Space motion sickness: etiological hypotheses and a proposal for diagnostic clinical examination.

The general notion that space motion sickness (SMS) is due to a "conflict" between vestibular, visual, and other sensory inputs has gained popular acceptance. We have reviewed three specific hypotheses for SMS and identified characteristic disorders of ocular motility that each hypothesis would predict. Accurate recording of horizontal and vertical eye movements during free head movements in space craft presents technical difficulties. We suggest that careful clinical examination may be useful, provided the examination is directed towards detecting those specific abnormalities predicted by each hypothesis.