Nystagmus A Clinical Approach Abdullah El-Menaisy, MD, FRCS Neuro-ophthalmology & Investigation Service, Dhahran Eye Specialist Hospital, Dhahran, Saudi Arabia

Nystagmus is a rhythmic biphasic oscillation of the eyes

There are three main control mechanisms for maintaining steady gaze: Fixation Vestibulo-ocular reflex Gaze-holding system (neural integrator)

Mechanisms of Gaze Stability The visual fixation mechanism:      Detection of retinal image drift Programming of corrective eye movements Suppression of unwanted saccades The vestibulo-ocular reflex:   Compensates for head movements Gaze-holding mechanism:      Sustains eye at an eccentric position in the orbit against the elastic pull of the globe's suspensory ligaments and muscles

Failure of any of these control systems will cause disruption of steady fixation There are 2 types of abnormal fixation: Nystagmus Saccadic intrusions & oscillations The difference between them lies in the initial movement that disrupts fixation In nystagmus, it is a slow drift, while in saccadic intrusions and oscillations, it is a fast movement that moves the eyes off target

Classification of Nystagmus Age of onset: congenital, acquired Nature of movement: pendular, jerk Plane of movements: horizontal, vertical, torsional Effect of fixation block: latent, manifest, latent-manifest

Pendular, Jerk

Horizontal, Vertical, Torsional

Latent, Manifest

Types Congenital Nystagmus Spasmus nutans Monocular Vestibular Gaze-evoked Dissociated Periodic alternating Downbeat Upbeat Convergence retraction See-saw Drug-induced Optokinetic Nystagmus (OKN)

Congenital Nystagmus At birth or during 4 m after birth No oscillopsia Pendular, horizontal (may be rotary or rarely vertical) May have jerk properties in end gaze Remains horizontal in vertical gaze Has null point Dampens with convergence Exacerbates with fixation Shows reverse optokinetic response Associated with high refractive error including astigmatism

Congenital Nystagmus Etiology: Sensory: due to disorders of afferent visual pathway - optic nerve hypoplasia - ocular albinism - Leber’s congenital amaurosis Motor: due to efferent pathway disorder - sporadic, autosomal dominant, recessive, X-linked

Congenital Nystagmus Evaluation: Vision Pupils Fundus Refraction VEP,ERG Treatment: Glasses, contact lenses Prism to shift null point to primary gaze Surgery (kestenbaum) Botox injection

Spasmus Nutans Triad of: (1) nystagmus (2) torticollis (3) head nodding Starts between 4 - 14 m Almost always resolved by 5y Pendular of low amplitude & high frequency May be horizontal, vertical or rotary May be associated by optic pathway glioma Neuroimaging is important

Monocular Nystagmus Slow vertical pendular oscillations Due to severe monocular visual loss (Heimann-Bielschowsky phenomenon) Can appear several years after visual loss May resolve if vision is restored May be associated with chiasmal glioma Needs neuroimaging

Vestibular Nystagmus Peripheral vestibular nystagmus: Horizontal rotary Horizontal in different directions of gaze Amplitude increases when eyes move in the direction of fast phase (Alexander’s law) The fast phase is opposite to site of the lesion Patients fall towards the site of the lesion Associated with vertigo, hearing loss or vomiting Causes includes: labyrinthitis, vestibular neuritis, Meniere’s disease, migraine, benign positional vertigo (BPV)

Vestibular Nystagmus Central vestibular nystagmus: Pure torsional nystagmus Asymmetric Vertical in primary position Change direction in different gaze positions Causes include: pontine & cerebellar lesions (stroke, tumor, MS,…..)

Gaze-evoked Nystagmus Asymmetric in right & left gaze High amplitude (< 4 degrees) Unilateral gaze-evoked nystagmus may indicate cerebellar or brain stem lesion Gaze-evoked upbeat nystagmus commonly due to bilateral INO When presents in horizontal & upgaze, it signifies toxic metabolic process Brun’s nystagmus may be seen in cerebellopontine angle lesions

Gaze-evoked Nystagmus Causes: lesions in - medial vestibular nucleus - nucleus prepositus hypoglossi - cerebellum - peripheral vestibular pathway Physiological gaze-evoked nystagmus: - symmetric in different directions of gaze - has low amplitude

Dissociated Nystagmus Nystagmus of abducted eye with impaired adduction of contralateral eye Occurs in INO due to adaptive phenomenon that attempt to increase the innervation to the week adducting eye

Periodic Alternating Nystagmus (PAN) Acquired or congenital Change direction every 90 sec with a rest period of 5 -10 sec May be due to degenerative process of cerebellum May associate downbeat nystagmus or skew deviation Persists during sleep & remains horizontal in vertical gaze Baclofen ameliorates the acquired form while the congenital form can be corrected by large horizontal recti resection

Downbeat Nystagmus Craniocervical junction lesion Other causes are hypomagnesemia, thiamine & vit B12 deficiency, phenytoin, alcohol & lithium toxicity Congenital cases show spontaneous remission Treatment by clonazepam, gabapentin, baclofen. Prism therapy can help

Upbeat Nystagmus Due to midbrain, cerebellum or medullary lesions 2 types: (1) a course large amplitude nystagmus increases in upgaze (cerebellar vermis lesion) & (2) a small amplitude nystagmus in primary position (medullary lesion) Causes are MS, infarction, cerebellar degeneration & tumors Tobacco smoking can produce upbeat nystagmus in normal subjects when fixation is removed

Convergence Retraction Nystagmus It is not a true nystagmus (no slow phase) Convergent saccades in attempting upgaze In pretectal dysfunction Due to cofiring of horizontally & vertically acting EOM

See-Saw Nystagmus Pendular Spontaneous elevation & intorsion of one eye with depression & extorsion of the other eye and the cycle is reversed Usually due to sellar mass lesion Some patients display ½ see-saw cycle with corrective quick phase (hemi or jerk see-saw nystagmus). It is typically due to midbrain lesion Baclofen or clonazepam may help in treatment

Drug-induced Nystagmus Common In horizontal endgaze & upgaze and not in downgaze Symmetric & doesn’t fatigue Medications include: anticonvulsants, sedatives, barbiturates & phenothiazines Carpamazepine, phenytoin & lithium may produce downbeat nystagmus Acute alcohol intoxication can cause horizontal endgaze nystagmus (positional alcohol nystagmus)

Optokinetic Nystagmus (OKN) A physiological involuntary reflex Elicited by moving a striped tape or drum in front of the patient A slow phase in the direction of movement of tape or drum & a corrective fast phase in the opposite direction

Optokinetic Nystagmus (OKN) OKN is a diagnostic tool in: 1 - a reverse OKN is characteristic of congenital nystagmus 2 - preserved vertical OKN indicates intact vision in congenital nystamus 3 - asymmetric OKN indicates deep parietal lesion 4 - In malingerers, intact OKN means that vision is at least CF 5 - moving the tape downwards to elicit convergence retraction nystagmus in patients with Parinaud’s syndrome

Nystagmoid Eye Movements Not pure forms of nystagmus (no slow phase) Saccades interrupt fixation Represent disorder of saccades Includes: - Square wave jerks - Ocular dysmetria - Opsoclonus - Ocular flutter - Ocular bobbing - Superior oblique myokymia

Square Wave Jerks Horizontal saccades with intersaccadic interval Can be seen in normal individuals (> 9 jerks per min) Causes include: cerebellar disease, Schizophrenia, Parkinson’s disease

Opsoclonus Involuntary conjugate multidirectional saccades (saccadomania) occur without intersaccadic interval Associated with eye blinking, facial twitching, myoclonus & ataxia 50% of children with opsoclonus has neuroblastoma Responds to tumor removal, ACTH, prednisone, gamma globulin, plasmapheresis Other causes include: parainfectious cerebellitis or encephalitis, paraneoplastic disease, drug induced (amitriptyline, lithium, cocaine)

Ocular Flutter Horizontal saccades without intersaccadic interval (no vertical component) Can be associated with ocular dysmetria Has the same localizing value & differential diagnosis of opsoclonus

Ocular Bobbing Quick conjugate down movements followed by slow drift back to midline Some patients show movements in the opposite direction Reflects pontine dysfunction May be associated with horizontal gaze palsy Causes includes: stroke, tumors, toxic-metabolic conditions or inflammatory process

Superior Oblique Myokymia High frequency monocular oscillations produced by spontaneous firing of one SO muscle Idiopathic, but could be due to midbrain lesion Treatment by carbamazepine, bacolfen, propranolol Muscle surgery (SO tenotomy +/- IO resection or Harado-Ito procedure)

Nystagmus with Localizing Value Downbeat: cervicomedullary junction Upbeat: pons, midbrain See-saw: parrasellar, midbrain Convergence retraction: dorsal midbrain Spasmus nutans: chiasmal glioma

Evaluation History Visual acuity Inspection Cover test Ocular motility Saccade & pursuit VOR Pupils Fundus Electronystagmography

Evaluation History: Onset : Associated symptoms: Medications - Birth to 4 m: congenital - < 4 m: acquired Associated symptoms: - Oscillopsia: acquired nystagmus - Nausea & vomiting: peripheral vestibular disease - Diplopia, dysarthria, facial numbness, dysphagia: brain stem lesions Medications Similar condition in the family

Evaluation Inspection: Type of nystagmus: Pendular: slow phases are of equal velocity (no corrective saccades) Jerk: slow & fast phases (the direction is defined by the fast phase). In torsional nystagmus (direction is defined towards patient’s right or left shoulder)

Type

Plane

Fixation Block

Amplitude & Frequency

Evaluation History Visual acuity Inspection Cover test Ocular motility Saccade & pursuit VOR Pupils Fundus Electronystagmography

Videonystagmography Vestibular nystagmus: slow phase is linear Congenital nystagmus: slow phase shows increasing velocity Gaze paretic nystagmus: slow phase is declining

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Latent Nystagmus Congenital Induced by covering one eye Jerk Fast phase in the direction of the uncovered eye May be associated by congenital esotropia or DVD

Rebound Nystagmus Jerk When eyes turned from eccentric gaze to primary position, the eyes beat in the opposite direction for about 30 sec Occurs inn cerebellar disease

Pendular Nystagmus Eyes move back & forth with equal velocity Slow phases without jerk or fast component Horizontal, vertical, oblique, elliptical or circular May be dissociated when one eye has impaired vision Acquired pendular nystagmus in adults is most probably due to MS or brain stem infarction

Ocular Dysmetria During fixation the eyes overshoot (hypermetria) or undershoot (hypometria) then saccade back to fixation point A sign of cerebellar dysfunction (similar to limb dysmetria)