Experiment 1. Different from theoretical model and existing
data, the VOR gain manifested as a bell curve with angle increased
Among the daily tests, certain number of patients complain that they
can’t stare at the target right ahead when head tilted 45 degrees away.
In this case, we first investigated which angle is better to stare when
their head position was insured. To carry out this experiment, we
applied the head impulse of each vertical semicircular canal while
asking the participants to gaze at targets at 0°, 15°, 25°, 35°, and 45°
(Figure 1F). As claimed by the existing data and protocols (10), VOR
gain should be decreased with angle increased that 0 degree has the
highest gain. However, different from expectations, during our tests,
the VOR gains displayed rather a bell curve with angle increased. The
gain was increased with the gaze angle increased that reach the peak
around to 25°. For the left anterior (LA) and left posterior (LP) canal,
highest gain was obtained at 25°. The best angle for right anterior (RA)
and right posterior (RP) canal was 15° and 35°, respectively.
To understand if the angle caused a significant difference of VOR gain,
we performed one-way repeated measure ANOVA analysis. Our data
demonstrated the gaze angle do lead to statistical significance on the
VOR gain (Figure 2). We further analysis which angle was significant
better. The results revealed that 25° has the lowest p-value for LARP
and LP plane. For the RA plane, the 15° was significant better. Given
the uniformity requirement during clinical practice, we proposed a new
gaze angle at 25° during vHIT on vertical semicircular canals. Placing
the target at 25 degrees away from right-ahead after tilted the head of
patients to 45 degrees will give the examiners a more accurate result.
To exclude any system bias, we conducted an inter-examiner test. Two
independent examiners were recruited to performed the vHIT on the same
participant, respectively. Our results indicated that there were no
differences in VOR gain of either semicircular canals between examiners
(Figure S1).