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VHIT test -- technical issues

This material is intended for clinicians . See also: main VHIT page

Timothy C. Hain, MD button Page last modified: April 27, 2018

The VHIT is an instrumented bedside technique used to diagnose reduction in vestibular function in one ear vs. the other. As of 3/8/2018 we had done 1161 VHIT tests at Chicago Dizziness and Hearing, and we have run into a modest number of technical issues. Although we have both of the most common types of VHIT devices, we almost only use the interacoustic version (i.e. German version). This is the one on the left.

While we are discussing problems here, I want to be clear that we think the VHIT is very useful, and especially it is good at detecting vestibular neuritis as well as bilateral vestibular loss. It is better than the rotatory chair for detecting vestibular neuritis. It is worse than the rotatory chair for bilateral loss. It is not really a good test for normal subjects, as it only assess the high frequencies. The rotatory chair does a better job.

VHIT variants
GN otometrics VHIT VHIT-IAC version Micromedical VHIT test
Dr. Hain modelling the GN-otometrics VHIT device. (Branded "Impulse").

Interacoustic VHIT (from http://www.hearingreview.com/2013/08/video-head-impulse-testing-vhit-vor-analysis-of-high-frequency-vestibular-activity/).

Branded "eyeseecam".

Micromedical VHIT device -- looks just like their regular VENG goggles. This is branded "VisualEyes".

http://www.micromedical.com/Downloads/358/VHIT.pdf

Goggle slip.

Certainly the biggest problem with the VHIT is that the goggles may not adhere firmly to the face. There are a lot of moving parts here, and they don't always stick together. When the head is thrust one way, the camera tries to stay behind due to inertia, and thus the eye velocity can be wrong as the camera bounces around on the face (I am exaggerating).

When severe, this causes a "backlash" pattern on the VHIT trace where the eye velocity first goes one way, and then retraces. This presumably happens as the head and goggles rejoin company.

Usually this causes a too high gain problem. One knows that this is impossible because there are no corrective saccades. One also knows that this is impossible because almost nobody has a VOR gain of 1.2, and this is commonly seen. The GNO goggles have less of this problem, but it is still there. The GNO goggles are much heavier and have a lot of weight eccentrically, which causes the goggles to slip more in one direction than in the other, and causes the VOR to the left to be wrongly low.

Too high gain

Similarly, the gain may be too high, but there is no backlash pattern. We PRESUME that this is also due to goggle slip, but we are not sure. This pattern is VERY COMMON. VOR gains are often about 1.2. One knows that this is impossible because there are no corrective saccades.

See the main VHIT page for what others report about too high gain -- actually the gain is all over the place.

Practically what this means is that the norms for VHIT, in practical clinical situations, have to be rather broad. The clinician must rely on the corrective saccades to validate the test.

Patient not following instructions

If a patient is told to look here, and actually looks there, the traces will be very odd because there will be corrective saccades based on the wrong position offset. This is rare.

Interocular lens artifact

IOL artifact

Occasionally, patients with cataract surgery, will have very noisy VHITs, presumably from camera tracking issues. For these patients, the test is basically useless.

Attempts to measure the vertical canals

If you think doing a VHIT is hard with the horizontal plane, just think about the vertical oblique plane. The camera above is eccentric to the center, so if you rotate the head through the plane of the camera, it will bounce around even MORE. As torsional eye movements are not recorded in the VHIT, it all becomes so much guesswork.

We don't think the 3-axis VHIT test really works. It is fine to do it, but we think best to not to depend on the results.


References

  1. Janky KL, et al. Effects of device on video head impulse test (vHIT) gain. JAAA 28:778-885 (2017).

Copyright April 27, 2018 , Timothy C. Hain, M.D. All rights reserved. Last saved on April 27, 2018
Copyright April 27, 2018 , Timothy C. Hain, M.D. All rights reserved. Last saved on April 27, 2018