Adduction-abduction asymmetry in video head impulse test gain

Abstract

The video head impulse test (vHIT) has become a standard method for assessing the vestibulo-ocular reflex (VOR) of the semicircular canals. It has been reported that the adducting VOR gain is higher than the abducting VOR gain in vHIT, probably due to a difference in the firing characteristics of the abducens and oculomotor nuclei and a greater maximum active force of medial rectus muscle than that of the lateral rectus muscle [ 1 Kim T.H. Kim M.B. Effect of aging and direction of impulse in video head impulse test. Laryngoscope. 2018; 128: e228-e233 Crossref PubMed Scopus (18) Google Scholar , 2 Park J.W. Kim T.S. Cha E.H. Kang B.C. Park H.J. Differences in video head impulse test gains from right versus left or outward versus inward head impulses. Laryngoscope. 2019; 129: 1675-1679 Crossref PubMed Scopus (7) Google Scholar , 3 Collins C.C. Carlson M.R. Scott A.B. Jampolsky A. Extraocular muscle forces in normal human subjects. Invest Ophthalmol Vis Sci. 1981; 20: 652-664 PubMed Google Scholar ]. However, these previously reported measurements were performed with one eye (right side) due to the construction of a measuring device (ICS impulse system), and thus, it is unclear whether the gain difference is due to the adduction-abduction difference or the right-left difference. Thus, we measured the lateral semicircular canal vHIT gain of each eye in 22 healthy volunteers (mean age, 43 years) (Supplement 1) using the EyeSeeCam system (EyeSeeCam VOG; Munich, Germany).