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How to perform the Functional Vision Head Impulse Test (fvHIT™)

23 April 2025

10 mins

Reading

In this quick guide, you will learn how to perform the Functional Vision Head Impulse Test (fvHIT), which provides functional information about how clearly the patient sees in response to quick head impulses and is similar in technique to the Video Head Impulse Test (vHIT).

Computer setup

A high-speed monitor (240 Hz) is recommended to ensure the most accurate optotype display time at the peak of the head impulse. Whether you have a high-speed monitor or not, you may still have the ability to adjust the refresh speed rate for your stimuli display. Go to computer display settings and advanced display settings. Choose the highest refresh speed rate you have for your stimuli.

**Figure 3:** Choose the highest refresh speed rate on your monitor to make sure all optotype tests (DVA, GST, and fvHIT) are as accurate as possible.

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. It is suggested to consider utilizing a smaller monitor than your oculomotor screen for optotype tests (DVA, GST, fvHIT).

In inches, the user can alter the boundaries width, boundaries height, and patient distance. — **Figure 4:** System Default Settings for monitor set up for fvHIT.

Protocol setup

The default protocol is automatic, but you can also choose a manual target presentation for the Static Visual Acuity and Visual Processing Time tests in the fvHIT protocol. You can choose the options in Summary Parameters.

The user can enable the following tests in the fvHIT protocol. Static Visual Acuity, Visual Processing Time, Lateral, LARP, and RALP. It is also possible to toggle the target presentation between automatic and manual. — **Figure 5:** Summary Parameters protocol set up for fvHIT.

Preparing for the test

While in a test session with a patient, you can select fvHIT from your default, VORTEQ™ Assessments, or VORTEQ Functional Assessments protocols if you have not done so already.

Make sure you have attached the sensor to the headband and turned it on. Below the start button, you should see “Head Sensor is connected. Ready!” before pressing start.

**Figure 7:** Expected message before starting the test: “Head sensor is connected. Ready!”.

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

**Figure 8:** Start button will be inactive if the sensor is not turned on.

If your head sensor is on but still not connected, you can check System Default Settings, Head Sensor to make sure the Connection Type (Bluetooth, USB) matches what you are using.

**Figure 9:** If the sensor is on but not connected, check System Default Settings > Head Sensor to make sure your Connection Type matches what you are using.

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.

As the clinician, you can also use the keyboard shortcut arrow keys or touch the software to select the direction of the optotype.

**Figure 10**: Optotype selection options: remote control (left), keyboard arrows (middle), or software touch (right).

If the patient does 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.

There is also a five second timer (labeled “waiting for response”). If no optotype response is selected in 5 seconds, the “I don’t know” is automatically chosen. The user can also press the spacebar on the keyboard to enter an “I don’t know” response.

**Figure 11:** Patient options for optotype direction. The ”waiting for response” timer is 5 seconds long. If no response is selected in 5 seconds, "I don’t know” is automatically chosen.

How to perform the Static Visual Acuity (SVA) test

The Static Visual Acuity (SVA) test assesses the smallest optotype the patient can clearly see when their head is stable. For the test, you will instruct the patient to tell you which way the open part of the U optotype is facing (left, right, up, down, or I don’t know). The test will complete a thresholding process to find the smallest optotype the patient can correctly identify twice.

If you have not already completed the SVA test, then you must complete it before moving on to the other subtests. If you have already completed the SVA in the DVA or GST test, then you can copy the values over to the fvHIT.

**Figure 12:** Copy static result from DVA or GST testing completed in the same session.

How to perform the Visual Processing Time (VPT) test

Following the SVA test, you will be prompted to complete the Visual Processing Time (VPT) test. This test presents the optotype two lines above the static acuity number and varies the time that the stimulus flashes on the screen. As the patient gets correct responses, the stimulus flash time will get progressively shorter.

If you have already performed the VPT test in the DVA or GST, you can copy the values over and begin fvHIT with the first subtest.

The lowest VPT result is 30 ms. Any response over 70 ms is considered an invalid response and any following results should be interpreted with caution.

If the patient cannot identify the optotype correctly in less than 70 ms, you will see the following warning message.

The message reads as follows. The established VPT is above acceptable levels. If you proceed, results may be invalid. — **Figure 14:** Warning message if patient identifies optotypes in greater than 70 ms.

If the patient cannot identify the optotype correctly in less than 100 ms, you will see the following message warning you to either redo the test or use the max visual processing time value (100 ms). It is recommended that you proceed cautiously, as test results over 70 ms may not be valid.

**Figure 15:** Warning message if patient correctly identifies an optotype at a display duration greater than 100 ms.

How to perform the fvHIT

fvHIT testing is composed of 5 discrete subtests:

SVA
VPT
Lateral
LARP
RALP

After completing SVA and VPT, you are ready to begin fvHIT testing.

The test procedure for fvHIT should be identical to vHIT testing with randomized quick head impulses. Firmly grasp the patient’s head (avoiding the headband) and thrust the head in appropriate direction and canal plane. It is recommended to get at least 30 impulses in each direction, at a variety of head speeds/accelerations.

The test screen is composed of a variety of indicators to assist you during testing:

The test screen includes the following. Acceleration bins that will progressively darken as you get more impulses in each acceleration. Direction of optotype. Head movement graph. Numerical information on your last impulse. Finally, velocity and acceleration graphs that will show each impulse. — **Figure 16:** fvHIT Lateral test screen.

After one head impulse, the screen will look like this:

Green surrounding the velocity and acceleration graphs means it was a proper acceleration impulse. — **Figure 17:** fvHIT test screen following one impulse.

If the velocity of the head movement is too slow or too fast, you will see an orange bar surrounding the head impulse graphs and see the “Redo impulse” message.

**Figure 18:** Example of a rejected impulse.

After each impulse, you will have your patient respond with which way the optotype was facing. You will be able to see if the answer was correct or incorrect.

**Figure 19:** Example of an accepted impulse with a correct patient response.

As you continue to increase the number of head impulses, you will see the counter on the left increase in number and you’ll also see the acceleration bins get progressively darker. As the bins get darker, you should focus on other acceleration bins.

**Figure 20:** Example of test screen after multiple head thrusts.

fvHIT results

Following completion of one canal plane, you will see the following summary screen (Figure 21). Acceleration and velocity graphs show raw tracings of each head movement. On the right, you see two bar graphs, one that represents the percentage correct score for each acceleration bin and one that shows the number of correct responses versus total responses collected.

**Figure 21:** fvHIT lateral subtest summary screen.

If there are any artifacts, you can select edit tools, select the trace or traces you want to remove, and click delete. The selected trace will be highlighted on the velocity and acceleration graphs, as well as the bins on the right.

**Figure 22:** The selected traces are shown in red.

**Figure 23:** Summary screen after the selected traces were deleted.

You always have the ability to press “reset” if you would like to undo any edits or deleted traces.

**Figure 24:** Click Reset to undo any edits or deleted impulses.

If you have completed multiple runs in the same canal plane, you have the option of which test you would like to display on the summary screen by selecting the black arrow by the appropriate canal plane name.

**Figure 25:** Option for selection of multiple runs.

Following completion of all planes tested, you will see this summary. On the left side of each plane tested will be an average correct response rate for you to have a pulse on how well the patient did in each plane.

**Figure 26:** Test summary screen. The correct response rate for rightward and leftward is displayed on the left of the fvHIT summary screen.

Presenter

Dr Liz Fuemmeler

Dr. Liz Fuemmeler is a Clinical Product Manager with Interacoustics and Vestibular Program Director at Professional Hearing Center in Kansas City, MO. She graduated with her doctorate in 2019 from Purdue University and received specialty training in vestibular and balance disorders at Boys Town National Research Hospital and the Mayo Clinic. While at Mayo Clinic, she trained in a concussion evaluation and rehabilitation program, which focused on utilizing vestibular testing to identify the presence and extent of issues following a concussion. Utilizing this training, she established a concussion program at a private practice in Kansas City, MO and participated in interdisciplinary evaluations for the Concussion Management Center at the University of Kansas Medical Center. She is actively involved in vestibular and concussion research and regularly lectures for local, national, and international conferences. Outside of her role with Interacoustics, she co-hosts a monthly podcast called "A Dose of Dizzy'' that reviews current vestibular protocols and research. She also is the past-president of the Missouri Academy of Audiology and volunteers with the American Academy of Audiology.