Signal analysis of three-dimensional nystagmus for otoneurological investigations

Three-dimensional signal analysis can be applied to eye movements called nystagmus in order to study otoneurological patients suffering from vertigo and other balance problems. We developed an analysis and modeling algorithm for three-dimensional nystagmus measured by a video-oculography system. We were also interested in verifying an otoneurological hands-on convention called Ewald's first law in a strict physiological sense in vestibular patients. We recorded nystagmus from 42 patients all suffering from vertigo or dizziness. The underlying pathology was unilateral in 39 patients, bilateral in one patient, and central in two patients. Video-oculography was used to record three-dimensional nystagmus to separately produce horizontal, vertical, and torsional signals for each eye. On the basis of signal analysis techniques and straightforward vector calculus, we were able to recognize slow phases of nystagmus to compute their angular velocities to estimate from which part of the inner ear the disorder originated. We found that for all 42 patients the plane of one of the two horizontal semicircular canals was the closest. We were able to quantitatively estimate the influence of different semicircular canals, and, despite the pathology, horizontal canals seemed to be predominant in driving the nystagmus. The signal analysis and modeling algorithm developed is effective in studying otoneurological problems registered with nystagmus and opens new insights in three-dimensional nystagmography. Our results strongly support Ewald's first law.