2. Road Map
Electronystagmograph
y
Calorie Test
Bithermal Caloric
test
Computed Dynamic
Posturography
Miscellaneous Tests
a) Rotatory Chair Test
b) Dynamic Visual Acuity
Test
c) Vestibular Evoked
Myogenic
Potential
d)Craniocorpography
3. • Most important diagnostic tool is careful history
• More than 70% of balance disorder is diagnosed by
history
• If clinical neurotological tests are combined -85%
• High-tech investigation modalities are necessary in about
10-15% only
• “In 80% of cases if one doesn’t have an idea of diagnosis
at the end of history, one is unlikely to have it at the end
of the examination and investigations”
Introduction
4. Objectives of investigations in vertiginous patients:
To estabished whether the patients has any definite vertiginous
problem and/or balance disorder
To establish and objectectively document the degree of functional
impairment
To localize the lesion topographically
To established etiological diagnosis
To established management protocol
Introduction contd…
6. • Congenital nystagmus & squint rule out
• Stop taking for 3days :
Medications that reduce vertigo.
Sedatives and tranquilizers.
Drinks containing alcohol.
Stimulants, including foods that contain caffeine
(coffee, tea, cola, and chocolate)
Before test
7. • Monitors eye movements using electro-oculography
• Assess labyrinthine dysfunction and degree of
dysfunction
• Electroocolography types
Electronystagmography
Magnetic potentials (search coils)
Video-nystagmography
Infrared
8. • Corneoretinal potential
(CRP)-between the cornea
and the retina
• Retina is negatively
charged relative to the
cornea
• Electrical potential can be
measured -skin surface
electrodes
9. Advantages:
Results of test quantified
Bithermal caloric test not accurately done without precise
stimulus control and response quantification provided by ENG
ENG provides documentation of results
F/U of patients
Medico-legal and workers compensation cases
Assesses each ear separately and can give side of lesion
localizing information
10. Limitations:
ENG tests only lateral semicircular canal
Traditional ENG testing using electrooculography relatively
insensitive to torsional nystagmus
Two of more common illnesses BPPV and Meniere’s disease
can have normal ENG despite “classic” symptomatology
ENG finding may be incidental and must be considered in light
of clinical history and physical examination
11. Videonystagmography
• computer-based system for
eye movement
• records eye movements
with digital video technology
using
– infrared illumination
– high-technology goggle
• visualization and recording
of eye movements
12. Videonystagmography contd..
Advantages:
• Easier and quicker than
using electrodes
• Only one calibration is
necessary
• Records rotational
nystagmus
Limitations:
• more expensive
• patients with
claustrophobia may not
tolerate
• patients with ptosis
• pupil-obscuring
eyelashes difficult to
test.
13. Magnetic search coil technique
• Involves patient sitting in a low-strength alternating
magnetic field
• soft contact lens in which a wire coil is embedded
• Motion of the coil of wire in the alternating magnetic field
induces a very small current in the wire
14. Magnetic search coil technique
contd…
Advantages:
• very precise
determination of eye
position in three
dimensions
• allows eye position to
be recorded very
rapidly
(500-1,000 times per sec).
Limitations:
• requires a
sophisticated
laboratory
• highly experienced
personnel
15. • based on the differing reflectance properties of the
iris compared to the sclera
• photocells of the eye remain stationary while the
edge of the iris moves with the eye
• light sensed by the photocells differs according to
eye position
Infrared oculography
16. Infrared oculography contd…
Advantages:
• Direct estimate of the eye
position as a function of
time can be calculated
Limitations:
• Bulk of the equipment
limits visual stimulation-
interference with eyelid
motion makes vertical
recording difficult
17. • Comprises of several
tests:
Test for sponataneous
nystagmus
Gaze nystagmus test
Saccade(caliberation) test
Pendulum tracking test
Optokinetic test
Positional and
posinoning test
Caloric test
Rotational test
Fistula test
26. • Slow velocity saccade:
Degenerative/metabolic CNS diseases
Internuclear opthalmoplegia
Cerebral hemisphere disturbances
Drug intoxication
Inattentive patient
• Abnormal fast velocity saccade:
Orbital tumours
Myasthenia gravis
Saccade(calibration) test
contd…
27. • Cerebellum plays an important role in determining
the accuracy of saccadic movements
• Inaccurate saccades, or ocular dysmetria are
classified as
– hypermetria (overshooting the target)
– hypometria (undershooting)
Saccade(calibration) test
contd…
28. • Saccadic latency abnormalities may be seen
in patients with
Abnormal vision
Parkinson's disease
Huntington's chorea
Alzheimer's disease
Focal hemispheric lesions
Saccade(calibration) test
contd…
29. • Allows continuous tracking of moving objects
• Used to track targets at slower speeds and operates when
eyes move within orbit with head still
• VOR used when target move at faster speeds with
head moving
• Smooth pursuit system:
Computer-controlled visual target moves back and forth
(at frequencies from 0.2 to 0.7 Hz) in horizontal plane
Pursuit and Optokinetic test
contd…
30. • Normal individuals follow target smoothly in both
directions
at all target frequencies
• Deficits in smooth pursuit may from
Age
Medication
visual problems
attention deficit
lesions of brainstem, cerebellum, and occipitoparietal
junction
Pursuit and Optokinetic test
contd…
31. • Optokinetic Test
– images of whole visual
field fixed in retina and
prevent retinal slip.
Pursuit and Optokinetic test
contd…
33. • Determine if different head positions induce or modify vestibular
nystagmus
• Positional nystagmus
• Patient’s eye movements monitored while at least four
head positions
1) sitting
2) supine
3) head right (right ear down)
4) head left (left ear down
•Eye movements monitored in each position for about 20s with
visual and without visual fixation
Positional Test
Positional Test
34. • Positional nystagmus
i) intermittent
ii) persistent
• Nystagmus induced by ampullopetal stimulation
• Persistent positional nystagmus sustained as long as
head
position maintained
• Geotropgic, Ageotrophic
• Direction fixed or changing
• Eliminated or diminished with visual fixing
Positional Test
35. • Many patients complain of vertigo or dizziness with
head
movement
• Nystagmus differs from positional nystagmus
• Most frequently employed test
Dix-Hallpike maneuver
• If nystagmus elicited same maneuver repeated to
assess
Positioning Test contd…
36. • Torsional nystagmus
counterclockwise fast phase (right ear)
clockwise fast phase (left ear)
• Electronystagmography insensitive to torsional
component
• Horizontal: fast phase away from undermost ear
• Vertical: upbeating fast phase
Positioning Test contd…
41. Bithermal Caloric test
• Highly sensitive to unilateral
lesions of the peripheral
vestibular system
• Integrity of the lateral
semicircular canals and their
afferent pathways.
Caloric Test
43. Bithermal Caloric Test
contd…
Helps us to accurately calculate the percentage of canal
paresis
Directional preponderance
• Tests integrity of lateral semicircular canals and their
afferent pathways
44. • Five characteristics of calorically induced nystagmus
1) Latency
2) Duration
3) Amplitude
4) Frequency
5) Velocity (most important)
• Slow-phase eye velocity equally strong in both directions
• Comparison of peak slow-phase eye velocity of cool and
warm caloric
Bithermal Caloric Test contd…
47. • Unilateral Weakness (UW):
[(RC+RW)- (LC+LW)/RC+RW+LC+LW]X 100%
• Directional Preponderance (DP):
[(RC+LW)-(LC+RW)/RC+RW+LC+LW]x100%
• UW >20% and DP > 25% usually considered
significant
Bithermal Caloric Test contd…
48. • UW sign of decreased responsiveness of horizontal semicircular
canal or the ampullary nerve
• DP
spontaneous nystagmus
central sign indicating asymmetric sensitivities
Meniere’s Disease
• Bithermal caloric test highly sensitive to U/L peripheral vestibular
dysfunction
• Relatively insensitive to bilateral dysfunction
• Rule of thumb: Caloric responses (warm response plus cool
response) of both ears fall below 12
degrees/second per side
Bithermal Caloric Test contd…
50. • Posturography is quantitative balance test
• Assesses standing balance function under variety of
conditions
• Device consists of
platform capable of
moving back and forth
• Sensory organisation test
Motor control test
Computerized dynamic
posturography
54. Use of Posturography
1) Planning and monitoring course of postural
rehabilitation
2) Documentation of postural responses in
suspected
a) malingering
b) exaggeration of disability for compensation
c) conversion disorder
Computerized dynamic posturography
contd...
55. • Another method of testing for VOR
• Passive rotational test
Patient’s body is rotated without any movement
between the head and body
• Active rotational test
patient rotates his or her own head back and
forth while the body remains stationary
Rotational Test
56. • most useful
• passive test
• vertical axis through head
• LSCC in the plane of rotation
• Horizontal eye movements monitored
using
electro-oculography
Rotational chair test
57. The patient is seated in a chair so that the horizontal semicircular canals are
in the plane of rotation. Electro-oculography is used to monitor eye
Rotational chair test contd…
58. • Patient oscillated in sinusoidal fashion about vertical
axis at
various test frequencies (ranging from 0.01 to 01.28 Hz)
• Patient undergoes multiple cycles of oscillation at each
frequency
• Stimulus level delivered by rotary chair much greater
than that delivered in caloric testing(0.002 and 0.004 Hz)
• Computer compares head velocity and slow-phase eye
Rotational chair test contd…
59. Clinical Indications for Rotational Chair Testing
1. when the ENG is normal and oculomotor results are either
normal or observed abnormalities
2. when the ENG suggests a well compensated state despite the
presence of a clinically significant unilateral caloric weakness
3. when the caloric irrigations are below 12 degrees/s bilaterally
or when caloric irrigations cannot be performed
4. When a baseline measure is needed to follow the natural
history of the patient's disorder (MD)
Rotational chair test contd…
60. • Components of Rotary Chair Testing
Gain : slow eye velocity/head velocity
indicator of overall responsiveness
Phase: temporal relationship between eye and
head velocities m
measured in degrees
greatest clinical significance
increased phase lead implies peripheral
vestibular system dysfunction
decreased phase lead suggest cerebellar lesion
Rotational chair test contd…
61. Symmetry: ratio of rightward to leftward slow- phase eye
velocity
asymmetry result from peripheral vestibular weakness or
contralateral excitory lesion
Rotational chair test contd…
63. • abnormalities seen on RCT can be
classified into four categories:
1. vestibular habituation and asymmetry
2. vestibular habituation
3. vestibular deficit
4. vestibular asymmetry
Rotational chair test contd…
68. Vestibular Autorotational Testing
• Active rotation test
• Patient actively shakes his/her head
from side to side with increasing
frequency
• Angular sensor is fixed to a
headband
• Advantages
– Portable
– relatively brief (18 sec) duration of
the test
– ability to test high-frequency (2-6
kHz) oscillations
69. • Test of inferior vestibular nerve
• Records myogenic potential in
cervical muscles(SCM) originating
from saccule
• Recorded by surface electrode
– Active electrode upper half SCM
– Reference electrode on sternal head
Vetibular Evoked Myogenic
Potential
70. – Alternate click of 105dB of 0.2
ms width is fed on test ear
and white noise of 30dB in
another ear for masking
– EMG is recorded
– Two trial in done for each ear
h
Vetibular Evoked Myogenic Potential
contd…
71. In healthy subjects
– Definite VEMP is recorded in 95% of cases
– Peak latency of positive and negative wave is 13.5
ms and 23ms respectively
In patients with dead vestibular labyrinths
– No VEMP recorded
h
Vetibular Evoked Myogenic Potential
contd…
73. • Test of VOR while
reading
acuity chart
• Examiner oscillates
patient’s head at 1 Hz;
new VA recorded
• 2 lines suspicious;>3
VOR grossly reduced
74. • Consist of graphically recording
patient’s head and body
movement
• Unterburger’s stepping
• Romberg’s test
Craniocorpography
75. References
• Glasscock-Shambaugh,Sugery of the Ear,6th edition
• Scott-Brown’s otorhinolaryngology head and neck surgery-
7th edition
• Scott-Brown’s otorhinolaryngology head and neck surgery-
6th edition
• Cummings otolaryngology head and neck surgery-5th
edition
• Diseases of Ear,Nose and Thoroat-PL Dhingra5th edition
• Ballenger’s Otorhinolaryngology Head and Neck Surgery-
16th edition
Editor's Notes
localise the lesion topographically-whether it is perpheral (rt/Lt) or central,the pathway between the vestibular labrynth and vestibular nuclei is conventionally termed as perpheral VS and vestibular area oc cortex-central
To established management protocol-minisimizing discomfort and maximising functional capacity of patients
Three arc neuron representation of the vestibuloocular reflex. Upon head rotation to the right (CW acc, clockwise
acceleration), the hair cells on the 'leading ear' side are excited and increase their discharge rate, whereas the hair cells on the
following ear are inhibited, thereby decreasing the discharge rate. The vestibular nuclei encode the increased discharge rate and redirect
the excitation to the ipsilateral ocumolotor nuclei to contract the medial rectus of the right eye, while the contralateral abducens
nucleus is triggered generating a contraction of the contralateral lateral rectus. Consequently the eyes are driven to the left to
compensate for the head movement to the right. This is the essence of the VOR
Electro-oculography (EOG).The cornea is relatively positively charged in comparison to the retina; thus, an electric
potential exists between the two. Electrodes are placed around the eyes, and rotation of the eye brings the cornea closer to one electrode and the negatively charged retina closer to the other. The relative voltage difference provides the basis for
EOG. By convention, rightward movement of the
eye is recorded as an upward deflection on the
electronystagmographic tracing
-"of central vestibular neurons to inhibitory-excitatory stimuli or asymmetries in the inputs from these central vestibular neurons to extraocular motoneurons
because the
caloric stimulus is uncalibrated
-"of central vestibular neurons to inhibitory-excitatory stimuli or asymmetries in the inputs from these central vestibular neurons to extraocular motoneurons
because the
caloric stimulus is uncalibrated
helpful for later study and for teaching
personnel and patients. This capacity is particularly useful in
evaluating patients with benign paroxysmal positional vertigo
(BPPV)—one of the most common vestibular abnormalities
encountered. Videonystamographic tracings are clean with no
drift, which improves the accuracy of analysis and interpretation.
This technique is easier and quicker than using electrodes
and only one calibration is necessary. There are limitations to
the VNG that are noteworthy. Test equipment is more expensive,
some patients with significant claustrophobia may not tolerate
the sensation of confinement, and patients with ptosis,
pupil-obscuring eyelashes, or other eye abnormalities may be
difficult to test.
helpful for later study and for teaching
personnel and patients. This capacity is particularly useful in
evaluating patients with benign paroxysmal positional vertigo
(BPPV)—one of the most common vestibular abnormalities
encountered. Videonystamographic tracings are clean with no
drift, which improves the accuracy of analysis and interpretation.
This technique is easier and quicker than using electrodes
and only one calibration is necessary. There are limitations to
the VNG that are noteworthy. Test equipment is more expensive,
some patients with significant claustrophobia may not tolerate
the sensation of confinement, and patients with ptosis,
pupil-obscuring eyelashes, or other eye abnormalities may be
difficult to test.
Faraday*s lawinvolves the patient sitting
in a low-strength, alternating magnetic field. The patient
wears a soft contact lens in which a wire coil is embedded. The
advantages of this method: it provides
very precise determination of eye position in three dimensions
and it allows eye position to be sampled and recorded very rapidly
(500-1,000 times per sec). These features are responsible for
the search coil technique providing the most accurate measurement
of eye movements. The major disadvantage of the search
coil technique is that it requires a sophisticated laboratory and
highly experienced personnel
Infrared oculography is based on the differing reflectance
properties of the iris compared to the sclera and the fact that
the photocells of the eye remain stationary while the edge of
the iris moves with the eye. As a result, the light sensed by
the photocells differs according to eye position.
The advantage of this technique is that a direct estimate of the eye position
as a function of time can be calculated. The disadvantages of
this technique include the bulk of the equipment, which limits
visual stimulation somewhat, and the interference with eyelid
motion (eg, blink), which makes vertical recording difficult
at times
Fig:records first with eye open and than close.A-eye movement in vertical axis.-no vertical nystagmus
B-eye movement in horizental axis-right beating nystagmus
C-not a recording of eye movement tthis is a time marker and every second there is a vertical mark.
Pt with right vertibular neuronitis-
Test for gze nystagmus in normal person:there is no nystagmus in either left or right lateral position
Test for gze nystagmus in pt suffering from cebellar tumour A right beating nystagmus in right lateral position
Visual-Oculomotor function
(Saccade, Smooth Persuit, Optokinetic test)
ii) Abnormal eye movements
(Gaze test, Positional test, Positioning test)
iii) Vestibulo-Oculomotar function test
(Bithermal caloric test)
The purpose of the saccade system is to rapidly capture interesting visual targets in the periphery of the visual field onto the fovea. This quick foveating eye movement is a saccade
The complete sequence often consists of
80 target jumps (40 to the right and 40 to the left), with amplitudes
ranging from 5 to 25 degrees. After testing, the computer
calculates three values for each saccade: peak velocity, accuracy,
and latency.
The purpose of the saccade system
is to rapidly capture interesting visual targets in the
periphery of the visual field onto the fovea. This quick
foveating eye movement is a saccade
cerebellum plays an important role in determining the accuracy
of saccadic movements. Inaccurate saccades, or ocular dysmetria,
are classified as hypermetria (overshooting the target) or hypometria (undershooting) and may be seen with cerebellardisease or brainstem disorders
cerebellum plays an important role in determining the accuracy
of saccadic movements. Inaccurate saccades, or ocular dysmetria,
are classified as hypermetria (overshooting the target) or hypometria (undershooting) and may be seen with cerebellardisease or brainstem disorders
Pursuit tracking,or the smooth pursuit system, allows continuous tracking of moving objects and works with the saccade system to maintain images on the fovea when the target is moving moving. The smooth pursuit
system is used to track targets at slower speeds and operates
when the eyes move within the orbit and the head is still. The
VOR is used to maintain the stability of images on the fovea
when the head is moving. The VOR is particularly important in
maintaining stable gaze during rapid head movements
After testing, the computer
differentiates the eye position signal, calculates the gain of eye
velocity with respect to target velocity separately for rightward
and leftward tracking at each target frequency, and plots these
data. Normal individuals are able to follow the target smoothly
in both directions at all target frequencies. Deficits in smooth
pursuit may result from age, medication, visual problems, attention
deficit, or lesions of the brain stem, cerebellum, and occipitoparietal
junction
The function of optokinetic system to keep the images of whole visual field fixed in retina and prevent retinal slip.
Stripe of drum or light in the bar is both moved in horizentl and vertical direction-Nystagmus
Movement for 20 sec
Asymmetrices in eye movement –CNS lesion
The optokinetic pathways are subcortical, involving the accessory optic system. In humans, there is an
overlap in function by neurons in the cortical and subcortical visual systems. The smooth pursuit system dominates
the operation of the overall pursuit system.
FIGURE 11-3 • The results of the tracking test in a patient with a unilateral pursuit defect. The patient was unable
to follow the rightward-moving target smoothly and instead approximated its motion using successive saccades,
producing a stair-step pattern on the eye movement tracing. Tracking of leftward-moving targets was normal. This
patient's abnormality indicates an asymmetric central nervous system lesion involving the pursuit eye movement
control system.
The optokinetic pathways are subcortical, involving
the accessory optic system. In humans, there is an
overlap in function by neurons in the cortical and subcortical
visual systems. The smooth pursuit system dominates
the operation of the overall pursuit system
nystagmusdifferent head positions,not head movement, elicit nystagmus
Electronystagmographic tracing demonstrates horizontal and vertical components of the
nystagmus seen in benign paroxysmal positional vertigo.
Dix-Hallpike maneuver. The patient’s head is first turned to the left. The patient is then rapidly brought into the head-hanging
position. Patients with benign paroxysmal positional vertigo typically demonstrate a geotropic, torsional nystagmus with the affected ear down.
Frenzel’s lenses are used to prevent fixation-suppression. The test is repeated on the opposite side
Bojrab-Calvert maneuver for benign paroxysmal positional vertigo. This positioning maneuver is useful in assessing positioning
nystagmus in elderly or other individuals who cannot tolerate the neck extension position used in the Dix-Hallpike maneuver
bithermal (Hallpike) caloric tests evaluate the integrity
of the lateral semicircular canals and their afferent pathways.
The patient is placed in the supine position with the head elevated
30 degrees, thereby placing the lateral semicircular canal
in the vertical plane (Figure 11-8). Testing is properly done with
the patient wearing Frenzel goggles to prevent fixation-suppression.
Asking the patient to engage in mental tasks can also be
helpful in releasing the nystagmus.
Caloric testing may be performed with air or water.
The correct position places the patient in the reclined position,
30 degrees elevated from the table, which places the horizontal canal
in the vertical plane.
Convective flow mechanism of the caloric response. Irrigation with warm or cold water (or air) results in a temperature gradient across the horizontal semicircular canal. With the horizontal canal oriented in the earth-vertical plane, gravity induces the convective flow of endolymph from the cooler area of the canal in which endolymph is more dense into the warmer area of the canal in which endolymph is less dense. For the warm caloric irrigation shown in this diagram, am ampullopetal deflection of the cupula results from this flow of endolymph. Vestibular-nerve afferents innervating the horizontal semicircular are excited, and a horizontal nystagmus with slow phase components directed toward the opposite ear is produced. A cold caloric stimulus results in an oppositely directed response with ampullofugal deflection to the cupula, inhibition of horizontal canal afferents, and a nystagmus with slow phase components directed toward the ear to which the cold caloric is applied. (From Baloh RW, Honorubia V: Clinical neurophysiology of the vestibular system, ed 2, Philadelphia, 1990, FA Davis
responses of the right ear with those of the left ear allows the examiner to determine whether a unilateral vestibular weakness exists
responses of the right ear with those of the left ear allows the examiner to determine whether a unilateral vestibular weakness exists
responses of the right ear with those of the left ear allows the examiner to determine whether a unilateral vestibular weakness exists
-"Jongkee'sformula"ts
-"of central vestibular neurons to inhibitory-excitatory stimuli or asymmetries in the inputs from these central vestibular neurons to extraocular motoneurons
because the
caloric stimulus is uncalibrated
Caloric responses in a patient with unilateral labyrinthine hypofunction. Patient had no response in the left ear, although right ear responses were normal to warm and cold irrigations
Evaluation of all sensory systems that provide information important for maintaining balance
1) vestibular
2) visual
3) somatosensory
FIGURE 11-21 • Posturography test of a patient with total bilateral loss of vestibular function owing to ototoxicity. He has normal postural stability when tested under conditions 1 through 4 but marked instability on conditions 5 and 6, in which he had to rely solely
on vestibular cues. This type of result may be seen in patients with
acute unilateral peripheral vestibular lesions. Only rarely is it seen in
patients with chronic unilateral vestibular dysfunction.
Rotationaltests can be classified as either passive rotational tests, in which the patient’s body is rotated without any
movement between the head and body, or as active rotational
tests, in which the patient rotates his or her own head
back and forth while the body remains stationary.
Rotational
tests can be classified as either passive rotational
tests, in which the patient’s body is rotated without any
movement between the head and body, or as active rotational
tests, in which the patient rotates his or her own head
back and forth while the body remains stationary.
Phase, gain, and asymmetry values
in relation to oscillation frequency for a
patient with an acute right peripheral vestibular
lesion. At lower oscillation frequencies, this
patient shows progressively greater than normal
phase leads. The patient also has a rightward
asymmetry. This response pattern — abnormal
low-frequency phase leads and high-frequency
asymmetry — is routinely observed in patients
with acute unilateral vestibular loss. The asymmetry
is always toward the side of the loss
Rotary chair testing stimulation generates right-beating
nystagmus when the patient is moving rightward and leftbeating
nystagmus when moving to the left
Rotational chair testing stimulates both peripheral vestibular
systems simultaneously; however, it may be helpful in determining
the site of lesion in certain disorders.
the patient's disorder (eg, possible early Meniere's disease
Normal individuals,movement of the head to the right results in deviation
of the eyes to the left. If the patient is rotated at a low frequency for a prolonged period of time, eye movement
actually precedes the head movement
Symmetry
Symmetry is the ratio of rightward to leftward slow-phase eye
velocity. This parameter gives information as to whether any
bias is present in the system, favoring one direction over the
other. Asymmetry may result from a peripheral vestibular
weakness on the side of the larger slow-phase component or an
excitatory lesion of the contralateral labyrinth.
The purpose of the VOR is to produce
eye movements that compensate for head movements, and the
eye velocity is approximately 180 degrees out of phase with head
velocity. When a normal individual is oscillated at low frequencies,
slow-phase eye velocities exhibit progressively lower gains
and are no longer exactly opposite in phase
FIGURE 11-14 • Phase, gain, and asymmetry values in relation to oscillation frequency from a normal individual.
Note that eye velocity signal is inverted during the analysis so that a phase angle of 180 degrees is expressed as
a phase angle of 0 degrees. Phase leads become progressively larger and gains become progressively lower as
oscillation frequency decreases. Symmetry values are approximately zero at all frequencies.
FIGURE 11-15 • Phase, gain, and asymmetry values in relation to oscillation frequency for a patient with an acute
right peripheral vestibular lesion. At lower oscillation frequencies, this patient shows progressively greater than
normal phase leads. The patient also has a rightward asymmetry. This response pattern—abnormal low-frequency
phase leads and high-frequency asymmetry—is routinely observed in patients with acute unilateral vestibular loss.The asymmetry is always toward the side of the loss.
FIGURE 11-16 • Phase, gain, and asymmetry values in relation to oscillation frequency for a patient with a chronic
left peripheral vestibular lesion (vestibular schwannoma). Electronystagmography showed a severe right caloric
weakness. The rotational chair test shows greater than normal phase leads at lower test frequencies, reflecting a
loss of velocity storage. This loss can be persistent, remaining for years following vestibular malfunction, although
there is nearly always some recovery. The absence of tonic asymmetry in this individual illustrates the effect of
vestibular compensation. If a peripheral vestibular lesion develops slowly, compensation is able to gradually
rebalance the asymmetric input, preventing the vertigo and spontaneous nystagmus that would otherwise occur.
Even when lesions develop suddenly, compensation quickly rebalances the tonic asymmetry over a period of days.
FIGURE 11-17 • Phase, gain, and asymmetry values in relation to oscillation frequency for a patient with bilateral
absence of caloric responses, showing absent responses at all oscillation frequencies. Phase values were not plotted owing to low response gains.
FIGURE 11-18 • Phase, gain, and asymmetry values in relation to oscillation frequencies for a patient with bilateral
absence of caloric responses, showing normal response gains at the higher frequencies.
Vestibular autorotational testing is an active rotation test in which the patient actively shakes his/her head from side to side with increasing frequency. An angular sensor is fixed to a headband which is worn by the patient, and the eyes are evaluated with electro-oculography (Figure 11-19).
Advantages of VAT over the other tests include portability
of testing equipment, relatively brief (18 sec) duration of the test,
and ability to test high-frequency (2-6 kHz) oscillations (when
the VOR is active).
Pt is made to sit in reclining chair in sound tret room head turnes to opposite side (making SCM contaction)
Electromyography is recorded
Electromyography is recorded
FIGURE 11-25 • Unilateral weakness for responses to the right VEMP stimulus is demonstrated in this
figure.
Normal individuals,movement of the head to the right results in deviation of the eyes to the left. If the patient is rotated at alow frequency for a prolonged period of time, eye movement
actually precedes the head movement
2 test are done in dark room in which there is a convex mirror with convex surface downwards fitted in roof.
Pt is blindfolded and made to weare crown on head in wich 3 LED light are palced.
Inbetween head and convex mirror –camera is place in adustable stand with lens directed upwards.
Two extrem LED light are -40cm and at a scale to which the pts movement are compared for movement.
Middle light –is the recording light.
