REAL-TIME BINOCULAR DETECTION OF HORIZONTAL VERTICAL AND TORSIONAL EYE-MOVEMENTS BY AN INFRARED VIDEO-EYE TRACKER

So far it has only been possible to detect horizontal and vertical eye movements during real time; torsional eye movements have to be calcul ated from video-tape that have been processed several rimes, and each investigation takes considerable time. We developed a real lime binocu lar infra red video eye tracker for routine clinical examination which allows real time graphical visualization of horizontal, vertical and torsional eye movements with a bandwidth of 12 Hz (25 Hz refresh frequ ency). Eye movements in three dimensions can now be obtained as easy a s has been done before with electronystagmography for the horizontal c omponent. In contrast to previous systems described, we analyze only t hose parts of the video-frame that are essential for detection of all three eye movements. This results in a huge data-reduction accompanied by a speed-up of analysis. The black pupil centre is detected by an i terative process of analyzing several horizontal and vertical lines of the even video field. The algorithm searches for regions of minimal i ntensity. Horizontal and vertical eye rotation is then calculated and transformed into Fick's coordinates. Based upon the centre of the pupi l four concentric segments are defined in the iris to detect torsion a nd to enable correction for false rotation. Torsion is detected by cro ss-correlation of each segment and estimated from the outcome of the c orrelation coefficients. All transformations are established by predef ined stored transformation matrices thus making real time calculations for transformation unnecessary. After corrections for eccentricity an d assuming that fixation of the subjects tested was perfect, accuracy appears to be within 0.3 degrees-1.0 degrees for all three dimensions. Linearity after all corrections is within 4-9% within a visual field of 60 x 40 degrees (horizontal x vertical).