Transcript AHD - Neuro-opthalmology - V. Patel

Overview of NYSTAGMUS
Vivek Patel MD
OBJECTIVES
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Definition, description
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Neuroanatomical basis
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Instrinsic localizing value
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Representative cases
DEFINITION
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Disorder of ocular motor instability resulting in
spontaneous, involuntary, rhythmic oscillations
of the eyes
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Congenital vs. acquired
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“jerk” nystagmus vs. pendular
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“true” nystagmus vs. nystagmoid movements
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Conjugate vs. disconjugate vs. dissociated
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Trajectory may be horizontal, vertical, torsional,
or mixed
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Description of amplitude, frequency, velocity,
and intensity
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may vary with changes in gaze position
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May be influenced by the integrity of the
afferent visual system
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May exhibit a “null” point
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3 main mechanism of maintaining steady
gaze:
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1) fixation: a) prevent retinal image drift
b) suppress unwanted saccades
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2) VOR
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3) eccentric gaze holding
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Pulse (phasic) and step (tonic) outputs must be
balanced for appropriate gaze-holding.
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Significant cerebellar (vermis) calibration
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Horizontal: phasic = PPRF
tonic = NPH, MVN = neural integrators
Vertical: phasic = riMLF
tonic = iNC = neural integrator
NEUROANATOMICAL BASIS
Leigh & Zee, Neurology of Eye Movements, 3rd ed., 1998
Not always a sign of disease…
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Physiological:
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Usually conjugate
Preserves clear vision during self-rotation
unsustained end-point nystagmus
Vestibular nystagmus (brief sustained rot.)
OKN (visually driven….uses pursuit mech.)
CHILDHOOD NYSTAGMUS
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Congenital nystagmus:
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usually recognized in first few months of life – life long
May have good vision or poor vision
Most often occurs in isolation (motor), but may be associated
with 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 tested
monocularly
 Manifest latent nystagmus:
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Present even when both eyes are open
Loss of peripheral fusion
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Monocular nystagmus of childhood:
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Usually monocular, vertical, low amplitude oscillation
Eye with nystagmus may have afferent visual dysfunction
Requires neuroimaging (chiasmal glioma)
Spasmus Nutans:
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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
ACQUIRED NYSTAGMUS
PERIPHERAL VS. CENTRAL
VESTIBULAR NYSTAGMUS
PERIPHERAL
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Severe vertigo
Days to weeks duration
Hearing loss, tinnitus
associated
Usually horizontal with
torsion
Very rarely purely vertical or
torsional
Dampened with visual
fixation
Commonly peripheral
vestibular organ dysfunction:
labyrynthitis, meniere’s
CENTRAL
• None or mild vertigo
• Often chronic
• May be purely vertical or
torsional
• 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 central
nystagmus
 Inability to maintain eccentric gaze
 “leaky integrator” -- miscalibration between pulse
and step inputs
 Symmetric
 cerebellar flocculus implicated
 Age, anti-convulsant therapy, alcoholic
degeneration, stroke, demyelination
 Baclofen effective
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Downbeat nystagmus:
Defect in vertical gaze holding
 Asymmetric inputs from vertical semi-circular
canals produce upward slow drift of eyes
 Defect in fastigial nuclei calibration
 Secondary downward corrective fast phase
 Obeys Alexander’s law
 Localizes to cervico-medullary junction
 Arnold-Chiari malformation
 Treatment with baclofen, clonazepam, base-out
prisms
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Upbeat nystagmus:
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Present in primary position or upgaze
Classically localizes to a lesion of anterior cerebellar
vermis
More generally implicates posterior fossa disease
Etiologies include stroke, cerebellar degeneration,
demyelination, toxic exposures
Periodic alternating nystagmus:
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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
•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:
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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:
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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
Acquired pendular nystagmus:
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Can be vertical, horizontal, torsional, or any
combination (usually one predominates)
Usually disconjugate or dissociated
Oscillopsia ++
MS, whipple’s, oculopalatal myoclonus
Combination of afferent dysfunction and
cerebellar calibration
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Oculopalatal myoclonus:
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Vertical pendular eye movements associated with rhythmic
upward movement of palate
Caudal brainstem pathology: red nucleus, inferior olive, and
dentate nuc.
Convergence-retraction nystagmus:
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Commonly associated with dorsal midbrain syndrome
May be associated with other Parinaud’s 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
SUMMARY
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Recognize physiologic vs. pathological
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Appropriate characterization important
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Presence of nystagmus may correlate with significant
afferent visual dysfunction
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Recognition of nystagmus may facilitate subsequent
neurological or medical investigations (know where to
look)
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Treatment options do exist