Catch-up Saccades a More Sensitive Parameter than Gain
When interpreting video Head Impulse Test (vHIT) data you should not rely on gain alone. The eye traces are more important and provide more information. Always look at the eye traces first and the gain second. The below data was collected by ICS Impulse customers.
70 YR old Male, a classic, complete bilateral loss in all 6 canals with plenty of overt saccades.
76 YR old Male, a partial bilateral loss with plenty of overt saccades. Dr Konrad Weber reviewed this data and also concluded: “The reason for the apparent shift of the eye traces to the left (even slightly before the head) is most likely slippage. Slippage results in a biphasic trace with a very early peak. This makes the gain appear a bit higher than it actually is, although the ICS Impulse algorithm compensates for this, as it also includes the following artifact trough, which is well concealed within the VOR response. These are subtleties, which 99% of the people typically do not notice.” Please see the ICS Impulse Interpretation Guide for more information.
95 YR old Female, No symptoms, having a vestibular work-up for cochlear implant candidacy. vHIT data suggests a mild bilateral vestibular loss since the eyes do not perfectly follow the head curves during the head impulses. As a result she is making catch-up saccades to compensate. Even though the gain is symmetrical, there are more catch-up saccades to the right.
75 YR old Male, a unilateral lateral
vHIT gain data show both sides in the abnormal range. However, the right side is so impaired that is it affecting the left side and pulling the gain down. Remember as one side is excited the other is inhibited. When the left side is stimulated, the right side is not providing the inhibition causing the left side to have a lower gain. This is a unilateral Loss of the right side.