Der Einfluß verschiedener Elektrodenanordnungen und willkürlicher, reproduzierbarer Artefakte auf die computergestützte Nystagmusanalyse*, **

Abstract

There is no detailed information in the current literature about the best position for the electrodes with regard to electronystagmography. The computer nystagmograph registers potential changes resulting from electrodes on the forearm as nystagmus (pseudonystagmus). This phenomenon led us to investigate more closely the effect of various electrode arrangements and artifacts on the result of computer nystagmography. The following four electrode arrangements were investigated on 20 human subjects: distance between the horizontal electrode 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 artifacts on the computer nystagmography was investigated, namely blinking, contractions of the masticatory muscles, swallowing, facial expression, and squinting. The arrangement in which the horizontal electrodes were placed 1 cm away from the lateral canthus showed the greatest 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 one to achieve the same needle deflection. For this reason, the artifacts experience a smaller degree of amplification. We think the following arrangement of the electrodes guarantees the best signal reproduction: a distance between horizontal electrodes and the lateral canthus of 1 cm. The medial electrode is centered between the eyes on 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 physiological nystagmus, e.g. on rotation. In the absence of nystagmus, the analysis program is too unreliable and produces a multiplicity of pseudonystagmi. To avoid this we have to improve the recognition of nystagmus in the analysis program.