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).