Interocular nystagmus asymmetry and motion sickness

Abstract

Binocular videonystagmography (VNG) was used to study the vestibulo-ocular response to a double rotation test as a pre-flight medical examination (PFME) for assessing an aircrew’s vestibulo-autonomic stability. The objective of our study was to identify the relationship between the degree of the nystagmus response to rotation and the severity of motion sickness (MS). The investigated cohort included 135 subjects selected from flight crews aged 23 to 47 years, who were qualified healthy according to the PFME criteria. The test used was based on the intermittent cumulation of Coriolis accelerations by Bryanov’s method. The post-testing vestibular reactivity was assessed using criteria for determining the level of autonomic reactivity and protection movements. Binocular videonystagmography (VNG) with a mask cover was performed during and after rotation. The degree of interocular asymmetry of nystagmus velocity was shown to be directly associated with the severity of MS. We suggested the following asymmetry coefficients: the asymmetry coefficient of unidirectional nystagmus during flexions (AC_f) and extensions (AC_e); and the duration of convergence rotatory nystagmus during flexions (DCN_f) and extensions (DCN_e). It has been found that AC_f and DCN_f are correlated with the severity of MS (p < 0.05). On the basis of our data, we formulated the idea of the mechanism for MS development due to double rotation, which was understood as the occurrence in these conditions of intravestibular interlabyrinth conflict.