Electrooculography: technical standards and applications

The term electronystagmography (ENG) refers to the recording of eye movements and nystagmus during ®xation and in response to vestibular, visual, caloric, rotational, or positional stimulation. Typically, electrooculography (EOG) is the method used to record eye movements during ENG, with the exception that the classical EOG uses DC (direct current coupling) ampli®cation, whereas ENG in clinical routine often uses condensercoupled AC (alternating current coupling) ampli®cation with a time constant of 5 or 10 s, resulting in a high pass ®ltered signal, in which slow baseline drifts are damped. Other methods for recording eye movements, especially when used to record ocular nystagmus, also have been labeled as `electronystagmography', such as the term `video-ENG' for computer-aided video-based eye movement recording systems. Eye movement recording has been in use since the beginning of this century. Up to the 19th century, eye movements could only be monitored by an experimenter who was sitting closely to one side of the subject and watching his eyes (review: Carpenter 1988). Alternatively, subjects traced their own eye movements according to the path of a moving afterimage. Some of the ®rst mechanical recording methods that required the suture of a lever system to the sclera are only of historical interest. Optical methods using a small mirror system attached to the sclera were more precise, but were also uncomfortable for the subjects and thus were also abandoned. Direct photographic recording is hardly used, because the evaluation procedure is time consuming and is presently replaced by computer assisted analysis of video images. A breakthrough was achieved in 1922 when the potential difference between the cornea and the retina, known as the corneo-retinal potential, was used for the recording of ocular nystagmus. This technique, called electrooculography (EOG), was introduced for diagnostic purposes in neurology and otology in the 1930s by R. Jung and others, and it is still the most widely applied technique for eye movement recording in clinical routine, used by otolaryngologists and neurologists alike (review: Jung and Kornhuber 1964). Since the late 1950s, other techniques have been developed: infrared re ̄ection oculography, photoelectric methods, the magnetic scleral search coil technique, and videooculography. All these eye movement recording techniques are still in use, 223 Recommendations for the Practice of Clinical Neurophysiology: Guidelines of the International Federation of Clinical Physiology (EEG Suppl. 52) Editors: G. Deuschl and A. Eisen q 1999 International Federation of Clinical Neurophysiology. All Rights Reserved. Published by Elsevier Science B.V.