Differences in video head impulse test gains from right versus left or outward versus inward head impulses.

Objective: To investigate the effect of the right/left and outward/inward head impulses on video head impulse test (vHIT) gains.

Methods: Video head impulse test gains were calculated by recording the right eye movements with an infrared camera in a cohort of 24 healthy subjects (26-39 years old, 30 ± 9 years old). We compared the vHIT gains in four different situations in which the right and left lateral semicircular canals (LSCC) were stimulated through outward or inward head impulses.

Results: The vHIT gains from stimulating the right LSCC were significantly larger than those stimulating the left LSCC, regardless of whether the head impulse was outward or inward (1.06 ± 0.1 by right outward vs. 0.98 ± 0.08 by left outward, P = 0.003; 1.02 ± 0.1 by right inward vs. 0.92 ± 0.07 by left inward, P < 0.0001). The mean difference in vHIT gain between stimulating the right or left LSCC was 0.09. The gains from outward vHITs were significantly larger than those from the inward tests, regardless of the LSCC side stimulated (1.06 ± 0.1 from right outward vs. 1.02 ± 0.1 from right inward, both stimulating the right LSCC, P = 0.013; 0.98 ± 0.08 from left outward vs. 0.92 ± 0.07 from left inward, both stimulating the left LSCC, P = 0.001). The mean difference in the vHIT gains between the outward and inward tests was 0.05.

Conclusion: The right/left vHIT gain difference (0.09) is higher than the outward/inward vHIT gain difference (0.05). These are independently significant differences when using a vHIT system, which records movements in the right eye. An understanding of these differences may be helpful when interpreting vHIT results.

Level Of Evidence: 4 Laryngoscope, 129:1675-1679, 2019.