AHD - Neuro-opthalmology - V. Patel - NYSTAGMUS

8/11/2019 AHD - Neuro-opthalmology - V. Patel - NYSTAGMUS

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Overview of NYSTAGMUS

Vivek Patel MD


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OBJECTIVES

Definition, description

Neuroanatomical basis

Instrinsic localizing value

Representative cases


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DEFINITION

Disorder of ocular motor instability resulting inspontaneous, involuntary, rhythmic oscillationsof the eyes

Congenital vs. acquired

jerk nystagmus vs. pendular

true nystagmus vs. nystagmoid movements


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Conjugate vs. disconjugate vs. dissociated

Trajectory may be horizontal, vertical, torsional,

or mixed

Description of amplitude, frequency, velocity,

and intensity

may vary with changes in gaze position

May be influenced by the integrity of theafferent visual system

May exhibit a null point


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3 main mechanism of maintaining steady

gaze:

1) fixation: a) prevent retinal image drift

b) suppress unwanted saccades

2) VOR

3) eccentric gaze holding


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Pulse (phasic) and step (tonic) outputs must be

balanced for appropriate gaze-holding.

Significant cerebellar (vermis) calibration

Horizontal: phasic = PPRF

tonic = NPH, MVN = neural integrators

Vertical: phasic = riMLF

tonic = iNC = neural integrator


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NEUROANATOMICAL BASIS

Leigh & Zee, Neurology of Eye Movements, 3rded., 1998


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Not always a sign of disease

Physiological:

Usually conjugate

Preserves clear vision during self-rotation

unsustained end-point nystagmus

Vestibular nystagmus (brief sustained rot.)

OKN (visually driven.uses pursuit mech.)


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CHILDHOOD NYSTAGMUS

Congenital nystagmus:

usually recognized in first few months of lifelife long

May have good vision or poor vision

Most often occurs in isolation (motor), but may be associatedwith albinism, LCA, achromatopsia, or optic atrophy

Uniplanar, horizontal trajectory irrespective of gaze position

No oscillopsia Reversal of OKN direction

Exponential increase in slow phase velocity

Conjugate

Null point (may have resultant head turn)

Amplified by attempted fixation (distant) Dampened by convergence and darkness

Absent in sleep

Association with esotropia


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Latent nystagmus:

Usually appears within first few months of life Horizontal jerk nystagmus appearing only

under monocular viewing conditions

Fast phase beats away from occluded eye

Strong association with esotropia Usually poor stereopsis

May explain subnormal visual acuity testedmonocularly

Manifest latent nystagmus:

Present even when both eyes are open

Loss of peripheral fusion


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Monocular nystagmus of childhood:

Usually monocular, vertical, low amplitude oscillation Eye with nystagmus may have afferent visual dysfunction

Requires neuroimaging (chiasmal glioma)

Spasmus Nutans:

Asymmetric or monocular low-amplitude oscillations

May be horizontal, vertical or torsional

Head nodding

Torticollis or abnormal head posture

Begins in infancy, usually resolved by age 3 to 5

Requires neuroimaging


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ACQUIRED NYSTAGMUS


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PERIPHERAL VS. CENTRAL

VESTIBULAR NYSTAGMUS

PERIPHERAL

Severe vertigo

Days to weeks duration

Hearing loss, tinnitusassociated

Usually horizontal withtorsion

Very rarely purely vertical ortorsional

Dampened with visualfixation

Commonly peripheralvestibular organ dysfunction:labyrynthitis, menieres

CENTRAL

None or mild vertigo

Often chronic

May be purely vertical ortorsional

visual fixation usually has no

effect

Etiologies commonly

vascular, demyelination,pharmacologic, toxic

Downbeat, upbeat, torsional


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Gaze evoked nystagmus:

One of the most common forms of centralnystagmus

Inability to maintain eccentric gaze

leaky integrator -- miscalibration between pulseand step inputs

Symmetric

cerebellar flocculus implicated

Age, anti-convulsant therapy, alcoholicdegeneration, stroke, demyelination

Baclofen effective


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Downbeat nystagmus:

Defect in vertical gaze holding

Asymmetric inputs from vertical semi-circularcanals produce upward slow drift of eyes

Defect in fastigial nuclei calibration Secondary downward corrective fast phase

Obeys Alexanders law

Localizes to cervico-medullary junction

Arnold-Chiari malformation Treatment with baclofen, clonazepam, base-out

prisms


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Upbeat nystagmus:

Present in primary position or upgaze

Classically localizes to a lesion of anterior cerebellarvermis

More generally implicates posterior fossa disease

Etiologies include stroke, cerebellar degeneration,demyelination, toxic exposures

Periodic alternating nystagmus:

Horizontal oscillation characterized by a periodic reversal

in the direction of nystagmus due a shift in the null point Duration of cycles from 30 seconds to 6 minutes

Classically a lesion of the cerebellar nodulus

MS, drugs, ethanol, paraneoplastic syndromes

Baclofen effective


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Bruns nystagmus:

associated with CPA tumors

high frequency, low amplitude

nystagmus (fast-phase away from lesion)

low frequency, large amplitude

nystagmus on ipsilateral gaze (fast phase

toward lesion)

shift from eye movement response to

vestibular imbalance to that of defective

gaze holding


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See-saw nystagmus:

Disconjugate vertical nystagmus (pendular vs. jerk)

Upward moving eye intorts while downard eye extorts Localizes to lesions of diencephalon

Visual fields may be useful (disruption of afferents to cerebellum)

Ocular flutter/opsoclonus:

Burst-like, incoordinated saccadic excursions with high frequency,low amplitude

No intersaccadic latency

Purely horizontal: ocular flutter Multiplanar: opsoclonus

Reflect pause cell dysfunction (pons)

Must consider paraneoplastic etiology: SCC of lung, ovarian,breast CA

Neuroblastoma in children


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Acquired pendular nystagmus:

Can be vertical, horizontal, torsional, or any

combination (usually one predominates) Usually disconjugate or dissociated

Oscillopsia ++

MS, whipples, oculopalatal myoclonus Combination of afferent dysfunction and

cerebellar calibration


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Oculopalatal myoclonus:

Vertical pendular eye movements associated with rhythmicupward movement of palate

Caudal brainstem pathology: red nucleus, inferior olive, anddentate nuc.

Convergence-retraction nystagmus:

Commonly associated with dorsal midbrain syndrome

May be associated with other Parinauds findings

Not a true nystagmus: co-contraction of horizontal recti on

attempted upgaze Localizes to pretectal area, posterior commissure, INC

Pineal cyst or tumor, demyelination, stroke


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SUMMARY

Recognize physiologic vs. pathological

Appropriate characterization important

Presence of nystagmus may correlate with significantafferent visual dysfunction

Recognition of nystagmus may facilitate subsequent

neurological or medical investigations (know where tolook)

Treatment options do exist

AHD - Neuro-opthalmology - V. Patel - NYSTAGMUS

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