Training in VNG
Performing spontaneous nystagmus testing (VNG)
Let's now go through how to perform a spontaneous nystagmus test. The spontaneous nystagmus test is the first test to do in any VNG test battery. That's because we want to ensure that there aren't any underlying eye movements which are going to impact later tests which we're going to perform.
How to instruct your patient
Tess, what I'm going to do is I'm going to take this cover and put it on top of the goggles, putting you in darkness. What I'd like you to do is to look straight ahead. You'll be in darkness for about 30 seconds.
During that time, I will turn a light on inside the goggle. When the light switches on, if you could just look at that light for me. And then when the light switches off, just continue looking straight ahead.
Okay, any questions before we begin? Fantastic.
Test procedure
I'm just going to put the cover on the goggle now. Excellent. And if you can look straight ahead. If you can keep your eyes nice and wide open. I'm going to start the test now counting down from 30.
So here I can see Tess' eyes on the screen. If you can keep those eyes nice and open for me that'd be fantastic. After 15 seconds a light is going to appear inside the goggle. Here we can see that in the software. Can you look at that light for me? And then that light's going to switch off after 10 seconds. If you can keep your eyes as wide open as possible. Zero. Fantastic.
That completes the spontaneous nystagmus test. I can take the goggles off and then we are placed inside the test results screen. We can see horizontal and vertical eye movements. If there is any nystagmus, this will be displayed on the right-hand side of the screen.
Abnormal spontaneous nystagmus test
What we can see is a left-beating spontaneous nystagmus of six degrees per second. However, what we can see is as the results continue, when the fixation light switches on, that nystagmus suppresses and therefore vanishes.
So this was an example from a patient which had a peripheral vestibular lesion. That concludes the spontaneous nystagmus test and we're now ready to perform the next test in our VNG test battery.
Description
The spontaneous nystagmus test forms part of the ocular motor sub-tests within the VNG test battery.
There are three clear reasons for performing this test.
The first is that a recorded spontaneous nystagmus can be a strong indicator for a vestibular lesion. The strength and direction of nystagmus can help localize this lesion.
The second is to record any underlying eye movements that might be picked up during subsequent tests. By knowing what these eye movements are, we can correct for them in the other tests.
The final reason is that by adding a fixation target in the goggle, we can have a gross estimation of central involvement. If there is spontaneous nystagmus and this is not suppressed by the fixation light, then there may be central involvement that needs further investigation.
How to perform spontaneous nystagmus testing is detailed and demonstrated in this video.
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