VNG & Oculomotor Tests Flashcards
Videonystamograoghy and oculomotor tests
What is a Head Impulse test? Abnormal and normal test?
A test that evaluates the patients ability to keep their gaze fixated on a visual target during a rapid, passive test.
Normal Response: The eyes remain fixed on the target, suggesting that the VOR is functioning properly.
Abnormal Response: The eyes make a corrective saccade (a quick eye movement back to the target) after the head movement. This indicates a possible vestibular weakness or deficit on the side of the head movement direction.
Looking for saccades and not nystagmus. It can be used to test al 3SSC, but usually tests the horizontal semi circular canals.
What is a Head Shake Test? How do you do it? what does a normal and abnormal result look like?
A test that assess the patients ability to maintain their gaze straight ahead following a vigorous passive head shake. Can be done using VOG.
By shaking the head from side to side, clinicians can observe eye movements (nystagmus) that may reveal asymmetry in vestibular function. This helps in identifying issues in the vestibular system, including semicircular canal function.
When the head shaken there is an increased input in the healthy side and low/no inout the affected side. The assymetry is stored and once we stop shaking the head, nystagmus is observed. Nystagmus usually beats away from the side of a lesion for a peripheral pathology.
Inverted nystagmus indicates a central problem
What is a Dynamic Visual Acuity Test? how does it work? What is a normal and abnormal test look like?
A test that measures the patients ability to stabilise their gaze while their head is moving rapidly in different planes.
Here’s how the DVA test generally works:
Static Test: The person is first asked to identify letters or symbols on a visual acuity chart while their head remains still. This establishes their baseline visual acuity.
Dynamic Test: The person then reads a similar chart while their head is moved side to side (or sometimes up and down) at a set pace, often controlled by a metronome. The goal is to maintain focus on the symbols while the head is moving.
Score Interpretation: The visual acuity during the dynamic phase is compared with the static score. A significant reduction in visual acuity during movement can indicate vestibular impairment, as the VOR may not be adequately stabilizing the visual field.
Normal response: visual acuity stays the same or worse by a line in the chart.
Abnormal response: Acuity worsens by 2 or more lines in the chart.
What do we asses in vestibular testing?
- eye movements
- postural control
- myogenic résponses
This will allow us to measure indirectly (the only way), easier to rule in then to rule out conditions.
We can test eye movements through the VOR tho.
What is the Gaze Stability Test: What does an abnormal result look like?
This is the only VNG test that can test for central or peripheral tests: This records eye movements as the patient fixates on a target.
1) Primary gaze = so looking ahead
2) 30 degrees rightwards
3) 30 degrees upwards
4) 30 degrees upwards
5) so degrees downwards
record first with fixation so the patient can see the target then place the VNG goggles and see if they can remain the eye on the stimulus. You measure the amplitude and direction of the nystagmus.
Abnormal results:
spontaneous nystagmus*, gaze evoked nystagmus**, central features which is nystagmus that changes through the test.
*Spontaneous Nystagmus is an abnormality observed from the Gaze Stability Test: Explain what spontaneous nystagmus looks like?
Due to unilateral assymetry in toxic firing rate of the vestibular system.
Sign of a peripheral lesion.
Type of nystagmus that is present in primary gaze part of the gaze stability test.
Commonly seen 3-7 days of an acute episode .
A primarily horizontal nystagmus is a unaltered by changes in head position in the test however when told to fixate, nystagmus is suppressed.
What is the gaze/ Spontaneous nystagmus test:
this evaluates involuntary eye movements whilst the patient looks straight ahead or holds gaze in different directions. You would use a VNG goggles.
How to assess the functioning of the peripheral vestibular system:
1) Eye movement recordings
2) Video Head Impulse testing
3) Caloric irrigation
4) Vestibular Evoked Myogenic Potentials
5) Posturography
6) Rotational chair.
Does the gaze/Spontaneous Nystagmus Test peripheral vestibular disorders or central disorders or both?
it can test for pathologies in both the central and peripheral disorders. A central disorder can be seen by vertical nystagmus.
What are the key things to look out for in a Gaze Nystagmus Test? What would you expect?
A central disorder result:
Spontaneous nystagmus beats in the direction of the gaze and changes. Nystagmus worsens when you fixates on the gaze. Not related to the ear, so nystagmus is present in any direction. The nystagmus does not fatigue.
A peripheral disorder:
Nystagmus beats in one direction regardless of the gaze. Nystagmus will reduce or disappear when fixating on gaze. Nystagmus will experience a fast phase so it will beat away from the side of the lesions. Nystagmus will fatigue over time.
what does a peripheral disorder mean?
Issue in the inner ear or the vestibular nerve.
What does a central disorder mean?
Issue in the brainstem or the cerebellum. usually presented as vertical nystagmus.
patient instruction of spontaneous gaze nystagmus test?
Please sit comfortable and look straight ahead at a fixed target in the distance. Keep your head still and focus on this target as I observe your eye movements. I will ask you to look at specific points to see your eye movements in diff directions.
factors that can affect testing:
- vision problems /blind
- wearing mascara
- lack of consent
- neck or back pain
- medication can suppress the symptoms
- alcohol
- drugs
- patients that already have spontaneous nystagmus
- recent eye surgery (cataracts)
- epilepsy
- patients that aren’t alert (dementia patients)
- good lock on visual target
why would you do spontaneous nystagmus test:
this is the 1st done when doing VNG, to rule out any spontaneous nystagmus.
What are saccade test?
Saccades are fast and voluntary eye movements that bring images of a new object onto the fovea, which is part of the retina that is responsible for successful visual acuity. So you test to see the accuracy of rapid eye movements. You would use VNG goggles.
Can you tell how an abnormal and normal test would look like?
THE IPAD PAGE 2.
normal response: the patient should be able to track the shoot, and not under shoot or over shoot. there is a small latency between the eye movement but it should be abel to hit the target.
How do you perform the saccade test?
The saccade test measures the patient’s ability to accurately move the eyes from one designated focal point to another in a single, quick movement. The ability to accurately perform saccade testing assesses the patient’s central vestibular system.
Does the Saccade Test peripheral vestibular disorders or central disorders or both?
Tests ONLY for central disorders?
What are key things to look out for in saccade test?
Latency: a delayed response
Accuracy: hypermetria (overshooting), hypometria (undershooting).
Velocity: show saccade brainstem.
could indicate a basal ganglia disorders.
What are the patient instructions for a saccade test?
“Sit comfortably and looks straight ahead. You will see a green dot on the screen. Simply look at the dot. If the dot moves, follow it with your eyes only as quickly as you can. Try not to move your head. Follow my instructions and make sure to return your eyes to the centre before looking at the next target.”
What is a smooth pursuit test?
Evaluates the ability to track and follow moving objects. In cases where the smooth pursuit system is impaired due to a central lesion, the eyes may lag behind the moving target, necessitating catch-up saccades to reestablish fixation on the target.
Patient instruction for a smooth pursuit test:
“You will see a green dot on the screen. The dot will move from one side of the screen to the other in a smooth, predictable motion. Your task is to follow the dot with your eyes while keeping your eyes precisely on the dot. Try not to move your head and try not to get “ahead of” or “behind” the target.”
Normal smooth pursuit test results:
a graph where it shows consistent smooth curved waves. There will be two lines following close together. Normal response; they should be able to follow the light and not have any rigid movements & track it. The responses for each cycle of the pursuit are represented on the graph by red dots for the right eye and blue dots for the left eye. Responses that are within threshold limits will fall in the white region and responses outside the threshold limits will fall in the grey shaded region.
IPAD
Caloric test: what does it test?
The caloric test is usually the last test that we perform in the VNG test battery. It tests the responsiveness and function of the lateral semicircular canals by measuring them and comparing the symmetry of their response. Can be done water or air irrigation.
Why do we change the temperature in calorics?
The temp of the air or water effects the embryo lymph fluid, changing its temperature in the canals to trigger nystagmus. his generates an asymmetry between the two vestibular systems in the inner ears and causes a nystagmus to occur. We call this caloric-induced nystagmus.
Do we use VNG in calorics?
Yes
Why do we place patients in a supine position?
so we start placing the patient in a supine position and head up in 30 degree angle. the ears and eyes should be levelled and be pointing up. This head position will place the lateral semicircular canals in the plane of gravity.
What are the temperatures for air and water irrigation in calorics?
AIR:
- warm air is 50 degrees and cool is 24 degrees
WATER:
- Water is 7 degrees above and below the body temp 30 to 44 degrees Celsius.
How long do we irrigate the ear?
- [ ] with air, we irrigate the ear for 60 seconds which is longer than we would irrigate for water (8litres)
- [ ] water is 230ml for 30 seconds
What canal does calorics test?
Horizontal canal only
How to do it?
- it’s important to perform otoscopy and tympanometry to assess the status of the ear canal and middle ear.
- Reassure your patient by explaining that any dizziness experienced is a normal reaction and that the test will not provoke an episode of their own dizziness.
- it’s important to record any nystagmus in the caloric test position. This is important because if there is a nystagmus present, you should take this into consideration during the results interpretation.
- After 15-30 seconds of irrigation, you will begin to see a nystagmus begin to generate and then increase in size. The response will reach its peak and then starts to subside, which usually occurs about 40 to 45 seconds after the end of the caloric irrigation. Once the response begins to subside, you should ask the patient to fixate for 10-15 seconds. this is with VNG goggles
- It’s important to record for a few seconds after the fixation light has been switched off again. Once the irrigation has finished, you should wait for 5 minutes before starting the next irrigation to ensure the nystagmus has completely stopped.
why does irrigation occur in the ears when you warm it?
The area of the semicircular canal that’s closest to the external auditory canal is going to heat up. In turn, the endolymph in the semicircular canal will get lighter and it will rise. This will put pressure on the cupula and bend it toward the utricular sac. This would cause excitation of the semicircular canal. In this case, the irrigated ear has a higher neural firing than the non-irrigated ear. That will give the patient a sensation of rotation toward the irrigated ear and the vestibulo-ocular reflex (VOR) will move the eyes away slowly from the irrigated ear.
COWS
why does irrigation occur in the ears when you make it cold?
the endolymph will get heavier, and it will sink. This type of cupular deflection away from the utricular sac will cause inhibition of the semicircular canal and the neural firing will decrease. Because the tonic neural activity in the opposite ear is higher than this, the patient will feel like they’re rotating toward the non-irrigated ear or away from the irrigated ear. Cool irrigations will generate nystagmus that beats opposite to the direction of the irrigated ear. COWS
What does COWS stand for?
Cool irrigation, nystagmus beat in the opposite direction of
ear being irrigated
▪ Warm irrigation – nystagmus beat in the same direction of
ear being irrigated
what is the unilateral weakness equation?
UW% = (RC + RW) - (LC+LW)/ RC+RW+LC+LW ALL*100
why do we mental alert when asking questions?
This is to stop patient from suppressing their vertigo and so we can observe nystagmus.
what are normal results for caloric testing?
you will see a response to stimulus 15-30 seconds into the irrigation procedure. Reach a peak 60-90 seconds of the irrigation. you would also observe cows. Usually shown in a butterfly graph. you have right warm right cool, left warm and left cool.
what is unilateral weakness?
Its compares the caloric response of the right and left ears. Caloric weakness can be calculated from the graph. if there is difference greater than 25% it is known as a weakness and significant and can be due to a vestibular weakness. under 25% is considered normal.
How does abnormal results look like?
it looks like an obvious assymetry on the butterfly graph. common causes of unilateral weakness are: Menderes disease, vestibular neuritis, Menderes disease, vestibular schwannoma, vestibular migraine.
What is bilateral weakness?
Bilateral weakness occurs when both vestibular systems are damaged. This is usually when their is no assymetry in the butterfly graph but the figures are still really small. This is less than 12 degree per second. It is not very common, so should be identified along a patient’s history.
most common causes are ototxitiy of vestibular bilateral weakness.
what is directional preponderance?
Directional preponderance is the relative difference between right‑beating vs left‑beating nystagmus. You take the total right‑beating nystagmus and subtract the total‑left beating nystagmus. Then you normalize it by dividing by the total beating nystagmus from both ears. This is when nystagmus in one direction is stronger than the left. There is an equation?
what is the equation for directional preponderance?
DP = (RW+LC)-(LW+RC)/RC+RW+LC+LW *100
IF RESULT IS GREATER THAN 30 % THAN DP EXISTS
Causes of DP?
Usually due to an undermining spontaneous nystagmus in the absence of fixations. The baseline of all the caloric irrigations will shift in one direction based on the slow phases of spontaneous nystagmus. This is the most common method and instead of using directional preponderance to diagnose that, you can make a much easier interpretation based on the spontaneous nystagmus.
There’s an extremely rare type of directional preponderance where the irrigation results for one direction of nystagmus are higher compared to the other direction without any substantial nystagmus. This is v rare.
what is fixation index?
The fixation index serves as a useful test of central vestibular function and is a core element of the caloric test.
what is the equation for fixation index?
fixation index = the intensity of slow phase velocity of nystagmus during fixation period divided by the intensity of nystagmus during no fixation period. *100
what is an abnormal fixation index result?
we expect to see a 60% reduction in nystagmus. however an abnormal fixation is If it exceeds that, you should consider it abnormal. In this patient, especially for right irrigations, It’s most common in patients with midline cerebellar abnormalities.
Why do you introduce the fixation light after the nystagmus has reached its maximum slow phase velocity?
To assess the central pathways for fixation suppression
Hyperactive caloric responses?
Sometimes the caloric response can cause a a nystagmus which is greater than what would be expected. This can be down to both technical and clinical reasons. This is when the total caloric response for each ear is greater than 140 degrees per second.
causes of hyperactive caloric responses:
perforated ear drum, open or altered mastoid, or technical error.
