This protocol helps clinicians optimize video head impulse testing by visualization of different techniques and by pointing out potential pitfalls and artifacts. The techniques demonstrated in this video enable fellow clinicians to perform video head impulse testing of all six semicircular canals. The participant in this video is Emil Riis Abrahamsen, co-author and physician.
vHIT systems used for demonstration in this video include the EyeSeeCam system, which will be referred to as vHIT system A, and the ICS Impulse system, which will be referred to as vHIT system B throughout this video. Begin by escorting the participant to a well-lit screening room and mount video Frenzel goggles. Perform a gross eye movement exam by asking the participant to move their eyes in the vertical and horizontal planes to the outer edge of the eye sockets, to ensure no eye muscle palsies are present.
Take notice of the area surrounding the eyes, and use proper precautions if the participant has one or two droopy eyelids. Evaluate eyelashes to ensure length is not too long such that they could compromise tracking of the pupils during the test. Next seat the participant in a non-rotating, solid chair one to 1.5 meters away from a fixation dot placed on a wall for video head impulse testing, or vHIT, depending on the type of vHIT system being used.
Note, as an alternative, place several dots in a vertical line at different heights. Adjust the height of the chair so that the eyes of the participant are leveled with the fixation dot. Then provide goggles and adjust them on the participant's head.
Tighten the strap firmly to ensure goggles will not shift during application of head impulses. Ensure that the eyes are wide open, with eyelids in a position where they do not interfere with pupil detection. For vHIT system B, position the region of interest around the pupil and select Auto-Threshold on the laptop.
Finally assess the tracking of the pupil by having the participant make short, horizontal head movements prior to initiation of the test. For calibration of vHIT system B, first turn the lasers on. Then ask the participant to move their head to position the left and right laser dots on each side of the fixation dot equidistantly.
Tell the participant to keep their head in that position, and ask them to follow the visible laser beam dot by moving their eyes only. Check the calibration by having the participant stare at the fixation dot. Move their head side to side about 10 degrees.
Finally check that eye and head velocities match. Calibration for vHIT system A consists of two separate calibrations if both horizontal and vertical testing is intended. Prior to initiation of vHIT testing, keep in mind that head impulses must be delivered abrupt, fast, and unpredictable.
Then to perform horizontal testing of the six semicircular canals, or SCC, place hands on the jaw or on the top of the head. Throughout the entire test, ask the participant to clench their teeth when head impulses are applied so that jaw movement is reduced. Next turn the participant's head 30 degrees forward in the pitch plane to position the horizontal SCCs completely horizontal, and deliver between 10 and 20 head impulses to each side.
To perform vertical SCC testing, place the dominant hand on top of the participant's head, and direct the fingers in the direction of the anterior SCC to be tested. Place the nondominant hand on the chin. Then use the 2D vHIT test method with system B by rotating the chair 45 degrees to either side.
Turn the solid chair 45 degrees to the left, and ask the participant to look at the fixation dot. Then, for anterior SCC testing, rotate the participant's head forward in the pitch plane perpendicular to the wall. Following that, for the posterior SCC testing, rotate the participant's head backwards in the pitch plane perpendicular to the wall.
In summation, rotate the participant's head forwards in the pitch plane perpendicular to the wall for anterior SCC testing and then backwards in the pitch plane perpendicular to the wall for posterior SCC testing. Use the 3D vHIT test method for examination with system A by first positioning the participant in front of the wall at the desired distance. Ask the patient to remain in this position throughout the entire test.
For the right anterior SCC, rotate the head forward and 45 degrees to the right of the sagittal plane. For the left posterior SCC, rotate the head backward and 45 degrees to the left of the sagittal plane. Remember head impulses need to be fast, abrupt, unpredictable, with high acceleration, and with low amplitude.
Finally, after completion of the vHIT test, evaluate and interpret the test report, which includes a 2D graphic depiction of the head impulse by means of time and head and eye velocities as well as calculation of a mean gain value. Results indicate normal findings for lateral SCCs such that curves for both head and eye velocities match. All mean gain values are within the normal range, and there are no pathological saccades present with both vHIT systems.
vHIT system B reports, shown at the top, and vHIT system A reports, shown at the bottom. Normal findings were also shown for all six SCCs following vHIT system A testing and vHIT system B testing. In order to conclude that the vestibular function is reduced, a low mean gain value and pathological saccades must be present.
Following complete testing of all six SCCs with vHIT system A, overt saccades are seen after head movement has stopped. Covert saccades are seen during the head movement, and sometimes a mixture of both are seen. Note, low mean gain values accompany the graphs displaying pathological saccades.
Further, following complete testing of all six SCCs with vHIT system B, again, overt saccades are seen after head movement has stopped. Covert saccades are seen during the head movement, and sometimes a mixture of both are seen. With overt and/or covert saccades, accompanying mean gain values also need to be too low in order for a test to be interpreted as being truly pathological.
For a complete examination of all 10 vestibular organs, vestibular-evoked myogenic potentials may be added upon completion of vHIT testing. Head impulses need to be fast, abrupt, unpredictable, with high acceleration, and with low amplitude. Potential pitfalls must be accounted for.
This protocol provides a better understanding and a more precise diagnosis of inner ear diseases, facilitating targeted treatment options. Do not perform this test if the participant experiences any neck problems.
