Analysis of the static and linear optokinetic dynamic subjective visual vertical using virtual reality

Abstract

Subjective visual vertical perception (SVV) is the ability to identify an object in the vertical position without any external reference. Until now, the rotational condition was the only dynamic SVV paradigm analyzed in the literature. Moreover, the minimum detectable change (MDC) and the minimum number of repetitions of SVV were not properly determined. In this study, we aimed to analyze the validity and reliability of the 3D immersive virtual reality system (3DISVV) to assess SVV, to explore the response of the novel linear optokinetic dynamic SVV (LDSVV) condition in healthy subjects and in patients with unilateral peripheral vestibulopathy. Also, we aim to determine the reference range, the MDC and the minimum number of repetitions for static SVV (SSVV) and LDSVV. Until now, we evaluated 66 healthy volunteers, 23,7% men, with a mean age of 37,24 ± 20,97. The SVV tests with the new 3DISVV method and the established bucket method were assessed in all subjects. In the SSVV, the subjects visualized only the virtual bar. In the LDSVV, subjects visualized additional optokinetic stimulation consisted by spheres in both sides of the virtual bar running in the anteroposterior direction. We tested two different velocities: 5km/h (LDSVV1) and 40km/h (LDSVV2). The partial results showed a mean of SSVV using bucket and 3DISVV methods of -0.18±1,74º and -0,58±1,48º, respectively. The mean LDSVV1 was -0.57±1,61º and LDSVV2 was -078±21,72º. In relation to the SSVV, the LOSVV1 and LDSVV2 showed statistical but not clinical difference. The ICC among ten repetitions of all tests was 0.86 or greater. In general, 6 repetitions are the minimum number to obtain reliable results of SVV. The 3DISVV is a valid tool to assess SVV. It is necessary to increase the number of healthy subjects in order to obtain the aimed representative sample. Also, the evaluation of these perceptions in patients with vestibular disease may clarify the impact of SVV misperception on the functional status of this population.