THE INFLUENCE OF VARIOUS ELECTRODE ARRANG EMENTS AND VOLUNTARY, REPRODUCIBLE ARTIFACTS ON THE COMPUTER-ASSISTED ANALYSIS OF NYSTAGMUS

Background: There is no detailed information in the current literature about the best position for the electrodes with regard to electronyst agmography. The computer nystagmograph registers potential changes res ulting from electrodes on the forearm as nystagmus (pseudonystagmus). This phenomenon led us to investigate more closely the effect of vario us electrode arrangements and artifacts on the result of computer nyst agmography. Methods: The following four electrode arrangements were in vestigated on 20 human subjects: distance between the horizontal elect rode and the lateral canthus (1 cm versus 2 cm), diagonal arrangement of the lateral electrodes, and changes to the lower vertical electrode . Recorded parameters included calibration potential, rotary nystagmus , post-rotary nystagmus, and optokinetic nystagmus. After determining the basic activity with closed eyes, the influence of five human artif acts on the computer nystagmography was investigated, namely blinking, contractions of the masticatory muscles, swallowing, facial expressio n, and squinting. Results: The arrangement in which the horizontal ele ctrodes were placed 1 cm away from the lateral canthus showed the grea test calibration potential and the smallest degree of human influence with regard to frequency and amplitude of the pseudonystagmus since a larger potential does not have to be amplified as much as a smaller on e to achieve the same needle deflection. For this reason, the artifact s experience a smaller degree of amplification. Conclusions: We think the following arrangement of the electrodes guarantees the best signal reproduction: a distance between horizontal electrodes and the latera l canthus of 1 cm. The medial electrode is centered between the eyes o n the bridge of the nose. The upper vertical electrode is placed above the left eyebrow in the line with the middle of the pupil. The lower vertical electrode is also in line with the middle of the pupil, 1 cm below the lower eyelid. The result is a clear recording of a physiolog ical nystagmus, e.g. on rotation. In the absence of nystagmus, the ana lysis program is too unreliable and produces a multiplicity of pseudon ystagmi. To avoid this we have to improve the recognition of nystagmus in the analysis program.