensity decreases with age.
• Ocular motor recordings show two types of
slow phases linear and decelerating.
• Nystagmus is not present, when both eyes are
open. It appears when one eye is covered. It is
a jerk nystagmus with rapid phase towards
the uncovered eye.
• While testing visual acuity in such patients,
one eye should be fogged (by adding plus
lenses in front) rather than occluding to
minimize induction of latent nystagmus.
• May be associated with congenital esotropia
and dissociated vertical deviation (DVD).
Nystagmus and Related Oscillations
399
• Becomes manifest under monocular viewing
conditions, i.e. in the presence of decreased
vision in one eye as in anisometropic
amblyopia, strabismic amblyopia, etc.
Symbolic recording of a case of FMNS is shown in
Fig. 14.5B.
Common associated findings
Conjugate, horizontal, uniplanar; usually no
associated sensory system deficits (e.g. albinism,
achromatopsia), may change with exaggerated
convergence (“blockage”), head posture
associated with fixing eye in adduction, no head
shaking, may exhibit “reversal” with OKN
stimulus, no (a) periodicity to the oscillation.
Dissociated strabismus may be present.
Decreases with increased fusion (binocular
function).
3. Spasmus nutans syndrome
Spasmus nutans syndrome (SNS), old name
spasmus nutans (SN) is the 3rd most common
nystagmus seen in infancy. This is a rare type of
nystagmus that usually occurs in young
children. It is characterized by a triad of
symptoms, including nystagmus, head nodding,
and head tilt. Spasmus nutans often
spontaneously resolves in childhood.
Fig. 14.5B Symbolic recording of a case of fusion
maldevelopment nystagmus syndrome (FMNS) depicting
right beating horizontal jerk nystagmus of medium amplitude
and moderate frequency. Intensity of the nystagmus
increases in the right gaze and decreases in left gaze.
Characteristic features CEMAS criteria for SNS
are as below:
• Infantile onset
• Variable conjugacy, small-frequency, low-
amplitude oscillation
• Abnormal head posture and head oscillation,
improves (disappears) during childhood
• Normal MRI/CT scan of visual pathways
• Ocular motility recordings—high-frequency
(>10 Hz), asymmetric, variable conjugacy,
pendular oscillations
• Usually spontaneously remits clinically in 2 to
8 years, remains present with eye movement
recordings
Common associated findings are: Dysconjugate,
asymmetric, multiplanar, family history of
strabismus, may be greater in one (abducting)
eye, constant, head posture/oscillation
(horizontal or vertical), usually no associated
sensory system deficits may have associated
400 Theory and Practice of Squint and Orthoptics
strabismus and amblyopia, may increase with
convergence, head bobbing, head posture may
be compensatory; normal fundus exam;
decreases with increased fusion (binocular
function).
B. LATE ONSET OR ACQUIRED NYSTAGMUS
Acquired nystagmus develops later in life
and may be associated with an underlying
medical condition, medication side effects, or
neurological disorders. It can be classified based
on the underlying cause or trigger
I. Nystagmus associated with diseases of the
visual system
Pathogenesis
As mentioned in pathogenesis, fixation
disorders can lead to nystagmus. The smooth
visual fixation mechanism stops the eyes from
drifting away from a stationary object of regard.
This fixation mechanism depends upon the
motion detection (magnocellular) portion of the
visual system which is inherently slow, with a
response time of about 100 milliseconds that
encumbers all visually mediated eye movements, including fixation, smooth pursuit, and
optokinetic responses. If the response time is
delayed further by disease of the visual system,
then the attempts by the brain to correct eye
drifts leads to ocular oscillations.
Vision is also needed for recalibrating and
optimizing all types of eye movements. These
functions depend on visual projections to the
cerebellum. Thus, signals go from secondary
visual areas concerned with motion-vision
project via the pontine nuclei and middle
cerebellar peduncle to the cerebellum. For
calibration of the ocular motor system, visual
signals are compared with eye movement
commands. At present, it is not certain how or
where this function is performed. A group of
cells in the paramedian tracts (PMT) in the
lower pons have been suggested as a probable
centre.
Diseases affecting any part of the visual
system, from retina to cortical visual areas, or
interrupting visual projections to pons and
cerebellum, may be associated with nystagmus.
Clinical types of nystagmus with lesions
affecting the visual pathways
Ocular jerk nystagmus
It is seen in disease of the retina. Congenital or
acquired retinal disorders causing blindness,
such as Leber’s congenital amaurosis, lead to
continuous jerk nystagmus with components in
all three planes, which changes direction over
the course of seconds or minutes. This is due to
inability to calibrate the ocular motor system.
This nystagmus often shows the increasingvelocity waveform earlier thought to be specific
for congenital nystagmus.
Vertical nystagmus
It is seen in vertical nystagmus disease affecting
the optic nerves. Optic nerve disease is associated
with vertical pendular nystagmus. With unilateral
disease of the optic nerve, nystagmus affects the
abnormal eye. The nystagmus has vertical, lowfrequency, bidirectional drifts (pendular),
unidirectional horizontal drifts with corrective
quick-phases (jerk) are less common. When
disease affects both optic nerves, the amplitude of
nystagmus is greater in the eye with poorer vision.
Monocular nystagmus of childhood
Causes Benign to sight threatening causes of
poor vision, i.e. from amblyopia to optic
neuropathy.
Characteristic features of monocular nystagmus
of childhood, a rare but important form of
nystagmus, are:
• Onset, almost always in early childhood
• Nystagmus movements occur in the same eye
at all times and may be vertical or elliptical
(of small amplitude)
• Heimann-Bielschowsky phenomenon, i.e.,
monocular vertical nystagmus in an eye with
long-standing poor vision, may be seen.
• Neuroimaging showed always be performed in
an infant presenting with monocular vertical
nystagmus associated with afferent pupillary
defect and optic atrophy; as it is suggestive of
an optic nerve or chiasmal tumour (glioma).
Pendular see-saw nystagmus
Characteristic features. See-saw nystagmus is
an unusual but dramatic type of dysconjugate
Nystagmus and Related Oscillations
401
nystagmus that has both vertical and torsional
components. If the 2 eyes are envisioned as
being placed on an imaginary see-saw, 1 at
either end, they "roll down the plank" as 1 end
of the see-saw rises, with the high eye intorting
and the low eye extorting. As the direction of
the see-saw changes, so does that of the eye
movement. Thus, the eyes make alternating
movements of elevation and intorsion, followed
by depression and extorsion.
This type of nystagmus is often associated
with rostral midbrain or suprasellar lesions,
most often craniopharyngioma in children.
Confrontation visual field testing may elicit a
bitemporal defect. Neuroradiologic evaluation
is necessary. A congenital form of see- saw
nystagmus can be seen in disorders of
decussation (usually associated with optic nerve
hypoplasia and temporal visual field defects),
such as those sometimes seen in Joubert
syndrome.
Etiology. It is seen in disease affecting the optic
chiasm. Parasellar lesions such as pituitary
tumours that affect the chiasm are associated
with see-saw nystagmus. See-saw nystagmus has
two types— pendular and jerk. Pendular seesaw is seen in lesions of optic chiasm. It is
because of the fact that, crossed visual inputs
are important for optimizing vertical-torsional
eye movements and if interrupted, lead to seesaw oscillations.
are in phase), elliptical. (If the horizontal and
vertical oscillatory components are out of phase)
or circular (phase difference of 90° and equal
amplitude of the horizontal and vertical
components). Further, the nystagmus may be
conjugate, or may appear convergent-divergent.
The frequency of oscillations ranges from
1–8 Hz, with an average value of 3.5 Hz and
remains constant for a given patient. Acquired
pendular nystagmus may be suppressed or
brought out by eyelid closure or evoked by
convergence.
Symbolic recording of a case of acquired
pendular nystagmus is shown in Fig. 14.6.
Conditions associated with acquired pendular
nystagmus are:
• Visual loss (including unilateral disease of the
optic nerve)
• Disorders of central myelin, such as:
– Multiple sclerosis
– Pelizaeus-Merzbacher disease
– Peroxisomal assembly disorders
– Cockayne’s syndrome
– Toluene abuse
• Oculopalatal myoclonus
• Acute brainstem stroke
Acquired pendular nystagmus
Acquired pendular nystagmus is one of the most
common forms of nystagmus associated with
disease affecting the visual system or its
brainstem-cerebellar projections and is associated with distressing visual symptoms. Its
pathogenesis is not entirely clear with more than
one mechanism responsible.
Features. Acquired pendular nystagmus has
horizontal, vertical, and torsional components
with the same frequency, although one
component may predominate (In congenital
pendular nystagmus, the oscillation usually is
predominantly horizontal). Depending on the
phase difference between various directions, a
pendular nystagmus may be oblique (If the
horizontal and vertical oscillatory components
Fig. 14.6 Symbolic recording of a case of horizontal acquired
pendular nystagmus of a low amplitude and moderate
frequency.
402 Theory and Practice of Squint and Orthoptics
Table 14.1 Differences between peripheral and central vestibular imbalance nystagmus
Features Peripheral Central
Direction Horizontal/torsional Bidirectional, pure vertical, pure
torsional, or mixed; fast phase changes
in different directions of gaze
Visual fixation Inhibits nystagmus No inhibition
Severity of vertigo Severe Mild
Associated eye None May have pursuit or saccadic defects
movement defect
Other findings
Response to Dix- Hearing loss May have other cranial nerve or long
Hallpike maneuver tract signs
Latency Present Absent
Duration <1 minute >1 minute
Fatigability Yes No
Reversal with Yes No
upright position
• Whipple’s disease
• Spinocerebellar degenerations
• Congenital nystagmus
II. Vestibular nystagmus
Nystagmus related to imbalance in the
vestibular pathway can be caused by damage
to peripheral or central structures. Difference
between peripheral and central vestibular
imbalance nystagmus in Table 14.1.
Peripheral vestibular nystagmus
Disease affecting the peripheral vestibular
pathway (i.e. the labyrinth, vestibular nerve, and
its root entry zone) causes nystagmus with linear
slow phases, which reflect an imbalance in the
level of tonic neural activity in the vestibular
nuclei. The slow phase of the nystagmus is
towards the side of the lesion. Gaze in the
direction of the fast component increases the
nystagmus intensity, and gaze in the direction
of the slow component decreases the intensity
(Alexander’s law). An imbalance of vestibular
tone also causes vertigo and a tendency to fall
towards the side of the lesion. The nystagmus
is suppressed by visual fixation and sometimes
may only become apparent, when visual fixation
is prevented. This is because in presence of
normal visual functions, the calibration
mechanisms discussed above prevent the
drifting of eyes.
Vestibular nystagmus is categorized as follows:
• First degree—if it is present only on looking in
the direction of the quick phases.
• Second degree—if it is also present in the central
position.
• Third degree—if it is present on looking in all
directions of gaze.
Pure vertical or pure torsional nystagmus.
almost never occur with peripheral vestibular
disease
Diagnosis of specific types of peripheral
vestibular nystagmus can be aided by observing
the effect of head position on nystagmus as
below:
• Complete unilateral labyrinthine destruction
leads to a mixed horizontal-torsional nystagmus
• In benign paroxysmal positional vertigo
(BPPV), a mixed upbeat-torsional nystagmus
reflecting posterior semicircular canal
stimulation is seen.
• Patients with dehiscence of the superior semi-
circular canal develop vestibular symptoms
and nystagmus, when exposed to certain
sounds (Tullio’s phenomenon).
Peripheral vestibular nystagmus induced by
caloric or galvanic stimulation
During caloric stimulation, a temperature
gradient across the temporal bone induces a
convection current in the endolymph of a
semicircular canal, if it is orientated vertical to
the earth:
Fig. 14.7 Symbolic recording of a case of peripheral
vestibular nystagmus depicting left beating mixed horizontal
jerk and rotary waveform caused by a right sided lesion.
Intensity of the nystagmus increases to the left (i.e. away
from the site of lesion) and decreases to the right (i.e.
towards the site of lesion).
• The subject is placed supine and the neck is
flexed at 30°.
• A cold stimulus (30ºC) induces horizontal
slow phase components directed towards the
stimulated ear (quick phases in the opposite
direction).
• A warm stimulus (44°C) and the same head
orientation, quick phases are towards the
stimulated ear (mnemonic, COWS: coldopposite, warm-same).
Symbolic recording of a case of peripheral
vestibular nystagmus is depicted in Fig. 14.7.
Central vestibular nystagmus
Imbalance of central vestibular connections
commonly leads to downbeat, upbeat, and
torsional nystagmus.
Downbeat nystagmus
Causes
• Downbeat nystagmus is usually associated
with lesions that effect the excitatory projections from posterior semicircular canals,
sites include vestibulocerebellum, flocculus,
Nystagmus and Related Oscillations
403
paraflocculus, nodulus and uvula and the
underlying medulla.
• Cerebellar degeneration, including familial
episodic ataxia, and paraneoplastic degeneration.
• Craniocervical anomalies, including Arnold-
Chiari malformation
• Infarction of brainstem or cerebellum
• Dolichoectasia of the vertebrobasilar artery
• Multiple sclerosis
• Cerebellar tumour
• Syringobulbia
• Head trauma
• Anticonvulsant medication
• Lithium intoxication
• Alcohol
• Wernicke’s encephalopathy
• Magnesium depletion
• Vitamin B12 deficiency
• Toluene abuse
• Congenital
• Transient finding in otherwise normal infants
Clinical features
• Present with the eyes in central position.
• Has a small amplitude (viewing the fundus
with an ophthalmoscope may be necessary).
It may occur intermittently.
• Generally, Alexander’s law is obeyed:
Nystagmus intensity is greatest in downgaze
and least in upgaze.
• The waveform is linear, but it may be
increasing in velocity.
• Downbeat nystagmus may be evoked by
placing the patient in a head-hanging position.
• Convergence may influence the amplitude
and frequency of the nystagmus or convert it
to upbeat nystagmus.
• Other ocular motor abnormalities accompany
downbeat nystagmus and reflect coincident
cerebellar involvement.
• Vertical smooth pursuit and the vertical VOR
are abnormal because of impaired ability to
generate smooth downward eye movements.
• Impairment of eccentric horizontal gaze-
holding, smooth pursuit, and combined eyehead tracking.
404 Theory and Practice of Squint and Orthoptics
Fig. 14.8 Symbolic recording of a case of downbeat
nystagmus in primary position with a superimposed
horizontal gaze-evoked nystagmus. Intensity of downbeat
nystagmus increases in downgaze and laterally. Oblique
trajectory shown in lateral gaze is due to superimposed
horizontal gaze-evolved nystagmus.
• The visual consequences of downbeat
nystagmus are oscillopsia and postural
instability.
Symbolic recording of a case of downbeat
nystagmus is shown in Fig. 14.8.
Upbeat nystagmus
Causes
• Upbeat nystagmus is most commonly seen in
patients with lesions affecting excitatory
connections from the anterior semicircular
canals. These include:
– The perihypoglossal nuclei and adjacent
medial vestibular nucleus (structures
important for gaze-holding).
– Ventral tegmentum (containing projections
from the vestibular nuclei that receive inputs
from the anterior semicircular canals).
– Caudal medulla
– Anterior vermis of the cerebellum
– Brachium conjunctivum and midbrain
• Cerebellar degenerations, including familial
episodic ataxia
• Leber’s congenital amaurosis or other
congenital disorder of the anterior visual
pathways
• Infarction of medulla, midbrain, or cerebellum
• Tumours of the medulla, midbrain, or
cerebellum
• Wernicke’s encephalopathy
• Brainstem encephalitis
• Behcet’s syndrome
• Meningitis
• Multiple sclerosis
• Thalamic arteriovenous malformation
• Organophosphate poisoning
• Tobacco
• Associated with middle ear disease
• Congenital
• Transient finding in otherwise normal infants
Clinical features
• It is present with the eyes close to central
position.
• Nystagmus intensity is usually greatest in
upgaze.
• It does not increase on right or left gaze.
• Removal of visual fixation has little influence
on slow-phase velocity.
• Convergence can enhance, suppress, or
convert upbeat nystagmus to downbeat.
• Placing the patient in a head-hanging position
increases the nystagmus in some individuals.
• There are asymmetries of vertical vestibular
and smooth pursuit eye movements, as well
as associated cerebellar eye movement
findings.
Torsional nystagmus
Causes
• Syringobulbia
• Brainstem stroke (Wallenberg’s syndrome) or
arteriovenous malformation
• Brainstem tumour
• Multiple sclerosis
• Oculopalatal myoclonus
• Head trauma
• Congenital
• Associated with the ocular tilt reaction
Nystagmus and Related Oscillations
405
Clinical features
• Least common form of central vestibular
nystagmus.
• It is difficult to detect and requires careful
observation of conjunctival vessels or noting
the direction of retinal movement on either
side of the fovea.
• Modulation by head rotations is similar to
upbeat and downbeat nystagmus.
• There are variable slow-phase waveforms
• Convergence suppresses the nystagmus.
Periodic alternating nystagmus
Causes
Periodic alternating nystagmus (PAN) does not
fall in a single pathological category. It occurs
in lesions affecting the cerebellum most notably
nodulus and uvula. These areas determine the
eye velocity of nystagmus seen after rotation
(both VOR and OKN). Their destruction leads
to un-inhibited, prolonged vestibular impulses
which leads to nystagmus.
Clinical features
• PAN is characterised by spontaneous
horizontal nystagmus, present in the central
gaze and periodically reverses direction
approximately every 90–120 seconds. The
changing direction of the waveforms is caused
by an actively shifting null zone.
• Acquired PAN has the same characteristics in
light or in darkness.
• Smooth pursuit and optokinetic nystagmus
are usually impaired.
Jerk see-saw and hemi see-saw nystagmus
See-saw nystagmus is a complex, vertical
nystagmus characterized by cyclic elevation of
one eye and depression of the other eye. It is
Fig. 14.9 Symbolic recording of a case of see-saw nystag-
mus (for explanation see text).
often associated with lesions in the brain or
visual pathways.
Causes
Jerk see-saw nystagmus (hemi see-saw
nystagmus) occurs in patients with lesions in the
region of the interstitial nucleus of Cajal (INC).
The associated ocular tilt reaction is due to an
imbalance of central otolithic projections from
vestibular nuclei to the INC.
Clinical features
• One-half-cycle consists of elevation and
intorsion of one eye and synchronous
depression and extorsion of the other eye. In
the next half-cycle, the vertical and torsional
movements reverse (Fig. 14.9).
• The waveform may be pendular or jerk. Some
authorities label the pendular form as see saw
and jerk form as hemi see-saw.
• See-saw nystagmus may be congenital, or
Acquired.
• Patients often have a contralateral ocular tilt
reaction.
• With a right sided lesion, the reaction consists
of a left head tilt, a skew deviation with a right
hypertropia, tonic intorsion of the right eye
and extorsion of the left eye, and misperception that earth-vertical is tilted to the left.
III. Nystagmus due to abnormalities of the
mechanism for holding eccentric gaze
Gaze-evoked nystagmus
Gaze-evoked nystagmus occurs when
nystagmus is triggered or exacerbated by
changing the direction of gaze. It can be a sign
of a neurological disorder or a medication side
effect. It is the most common form of nystagmus
encountered in clinical practice. Gaze-evoked
nystagmus is a general term that includes both
physiologic and pathologic nystagmus. When
the nystagmus is physiologic, the term end-point
nystagmus should be used. When the
nystagmus is associated with a paresis of gaze,
e.g. ocular motor nerve palsies or weakness of
the extraocular muscles, the term gaze-paretic
nystagmus is appropriate.
• Gaze-evoked nystagmus usually occurs on
lateral (Fig. 14.10) or upward gaze, seldom on
looking down.