Recording characteristics of the eye mark recorder in measurements of vertical eye movements

Electronystagmography (ENG) has been widely used in physiological studies of eye movements. It is generally known that ENG is at a disadvantage in recording the vertical component of eye movements, and thus there has been a great deal of difficulty in physiological studies of vertical eye movements using ENG. The eye mark recorder is an instrument which has already been used in the study of visual point movement in various situations. We tried to apply the eye mark recorder to the recording of eye movements in normal volunteers, and then compared its recording characteristics with those of ENG. When recording vertical eye movements with the eye mark recorder there is little baseline drift and no confusing waves caused by blinking, which is sometimes misinterpreted as nystagmus. The result is easy calibration of the device and more accurate measurement of the slow-phase velocity of nystagmus than ENG. Recording with the eye mark recorder is atraumatic and allows binocular visual stimulation. There are certain other techniques, such as search coil or video oculography, which allow more accurate recording of vertical eye movements than ENG. The search coil techniques, however, requires the attachment of a measuring contact lens during the examination and video oculography is still in development process, so both of them are difficult to use widely. Thus, we found that the eye mark recorder has a great advantage in recording the slow-phase eye velocity of vertical nystagmus and the vertical component of smooth eye movements in humans. We think that eye mark recorder can serve as a powerful new tool to investigate vertical OKN and OKAN.