Recent Advances in the Electro-Nystagmographic Investigation of Neurological Disorders of Ocular Movement

THE use of the corneo-retinal potentials for the recording of nystagmic eye movements is well established, and presents no great technical difficulties. Thus, the amplification used may be of the A.C. or resistance-capacity coupled type, which is easy to design and operate. When, however, we come to the nystagmographic analysis of certain derangements of nystagmus and other ocular movements which are present in many of the organic affections of the VIII nerve system which we encounter in the course of our otoneurological work at Queen Square, certain new and difficult problems arise. In particular, we have to face the need for accurate recordings, not only of nystagmic and other transient eye movements but also of sustained deviations of gaze. For this the use of direct coupled amplification has been widely considered and attempted. But the technical difficulties, arising in particular from voltage fluctuations within the amplifier and at the electrodes themselves, have proved insuperable and, so far as we know, no amplification system of this kind has yet been found of practical value for electro-nystagmography. The use of what is known as the "chopper" system of direct current amplification, combined with improvements in electrode design, now makes it possible to overcome these difficulties and to construct an electronystagmographic system of very high gain, combined with remarkable stability and freedom from distortion. For full technical details of the design, construction and performance of this equipment, reference should be made to another publication (Hallpike, Hood and Trinder, 1960, Confin. neurol., Basel, 20, 232). With such a system we have found it easy to record eye deviations of 1 degree of angle. In