Monocular electronystagmographic analysis of caloric nystagmus.

We compared the horizontal component of nystagmus of the right and left eyes using monocular recording of electronystagmography. We examined the eye movements of 135 patients during bithermal caloric testing and those of 50 patients during the rotation test. We measured the number of nystagmic beats, the slow-phase velocities, and the amplitudes during 10 seconds of the culmination phase of caloric response. We also measured the number of nystagmic beats during the first 30 seconds in postrotatory nystagmus. The eye on the cold-irrigated side moved significantly more strongly than did the eye on the nonirrigated side, whereas a warm irrigation did not induce a significant difference between the irrigated and nonirrigated eyes. The summated activities of each eye during the four different stimulations under bithermal caloric testing did not show any significant differences. The activities of postrotatory nystagmus were almost equal in both eyes in 50 patients. We concluded that the inhibitory effect of cold caloric stimulation is probably transmitted more intensively to the eye on the irrigated side.