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11 Nystagmus and Saccadic Intrusions and Oscillations / CHAPTER 11 Nystagmus and Saccadic Intrusions and Oscillations Louis F. DeU'Osso and Robert B. Daroff Nystagmus Induced Nystagmus Nystagmus in Infancy Caloric Congenital Rotational Latent/Manifest Latent Positional Nystagmus Blockage Syndrome Optokinetic Acquired Drug- and Toxin-Induced Secondary to Visual Loss Special Anatomic Categories Spasmus Nutans Acoustic Neuroma Acquired Pendular Nystagmus (Adults) Lateral Medullary Syndrome Acquired Horizontal Jerk Nystagmus Albinism and Achiasma Vestibular Cerebellum Gaze-Evoked (Gaze-Paretic) Nystagmus Saccadic Intrusions and Oscillations Special Nystagmus Types Square-Wave Jerks/Oscillations Physiologic (End-Point) Square-Wave Pulses Dissociated Macro-Saccadic Oscillations Torsional Saccadic Pulses/Pulse Trains See-Saw Double Saccadic Pulses Convergence/ Convergence-Evoked Dysmetria Periodic Alternating Flutter Downbeat Flutter Dysmetria Upbeat Opsoclonus Rebound Myoclonus Circular, Elliptic, and Oblique Superior Oblique Myokymia Cervical Bobbing/Dipping Muscle-Paretic (Myasthenic) Voluntary "Nystagmus" Lid Epileptic The day of the last hypothesis would also be the day of NYSTAGMUS the last observation. An hypothesis which becomes dispossessed by new facts dies an honorable death; and Nystagmus, the rhythmic to-and-fro oscillation of the if it has called up for examination those truths by which eyes, has been regarded as enigmatic. In fact, the distin­ it is annihilated, it deserves a moment of gratitude. guished neuro-ophthalmologist Wilbrand once advised, Jacob Henle (1809-1885) "Never write on nystagmus, it will lead you nowhere."! Although technologic advances have permitted quan­ L. F. Dell'Osso: Departments of Neurology and Biomedical titative insights into nystagmus analysis, the clinician Engineering, Schools of Medicine and Engineering, Case Western Reserve University; and Ocular Motor N europhysiol­ should not be daunted. Many useful, often diagnostic, ogy Laboratory, Veterans Administration Medical Center, observations can be made by physical examination Cleveland, Ohio alone. Figures 11-1 and 11-2 are examples of one con­ R. B. Daroff: Department of Neurology, Case Western Re­ venient method of diagramming nystagmus. Also, nys­ serve University; Medical Affairs, University Hospitals of Cleveland, Cleveland, Ohio tagmus can be further described when the globes are inspected under slit-lamp magnification, or when the See Chapter 11 for Glossary. fundus is viewed. 369 370 / NEURO-OPHTHALMOLOGY A B Nystagmus has traditionally been divided into two o types on the basis of the clinical impression of the wave­ form. Thus, if the eyes appeared to oscillate with "equal R 0 o --?l speed" in either direction, it was called "pendular" nys­ o tagmus; if movement in one direction was faster than in the other, it was called "jerk" nystagmus. True pendular c o nystagmus is sinusoidal, whereas jerk nystagmus has a slow phase away from the object of regard, followed by R � __ l R--"7 � __ l a fast (saccadic) phase toward the target. The direction of the fast component, by convention, defines the nys­ tagmus direction. These criteria can often be assessed only by accurate recordings. Nystagmus should be de­ Fig. 11-1. Simple diagrammatic method for depicting nys­ scribed not only by its waveform and direction but also tagmus. The velocity of the nystagmus phases (two arrow­ by its amplitude (A) and frequency (F), the product of heads) are equal (i.e., pendular). Jerk nystagmus (single ar­ which is intensity (I). The examiner should also note rowhead) points in direction of fast phase. Heavy lines the positions of gaze in which the nystagmus occurs and indicate more intense nystagmus. A. Pendular nystagmus in whether the intensity changes with gaze direction. Jerk primary position and up or down, converting to jerk on lateral gaze. B. First-degree jerk nystagmus present only on left nystagmus is usually accentuated in amplitude upon lateral gaze. C. Second-degree jerk nystagmus beating left­ gaze in the direction of the fast component, a character­ ward in primary position and increasing on left gaze. D. Third­ istic referred to as Alexander's law.2 degree leftward jerk nystagmus. The fieldof gaze in which nystagmus intensity is mini­ mal is termed the "null zone" (see Fig. 11-12). The "neutral zone" is that eye position in which a reversal This chapter is a coalescence of the traditional of direction of jerk nystagmus occurs and in which no neuro-ophthalmologic approach to nystagmus diagno­ nystagmus, any of several bidirectional waveforms, or sis and the impact of the newer capabilities of elec­ pendular nystagmus is present. The null and neutral tronic eye movement recording 'and mathematical "bi­ zones usually overlap; however, several cases have been , omodeling.' recorded where they do not. Eye movement recordings have allowed definition of Based on quantitative eye-movement recordings, we 47 types of nystagmus (Table 11-1) and new insights have identifiedthree underlying defects in the slow eye into their pathophysiology. For precise analysis, special movement (SEM) subsystem (see Chapter 9) that pro­ recording techniques are necessary, such as infrared, duce nystagmus: magnetic search-coil, or video recording systems, which can faithfully reproduce the eye-movement trajectories 1. High gain instability. In some persons, because of and provide accurate information on eye position with­ abnormally high gain in the SEM subsystem, a run­ out drift or noise. For quantitative purposes, all systems away (increasing velocity) movement or a pendular should record by way of direct current, with a bandwidth oscillation is evoked. In this chapter, the term high of 100 Hz. The eyes should be recorded separately in gain can also imply excessive delay for the gain pres­ horizontal, vertical, and (if possible) torsional direc­ ent (i.e. , the control loop may have a normal gain, tions, with the tracing analogs written on rectilinear but an increased delay). Control theory suggests how graph paper. Recording should be performed during particular changes in gain can result in either a pen­ fixationof visible targets and sometimes in the dark with dular or a jerk nystagmus. Pendular nystagmus can eyes open (see Chapter 9). For detailed quantitative be congenital or acquired, whereas horizontal jerk analysis, the data should be digitized at 200 Hz or nystagmus with slow phases of increasing velocity higher. usually is associated with congenital nystagmus; how­ ever, the latter may result from an Arnold-Chiari malformation.3 Vertical nystagmus with an exponen­ tial slow phase of increasing velocity may be second­ Amplitude ;. � ;- ary to acquired cerebellar disease.4 fine moderate gross 2. Vestibular tone imbalance. The nystagmus ofvestibu­ Frequency >----7 » > ») ) lar tone imbalance results from the imposition of slow moderate fast asymmetric vestibular input on an inherently normal -,-----..; Horizontal-Rotary )) horizontal gaze generator. This asymmetric input oc­ )- curs if one vestibular apparatus (labyrinths, nerve, Fig. 11-2. Nystagmus diagrams can be detailed and com­ and brain stem nuclei) functions abnormally or if plex if one uses these symbols. both sides are asymmetrically defective. The nystag- CHAPTER 11: NYSTAGMUS AND SACCADIC INTRUSIONS AND OSCILLATIONS / 371 TABLE 11-1. Forty-seven Types of Nystagmus* Acquired Gaze-evoked Pseudospon�us "Fixation" Deviational Induced Anticipatory Gaze-paretic Rebound Induced "Neurasthenic" Reflex Arthrokinetic "Seducible" Baer's Induced "Setting-in" See-saw Somatosensory Horizontal Somatosensory Associated Induced Induced Induced Prov oked Spontaneous Stransky's Intermittent vertical Stepping around Audiokinetic Jerk Apparent! real Induced Latent/manifest latent Induced Bartels' Monocular "fixation" Somatosensory Induced Unimacular Torsional Bruns' Lateral medullary Rotary Centripetal Lid Uniocular Cervical Miner'st Upbeat Neck torsion Occupational Vertical Vertebrobasilar art ery insufficiency Muscle-paretic Vestibular Circular/elliptic/oblique Myasthenic A(po)g eotropic/geo tropic Alternating windmill Optokinetic Alternating current Circumduction Induced Bechterew's Diagonal "Kinetic" Caloric/ caloric-after Elliptic "Optic" Compensatory Gyratory Optomotor Electrical/faradic/galvanic Oblique Panoramic Head-shaking Radiary "Railway" Induced Congenital Sigma L- "Fixation" "Train" Labyrinthine Hereditary Optokinetic after­ Perverted Convergence Induced Pneumatic/compression Convergence-evoked Postoptokinetic Positional/alcohol Dissociated Reverse postoptokinetic Positioning Disjunctive Pendular Post rotational Downbeat Talantropia Pseudocaloric Drug-induced Periodic/aperiodic alternating Rotational/perrotary Barbiturate Alternans Secondary phase Bow tie Physiologic Induced End-point Epileptic Fatigue Ictal Pursuit after- Flash-induced Induced Flicker-induced Pursuit-defectt Induced * Synonyms and other terms indented under either the preferred or the more inclusive designation; some nystagmus types may be acquired or congenital; quoted terms are erroneous or nonspecific. t May not ex ist. mus recording always shows a linear (straight line) a passive movement resisted by the viscous forces of slow phase, reflecting a persistent tone to drive the orbital soft tissues. The defect may reside in the brain eyes toward the side of the relatively damaged vestib­ stem "neural integrator" or its connections (such as ular apparatus. The slow-phase amplitude is reduced in the cerebellum), which mediate eye deviation. This by fixationand enhanced by darkness,
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