Ocular VEMP - Running the Test

This video demontrates a live recording of the ocular VEMP, and the identification of the biphasic response, and the marking of the waveform.

Transcript

Darren Whelan: Now that we have our patient prepared, we are going to conduct an ocular VEMP.

So we're using inserts with our protocol selected because we know that Leigh has satisfactory middle ear function.

Now before we put the inserts in, we're going to give our patient the instructions, so they know what to do throughout the test.

So in this test, we're going to ask Leigh to hold his eyes at a 30-degree angle whilst the test is being conducted.

And that would be when the sound is actually being present in his ear.

Now, I've actually got a marker at a 30-degree point on the wall so that Leigh knows where to keep his eyes positioned.

That's perfect, so you can maintain that position whilst we're testing, excellent.

So let's put these inserts into position.

Okay, if you can look up.

Now with our ear and intensity selected, we're going to start our recording, we have our patient looking at the 30-degree gaze angle, we press start.

And we'll start collecting some sweeps.

Now the ocular VEMP is a much smaller response than the cervical VEMP, so we do have to run more sweeps than you may typically see in a cervical VEMP assessment.

We can see the response coming through.

What we can do is we can start to keep our eye a little bit on the pre-stim area of the epoch, so the minus 20 to 0 and just see how much noise is coming into the response.

We expect some noise because this is a myogenic response, it's a muscular response, the muscle is responding to the stimulus at the utricle.

We have 240 sweeps.

And we can see the response coming through very nicely.

And in our pre-epoch measurement, we can see that it's very much leveling out, we've got about one microvolt of activity there.

So I'm going to pause that now at 320 sweeps, and we can take a look at the response.

So we can start to identify where N1 will be, and where our P1 will be.

And then we're N1 at 12 milliseconds and P1 at 15.33 milliseconds.

Now that we have the right oVEMP response measured, we're going to do a similar measurement on the left side.

So we're going to select the ear, select the same stimulus level of 95, check our patient is gazing at 30 degrees and start the measurement.

We're already at 40 sweeps.

But remember in the ocular VEMPs, you may need to record more sweeps than you would see in the cervical VEMP.

This is because it is a smaller response.

There is my myogenic activity that we're measuring, so it's a muscular response, so there is noise within the trace.

And we want to see that waveform come nice and clear.

So looking at the response, now we can look at the epoch at the pre-stim input period, the 0, the minus 20 to 0, and see how much noise is in there.

And that's settling down very well now.

We're at 200 sweeps. 240 sweeps.

And the noise is that we have in the trace now is actually a little bit low, below one microvolt.

So I'm going to stop that recording, and then we can take a look at the response.

So let's again mark the response, so we'll select the left ear, place our markers.

And then what we can do to look for symmetry is pair that with the other side.

And as we can see with Leigh's responses today at 95 dB, he has a 5% asymmetry.

That's well, very much within the normal limits.