Background and Objectives : Caloric nystagmus has been known since a century ago, and the thermal convection theory proposed by Barany has been widely accepted. Gravity plays an important role in thermal convection. In 1984, caloric nystagmus was reported in weightless space environments and although the response was weak, the nystagmus was found to occur in the same direction as the earth. This implies that factors other than thermal convection might participate in the caloric nystagmus.
Material and Methods : Using 50 normal ears as subjects, this study compared the responses of conventional caloric test and reversed caloric test, which places the plane of the lateral semicircular canal upside down.
Results: The direction of the nystagmus was reversed, and the maximal slow phase velocity was decreased compared to that of the normal caloric test.
Conclusion: The reversed direction of the nystagmus observed in this study basically supports the theory by Barany, however, the differences that are noted implicate that other factors with a certain direction maybe involved
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