Post-caloric secondary phase nystagmus.

Spontaneous direction reversal of a peripherally induced nystagmus, known as secondary phase nystagmus, can be found following a thermal stimulus. In 120 patients with various vestibular symptoms, post-caloric secondary phase nystagmus has been examined and its diagnostic value is discussed. Although the mechanism responsible for the post-caloric secondary phase nystagmus is not clear, there seem to be three factors that play a role in its occurrence: a the intensity of the stimulus; b the sensitivity of the vestibular and optokinetic systems; c the anatomical features of the external and middle ear. Because of these multiple factors, it is difficult to define the diagnostic value of the secondary phase nystagmus. However, we assume that secondary phase nystagmus is due to the adaptation of the organism to the peripheral vestibular stimulus, and factors mentioned above may induce or suppress its occurrence.