Ocular VEMP - Modifications of the Assessment

This video demontrates some modicfications that can be used to help record the ocular VEMP.

Transcript

Darren Whelan: So now, I'd like to demonstrate some modifications of the ocular VEMP assessment.

So the first one that we can look at is bone conducted oVEMPs, so here we have a B81 transducer.

This is very important so that we have the highest level of stimulus by bone conduction, it's a necessity for VEMP assessments.

We can use this if the patient has unsatisfactory middle ear performance, or differences between middle ear performance from the right to the left side, and that will minimize any artifact or stimulus issues around the middle ear.

The next modification that we can have a look at is fatiguing in eye position.

So as we've demonstrated earlier, the textbook gaze position is at 30 degrees which Leigh is doing now, but that can be fatiguing for some patients.

So a modification during testing would be to ask our patient to bring their head forward as I've got Leigh to do now.

And to gaze straight ahead, that brings his eyes in the upper part of the orbit and aligns then the inferior oblique muscle for the ocular VEMP test.

What we'll start to begin is we'll place the BC on the mastoid, so I'm going to place this on the right mastoid.

And we're going to conduct the first measurement with the 30-degree gaze position.

So I am gonna ask Leigh to bring his eyes to 30 degrees, I'm only going to do a short run because what I'd also like to demonstrate is a technique where we can do shorter runs and add those responses together if we have a patient that's fatiguing.

So we've selected right, we're stimulating at 60.

I'm going to run this now.

I'm keeping an eye on the recordings, we've got 20 recorded, 40.

Again, as before, I'm looking at the minus 20 to 0 line.

We've got 60 recorded, I'm going to stop that now.

So we've got one recording in position, I'm going to now demonstrate the technique of asking Leigh to bring his head forward, raising his gaze up to the top I'm going to record again.

So same stimulus level.

We'll record again.

Again, I'm going to deliberately demonstrate a short run, such as you might have in a patient that's fatiguing.

So we're at 40 responses. 60.

Again, I'm going to stop that, let Leigh relax.

While he's relaxing, I can take a look at both responses and select a response, and now add that response to the previous recording.

And what we now have is a response that contains 120 sweeps combined together so that we can identify the ocular VEMP that's present.

The one final thing, a little tip and trick that sometimes can catch us out in clinic, you'll see that actually in this BC VEMP measurement, we have removed a lot of the electrodes from behind the ear, whereas previously we had those tidied away whilst using inserts.

And there's a reason for that.

Sometimes when we have these situated right near the BC transducer, we can pick up a little bit of artifact, just from the stimulus.

So let me just demonstrate this for you.

So this would be how we had it earlier with the insert.

I'm going to run another measurement now.

We'll have our patient assume the gaze position.

So there we are.

Let's just collect that response.

Only do a short run, so we are 20, 40, 60, 80, so a relatively short run.

And what you can see quite clearly here is the difference at the very beginning of the response.

So just prior to the N1 and P1 complex that we'd marked earlier, we can see that we've got a stimulus artifact so we can almost see the stimulus envelope, prior to the response that we're trying to capture.

I hope those modifications help you think about oVEMP as a clinical test and help you integrate this into your clinic whilst testing patients with dizziness and imbalance.