Training in VNG
Performing the gaze test (VNG)
How to instruct your patient
The next test in the VNG test battery is the gaze test. The gaze test doesn't require the cover on the goggles because we're going to ask the patient to look at a target on the screen. So Tess, during this test, I'm going to ask you to look at the target on the screen. That target is going to move leftwards, rightwards, upwards, and downwards.
All you need to do is to as soon as the target moves, follow it with your eyes and keep looking at that target whilst it's in that position. What will happen is, we'll stop after 12 seconds, and then we'll move on to the next position. So I'll instruct you as we go through the test which direction to look at.
Any questions before we begin? Fantastic. So let's start the test.
Test procedure
Condition 1: Center
If I can ask you to have a look at the center dot for me, please, eyes open, and here we go. Counting down from 12.
Condition 2: Left
So what's going to happen this time is the target's going to move to the left, and I want you to follow that target with your eyes. Counting down from 12. Okay, looking at the center dot, and to the left. On the graph, we can see a yellow line representing the target moving, and the red and blue lines representing the right and left eyes.
Condition 3: Right
Okay, we're going to move on to the next condition where the target is going to move to the right. So again, if you can look at the center dot for me, eyes open, and here we go, counting down from 12. If there was any nystagmus seen on this test, we'd see it on the average slow phase velocity graph on the right-hand side of the screen.
Condition 4: Up
Okay, doing really well Tess. What we're going to do now is to make the target move upwards. So here we go, looking at the center dot and counting down from 12. Fantastic. With top positions or the vertical positions, we move the eyes 20 degrees, whereas in the horizontal positions, we move the eyes 30 degrees.
Condition 5: Down
Let's finish the gaze test by looking at the downwards position. And again, as this is a vertical test, we're going to be looking 20 degrees downwards. Okay, looking at the center dot please for me Tess and here we go. Counting down from 12. Zero. Excellent.
Results screen
So now that the test is finished Tess, you can relax your eyes whilst I have a quick look at the results screen. What we can see is the results for all five gaze positions. As I mentioned before, if there was any nystagmus present, this would be extracted and displayed in each of the average slow phase velocity graphs, which can be seen to the right of each test.
Abnormal gaze test
This is an example of an abnormal gaze test. What we can see is that when the patient's looking in the center condition and to the right, there isn't any gaze-evoked nystagmus. However, when they look towards the left, we can see a significant gaze-evoked nystagmus, which only occurs during the beginning parts of the gaze.
And this has then therefore been repeated, and we can see that that's consistent across two different test conditions. This is an example of a patient which over further testing revealed to have a central disorder. This concludes the gaze test and now we can move on to the next test we have in our VNG test battery.
Description
The gaze test measures any eye movement generated when maintaining gaze at various angles. Both central and peripheral lesions can cause extra eye movements when performing this test.
Nystagmus can be generated when the patient is unable to hold their eyes at the desired angle, so the eyes slowly drift back towards the center (in most cases). Corrective movements of the eyes then quickly move them back to the target and nystagmus is recorded.
Some clinicians like to perform gaze testing with both a vision stimulus and with eyes closed. The video shows a patient undergoing a gaze test using visual stimulus. The conditions being tested are left gaze, right gaze, up gaze, down gaze and center gaze.
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