What is the Video Head Impulse Test (vHIT)?
The simplest clinical indicator of a semicircular canal deficit is what I have just described - the head impulse test (also called the head thrust test, or the Halmagyi-Curthoys test, or the Halmagyi test). But detecting that saccade is subjective and relies on the clinician seeing the small corrective saccade after an abrupt head movement. The new indicator we describe below - the vHIT test uses a video camera to measure the eye movement and so it is objective and provides hard copy of the patient’s performance. But first we will describe the test procedure and its logic.
This head impulse sign was described by Halmagyi and Curthoys in 1988, and from that time to the present, the clinical use of the head impulse test has been to indicate deficient canal function by virtue of the clinician (subjectively) observing whether there was an overt saccade or not at the end of the head turn. However some vestibular-deficient patients were missed by the head impulse test, even by expert clinicians, probably because of covert saccades. Clearly the ideal would be to have objective measure of both the head movement stimulus and the eye movement response using a system fast enough and accurate enough to detect covert saccades. The scleral search coil method of measuring eye movement achieves this aim, but it is clinically unrealistic, because of its huge expense, the high cost of each coil, the complexity of processing the data and the fact that patients do not like having a contact lens placed on their eye. However we have developed a new lightweight video system procedure – which we have called the video head impulse test (vHIT) – which does measure eye velocity and does detect covert saccades and is non-invasive and practical in clinics. Most importantly we have shown by direct comparisons that the accuracy of vHIT matches the accuracy of the “gold standard” search coil technique. vHIT has been validated by direct measures of VOR performance in healthy subjects and patients by two independent methods
– search coils and vHIT. At exactly the same time: the same subject, the same eye movement responses were measured independently by these two methods and compared and found they both give essentially the same answer.
Go to Knowledge Center and read article:
The video head impulse test: Diagnostic accuracy in peripheral vestibulopathy