Eric R. Eggenberger

This chapter discusses the diagnosis, localization, and treatment of nystagmus. Despite most clinicians’ fear of nystagmus, it is a logical branch of neuro-ophthalmology, and an understanding of nystagmus provides the clinician with valuable information regarding this commonly encountered problem.

Classic Presentation

• This most commonly occurs in hypoxic ischemic encephalopathy, such as after rescue from cardio-pulmonary arrest.

• Sustained up- or downgaze in hypoxic-ischemic encephalopathy typically indicates a poor prognosis for general neurologic recovery.

• Sustained upgaze may be associated with sustained eye opening.

Red Flags

Beware drug overdose effects.

Beware of the possibility of seizure inducing abnormal eye movements after a central nervous system (CNS) insult, which can also occur in hypoxic-ischemic encephalopathy.

Beware locked-in syndrome with retained vertical gaze; the upgaze in locked-in syndrome is not sustained, but typically intermittent and voluntary because the patient is still conscious.

OCULAR BOBBING AND VARIANTS

Classic Presentation

• Ocular bobbing is a repetitive, vertical eye movement noted in coma, with fast downward deviation followed by slower return to primary position.

• Typical ocular bobbing denotes an abnormal response to vestibulo-ocular reflex (VOR) stimulation in addition to bobbing.

• The VOR may be checked with either head rotation or cold caloric stimulation.

• With an intact VOR in the comatose patient, the eyes deviate right with head movement left, and vice versa; the eyes deviate tonically (no resetting fast phase) toward the ear undergoing cold-water stimulation.

• Typical ocular bobbing indicates a destructive lesion of the pons and is a very poor prognostic sign for recovery.

Red Flags

Other variants of bobbing have very little localizing or prognostic value.

These variants include reverse bobbing (eyes demonstrating a slow downward movement followed by rapid return to primary) or dipping (slow or rapid upward movement followed by slow or rapid return to primary).

These variants of bobbing are associated with diffuse cerebral dysfunction and may result from any of several pathophysiologies including hypoxicischemic insult or drug overdose.

Beware locked-in syndrome, with a brainstem lesion that spares consciousness and vertical gaze; vertical eye movements in locked-in syndrome are volitional and not rhythmic but need to be specifically assessed because most locked-in patients are on a ventilator, nonverbal, and quadriplegic.

SUSTAINED LATERAL GAZE

Classic Presentation

• Sustained right or left gaze generally signifies any of three possibilities:

Gaze preference: indicates lesion of the ipsilateral hemisphere.

Supranuclear lesion: generally able to move the eyes to the opposite side with vestibular ocular reflex (either head rotation or cold caloric testing).

Gaze palsy: indicates contralateral brainstem lesion

Unable to move eyes into the opposite field of gaze with vestibular ocular reflex maneuvers.

• Seizure or postictal state: during the ictus, the eyes often deviate contralateral to a hemispheric seizure focus and may demonstrate nystagmus-like movements, then deviate ipsilateral to the focus in the postictal period.

Red Flag

Misdiagnosis of the actual pathophysiology may lead to inappropriate investigations.

PING-PONG GAZE

Classic Presentation

• Ping-pong gaze consists of rapid conjugate side-to-side eye movements with gaze shifting every several seconds.

• This typically indicates bilateral hemispheric lesions, most commonly stroke.

Red Flags

Beware more rapid eye movements deviating the eyes to one side, producing nystagmus-like movements related to seizure (lesion within the contralateral hemisphere). Following the seizure, the eyes may then deviate to the other side (ipsilateral to the seizure focus), but this will not be as rhythmic or predictable as ping-pong gaze.

Slower conjugate eye deviations with direction change every 1 to 3 minutes has been reported in hepatic encephalopathy.

Do not confuse with slower direction changing eye movements such as periodic alternating nystagmus.

SPONTANEOUS ROVING HORIZONTAL EYE MOVEMENTS

Classic Presentation

• Slow, conjugate, roving horizontal eye movements in coma are common and indicate the brainstem structures for horizontal gaze are intact.

• Generally only partial horizontal excursion

• Similar to the eye movements in light sleep

Red Flags

Needs to be distinguished from other horizontal gaze deviations in coma such as periodic alternating gaze deviation and ping-pong gaze

Spontaneous roving horizontal eye movements are generally smaller amplitude and less rhythmic or predictable.

PERIODIC ALTERNATING GAZE DEVIATION

Classic Presentation

• Conjugate periodic horizontal eye movements that change direction with an ~2-minute cycle

• Associated with persistent vegetative state or hepatic encephalopathy

Red Flag

Needs to be distinguished from the other periodic horizontal eye movements above by the slower cycle

VERTICAL PENDULAR OSCILLATIONS

Classic Presentation

• Rare, 2- to 3-Hz vertical oscillations

• Reported in association with pontine infarction

Beware locked-in syndrome, with a brainstem lesion that spares consciousness and vertical gaze; vertical eye movements in locked-in syndrome are volitional and not rhythmic but need to be specifically assessed because most locked-in patients are on a ventilator, nonverbal, and quadriplegic

BROAD CATEGORY 2: INDUCED NYSTAGMUS

CALORIC NYSTAGMUS

Classic Presentation

• This type of nystagmus is seen with cold or warm irrigation into the ear.

• “COWS,” refers to cold opposite, warm same; denotes the direction of the fast phase in an awake patient when cold or water is irrigated into the ear.

• Caloric testing is done in coma to help decide if the cause of coma is the brainstem or bilateral hemispheric dysfunction (the latter is much more common than the former as a cause of coma, e.g., post cardiac arrest hypoxic-ischemic encephalopathy).

• When cold caloric testing is done in a patient in coma, there is no fast phase (because the cerebral cortex is not functioning properly).

• If the brainstem components for generation of eye movements are intact, then there is a slow phase toward the side of cold irrigation (the eyes deviate toward the side of cold irrigation because there is no resetting fast phase).

Red Flag

If the brainstem components related to eye movements are damaged (the coma is likely related to brainstem dysfunction), then cold water irrigated into the ear produces no eye movements (same as cold water irrigation into a cadaver would produce) or there are abnormal movements, such as internuclear ophthalmoplegia

OPTOKINETIC NYSTAGMUS (OKN)

Classic Presentation

• OKN is a type of physiologic nystagmus induced by smooth movement of the environment across the retina.

• OKN consists of saccades and pursuit movements when stimulated by smaller rotating targets such as OKN drum or repeating pattern strip (e.g., a striped neck tie).

• OKN should be symmetric left- and rightward.

• OKN is diminished or absent when stimuli are rotated toward a temporal-parietal lesion [medial superior temporal (MST) area].

• OKN generation requires a combination of fairly good visual acuity and field; with poor visual acuity or a very constricted field, OKN may be lost. One cannot accurately discern the exact visual acuity and visual field from the responses generated by most OKN targets used at the bedside.

BROAD CATEGORY 3: DISSOCIATIVE EYE MOVEMENT ABNORMALITY

ABDUCTING NYSTAGMUS

The most common form of eye movement abnormality is abducting nystagmus associated with internuclear ophthalmoplegia (INO). Abducting nystagmus with INO likely results from Hering’s law applied to weakened adduction. The weakened adductor increased innervation to both eyes, and this produces overshoot in the intact contralateral abductor.

Classic Presentation

• Usually presents with diplopia and oscillopsia, whereas occasional patients report gaze-evoked oscillopsia only

Red Flag

If abducting nystagmus is present on exam, carefully observe horizontal saccades to look for an associated INO; adduction paresis may not be evident with simple assessment of versions, and may only be apparent as a slowing of the adducting saccade.

MONOCULAR NYSTAGMUS

Classic Presentation

• Often pendular

• Generally indicative of upper brainstem-midbrain disease

• In adults, acquired monocular pendular nystagmus often related to multiple sclerosis

• May be highly asymmetric rather than absolutely unilateral/monocular

• Monocular oscillopsia

• May be associated with other ocular motor symptoms such as diplopia

Red Flag

Beware the small amplitude monocular intermittent “shimmering” seen in children with ipsilateral anterior pathway gliomas.

MONOCULAR SHIMMERING NYSTAGMUS OF ANTERIOR VISUAL PATHWAY LESIONS

Classic Presentation

• Onset in childhood

• Often very small amplitude

• May be intermittent

• Indicative of anterior pathway lesion, most commonly optic nerve glioma

Red Flags

May be confused with other forms of monocular nystagmus

May be confused with spasmus nutans, but typically doesn’t have the head tilt/turn, binocular involvement (although often very asymmetric), or head nystagmus associated with spasmus nutans. Some authors feel these two disorders are difficult to differentiate, and advocate imaging in all suspected cases to rule out an anterior pathway glioma.

SPASMUS NUTANS

Classic Presentation

• Spasmus nutans presents in early childhood (usually in the first year)

• Classic triad includes asymmetric or monocular nystagmus, head tilt, and head shaking or head nystagmus.

• Nystagmus is small amplitude, pendular, rapid, and often highly asymmetric, and may change in amplitude and phase relationship between the two eyes over seconds to minutes.

• Typically spontaneously resolves with time (usually within 2 years of onset)

Red Flag