A comparison of some effects of three antimotion sickness drugs on nystagmic responses to angular accelerations and to optokinetic stimuli.
While the basic efficacy of antimotion sickness drugs is rooted in the reduction of motion sickness symptoms, adverse side effects are important practical considerations of their usage in aviation. This study examined the influence of three established antimotion sickness drugs on nystagmic eye movement responses to angular acceleration (whole-body movement) with vision either permitted or denied, and to optokinetic stimulation (visual field movement). Dimenhydrinate and promethazine hydrochloride, particularly at higher dose levels, reduced optokinetic nystagmus, thereby making less accurate the following ability of the eye. During whole-body motion in darkness, there was little placebo-drug difference in the vestibular response under alert conditions; under relaxed conditions, dimenhydrinate and promethazine hydrochloride produced significant declines in the vestibular eye movements. These same drugs also interfered with the ability of the individual to fixate adequately on a visual task during motion. Subjects who received a combination of promethazine plus d-amphetamine were able to suppress vestibular eye movements and maintain good visual fixation under the task condition. Thus, the effect of a drug on nystagmus may be a poor indicator of its value in preventing motion sickness. Moreover, assessments of antimotion sickness drugs for many practical situations should include, as a possible adverse side effect, the inability to maintain visual fixation during motion.