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Vestibular Foundations > Session 2: VOR & VNG > Flashcards

Session 2: VOR & VNG Flashcards

1
Q

what is the difference between VNG and ENG?
*think method, tech, accuracy & ease of use
SO: direct vs indirect?whats being measured?

A

METHOD:ENG is an indirect measurement via electrical signals WHEREAS VNG is a direct measurement via video recording

TECH: ENG measures cornea- retinal potential WHEREAS VNG tracks eye movements with infrared cameras

ACCURACY: ENG is less accurate for vertical movements WHERAS VNG is highly accurate for all eye movements

EASE OF USE: ENG requires electrode placement WHEREAS VNG requires goggles with cameras

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2
Q

What is VNG used for?

A

VNG is used to detect and localize vestibular dysfunction in patients who complain of dizziness and/or imbalance

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3
Q

Can we diagnose vestibular disorders with a single test?

A

no, the vestibular system is a intricate system, an assessment of the vestibular system requires a battery of tests each stimulating a particular anatomical structure in an effort to challenge that structure and identify dysfuntion

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4
Q

what tests does VNG consist of?

A
  • spontaneous nystagmus
  • gaze test
  • smooth pursuit/ tracking
  • saccade test
    -optokinetic test
  • positioning testing
  • caloric irrigation
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5
Q

what is the VNG set up?

A

*Key components:

VNG Goggles:
- Infrared diodes and a dichroic mirror track eye movements.
- Vision-denied condition prevents visual fixation.

Pupil Localisation Technology:
- Tracks pupil position using infrared cameras.

Examination Table:
- Allows the patient to lie comfortably and ensures proper positioning.

Computer Monitor:
- Displays real-time eye movements and tracings.

Sufficient Space:
- Allows the examiner to move freely around the patient.

*Steps
1) Place goggles snugly on the patient.
2) Perform equipment calibration.
3) Rule out spontaneous nystagmus (Block visual input and record eye movements in darknes- vision denied condition).
4) Analyze video signals using Hough transform (Identifies patterns like eye movements in noisy data.).

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6
Q

why do we calibrate the equipment for VNG?

A

to ensure valid and reliable test results

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7
Q

what types of eye movements are used in caliration?

A
  • Saccades: Quick, jerky movements shifting focus between targets.
  • Sinusoidal movements: Smooth, wave-like oscillating movements.
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8
Q

What is the ANSI recommendation for calibration?

A

The American National Standards Institute (ANSI) recommends using a ±20-degree horizontal arc, where the patient’s eyes move 20 degrees to the left and right from the central resting position.

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9
Q

Why is the ±20-degree horizontal arc used for calibration?

A

The ±20-degree arc represents the normal field of eye movement, ensuring accurate tracking and reliable results during subsequent tests.

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10
Q

What can cause faulty calibrations in VNG testing?

A
  • Contamination by noise or artifacts (e.g., blinking or electrical interference).
  • Uncooperative patients (e.g., head movement or poor focus).
  • Inaccurate distance between the goggles and the light bar.
  • Poor instructions provided to the patient.
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11
Q

How can faulty calibrations be identified?

A
  • Misaligned Data: The system shows the eye looking in a different position than the actual target.
  • Erratic Measurements: Saccade amplitudes or pursuit patterns appear inconsistent or impossible.
  • Low Data Acceptance: Few data points are considered valid, indicating poor calibration accuracy.
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12
Q

What are the consequences of faulty calibrations?

A

Faulty calibrations can lead to misinterpretation of nystagmus, resulting in inaccurate diagnosis and treatment.

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13
Q

what are the advantages and disadvantages of VNG?

A

Advantages:
- no electrodes requires
-vision denied
-video recordings

Disadvantages:
- not suitable for some patients

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14
Q

Why is the distance set by the manufacturer important in VNG?

A

it ensures the correct 30-degree angle from the eye to the outermost light, allowing accurate measurement of eye movements within the natural range of motion.

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15
Q

what is spontaneous nystagmus?

A

-its an involuntary eye movement that can affect ALL other VNG subset’s

  • due to a unilateral asymmetry in tonic firing rate of the VS, usually associated with peripheral vestibular dysfunction
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16
Q

when is spontaneous nystagmus most prominent?

A

Greatest spontaneous nystagmus within 3-7 days of acute episode

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17
Q

What are the characteristics of primarily horizontal nystagmus?

A
  • Unaltered by changes in head position. (tis differentiates it from positional nystagmus)
  • Suppressed by visual fixation. (indicates peripheral Vestib disorder)
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18
Q

what are slow phase and fast phase?

A

*SLOW PHASE:
-this is the slower movement of the eye caused by the imbalance in the VS
-it moves the eyes away from the healthy side (toward the weaker ear/ lesion).

*FAST PHASE:
-this is the quick, corrective movement of the eye back to its original position.
- it is controlled by the brain to compensate for the slow phase
-the fast phase determines the direction of the nystagmus

  • fast phase is always the more vertical point and the slow phase is the sloped.
  • the direction its beating in, what hand matches the slope?
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19
Q

for a spontaneous nystagmus, which direction ear does the fast phase beat towards?

A

it beats towards the healthy ear - the side with greater neural activity

  • the fast phase of the nystagmus represents a corrective movement of the eyes back towards the stronger side (healthy ear)
  • the slow phase moves toward the weaker or affected ear
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20
Q

What do normal and abnormal results in a spontaneous nystagmus test indicate?

A

*Normal Result: The brain receives equal signals from both ears, resulting in steady eye movements with no abnormal activity. This is shown by balanced tonic activity between the right and left ear.

*Abnormal Result: Damage or dysfunction in one ear causes unequal signals, leading to involuntary eye movements (nystagmus). Abnormal results show significant differences in activity, often exceeding 6 degrees per second, indicating a vestibular system issue.

  • the graph shows the balance/ imbalance in tonic activity
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21
Q

how do we test spontaneous nystagmus?

A
  • place a mask over the video goggles
  • ask the patient to look where they think is straight ahead
  • if rhythmic eye movements of more than 6 degrees is noted, in this vision declined condition, this suggests spontaneous nystagmus to be present
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22
Q

what is the purpose of gaze testing?

A

-to assess the patients ability to maintain a steady gaze on an object without generating eye movements or nystagmus.

-basically no extraneous movements

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23
Q

what is gaze evoked nystagmus (GEN) and what does it indicate?

A
  • the inability to maintain a steady gaze, can be an indication of both peripheral and central vestibular system lesions.
  • (supressed by visual fixation indicates peripheral)

-It is characterised by fast phases of nystagmus in the direction of the gaze. (e.g. If the patient looks to the right, the nystagmus beats (rapid movements) to the right, and if they look to the left, it beats to the left.)

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24
Q

what are the conditions that gaze testing is done under?

A

1-primary gaze (meaning the patient is looking straight ahead)
2- 30° gaze rightwards
3- 30° gaze leftwards
4- 30° gaze up
5- 30° gaze down

*do mental alerting throughout VNG testing, like counting backwards, asking simple athematic, girls names starting with letters etc- this is to maintain focus, no drowsiness for true vestibular or oculomotor responses

*record for at least 15 secs in each gaze position, with and without fixation

*Measure the amplitude and direction of any nystagmus produced during each position.

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25
Q

how is the amplitude and the direction of the nystagmus measured with gaze testing?

A

*observe 2 traces on the screen:
-the black trace reps the stimulus or target movement
-the blue trace reps the patients eye movement

-the blue traces height of peaks= amplitude which is range of eye movement

-direction is whichever direction the fast beating is

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26
Q

What are the criteria for abnormal gaze-evoked nystagmus (GEN)?

A

Abnormal = persistent and >3 deg/sec

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27
Q

how can you differentiate between a peripheral lesion or central lesion with GEN?

A

*Peripheral Lesion:

  • Nystagmus typically beats away from the lesion (fast phase opposite the affected ear).
  • Usually suppressed with fixation.
  • Often associated with vestibular dysfunction.

*Central Lesion:

  • Nystagmus may exhibit direction changes depending on gaze position.
  • Persists or increases with fixation.
  • Indicates potential CNS involvement.
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28
Q

why is it important to record nystagmus with and without fixation?

A

-nystagmus that reduces with fixation is usually peripheral

-nystagmus that persists o increases with fixation is typically central

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29
Q

what are some patient instructions for gaze testing?

A

“you will see a yellow dot on the screen, simply look at the dot, if the dot moves follow it with your eyes, try not to move your head”

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30
Q

How do the features of central and peripheral nystagmus differ in VNG?

A

*Peripheral Nystagmus:

Nystagmus features: Horizontal or torsional
Direction: Fixed
Fixation: Supresses
During gaze testing: Adheres to Alexander’s Law

*Central Nystagmus:
Nystagmus features: Vertical, horizontal, torsional.
Direction: can vary
Fixation: No change or worsens
During gaze testing: Does not adhere to Alexander’s Law

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31
Q

What abnormalities can be identified during gaze testing?

A
  • Spontaneous nystagmus
  • Gaze-evoked nystagmus
  • Central features
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32
Q

How does Alexander’s Law describe the behavior of peripheral nystagmus?

A
  • Slow phase velocity Increases when the patient gazes in the direction of the fast phase.
  • Slow phase velocity Decreases with visual fixation.
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33
Q

How is peripheral nystagmus categorized according to its degree?

A

1- First-Degree Nystagmus:
Present only when gazing toward the fast phase direction (e.g., right or left).

2- Second-Degree Nystagmus:
Present in central gaze (straight ahead) and when gazing toward the fast phase.

3- Third-Degree Nystagmus:
Present in all three gaze directions: central, fast phase, and slow phase directions.

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34
Q

what are the 4 ocular motor tests commonly performed in VNG?

A

1) saccade test
2) smooth pursuit test
3) optokinetic test
4) gaze fixation test

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35
Q

what advantage does the gaze test have on the 4 ocular motor tests available in VNG?

A

gaze testing is the only one that can detect both central and peripheral vestibular disorders

36
Q

what is the purpose of testing smooth pursuit/ tracking?

A

-to assess the patients ability to accurately track a visual target with continuous movements across (or up and down) ,in a smooth, controlled manner.

  • can be tested at different speeds, its the dot moving across
37
Q

what system does smooth pursuit/ tracking test? and how?

A

-smooth pursuit tracking assess the patient’s central vestibular system

-often using a sinusoidal target of varying frequencies- 0.2Hz to 0.7Hz

38
Q

what are some patient instructions for smooth pursuit/ tracking?

A

“you will see a yellow dot, the dot will move from one side of the screen to the other in a smooth predictable motion. Your task is to follow to dot with your eyes, whilst keeping your eyes precisely on the dot, try not to move your head and try not to get ahead or behind the target”

39
Q

how do we know the patients smooth pursuit/ tracking results are normal or abnormal?

A

Normal= or the trace, the stimulus and the response will be virtually identical.

Abnormal= anything other than a smooth replicate of the stimulus is considered abnormal

  • we can look at gain as a measure of the eye movement vs the target movement
  • you can look at whether movement is within phase of the target movement.
  • we can look at asymmetry between eyes
40
Q

What is impaired smooth pursuit?

A

cannot follow a moving target and instead
approximates target motion using successive saccades

41
Q

what does abnormal smooth pursuit tracking show?

A

it implies the presence of a central vestibular pathology

42
Q

What factors can affect smooth pursuit performance?
A:

A
  • Attention
    – Fatigue
    – Medication

*AGE: Performance declines starting from the 3rd decade of life.
- Results are compared to age-related normative data.

43
Q

what is a special care consideration of smooth pursuit tracking?

A

-its susceptible to an age effect

-may require the examiner to acclimate the patient to the task prior to recording results

44
Q

what is the purpose of the saccade test?

A

-to assess the patients ability to accurately move the eyes from one designated focal point to another in a single, quick movement

-the saccade test tells us whether there is a central pathology that is precluding accurate fixation of the eyes onto moving targets

  • each of the saccades subtests can give anatomy specific information about the patients central vestibular system
45
Q

How are saccades tested during VNG?

A
  • Record eye movements as the patient follows a visual
    target that jumps back and forth on the light bar
  • Randomised amplitude and direction saccades for 30-60
    seconds
46
Q

what system is being tested with the saccade test?

A

-the patients central vestibular system

47
Q

which is the most useful of the saccade tests?

A

the random saccade paradigm

48
Q

what are some patient instructions for saccade testing?

A

“you will see a yellow dot, simply look at the dot, if the dot moves follow it with your eyes only, try not move your head”

49
Q

what are normal saccade test results?

A

the stimulus trace and the response trace will be virtually identical

50
Q

what are the parameters that the analysis of the saccade test considers?

A

Latency (ms) = time between target movement and first eye movement. Normal latency= 100-200ms & Abnormal latency= greater than 200ms- which could indicate a CNS dysfunction

Accuracy (percent)= whether the patient can move his eyes directly to the target without ‘overshooting’ or ‘undershooting’. (size of excursion compared with target excursion. A perfectly matched movement=100%

Velocity (deg/sec) = meaning how fast the eyes are moving from point to point (speed of eye movement)

51
Q

What are the two types of dysmetria and what do they indicate?

A

*Hypometric (undershoot)= consistently makes saccades that are too small in amplitude to reach the target.

*Hypermetric (overshoot)= consistently makes saccades that are too large in amplitude to reach the target.

52
Q

how are saccade results analysed?

A

-the dots should not be within the grey shaded area

  1. Latency:
    – Can be prolonged, shortened or asymmetric
    – Only relevant when using non predictable target
    – Affected by visual acuity, cooperation and brightness of target
  2. Velocity:
    – Can be too fast or too slow
  3. Accuracy:
    – Inaccuracy is known as dysmetria
    – True dysmetria always accompanied by corrective saccades
53
Q

what does the optokinetic test/ reflex do?

A

the optokinetic reflex/ test allows the eyes to follow objects in motion while the head remains stationary.

  • its the checked pattern moving across
54
Q

What does asymmetric or absent optokinetic nystagmus (OKN) suggest?

A

the inability to produce symmetric optokinetic nystagmus (OKN) implies a dysfunction of the central vestibular system.

55
Q

What is Optokinetic Nystagmus (OKN)?

A

Optokinetic nystagmus is a reflexive eye movement that happens when you watch a moving object or a pattern, like stripes on a rotating drum. Your eyes do two things during this reflex:

Smooth pursuit: The eyes follow the moving object or pattern smoothly.
Resetting movement (quick phase): The eyes quickly jump back to focus on the next part of the moving object or pattern.

This back-and-forth motion is what we call “nystagmus.”

56
Q

what are the patients instructions for the optokinetic test?

A

because the optokinetic response is a reflex, DO NOT over instruct the patient.

simply say “watch the lines on the screen”

56
Q

What are the visual field requirements and limitations of optokinetic testing?

A

-REQUIREMENTS: OKN requires a stimulus that fills 90% of the visual field to properly activate the optokinetic reflex

-LIMITATIONS: if only a partial field is used, the pursuit system dominates, reducing the accuracy of the OKN test

57
Q

What does it indicate if a patient can track a target accurately in one direction but not the other during an optokinetic test?

A

This often indicates an abnormality toward the side with a vestibular lesion.

58
Q

Why must the examiner ensure that the patient is actively watching the screen during an optokinetic test?

A

the examines needs to aware of whether the patient is actively watching the screen.

-optokinetic are usually disturbing to the patients vestibular system so in an effort to compensate, the patient may try to stare through the screen.

-the result will appear as a flat line on the tracing

59
Q

do we use standalone optokinetic testing to tell us about central vestibular pathology?

A

no, its best paired with smooth pursuit tracking as it gives a more complete picture of central vestibular function.

OKN out of the oculomotor tests has the least specificity in identifying a CNS pathology.

60
Q

what is the purpose of the Dix Hallpike Test?

A

to serve as a technique for differential diagnosis of positional vertigo by ruling out benign paroxysmal positional vertigo, or BPPV for short

61
Q

what are some patient instructions for Dix Hallpike Test?

A

“im going to place a make over your goggles, i would like you to cross your arms over your chest and tur your head to the left on the count of 3, i want you to lie back as quickly as you can while keeping your head turned and eyes open. I will support you throughout the entire purpose.”

62
Q

What do straight-line tracings without significant peaks or dips indicate during an optokinetic test?

A

hey indicate that the patient does not have any form of vertigo, although normal eye movement (with small peaks and dips) is still expected.

63
Q

what are hallmark signs/ characteristics of BPPV nystagmus?

A

-does the nystagmus have delayed onset of 2-20 seconds?

-is the nystagmus a torsional (rotary) nystagmus?

-does the nystagmus fatigue after a few seconds?

*other characteristically to watch out for:

-does the nystagmus reverse positions when you return the patient to a sitting position?

-is the nystagmus less intense upon retest?

*generally all these characteristics will appear together if the patient has BPPV

*if the nystagmus doesn’t meet these characteristics there usually a different peripheral vestibular dysfunction that is the source of the nystagmus

64
Q

what is the purpose of positional testing?

A

to determine whether a chnage in the position of the patients vestibular systems in space provoked nystagmus. It can evoke central or non localising findings

65
Q

why do we perform positional testing vision denied, using covered goggles?

A

so the patient does have any means to supress nystagmus by fixating on an object

66
Q

what are some patient instructions for positional testing?

A

“i am going to place a mask over your eyes. I will then assist you in moving into different positions.
It is important to keep you eyes open at all times so that the cameras can record your eye movements”

67
Q

what are the positions that should be tested in positional testing and why? (the whole test)

A

1) supine position as it provides a baseline for all other positions

-in the supine position, the patient lies on the able, vision denied, while their head is supported by the examiner and elevated at 30 degrees.
*the head is at this angle because this is the natural position of the head ,relative to the body in its natural state

2) the examiner will gently guide the patients head to one side and allow adequate ie for nystagmus to occur (approximately 15 seconds)

3)if no nystagmus occurs, return patient to the supine position and turn the head in the opposite direction and repeat the procedure

4) if nystagmus is noted in either the head right or head left positions, immediately turn on the fixation light and note whether the nystagmus changes.

5) after making note of changes in nystagmus, ask the patient to roll onto his shoulder towards the side of the effected ear, note changes in nystagmus

68
Q

what does an abnormal response, displayed as a nystagmus indicate? positional testing

A

Result interpretation:
An abnormal response, displayed as nystagmus, that is seen in any position is highly suggestive of vestibular disorder.

69
Q

what does the presence of a nystagmus as a result of a change in position indicate?

A

it could indicate, but is not limited to:
-cervical pathology
-lesion of the vestibular end organ.

Additional testing is required to further differentiate pathology.

70
Q

what is the purpose of the caloric test?

A
  • The caloric irrigation is the current gold standard vestibular test which allows the clinician to test horizontal semi- circular canal function.
  • The purpose of caloric irrigation is to assess the symmetry of the bilateral peripheral vestibular system and to analyse the excitatory and inhibitory responses of each vestibular end organ independently.
71
Q

What does caloric stimulation achieve and what does it indicate about the vestibular system?

A

*Caloric stimulation mimics a very slow, non-physiologic head movement (0.002–0.004 Hz) by moving the endolymph. It allows the examiner to stimulate each vestibular end organ independently to assess for:

  • Unilateral weakness: When one end organ is weaker than the other.
  • Bilateral weakness: When both vestibular end organs fail to provide sufficient vestibular information.
72
Q

How do caloric irrigators stimulate the vestibular system, and what is the typical response timeline?

A

Caloric irrigators use either air or water to stimulate the vestibular system, depending on the examiner’s preference. A fully functional peripheral vestibular end organ will typically begin to respond to the stimulation within 15-30 seconds of the irrigation process, reaching its peak response around 60-90 seconds after the process begins.

e.g. Air Fx
Aqua Stim

73
Q

How does cool and warm air or water affect the direction of nystagmus during caloric testing?

A

Cool air and water will produce nystagmus that beats away from the stimulus

Warm air and water will produce nystagmus that beats toward the stimulus

Cool
Opposite
Warm
Same

74
Q

normal vs abnormal caloric test results

A

-normal is symmetrical

Abnormal:
-Unilateral weakness an asymmetry of greater than 25% between ears
-Bilateral weakness- a symmetrical but weak respone from each ear

75
Q

what is directional Preponderance (DP)?

A

DP is a numerical measure used during caloric testing to compare the intensity of right-beating nystagmus to left-beating nystagmus. a DP of 30% or greater is considered abnormal

76
Q

What is nystagmus?

A

Nystagmus is a type of eye movement that can be generated by either the peripheral vestibular system or the central nervous system (CNS) structures.

77
Q

How is nystagmus measured?

A

1- Latency and duration of the nystagmus.

2- Direction of the nystagmus, which is determined by the fast phase.

3- Intensity, which reflects the amplitude (size of the eye movement) and frequency (number of beats per second) of the eye movements.

78
Q

What are the phases of nystagmus?

A

1- Slow phase: The slower movement of the eye in one direction.

2- Fast phase: The rapid movement of the eye in the opposite direction.
The direction of the nystagmus is named based on the fast phase.

79
Q

what is the sensitivity of oculomotor tests for detecting cerebellar/ brainstem lesions and how does combining them improve accuracy?

A

-smooth pursuit= 73%
- Gaze test= 47%
- Saccades= 40%

*combining all3 tests achieves a sensitivity of 87%

80
Q

why is vestibular testing only 1 part of diagnosing balance disorders?

A

because balance problems can be caused by various conditions including:
- metabolic
- cardiovascular
- endocrine
- neurological conditions
- medication side effects

Additional tests may include:
- MRI scans
- blood tests
- tilt- table tests
etc

81
Q

what are the 5 main categories of vestibular tests?

A

1- Oculomotor tests:
- check voluntary eye movement control
- can indicate peripheral or central pathologies.

2- Vestibulo- ocular reflex (VOR):
- use the VOR to check vestibular function.
- Usually indicate peripheral pathologies but sometimes central issues.

3- Positional and positioning tests:
- assess if specific positions or movements cause dizziness or nystagmus
- Diagnose specific conditions or add evidence for peripheral/ central disorders

4- Evoked potential tests:
- measure electrical; responses to vestibular stimulation (via muscle contraction)
- Identify peripheral disorders,

5- Posture and gait tests:
- evaluate overall balance function and impact on daily life.
- rarely provide diagnostic information.

82
Q

what is Head Impulse Testing?

A

A test that measures the patient’s ability to stabilize their gaze while their head is moving rapidly in different planes.

83
Q

what is Head Shake testing?

A

A test that assesses the patient’s ability to maintain their gaze straight ahead following a vigorous passive head shake.

84
Q

what is dynamic visual acuity testing?

A

A test that evaluates the patient’s ability to keep their gaze fixated on a visual target during a rapid, passive head turn

Vestibular Foundations (10 decks)

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