A predictive test for space motion sickness.

Eye torsion was examined in 13 astronaut subjects, tested during repeated episodes of 0 G and 1.8 G in parabolic flight aboard NASA's KC-135. Four findings are included. 1) A strong relationship between previous history of SMS and ocular torsional disconjugacy in novel gravitational states. 2) Responses were unchanged in 4 subjects retested a year later. 3) Ocular torsional disconjugacy scores increased as exposure to 0 and 1.8 G increased. This was particularly evident in subjects who had had SMS. 4) Torsional studies during 10 to 20 parabolas are required to accurately predict SMS. The hypothesis of otolith asymmetry, compensated in 1 G but becoming unmasked in novel gravitational states, is proposed to explain the torsional disconjugacy and ensuing SMS.