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Neuro-otology & Neuro-ophthalmology Clinical Techniques
Friday, November 05, 2004 10:46 AM Vestibulo-ocular reflex short latency reflex to generate eye movements that compensate for head rotations in order to preserve clear vision during locomotion. The most accessible gauge of vestibular function. Evaluation requires application of a vestibular stimulus and measurement of resulting eye movements. Describing Nystagmus Primary: only one direction of gaze Secondary: midline & direction of gaze Tertiary: in all directions of gaze Describe as: primary vs secondary vs tertiary Gaze evoked Horizontal /vertical / torsional components (whole multitude / facets that can be further described, refer to Baloh’s textbook) Clinical Scenarios Peripheral vestibular nystagmus Often suppressed by visual fixation, therefore maybe seen during fundoscopic examination in the dark. This is basis of Frenzel lenses (10+ diopter) which prevent fixation. Skew deviation & head tilt suggest a unilateral disturbance in otolith-ocular pathways. Usually occurs shortly after (otolith) vestibular loss, patients often perceive vertical as being tilted 10-30° towards the lesion side which diminishes when vestibular compensation takes place. *beware lateral medullary infarction can cause environmental tilt. Detection of unilateral vestibular deficits Usual exam with patient supine (finger-nose, dysdiadochokinesis, ballistic testing, heel-shin) will be normal but those that require vestibular input (walking, heel-toe, Unterberger) will be abnormal. Halmagyi head impulse Head shaking nystagmus Vibration induced nystagmus Tapping head nystagmus Detection of bilateral vestibular loss Dynamic visual acuity testing Especially useful for aminoglycoside and platinum toxicity. Detection of cerebellar problems Usual exam (finger-nose, dysdiadochokinesis, heel-shin etc) Ballistic testing Zee’s test Clinical Tests Eye movements Smooth pursuit tracking Eye movement tracking of a moving target Saccade testing Observe velocity, accuracy & latency of rapid eye movements from one target site to another. Hypometric versus hypermetric Square wave jerks Vertical saccade is slower than horizontal saccade. Example is progressive supranuclear palsy. Nystagmus Optokinetic nystagmus Eye movement response to an optokinetic stimulus Cerebellar lesion: absent response in direction of flag movement Reverses in congenital nystagmus. Spontaneous nystagmus Observe for fixation, stability and spontaneous nystagmus. Peripheral lesions reduces with visual fixation. Gaze evoked nystagmus Observe for nystagmus and gaze holding during eccentric gaze. Static positional nystagmus Observe for nystagmus during or after head position changes. Dix – Hallpike maneuver Observe for nystagmus after rapid positioning from the sitting to head hanging right or left position. Positive implies benign positional vertigo which is often correctable with Epley or Semont particle repositioning maneuvres. Caloric testing Head is at 30° from horizontal Brings horizontal semicircular canal into vertical and position of maximal sensitivity Each auditory canal stimulated for 30 sec at temp of 30° and 44°C (7° above & below body temp) with 5 minutes between each irrigation Cold stimulation: ipsilateral tonic deviation with nystagmus away Warm stimulation: nystagmus towards side of stimulation. Bilateral cold stimulation: tonic downward deviation with nystagmus upward Bilateral warm stimulation: tonic upward deviation with nystagmus downward. Clinical Tests of Vestibular Loss
Halmagyi head impulse test Entails horizontal (yaw plane) high acceleration head thrusts while patient maintains gaze on examiner. Look for a “catch-up” saccade when head is rapidly turned towards the lesion side. Reported to have 50% sensitivity and 100% specificity. Head shaking nystagmus Head is vigorously turned back & forth horizontally with eyes closed for 30 sec, to “charge” the brainstem’s velocity storage mechanism. Upon stopping & opening the eyes (even better with Frenzel lenses) nystagmus beats away from lesion (slow component often up & towards side of lesion). Tapping head nystagmus Head tapping can evoke nystagmus beating away from side of vestibular loss. Vibration induced nystagmus 60 Hz vibration stimulus is applied to mastoid bone can evoke nystagmus beating away from side of vestibular loss. Subjective visual vertical Patient directs bar or line to what he perceives to be straight vertical; in acute otolith dysfunction, bar or line deviates to side of unilateral (otolith) vestibular loss. Chronic form maybe the otolithic crisis of Tumarkin. Dynamic visual acuity Sometimes referred to as “wobble test” Look for a 3 line decrease in visual acuity during rapid head turning (must be more than 1 Hz) indicative of bilateral vestibular loss. Other Useful Clinical Tests Ballistic testing Patient
is asked to match the tip of their index finger with examiner’s index finger
whilst examiner initiates quick “ballistic” movements (much like sword
playing or fencing). Their action maybe normal / hypometric / hypermetric. Reflects
cerebellar dysfunction. Unterberger’s marching test Patient is asked to march on the spot with eyes closed. Patient will rotate slowly to the side of vestibular loss. Debatable sensitivity and specificity.
Fistula test Otoscope seals the ear in question; then quick, small insufflation is performed (pneumatic otoscopy). Tragal compression can be performed instead of pneumatic otoscopy. In presence of perilymph fistula, nystagmus is induced. Tullio’s phenomenon nystagmus induced by loud noise; represents semicircular canal dehiscence often seen in conjunction with vertigo induced by pressure changes, either at the external ear canal (Hennebert sign) or associated with the Valsalva maneuver. Zee’s test Rarely used for cerebellar testing. Formal Zee’s: conducted in dark room (therefore not allowing visual fixation or referencing) with eyes open, patient asked to look straight ahead and head is rotated rapidly side to side in small movements. Examiner carries out fundoscopy and optic disc will move paradoxically in those with cerebellar disease. Informal Zee’s: used when dark room not available. Patient covers one eye with their hand whilst examiner looks in other eye with ophthalmoscope, effectively blocking visual referencing as examiner’s head & ophthalmoscope will be in the way of the open eye’s path. Rest is carried out as above. References Fife TD, Tusa RJ, Furman JM, et al. Assessment: Vestibular testing techniques in adults and children. Report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology 2000; 55: 1431-1441 Zee DS, Fletcher WA. Bedside examination. In: Baloh RW, Halmagyi GM, eds. Disorders of the vestibular system. New York, NY: Oxford University Press, 1996: 178-190. |
