Caloric-eye tracking pattern test: I. Visual suppression and the possibility of simplified differential diagnosis between peripheral and central vertigo

During the examination of patients who complain of vertigo or who have equilibrium disorders, it is often difficult to determine the etiology of the disorders, that is, to determine whether it is dependent on a peripheral or central vestibular disorder. To attempt to guess the etiology in these cases, we devised a new method: the caloric eye-tracking pattern test. In normal subjects and in patients with peripheral disorders, as is well known, caloric nystagmus has little influence on the eye-tracking pattern. In contrast, in patients with central vestibular disorders, caloric nystagmus evoked abnormalities on the eye-tracking pattern, either superimposed or saccades, in spite of the fact that the eye-tracking pattern before the caloric stimulation is normal. These findings result from the visual suppression mechanism to the vestibular nystagmus. We can say that the visual suppression to the vestibular nystagmus is evoked more strongly bu pursuing a moving visual stimulus than by gazing at a stationary target. These results are interesting, not only form the physiological view point, but also from the clinical view point. There is a possibility of the differential diagnosis between peripheral and central vertigo.

The circular eye-tracking test. I. Simultaneous recording of the horizontal and vertical component of eye movement in the eye-tracking test

Almost all of the conventional clinical reports on the eye-tracking test are made on the horizontal component of the smooth pursuit function of oculomotor system; few are made on the vertical component. One reason is that during the conventional vertical eye-tracking test the artifacts caused by movement of the upper eyelids often make it difficult to analyze the data. To overcome this problem the authors have developed a method to record simultaneously the horizontal and vertical components of eye movement in the eye-tracking test, and moreover, to reduce artifacts as much as possible. Our method, the circular eye-tracking test, is performed by means of an apparatus that provides a visual stimulus drawing a circle clockwise, at a rate of 120 degrees/sec, with a radius of 25.5 cm, and viewed at a distance of 70 cm.