Nystagmus 101 Flashcards
What does nystagmus mean?
Derived from the Greek word, “nmstagmos”, which was used to describe the wobbly head movements of a sleepy or inebriated individual
Rhythmic, oscillating motions of the eyes are called nystagmus.
The to-and-fro motion is generally involuntary
What does vertical nystagmus generally mean?
Central pathology
Less common
Often a sign of serious brain damage
What are the two typical types of nystagmus?
Jerk - fast phase and slow phase (slow away from object or regard and a fast saccadic phase toward target)
Pendular - oscillate with equal speed, no fast and slow phase (sinusoidal)
What defines the nystagmus direction?
By the fast component
How do you measure the magnitude of nystagmus?
You need to look at cycles per second to measure the magnitude of pendular nystagmus
Find the slope for jerk
How should nystagmus be described?
Waveform
Direction
Amplitude
Frequency
Intensity
The examiner should also note the positions of gaze in which the nystagmus occurs and whether the intensity changes with gaze direction
What is alexander’s law/phenomenon?
Jerk nystagmus is usually accentuated in amplitude upon gaze in the direction of the fast component (hindered in the direction away from the fast phase and helped in the direction of the fast phase)
Becomes lesser if you look where the eye wants to go
What is torsional or rotary nystagmus?
Pure torsional nystagmus is a sign of a central disorder
Torsional or rotary nystagmus mixed with vertical or horizontal components is much more common is usually an indication of a peripheral disorder (like BPPV)
What is a runaway nystagmus?
Increasing or decreasing velocity
Is horizontal jerk nystagmus with slow phases increasing velocity usually congenital?
Yes
May result from chiari malformation
Is vertical nystagmus with exponential slow phases increasing velocity usually congenital?
No
May be secondary to acquired cerebellar disease
Can pendullar nystagmus be congenital or acquired?
Yes
When is the slow phase amplitude reduced?
Fixation
Enhanced by darkness, frenzel lenses, or closing the eyes
What is nystagmus caused by a leaky integrator?
Occurs only in an eccentric gaze position
Gaze evoked
The eyes are unable to maintain the eccentric position and drift back to the primary position with a decreasing velocity, reflecting a passive movement resisted by the viscous forces of orbital soft tissues
The defect may reside in the brain stem “neural integrator” or its connections (such as in the cerebellum), which mediates eye deviation
Also called gaze-paretic nystagmus
Are some nystagmus patterns specific and permit reasonably accurate neuroanatomic diagnosis?
Yes
Other patterns are more general and indicate dysfunction somewhere in the posterior fossa
Are there several types of benign nystagmus seen in infancy?
Yes
Congenital nystagmus (CN) is the most common infantile nystagmus
Others are latent/manifest latent nystagmus (LMLN) and the pendular nystagmus of spasmus nutans
What causes congenital nystagmus?
The direct result of an ocular motor control instability that may develop with or without an accompanying sensory deficit
What are some characteristics of congenital nystagmus?
Binocular
Similar amplitude in both eyes
Usually uniplanar (horizontal)
Distinctive waveforms
Diminished by convergence
Increased by fixation attempt (similar to central pathology, but not central)
Superimposition of latent component
Inversion of the optokinetic reflex
Associated head oscillation
No oscillopsia
Abolished in sleep
What is latent/manifest latent nystagmus?
A jerk nystagmus with either a linear or decreasing velocity exponential slow phase identical to that of gaze-paretic nystagmus
Occasionally, when both eyes are closed, a jerk nystagmus with a linear slow phase is present. Classically, “pure” or “true” latent nystagmus (LN) occurs only with uniocular fixation
There is no nystagmus with both eyes viewing, but when one eye is occluded, nystagmus develops in both eyes, with the fast phase toward the uncovered eye
LN is congenital
Several cases of MLN associated with fibroplasia
What is spasmus nutans?
There is no nystagmus with both eyes viewing, but when one eye is occluded, nystagmus develops in both eyes, with the fast phase toward the uncovered eye
A rare constellation of ocular oscillation, head nodding, and torticollis that begins in infancy (usually between 4 and 18 months of age) and disappears in childhood (usually before 3 years of age)
The nystagmus is generally bilateral (but it can differ in each eye and may even be strictly monocular), and it oscillates in horizontal, torsional, or vertical directions
Spasmus nutans may sometimes be mimicked by tumors of the optic nerve, chiasm, or third ventricle
What is acquired pendular nystagmus?
May reflect brainstem or cerebellar dysfunction or both
It occurs in patients with vascular or demyelinating disease.
In the latter, it has been regarded as a sign of cerebellar nuclear lesions
Multivectorial and usually associated with head tremor
Marked dissociation between the two eyes often exists and may not correlate with differences in visual acuity from coexisting optic neuropathy
Despite the dissociation, the oscillations of the two eyes are phase locked, even when there is a difference in their frequencies
What is acquired horizontal jerk nystagmus?
Vestibular
We generally delimit vestibular nystagmus as being consequent to dysfunction of the vestibular end-organ, nerve, or nuclear complex within the brain stem
It is a horizontal-torsional or purely horizontal primary-position jerk nystagmus with a linear slow phase
The nystagmus intensity increases with gaze toward the fast phase (obeying Alexander’s law); it decreases and, with central lesions, may reverse directions upon gaze toward the direction of the slow phase
The symptom of vertigo usually coexists
Acute lesions of the cerebellar flocculus (the vestibulocerebellum) can produce a similar nystagmus
Cases of discrete cerebellar infarction are quite rare
Nystagmus may accompany episodic attacks of ataxia
What is gaze evoked nystagmus?
Gaze-evoked nystagmus is elicited by the attempt to maintain an eccentric eye position, and it is the most common form of nystagmus encountered in clinical practice
Patients recovering from a central gaze palsy show a phase in which lateral gaze movement is possible but cannot be maintained in the deviated position; that is, the eyes drift back slowly toward primary position
What are three types of nystagmus that are considered normal phenomena?
Fatigue Nystagmus (extreme gaze position or for a time exceeding 30 seconds)
Unsustained end point nystagmus (few beats over the recommended degrees)
Sustained end point nystagmus
(30 degrees or less is generally the sweet spot)
What is torsional nystagmus?
A purely torsional nystagmus never occurs with vestibular end-organ disease the term “rotary nystagmus” is used interchangeably
When of small amplitude, torsional nystagmus may reflect a medullary lesion
Larger amplitude torsional nystagmus may be congenital, but when it is acquired it often indicates diencephalic (thalamic) involvement, in which case it is the underlying pattern in see-saw nystagmus
What is periodic alternating nystagmus?
An extraordinary ocular motor phenomenon in which a persisting horizontal jerk nystagmus periodically changes directions
May be congenital or acquired
What are some characteristics of congenital periodic alternating nystagmus?
May be associated with albinism
Has the slow-phase waveform of an increasing velocity exponential
Usually lacks the well-defined stereotypes periodicity seen in acquired PAN
Periodicity is markedly influenced by changes in gaze position, supporting the hypothesis that the PAN is a result of a temporal shift in the null zone
What is downbeating nystagmus?
Nystagmus gaze position with the fast phase beating in a downward direction
Do patients with brainstem disease or drug intoxications have downbeating nystagmus?
No
Usually lack gaze-evoked downward nystagmus despite nystagmus in all other fields of gaze
What is a major cause of downbeating nystagmus?
Craniocervical junction, such as arnold chiari malformations
Could also be spinocerebellar degeneration (correctable)
*difficult to ascertain if it is the most common cause
Can downbeat nystagmus coexist with PAN?
Yes, both can be suggestive of an abnormality of the craniocervical junction
A variety of miscellaneous conditions have also been reported to produce downbeat nystagmus
Examples: anticonvulsant, alcohol, and lithium intoxication; magnesium deficiency; B12 deficiency; brain stem encephalitis; alcoholic cerebellar degeneration; dolichoectasia of the ventral artery; and vertebral artery occlusion (systemic things can affect the central system too)
What is upbeating nystagmus?
Fast phase beating upward
Rarely reflects drug intoxication
Less common
Most often, the nystagmus is acquired and indicates structural disease, usually of the brain stem
Could be a result of meningitis, Wernicke’s encephalopathy, or organophosphate poisoning (site of lesion unknown)
With convergence, upbeat may enhance or convert to downbeat
The slow-phase waveform is usually linear but may be an increasing-velocity exponential
What is rebound nystagmus?
Direction of gaze-evoked horizontal nystagmus
During sustained ocular deviation or a horizontal gaze-evoked nystagmus that, on refixation to primary position, transiently beats in the opposite direction
The sign is often present in patients with cerebellar disease
Can schwannomas result in obscure clinical vestibular manifestations?
Yes, because they are slow growing
Vestibular nystagmus beating contralateral to the lesion may be present, particularly if fixation is eliminated
As the tumor expands to compress the brain stem, a slow, gaze-evoked ipsilateral nystagmus is often added
