Overview of NYSTAGMUS

1. Overview of NYSTAGMUS Vivek Patel MD

2. OBJECTIVES • Definition, description • Neuroanatomical basis • Instrinsic localizing value • Representative cases

3. DEFINITION • Disorder of ocular motor instability resulting in spontaneous, involuntary, rhythmic oscillations of the eyes • Congenital vs. acquired • “jerk” nystagmus vs. pendular • “true” nystagmus vs. nystagmoid movements

4. 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 the afferent visual system • May exhibit a “null” point

5. 3 main mechanism of maintaining steady gaze: • 1) fixation: a) prevent retinal image drift b) suppress unwanted saccades • 2) VOR • 3) eccentric gaze holding

6. 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

7. NEUROANATOMICAL BASIS Leigh & Zee, Neurology of Eye Movements, 3rd ed., 1998

8. 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.)

9. CHILDHOOD NYSTAGMUS • Congenital nystagmus: • 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

10. 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: • Present even when both eyes are open • Loss of peripheral fusion

11. 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

12. ACQUIRED NYSTAGMUS

13. PERIPHERAL VS. CENTRAL VESTIBULAR NYSTAGMUS • 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 PERIPHERAL • 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

14. 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

15. 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

16. Upbeat nystagmus: • 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: • 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

17. 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

18. 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

20. Acquired pendular nystagmus: • 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

21. Oculopalatal myoclonus: • Vertical pendular eye movements associated with rhythmic upward movement of palate • Caudal brainstem pathology: red nucleus, inferior olive, and dentate nuc. • Convergence-retraction nystagmus: • 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

22. SUMMARY • Recognize physiologic vs. pathological • Appropriate characterization important • Presence of nystagmus may correlate with significant afferent visual dysfunction • Recognition of nystagmus may facilitate subsequent neurological or medical investigations (know where to look) • Treatment options do exist