Gaze Stabilization Test (GST)

What is the Gaze Stabilization Test (GST)?

The Gaze Stabilization Test (GST) is a behavioral assessment of the vestibulo-ocular reflex (VOR) function in response to functional head movements. It is often paired together with the Dynamic Visual Acuity (DVA) test. If you have purchased the VORTEQ™ Assessment bundle, you will be able to perform the GST.

Figure 1 - Tests in the VORTEQ™ assessment bundle

For this test, the patient will move their head at different speeds but the optotype will always stay the same size, which has been determined from their static acuity score.

Screen setup

Select the Optotype Stimuli display source and set the screen size and patient distance in the System Default Settings before beginning the first test. A suggested patient distance will be identified for your screen dimensions. If the distance is too much for your room set up, then choose a smaller display input.

Figure 2 - Optotype stimuli settings for GST

Protocol setup

The default protocol is automatic, but you can also choose a manual target presentation. You can choose the options in Summary Parameters.

Figure 3 - Summary parameters protocol setup for GST

The default starting head speed is 75 degrees per second, but you can adjust that if needed.

Figure 4 - Test parameters protocol setup for GST

The metronome should be “ON” to give the patient feedback on how fast to move their head. The metronome sound will stop after each optotype appears to give the patient time to enter their response with the remote control. The sound will start again when they move their head.

Preparing for the test

Select Gaze Stabilization from your default protocol if you have already set it up. If not, you can add it from the subtest menu for VORTEQ™ Assessment tests.

Figure 5 - GST protocol selection

Make sure you have attached the sensor to the headband and turned it on.

Figure 6 - Warning message for mounting sensor on headband and patient wearing the headband

If the IMU is not turned on, you will see this error message.

Figure 7 - Start button will be inactive if the sensor is not turned on

Once you have mounted the headband on the patient, you can hand them the remote control. Instruct the patient to press the arrow that matches the direction of the optotype they see during the testing.

Figure 8 - Remote control for GST

If they do not know the direction, they can tell you “I don’t know” and then you can click on the “?” on the screen to enter the “I don’t know” response for them.

Figure 9 - Patient options for optotype direction

How to perform the Static Visual Acuity (SVA) test

If you have not already completed the Static Visual Acuity (SVA) test, then you must complete it before moving on. If you have already completed the SVA in the DVA test, then you can copy the values over and begin the GST with the first subtest.

Figure 10 - Copy DVA static option

For the SVA test, the patient keeps their head still and responds to the direction of the optotype that appears in the white square on the TV screen.

Figure 11 - Option to start a new SVA test

How to perform the GST

Complete the four subtests in order.

Have the patient move their head so that the speed of their head movement peaks in the green area of the velocity bar. Their head movement is the solid line. The acceptable range for head movement is the green shaded area. When they peak the head movement in this area, the optotype will appear. You can see this on the screen as the direction arrows will become highlighted in white when the optotype has appeared.

Figure 12 - GST head velocity monitoring: correct speed

If the patient’s head movement is too slow, then you will see a red solid line that peaks before the green shaded area. You will see the progress of the head movement as a grey bar that ends at the red solid line. Instruct the patient to move their head faster and follow the beat of the metronome so they can reach the green shaded area.

Figure 13 - Head velocity monitor: too slow

If the patient’s head movement is too quick, then you’ll see a red solid line that peaks after the green shaded area. You will see the progress of the head movement as a red shaded area that ends at the red solid line. Instruct the patient to slow down their head movements so they can reach the green shaded area.

Figure 14 - Head velocity monitor: too fast

GST results

After you have completed the test, you will get a summary screen that reports the fastest head movement the patient could achieve, in each direction, while identifying the correct optotype direction.

Figure 15 - GST results summary screen

If you have recorded more than one run in any direction, you can use the drop-down arrows to select which run you would like to display in the summary report.

Figure 16 - Option for selection of multiple runs

If you record with the room camera active, you can playback the video using the play arrow. You can also add notes to attach to your video playback timeline.

Figure 17 - Option to add notes

Manual test mode

You can also run the test in Manual mode. In this mode, you change the head velocity speed manually. When you are confident that your patient is accurately determining the optotype at a given speed, increase the speed until you reach the patient’s threshold and then set the velocity.

Figure 18 - Option to run the test manually

Figure 19 - Manual test screen

Troubleshooting

If the head sensor is connected via Bluetooth and the battery’s getting low, you will see this error message.

Figure 20 - Error message for low battery