General
- Definition:
- Involuntary rhythmic oscillation of eyes that is conjugate (both eyes doing the same)
- occurring with the eyes in the primary position or with ocular deviation.
- Direction defined by: direction of fast (cortical) component
- Fast component: is NOT the ABNORMAL component
- Slow component: the true labyrinth-stimulated movement
- Horizontal nystagmus: sedatives or AEDs
- Vertical nystagmus: posterior fossa pathology
3 mechanisms that normally hold gaze still
Visual fixation
- Vergence
Vestibulo-ocular reflex
- A unique characteristic of peripheral vestibular nystagmus is the dampening effect on the nystagmus by visual fixation, which is in contrast to central vestibular nystagmus
- Because of the disruption of the vestibular input into the neural integrator which routes the signal to the contralateral paramedian pontine reticular formation (PPRF), the resulting nystagmus has slow-phase toward the side of the problematic vestibular system.
- The nystagmus follows Alexander's law
- Spontaneous nystagmus that occurs after an acute unilateral vestibular loss.
- The first element says that spontaneous nystagmus after an acute vestibular impairment has the fast phase directed toward the healthy ear.
- The second element says nystagmus is greatest when gaze is directed toward the healthy ear, is attenuated at central gaze and may be absent when gaze is directed toward the impaired ear.
- The third element says that spontaneous nystagmus with central gaze is augmented when vision is denied.
- This became apparent with the implementation of electrographic testing.
- Generally, peripheral vestibular nystagmus follows a horizontal-torsional pattern, which is in contrast to the purely vertical or torsional nystagmus seen in central vestibular nystagmus.
- Difference between peripheral and central nystagmus
Clinical features/symptoms | Peripheral | Central |
Severity of Vertigo | Typically more severe | Usually mild |
Purely Horizontal Nystagmus without torsion | Rare | Common, could be present |
Mixed Nystagmus (horizontal + torsional) | Common | Uncommon |
Duration of symptoms | Recurrent, self-limiting episodes; clearly defined in time | Chronic |
Tinnitus/Hearing Loss | Common | Uncommon |
Purely vertical or torsional nystagmus | Rare | Typically diagnostic |
Visual Fixation | Dampens nystagmus | No change |
Dix-Hallpike | 1. Time: 2–20 sec before onset of nystagmus | 1. Time: immediate onset of nystagmus |
ㅤ | 2. Duration: <1 min | 2. Duration: > 1 min |
ㅤ | 3. Fatigability: yes with repetition | 3. Fatigability: no |
Common causes | Labyrinthitis, Meniere disease, trauma, toxicity (aminoglycosides, phenytoin, phenobarbital, quinine, carbamazepine, salicylates) | Demyelination (MS), vascular (cerebellar infarction/hemorrhage, vertebrobasilar insufficiency) |
- Caloric reflex test (See Brainstem death testing)
- Warm water (> 44 °C):
- Endolymph in the ipsilateral horizontal canal rises, causing an increased rate of firing in the vestibular afferent nerve.
- This situation mimics a head turn to the ipsilateral side.
- Both eyes will turn toward the contralateral ear, with horizontal nystagmus (quick horizontal eye movements) to the ipsilateral ear.
- Cold water (< 30 °C)
- The endolymph falls within the semicircular canal, decreasing the rate of vestibular afferent firing.
- This situation mimics a head turn to the contralateral side.
- The eyes then turn toward the ipsilateral ear, with horizontal nystagmus to the contralateral ear.
Eccentric gaze
- Holding mechanism
- Required because
- Once the eyes reach eccentric orbital position, the tissue suspending the globe pulls the eyes back to the centre due to inherent elastic properties, the neural integrators must generate additional signal after the velocity command to sustain the eyes in eccentric orientation.
- The neural integrators accomplish this function
- Involves a number of areas of the brainstem called the neural integrator.
- Horizontal gaze neural integrator:
- Nucleus prepositus hypoglossi (NPH) and
- Medial vestibular nuclei.
- Vertical and torsional gaze neural integrator
- Interstitial nucleus of Cajal.
- Other components of the neural integrator include
- Flocculus
- Nodulus of the cerebellum.
- All of these components are necessary to sustain eccentric gaze. When any part of the mechanism fails, defective gaze-holding manifests as nystagmus (gaze-evoked nystagmus).
Mechanism
Peripheral (vestibular) nystagmus
- Physiological stimulation of a labyrinth produces nystagmus
- In the plane of that labyrinth
- A conjugate slow movement away from the stimulated labyrinth followed by a quick component in the opposite direction.
- Pathological nystagmus:
- Is due to alteration of the balance of tonic activity in the labyrinth
- Damage to the left vestibular labyrinth or nerve → Unopposed Rt-sided tonic activity → Slow phase going away from the right → fast phase towards the right
- Nystagmus that is indistinguishable from that produced by right-sided stimulation.
Central-induced nystagmus
- Due to interruption of central vestibulo-ocular pathways is distinctive in the following two respects:
- Direction of central-induced nystagmus is less predictable and may vary with the subject's direction of gaze; and
- Visual fixation, which inhibits peripheral vestibular nystagmus, does not inhibit nystagmus due to central lesions.
2 clinical types
- Jerk (named for fast phase) or pendular, variable amplitude and frequency, and can be worsened or improved by gaze position, fixation, or covering one eye (latent).
- Saccadic intrusions" or "saccadic oscillations": fast, back to back (without intersaccadic interval)" eye movements driving the eye off the visual target.
Classification of nystagmus by location
Type | Subtype | Description |
Monocular (not true nystagmus | Internuclear ophthalmoplegia | Horizontal gaze nystagmus that occurs in the abducting eye contralateral to side of MLF lesion |
ㅤ | Heimann-Bielschowsky phenomenon | Long-standing visual loss can lead to low frequency, monocular vertical pendular/jerk nystagmus in affected eye. |
ㅤ | Spasm nutans | Triad of nystagmus (vertical, pendular), head nodding and torticollis. |
ㅤ | Superior oblique myokymia | Periodic intorsional oscillation lasting <10 s, multiple per day. |
Binocular (Physiological) | End-point nystagmus | Fine jerk nystagmus seen in extremes of gaze. |
ㅤ | Optokinetic nystagmus | Jerk nystagmus elicited by repetitive stimuli moving across the visual field (slow phase in direction of target). |
ㅤ | Vestibular (Caloric testing) | Vestibular nystagmus due to activation of vestibulo-ocular reflex in response to cold (fast phase in opposite direction) or warm water (fast phase in same direction as stimulus). |
Binocular (Pathological)—Dissociated | Convergence-Retraction nystagmus | Convergence-like movements associated with retraction of globe into orbit. Lesion in dorsal midbrain (Parinaud's syndrome). |
ㅤ | See-saw nystagmus | One eye elevates and intorts, the other depresses and extorts. Lesion optic chiasm or third ventricle, usually associated with bitemporal hemianopia. |
Binocular (Pathological)—Non-dissociated | Congenital nystagmus | As described previously. |
ㅤ | Upbeat nystagmus | Fast phase is upward, greatest amplitude in upgaze. Lesions of brainstem, cerebellar vermis, posterior fossa and drugs (phenytoin). |
ㅤ | Downbeat nystagmus | Fast phase is downward, usually greatest amplitude in downgaze. Caused by lesions in craniocervical junction or cerebellum. |
ㅤ | Rebound nystagmus | Jerk nystagmus in which the fast phase is in the direction of gaze, reverses with sustained gaze then increases in the direction of return to primary position. Lesion in cerebellum. |
ㅤ | Periodic alternating nystagmus | Jerk nystagmus where direction of the fast phase changes in cycles of 60–90 s. |
ㅤ | Gaze-evoked nystagmus (e.g., Bruns’) | Nystagmus is absent in the primary position. Bruns’ nystagmus is characterized by a slow, large amplitude (gaze paretic) nystagmus when looking toward the side of the lesion, and a rapid small amplitude (vestibular) nystagmus when looking away from the lesion. Lesion of cerebellopontine angle (vestibular schwannoma). |
Midbrain
- See-saw nystagmus
- Video
- A dysconjugate nystagmus
- One eye rises and intorts while the other eye falls and extorts..
- Also reported with chiasmal compression (occasionally accompanied with bitemporal hemianopia in parasellar masses)
- Convergence Nystagmoid (tectal plate)
- Not a true nystagmus
- Slow abduction of eyes followed by adducting (converging) jerks
- Associated with Parinauds
- Nystagmus retractorius (tegmentum)
- Co-contraction of all EOM
- May accompany convergence nystagmus
Pons
- Abducting nystagmus
- INO
- The contralateral eye to the lesion has an abducting nystagmus
- Hering's law as an explanation for it
- The medial rectus on the ipsilateral eye has increased innervation due to a lack of impulse traveling to it so the yoke muscle of the contralateral eye is overly stimulated
Ponto medullary junction
- Brun's nystagmus
- Combination of peripheral and central vestibular nystagmus
- Due to the involvement of 2 different neural pathways
- Cerebellar flocculi
- Peripheral vestibular components of the cerebellum
- Sequence
- Peripheral CN8 involvement:
- Initially
- Abnormal slow phase: towards the side of the lesion,
- Normal fast corrective phase: Away from lesion.
- Rapid, small amplitude nystagmus fast phase is directed away from the side of the lesion.
- Ipsilateral brainstem involvement
- Lesion expands → Cerebellar flocculus compression → the ability to hold ipsilateral eccentric gaze becomes impaired (slow phase goes back to neutral and fast phase directed towards ipsilateral gaze)
- The nystagmus is slower, with an increase in amplitude and change in direction towards the side of the lesion—
- Slow, large amplitude nystagmus towards the side of the lesion.
- Thus, this specific type of nystagmus consists of two simultaneous nystagmus:
- (1) Coarse, large amplitude, low frequency evoked on gaze ipsilateral to the lesion
- (2) Fine, low amplitude, high frequency evoked on gaze contralateral to the lesion.
- If the brainstem compression was severe enough the null position of the eye will be towards the side of compression.
- The head will turn to face the contralateral side so that the new null position is facing forwards when the head is turned.
- Disease
- Chiari malformation
- Cerebellar pontine angle tumors (e.g., acoustic neuromas or meningiomas) greater than 3.5 cm.
- Vestibular nystagmus
- Normal
- Vestibular apparatus sends impulses to the paramedian pontine reticular formation (PPRF).
- PPRF sends impulses that reach the ipsilateral lateral rectus muscle and the contralateral medial rectus muscle via the medial longitudinal fasciculus.
- Disease
- Any disturbance in the balance of vestibular input between the two sides will result in vestibular nystagmus with a slow component to the side opposite the lesion.
- This nystagmus is typically associated with a rotatory component. It may be induced by caloric stimulation or rotation of the head.
Medulla
- Upbeat nystagmus
- Lesion location
- Medullary
- Characterized by a
- Slow component in the downward direction
- Fast component in the upward direction.
- Unlike gaze-evoked upbeat nystagmus, which only occurs when the eyes are not in the primary position, true upbeat nystagmus is present in the primary position.
Post fossa (Vertical nystagmus)
- Down beat nystagmus
- Structure lesion @ cervicomeduallary junction-Foramen magnum
- Chiari 1
- P-fossa tumours
- Syringobulbia
- A type of central vestibular nystagmus characterized by involuntary, slow upward drifting of the eyes immediately followed by a fast, downward saccade
- Due to
- Disruption in the neuronal transmission between vestibulocerebellum, the anterior semicircular canals, and the ocular motoneurons
- Characterized by a slow component in the upward direction and a fast component in the downward direction.
- Unlike gaze-evoked downbeat nystagmus, which only occurs when the eyes are not in the primary position, true downbeat nystagmus is present in the primary position.
- Periodic alternating nystagmus (PAN) :
- Lesion in FM and cerebellum
- A horizontal jerk nystagmus that periodically (e.g., every 60 to 90 s) changes direction.
- Square wave jerks
- Macro square wave jerks, macro saccadic oscillations.
- Lesion in cerebellar pathways
- Comprise pairs of saccades that are directed away from and then back to fixation.
- Ocular myoclonus
- Lesion in myoclonic triangle (Dentato-rubro-olivary pathway)
Rebound nystagmus
- Rebound nystagmus is specific for cerebellar disease, although it is poorly localised within the cerebellum.
- Horizontal jerk nystagmus that is associated with cerebellar disease.
- A primary position nystagmus
- Provoked by prolonged eccentric gaze holding. It appears after the eyes are returned to primary position.
- It characteristically appears to fatigue and change direction when lateral gaze is sustained or when the eyes are returned to primary position.
- It essentially represents a type of gaze-evoked nystagmus that changes direction after sustained lateral gaze or after refixation to the primary position.
Gaze evoked nystagmus
- Gaze-evoked nystagmus occurs when an individual cannot maintain conjugate eye deviation away from the midposition.
- Aetiology
- Similar to that induced by drugs.
- Associated with brainstem or cerebellar disease
- Mechanism
- Eye is attempted to be kept at an Extreme position (eccentric gaze).
- Dysfunction of the neural integrator (as mentioned above)
- Thus, the eyes cannot be maintained at an eccentric orbital position and are pulled back toward primary position by the elastic forces of the orbital fascia.
- Then, corrective saccade moves the eyes back toward the eccentric position in the orbit.
- The result is a to-and-fro oscillation of the eyes involving a fast component in the direction of gaze and a slow component away.
- Clinical feature
- Conjugate lateral gaze is accompanied by a slow, involuntary drift of the eyes back to midposition, followed by a rapid corrective return of the eyes to the laterally located target.
- Gaze-evoked nystagmus is usually also associated with nystagmus on upgaze, but rarely is there downbeat nystagmus on downgaze.
- vs Gaze paretic nystagmus
Feature | Gaze-Evoked Nystagmus | Gaze Paretic Nystagmus |
Main Mechanism | Failure of central neural integrator | Weakness or fatigue of extraocular muscles, or incomplete recovery after gaze palsy |
Clinical features | In eccentric gaze, sustained or pathologic | After partial recovery from gaze palsy or with neuromuscular weakness |
Causes | Brainstem/cerebellar dysfunction, drugs, physiologic at extremes | Myasthenia gravis, Guillain-Barre, recent gaze palsy |
Drift Direction | Toward primary position (center) | Toward weak/paralyzed direction, then corrective saccade |
Relationship | General category of nystagmus | Subtype of gaze-evoked nystagmus |
Normal
Physiologic end-point nystagmus
- Observed on extreme lateral or upward gaze.
- When gazed evoked nystagmus occurs in normal patients it is called end point nystagmus
- Distinguished from pathological nystagmus by
- Symmetry on the right and left side and by the absence of associated neurologic signs.
Vestibular nystagmus (described above)
Optokinetic nystagmus
- A nonpathological nystagmus that develops normally when an individual attempts to count the stripes on a rotating drum or a moving cloth strip.
- Aka pendular nystagmus
- Elicited by moving a repetitive visual stimulus through the visual field.
- Slow phase of this nystagmus comprises a pursuit movement that follows the moving target.
- Fast phase comprises a saccade in the opposite direction.
- A lesion that involves the pursuit or saccadic pathways will disrupt this induced form of physiological nystagmus.
- In the presence of cerebellar disease, optokinetic nystagmus may become exaggerated, producing unusually large amplitudes of both the fast and the slow components.
Other types of nystagmus
- Drug induced nystagmus
- Most common type of nystagmus seen in clinical practice.
- Features
- Horizontal gaze-evoked nystagmus (either L or R)
- Common aetiology
- Alcohol
- Phenytoin (Dilantin),
- Phenytoin toxicity may be quantitated by the degree of associated nystagmus.
- Barbiturates.
- Barbiturate intoxication will cause degeneration of smooth pursuit movements, followed later by degeneration of saccadic eye movements.
- Severe barbiturate intoxication eliminates even caloric responses.
- Thus, the patient with absent caloric responses but an intact pupillary light reflex may be in a metabolic (barbiturate) coma.
- Spasmus Nutans
- A syndrome of infancy
- Benign disorder
- Typically resolves spontaneously when the child is 3 or 4 years old.
- Clinical triad of
- Head nodding,
- Nystagmus,
- The nystagmus is frequently monocular and variable.
- Head turning
Pseudo-nystagmus - “Nystagmoid” eye movements
Ocular bobbing
- Lesion in pontine tegmentum
- Where as pontine tectum lesion causes parinaud syndrome's convergence retraction nystagmus
- Rapid downward movements of the eyes with a slow return to the primary position.
- Opposite to upbeat nystagmus, which is slow down and fast up
Ocular dysmetria
- Defined as the conjugate overshoot of a target with voluntary saccades.
- The eyes appear to jerk back and forth because of repeated inaccuracies in saccadic movements intended to bring the target to the fovea.
- Characterized by a series of undershooting and overshooting saccades followed by diminishing oscillations until eye “hones in” on target (may be seen in Friedreich’s ataxia)
- Like limb dysmetria, it is associated with lesions of the cerebellar pathways.
Ocular flutter
- A series of small saccades with normal intervening movements that occur upon attempts at fixation.
Opsoclonus
- Characterized by repetitive, chaotic, saccadic movements that occur in all directions (dancing eyes), preventing fixation.
- Aetiology
- In an adult or older child, opsoclonus may be associated with a postinfectious encephalopathy.
- In younger children, opsoclonus may develop as a remote effect of neuroblastoma.
Ocular myoclonus
- Characterized by a continuous rhythmic oscillation of the eyes.
- Invariably accompanied by myoclonic movements of the branchial musculature, such as the palate, the pharynx, or the face.
- Associated structural lesions typically involve the myoclonic triangle, which comprises
- Red nucleus
- Ipsilateral inferior olive
- Contralateral dentate nucleus.
Ping-pong gaze (periodic alternating gaze)
- Periodic alternating gaze
- Eyes deviate side to side with frequency of ≈ 3-5 per second (pausing 2-3 secs in each direction). Usually indicates bilateral cerebral dysfunction
Windshield wiper eyes
- Non-localizing random roving conjugate eye movements
- Intact CN3 nucleus and medial longitudinal fasciculus
Convergence retraction nystagmoid in Parinauds syndrome
- Attempts to gaze upward, in this condition, elicit jerky bilateral eye movements of retraction or convergence or both.
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