Video Head Impulse Characteristics in Individuals with Corrected and Normal Vision

Abstract

The video head impulse test (vHIT) is a test of balance function, which records reflexive eye movement following brisk head rotations i.e., the vestibulo-ocular reflex (VOR). Studies suggest that the VOR is affected by corrective spectacle induced adaptation, however there is a current gap in the literature regarding its effect on the vHIT (1-3). The objective of this study was to investigate the effect of habitual spectacle use, reduced visual acuity, as well as normal vision on the vHIT outcome measures of gain and saccade presentation. Gain and saccade rate were recorded for 25 individuals with normal vision, 21 with corrective spectacles for myopia, and 11 with contact lenses for myopia. vHIT measurements were made in light, and dark; visual acuity was investigated by recording the vHIT in contact lens wearers with their lenses out. Analyses were conducted between the normal vision and corrective spectacle groups, and within-subjects in the contact lens group. There was evidence of an adaptation effect in the corrective spectacle group. A significant decrease in gain, with a mean difference of 0.035 (95% CI: 0.013-0.057), and increase in saccade rate was recorded relative to the normal vision group. The gain change occurred irrespective of lighting, and higher power lenses coincided with a greater drop in gain (with an average 0.014, 95% CI (0.002, 0.026) decrease in gain for every dioptre under -3.0D). There was no evidence of an effect of visual acuity on gain nor saccade presentation, supporting the occurrence of spectacle-induced adaptation. Overall, outcome measures were also affected by rotational head direction, and lighting condition. Gain showed consistently greater values when head movements were directed to the right relative to the left, regardless of lighting and participant visual status. In the dark however, gain was significantly lower and more variable. Saccades also notably showed greater variability in the dark, however they were more scarce relative to the light. This research highlighted the effect of vision on the vHIT, and has implications on vHIT clinical use. The current study presents gain asymmetry and saccade presentation as potential adjuncts to gain in the current vHIT paradigm. Additionally, findings suggest that spectacle lens use should be outlined in normative studies, and accounted for in clinics to better interpret the vHIT results.