The next test in the VNG test battery is the smooth pursuit test. This test requires the patient to follow a target, which is moving back and forth on the screen. So again, we don't need the cover for this test.
Tess, during this test, the target is going to move backwards and forwards on the screen. I'd like you to keep your head still and follow the target with your eyes. As this test goes on, that target is going to increase in its speed. I want you to follow that target as closely as you possibly can. Try not to jump ahead of the target, but to follow it as smoothly as possible. And then the test will last for around about 50 seconds.
Do you have any questions before we begin? No. Fantastic. Okay, let's start the test.
If you can have a look at the dot in the center of the screen, here we go, counting down from 49. So we can see that the target is now moving in a smooth fashion. Sometimes this is called the tracking test, because we're looking at how well the eyes can track that target. So you're doing a great job there Tess, if you can just keep your eyes following that target as smoothly as possible.
And what's going to happen is that that's going to speed up as the test continues. Here we can see the target speeding up. And in the software, we can see a yellow line representing the target and the blue and red lines representing the left and right eyes. On the far side of the screen, we can see that the results are populating in real time. So we can start to analyze the test, even whilst Tess is still performing the test.
Once the test is complete, we get a result screen. And what we're interested in looking at here is primarily the gain. So how well the eye is tracking the target, and then also the symmetry to see if there's any differences between the right and left movements of the target.
What's interesting in this test is that we can see that the gains in the right eye are different from the gains in the left eye. We can see that the gains in the right eye are within the normal range. However, the gains in the left eye are reduced. This is an example of a patient which has deconjugate eye movements and was later diagnosed of a central condition. That concludes the smooth pursuit test and now we're now ready to move on to the next test in the VNG protocol.
The smooth pursuit system allows us to track a moving target.
Smooth pursuit tracking assesses the patient's central vestibular system and is normally un-affected by peripheral lesions (unless there is a spontaneous nystagmus) - although it is susceptible to age related effects.
Testing can be performed horizontally and vertically. This video demonstrates a patient undergoing a horizontal smooth pursuit test.