Question
What is the difference between monocular and binocular video-recordings during a VNG? If I were to record ONLY one eye will I miss a possible diagnosis?
Answer
The only problem I can see with recording eye movements using monocular techniques (i.e. either ENG or VNG) is missing the finding that one eye is moving differently than its mate. That is, there is a possibility that you could miss the ability to record disconjugate eye movements that could be caused by either paralyses of one (or more) of the extraocular muscles of one eye, or, as a result of a lesion affecting the medial longitudinal fasciculus (MLF). This is the major pathway that provides the capability of both eyes being "yoked" together for versional horizontal eye deviations. One can reduce the possibility of missing such a significant finding by doing an informal assessment of ocular motility prior to placing either electrodes or goggles on the face of the patient. That is, you can have the patient gaze approximately 30 degrees to the left and right (30 degrees eccentric from midline places the iris of the abducting at approximately the outer canthus). Also, you can have the patient smoothly pursue the tip of a pen or refoveate rapid moving targets (e.g. your left and right fingers, at shoulder width, alternately popping up) to determine whether disconjugate eye movements exist. By doing this you can ensure that eye movements are conjugate and you are safe in using monocular eye movement recording techniques.
Dr. Gary Jacobson is Professor and Director of the Division of Audiology at the Vanderbilt Bill Wilkerson Center at Vanderbilt University Medical Center. Prior to this he was the Director of the Division of Audiology, and Adjunct Staff in the Department of Neurology for the Henry Ford Health System in Detroit, Michigan.
Dr. Jacobson is a Past President of the American Society of Neurophysiological Monitoring, and currently serves on the Scientific Advisory Board and Board of Directors of the American Tinnitus Association. He is the past-editor of the American Journal of Audiology (American Speech-Language Hearing Association) and an Assistant Editor (Evoked Potentials) for the Journal of the American Academy of Audiology (American Academy of Audiology). He is on the Editorial Board of the journals Brain Topography and Seminars in Hearing and is an Ad Hoc reviewer for 10 other scientific journals. He has authored and co-authored over 100 publications that cover the areas of tinnitus, dizziness, auditory function, outcome measures development, brain mapping and intraoperative neurophysiology He is co-editor of the text Handbook of Balance Function Testing (Thomson Singular). He is a Fellow of the American Speech-Language Hearing Association, and, most recently, was recipient of the Jerger Career Award for Research in Audiology from the American Academy of Audiology.
