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