"For recording eye positions, the method of three dimensional infrared video-oculography (3D-VOG) was used. The patient had to put on a mask, which is similar to a diving mask, as shown in figure 1. In order to obtain a stable position, a chin rest together with a bite bar was used. The device is formed of two high resolution video cameras and 3 infrared LED sources in a pair of goggles and a computer with especially designed video cards....The position of the eyes is analyzed in three dimensions. This is performed for the calculation of horizontal and vertical position movements and deviations by the ‘‘black pupil technique’’—that is, by infrared measurement and localization of the individually calibrated pupil. The difference in horizontal and vertical position between both eyes gives the angle of deviation, and the graph of these positions, measured all 0.02 seconds, leads to the horizontal and vertical eye movements.

"....Illumination of each eye was provided by three infrared LED sources with a wavelength of 920 nm (intensity ,1 mW/ cm2). Torsional movements were sampled with a frequency of 50 Hz. A measurement was taken every 0.02 seconds. Thus, 3000 measurements for both torsion of the right and left eye (cycloposition) could be obtained during a measurement of 1 minute."