Videonystagmography (VNG) is a diagnostic test that records and analyzes eye movements using video imaging to differentiate between central and peripheral vestibular disorders. It includes tests of oculomotor function like saccades and smooth pursuit, as well as tests of the vestibulo-ocular reflex like caloric irrigation and positional maneuvers. VNG provides information about abnormalities in eye movement, nystagmus, and vestibular function to localize lesions in the brainstem, cerebellum or peripheral vestibular system.

1. Videonystagmography

2. • Balance of the body is controlled by two major reflex
systems,Vestibulo-ocular (VOR), Vestibulo-spinal (VSR) reflex systems.
One of the easiest ways to assess the function of balance systems is
to measure the abnormal eye movements either spontaneously or in
response to a stimulation.
• A variety of techniques have been used for documenting qualitatively
and quantitatively different types of eye movements. These include
Electronystagmography (ENG); Scleral Search Coil (SSC), photoelectric
Techniques and Video Nystagmography (VNG)

3. • Videonystagmography (VNG) is a diagnostic system for recording,
analysing, and reporting the eye movements using video imaging.
• It includes a battery of tests used to differentiate between a central
and a peripheral vestibular lesion.
• It can also differentiate between unilateral and bilateral vestibular
loss.
• This test is very useful in picking up subtle functional lesions that are
missed by imaging techniques like MRI scans which can only pick up
structural defects.38

4. • It answers the following clinically relevant issues:
• Is it a vestibular disorder or is it a CNS disorder? Is there any defect in
the oculomotor system?
• Is the vestibular labyrinth weak on one side and if so on which side or
both sides?
• How weak is it 25%/50%/80°/»....or is it dead?

5. • it does not tell about the compensation done by brain for loss of function.
• It does not tell us the etiology, i.e. the cause of the disorder like Meniere‘s
disease,Vestibular neuritis, labyrinthitis , perilymph fistula, etc.
• It also does not tell us anything about defects in the vestibulo—spinal
system and also about any postural defects that the patient may be having.
• Even within the vestibular labyrinth, it does not pick up if there is any
defect in the anterior or posterior semi-circular canals or in the saccule or
utricle or in the inferior vestibular nerve

6. Advantages of VNG over ENG
• Less time consuming
• Uses infrared camera to record eye movement
• Eye goggle makes the surrounding completely dark
• Lesser artefacts than ENG
• ENG tracing is available after the test is done; if any adjustments to be
made the test must be repeated entirely
• VNG records torsional nystagmus

7. • VNG tests include the following:
• Tests of oculomotor function (with fixation): includes saccade, smooth
tracking, and optokinetic tests.
• Tests of gaze stabilization (with or without fixation): includes
gaze,spontaneous nystagmus, static position tests.
• Caloric test
• Tests for specific etiologies: includes Dix–Hallpike maneuver (dynamic
positioning), pressure test (fistula).
• Others: head impulse test, hyperventilation test, etc.39

8. Set up for VNG

9. Routine procedures before starting VNG test
• Some medications that affect the CNS or the vestibular system can
contaminate results of vestibular function tests and should be stopped 2
days before the VNG is done. Such medicines include all vestibular
sedatives like prochlorperazine, cinnarizine, betahistine, meclizine,
dimenhydrinate and promethazine; antidepressants and anxiolytics
especially benzodiazepines, phenothiazines and SSRIs, CNS depressants,
tranquilizers, and sleeping pills and anti- allergic that cause sedation.
Antiepileptic drugs should also be avoided if possible.
• The test process needs to be very thoroughly explained to the patient
such that the patient can cooperate with the examiner while the test is
on. The examiner must reassure the patient and explain the benign nature
of the test.

10. • The patient must be told that the test could cause vertigo for brief
periods.
• History of significant heart block, a seizure disorder, neck disorders
causing severe restriction of neck movement, history of ear
discharge or history of surgery to the ear and whether the patient has
contact lenses or has significant visual impairment must be taken.
• Clinical examination of the ear.
• Clinical examination of the eyes- look for ptosis, restrictions in eye
movements, visual acuity

11. VNG graph
• Infra red goggle creates a videograph which is converted by the software
into a graph.
• Graph depicts the eye movement during the test in the vertical as well as in
the horizontal axis.
• If there is no eye movement during a particular test then a flat line is
obtained.
• Commonest form of eye movement recorded is nystagmus which has a fast
and slow component.
• Nystagmus in horizontal axis could be right or left beating and in vertical
axis could be up beating or downbeating according to the fast phase.

13. • The intensity of the nystagmus can be calculated in many ways but the most
accurate method is by calculating the speed of the slow phase which is known as
(SPV). The speed of slow phase is calculated in degrees of eye movement per sec.
If the eyes move by 20° in 2 sec, this speed of slow phase will be 10°/sec. The
movement of the eyes is always measured in degrees per second and not in
terms of the distance covered like centimeters per second or meters per second.
This is so as the movement of the eyes is measured in terms of the amount of the
visual field that is covered by the eye movement.
• The other commonly used parameter for estimating the intensity of the
nystagmus is the number of beats in the 30 sec span where the nystagmus was
most robust when a test was done. This is known as the culmination frequency
(CF) of the nystagmus.
• Since the speed of slow phase is the most reliable nystagmus parameter, most
calculations are based on the speed of slow phase estimation.

14. Saccade
• The saccadic system is responsible for stabilizing the image of a new object of
interest as soon as it enters the visual field.
• Part of the VOR
• The saccades are very fast eye movements carried out by the CNS.
• Function is to execute movement of the eyes very rapidly towards an object of
interest as soon as the brain finds a new object of interest and then bring the
image of the new object into the fovea and fix the image of the new object of
interest in the fovea.
• The object of interest usually enters the visual field from the periphery and so the
eyes have to move quite a distance and then to suddenly stop and fixate the
vision on the target .
• Defect in the saccadic system, causes overshoot or an undershoot, the initiation
of the movement may be slow (high latency) or the movement may not be as fast
as it should be (low velocity).

15. Procedure
• The patient is made to sit at the specified place and instructed to
follow a visual target generated by the VNG machine‘s software.
• The target does not move constantly, but jumps from one position to
the next about 20 times in 30 sec.
• The patient is asked to fixate his/her vision on the target and then
move the eyes to the next point as soon as the target appears at the
new point.

16. Interpretation
• Latency of saccadic eye movements range from 150-250msec.
• If there is a consistent delay above 300 ms for random saccades, the
latency is accepted as abnormally high and suggests a CNS lesion.

17. • Velocity of the saccade is the speed at which the eyes move when
fixing the gaze from one target to another.
• Velocity of the eye movement is between 250°/sec and 600 ° /sec.
Velocities lower than 250°/sec is considered abnormal.
• Slowing of saccades denote a central lesion involving the brainstem
(most commonly pons), cerebellum , basal ganglia or the peripheral
oculomotor nerves or muscles.

18. • Overshoot or undershoot by up to 20% is considered as normal .
• >20%- hypermetria – suggestive of cerebellar (vermis) lesion
• <20%- hypometria- suggestive of cerebellar (flocculus) lesion.

19. Smooth tracking
• The function of the smooth tracking system is to fixate on the fovea
the image of a moving object that is moving slowly and smoothly in a
predictable trajectory at a predictable speed.
• Example-
• Procedure- patient is asked to visually follow a target moving back
and forth at a fixed speed first horizontally then vertically. The speed
at which the visual target moves is controlled by the computer and is
between 0.2 Hz and 0.7 Hz. Amplitude of the movement of the visual
target is between 10° and 20 °.

20. Interpretation
• If the eyes cannot follow a moving target and instead approximates
target motion using successive saccades (giving a cogwheel or
stepladder appearance), it suggests a CNS lesion.
• GAIN
o expressed as percentage
oIf the patient‘s eyes follow the target with a completely smooth eye
movement- gain is 100%
oGiven by- Gain= amplitude of smooth eye movt x100
o amp of smooth eye movt + amp of saccadic eye movt

21. • Gain below 80% considered abnormal s/o CNS pathology if unilateral.
•

22. • Structures involved in maintaining smooth tracking are- visual cortex,
the cerebellum, the vestibular nuclei, the oculomotor nuclei, the
dorsal pontine nuclei, the medial longitudinal fasciculus.
• An asymmetry between left and right gain is suggestive of a CNS
disorder.
• Gross asymmetry s/o degenerative disorder involving cerebellum or
extrapyramidal system.
• Unilateral abnormality in smooth pursuit – ipsilateral cerebellar
lesion, bilateral abnormality – diffuse cerebellar lesion or basal
ganglia lesion.

23. Optokinetic test
• Movements of the entire visual field in the environment (e.g. when
we are sitting in the car and looking out through the side windows)
cause nystagmus beats that are used to avoid blurring of the visual
field due to rapid image movement on the retina and to stabilize the
moving images on the retina.
• It has 2 phases
• During the slow phase of the nystagmus, the eyes move with the
velocity of the projection pattern. They then quickly travel in the
opposite direction as they jump back to the original position. This
jerky eye movement is called optokinetic nystagmus
• It is a reflexive response.

24. Procedure
• Patient is asked to look at the visual stimulus of the moving stripes
as projected from the projector and try to count the moving
stripes/lights without moving the head, and is also asked to avoid eye
blinking.
• Visual stimulus is moved at a constant speed of 15—45°/sec.
• Gain- SPV of elicited nystagmus
• stimulus velocity

25. Interpretation
• Nystagmus generated by the optokinetic stimulus beats in the
direction opposite to that of the optokinetic stimulus.
• Normal result- the gain is above 75%,
• there is no significant asymmetry of the gain between the left and
right movement of the optokinetic stimulus and
• the direction of the optokinetic nystagmus is opposite to the
direction of movement of the stimulus.

26. Gaze holding test
• After the saccadic eye movement has rapidly moved the eyes to the
object of interest, maintaining the position of the eyes at that
position is gaze holding
• Nystagmus during the gaze test is indicative of CNS pathology when
gaze if fixed within 30° of center of visual field.
• Procedure - projected image is first beamed in the center and then it
is shifted to a new position 25 °or 30 ° away from the center. The
patient is asked to keep the vision fixated to the new point for a
minimum of 20 sec. The test is carried out for visuaI target positions
at 25 ° /30 ° to the left, right, up, and down.

27. • Gaze nystagmus in any form is always indicative of a central lesion
most often a cerebellar or a brain stem disorder provided medication
like anticonvulsants, antiepileptic drugs and alcohol is ruled out
• If the gaze nystagmus is one side only chances are very high of it
being an infarct or a tumor in the brainstem or in the cerebellum

28. Spontaneous nystagmus
• spontaneous nystagmus is any nystagmus that is present without any
visual or vestibular stimulation.
• conducted both without optic fixation (vision denied) as well as with
optic fixation (i. e. with the eyes fixating at a point)
• Horizontal nystagmus originating from peripheral vestibular lesion
diminishes at least by 50% on visual fixation, whereas central
nystagmus does not diminish or get aggravated on fixation.

29. Procedure
• Eyes are covered with the visor and the patient is instructed to
keep the eyes wide open without blinking.
• The recording is carried out without optic fixation for at least 30 sec
and then the optic fixation bulb is put on (under the cover of the VNG
goggles) when a green LED lamp glows and the patient is asked to fix
the vision on the light.

30. Interpretation
• ( 1) whether the patient has any nystagmus, (2) whether optic
fixation has any effect on the nystagmus and also (3) whether the
direction of the nystagmus is fixed or it changes with time.
• Nystagmus of peripheral origin is always direction fixed, so
change in direction is s/o CNS lesion
• congenital nystagmus- pendular eye movement, or a pure left-
beating or right-beating nystagmus where the speed of slow phase is
not fixed but increases slowly in each beat giving the slow phase of
the nystagmus a rounded appearance, is unaffected or sometimes
increases in intensity on optic fixation, is present from birth (as per
history).

31. • Up beat nysatgmus- caused by multiple sclerosis, encephalitis, brain
abscess, tumors in the brain stem and cerebellum ; brainstem or
cerebellar infarction, brainstem or cerebellar hemorrhage and also by
drug intoxication and degenerative changes in the brain stem like
Wernicke’s encephalopathy caused by chronic alcoholism
• Down beat nystagmus- herniation of cerebellar tonsils,Arnold- Chiari
malformation and cerebellar degeneration, infarction or a tumor in
the cerebellum, multiple sclerosis, syringobulbia, brainstem
infarction, encephalitis and alcohol induced cerebellar degeneration

32. Positional tests
• 2 different tests are done- static position test and dynamic test
• Procedure- tests for positional/positioning vertigo are performed with the eyes
open but without optic fixation
• 1. Static position tests- patient wearing the VNG goggles is put in different
positions like sitting up with the head straight, sitting up with a head
completely flexed that is bent forwards, sitting up with the head extended
backwards, sitting up with the head turned to the right, sitting with the head
turned to the left, then lying down straight with the head hanging backwards,
lying down with the head turned to the right, lying down with the head turned to
the left and the eye movement is recorded and analyzed for any nystagmus. A
minimum of 20 sec recording is necessary for each head position.
• If the nystagmus is of peripheral origin, i.e. a BPPV, the nystagmus does not last
beyond 30 sec in most cases.

34. • 2. Dynamic position test/positioningtest Dix- Hall pike positioning
test- a test for the posterior semi- circular canals.
• to determine whether the act of the head moving to a particular
position is generating any nystagmus.
• While in the sitting position, the head is turned 45° towards one side
— either to the left or to the right, the examiner grasps the head
firmly and then immediately brings the head down very rapidly to a
position that is about 30° below the horizontal.
• recording of the nystagmus is started from the point the examiner
grasps the head of the patient in the sitting posture and the recording
is continued for about 30 sec in the head hanging position

36. Interpretation
• slight amount of positional/positioning nystagmus is common even in
normal persons
• Positional/positioning nystagmus with the SPV below 4°/sec is not
considered abnormal.
• Nystagmus originating from the posterior canals which is elicited by
the Dix-HalIpike positioning tests is always a torsional (i.e. a rotatory)
nystagmus with a strong vertical component.
• peripheral origin-nystagmus is always accompanied by a strong sense
of vertigo; usually has a well identifiable latent period, is transient
and is fatigable.

37. • Purely vertical nystagmus without torsional component on DHM suggests
central pathology.
• To test horizontal canal-patient is made to lie down flat with the head
slightly flexed —(head on a shallow pillow) and then the head is rapidly
turned to the side. If, there is any purely horizontal nystagmus when the
head is turned to one side, it is a lateral canal BPPV.
• Lateral canal BPPV may be geotropic or ageotropic. If there is a left beating
nystagmus with the head turned to the left (the eyes beating towards the
floor), the nystagmus is geotropic but if the nystagmus beats to the right
(away from the ground and towards the ceiling) when the head is turned to
the left the nystagmus is ageotropic (s/o cupulolithiasis)

38. Caloric tests
• First described by Robert Barany, the caloric test assesses lateral vestibular
canal function.
• Each of the semicircular canals, at their end, dilate into the ampulla. The
ampulla is a fluid filled sac containing the sensory component of the
vestibular system. When the endolymph is warmed either by air or water, it
creates a current which moves the hair in the lateral semicircular canal,
thus, causing an imbalance between the right and left vestibular-ocular
reflexes (VOR). This results in nystagmus.
• Depending on the current of the ampulla, this has both fast- and slow-
beating components. When cold temperature is applied, it causes fast-
beating nystagmus in the direction opposite to the side being challenged
and a slow-beating nystagmus on the contralateral side. The opposite is
true for when warm temperature is applied.This can be remembered by
the anecdotal mnemonic COWS- Cold Opposite Warm Same

39. • Types of caloric test:
• Bithermal caloric test ( water stimulation at 7 degrees above and
below the body temperature or by air at 24 or 50 degrees Celsius)
• Monothermal caloric test
• Ice caloric test

40. • Traditionally, Water caloric system was used for assessment of
vestibular system. It was proposed that the temperature used for
irrigation should be set at 7℃ above and below the body temperature
assuming that warm and cold caloric tests gave same response
• The contraindications for use of water in caloric testing are tympanic
perforation, external otitis and mastoid diseases. With further
advancement other methods for irrigations were discovered like
closed loop water irrigation.

41. • The air caloric examination was described in 1960
• The advantage with air caloric system is that it can be used in
tympanic perforations where water caloric testing is contraindicated
• The caloric test stimulates the vestibular system at 0.005 Hz
frequency

42. Procedure
• Conventionally, right ear is stimulated with warm water/air followed by left ear
followed by cold stimulation of right ear followed by left ear.
• A gap of 3-5 mins is given between these procedures.
• Water irrigation is done using 250 ml of water at 2 different temperatures- warm
44℃ for 30 sec and cold 30℃ for 30 sec.
• Air stimulation is done using 8lts/min of air at 2 different temperatures – warm at
50℃ for 60 sec and cold at 24℃ for 60 sec.
• The nystagmus is recorded using VNG machine.
• There are various parameters of nystagmus that are evaluated using VNG
machine. These parameters are- angular velocity (SPV), frequency, excitability,
vestibular deficit (canal paresis), and directional preponderance. Unilateral
weakness (canal paresis) is considered when difference between right and left
response is >25%, DP is considered when difference between right beating and
left beating exceeds 30%.

43. • Angular velocity (SPV) – it is the distance that the eye travels during the slow phase
divided by the amount of time, measured as degrees of eye movement per second. A
value more than 6°/sec is considered abnormal.
• Frequency – it is the number of nystagmus beats in 30 seconds
• Excitability – it is the sum of all SPVs. A value less than 140°/sec is considered normal
• Vestibular deficit (canal paresis) - it compares nystagmus strength induced by irrigation
of left ear with to that of right ear. It is calculated by using a formula
right ear SPV- left ear SPV x100. Value of 25% or less is considered normal
right ear SPV + left ear SPV
• Directional preponderance- it compares nystagmus intensities in right beating direction
with those in left beating direction. It is given by the formula
• SPV left beating- SPV right beating x100. Value of 30% or less is considered normal
SPV left beating + SPV right beating

45. • The caloric test findings can be presented synoptically in many
formats like Claussen‘s Butterfly chart, Haid/Stott Diagram, Freyss
diagram, Scherer Diagram etc.

46. • Freys Diagram synoptically represents the average slow phase velocities
during of each irrigation. These values are also denoted by numbers in the
diagram.
• On the left vertical axis, the a.SPV calculated for the irrigations of the right
ear are plotted and those for the left ear irrigations are on the right side.
• The diagram is completed by two lines: one connecting the data points
obtained for the two warm irrigations, the other one connecting the data
points representing the two cold irrigations.
• The normative data range in the Freys Diagram has the shape of a box and
refers to the junction of the two lines above which should be close to the
center of the graph.

48. • The Claussen diagram is plotted on the basis of frequency of each irrigation.
• This is not based on calculation of the SPV though it can also be done. Each
quadrant represents data from one caloric irrigation.
• On the outer verticaI axis of each quadrant, the number of nystagmus beats is
plotted. For better graphical representation, a line is drawn from each data
point to the center of the diagram. The normative data range shown refers to the
lînes
• For 90°/o of healthy subjects the lines should be within the yellow marked area .
• For 94% of healthy subjects the lines should be within the grey bounded area

50. • Haid/Stoll diagram is also plotted on the basis of CF and not on the
basis of speed of slow phase.
• The responses from the right ear are shown on the left of the diagram
and responses from the left ear are shown on the right side of the
diagram.
• Zone of normal readings- yellow colour.

51. • Scherer Diagram consists of two parts one depicting DP and the
other depicting unilateraI weakness.
• For 90 % of normal subjects the crosses will be within the yellow
marked areas.
• -For 94% of normal subjects the crosses will be within the grey
bounded area

52. Cut off
• Bilateral weakness is present when total responses from the right and the
left ear are both less than the cut-off value of 12°/sec.
• Caloric responses are hyperactive when total responses from either the
right ear or the left ear exceed the cut-off value of 140°/sec.
• Spontaneous nystagmus is abnormal when it exceeds the cut-off value of
6°/sec.
• Unilateral weakness is present when the difference between the right and
left ear responses exceeds the cut-off value of 25%.
• Gain asymmetry/DP is present when the normalized difference between
right beating and left beating responses exceeds the cut- off value of 30%.

53. Rotational chair test
• Here, vestibular stimulation is a rotational stimulus and the
vestibular labyrinth is stimulated by causing a movement of the
endolymph in the lateral semi-circular canal by rotating the
patient.
• Two types of rotational chair tests may be done as a part of the VNG
protocol,
• the Sinusoidal pendular rotational chair test – patient is rotated on
left and right side alternatively.
• the Step ladder Rotational chair test- chair is rotated in 1 direction for
45secs.

54. THANK YOU.