Kingma H, Gullikers H, de Jong I, Jongen R, Dolmans M, Stegeman P
Department of Otolaryngology, University Hospital Maastricht, The Netherlands.
Acta Otolaryngol Suppl. 1995;520 Pt 1:9-15. doi: 10.3109/00016489509125176.
So far it has only been possible to detect horizontal and vertical eye movements during real time; torsional eye movements have to be calculated from video-tape that have been processed several times, and each investigation takes considerable time. We developed a real time binocular 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 frequency). Eye movements in three dimensions can now be obtained as easy as has been done before with electronystagmography for the horizontal component. In contrast to previous systems described, we analyze only those 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 iterative process of analyzing several horizontal and vertical lines of the even video field. The algorithm searches for regions of minimal intensity. Horizontal and vertical eye rotation is then calculated and transformed into Fick's coordinates. Based upon the centre of the pupil four concentric segments are defined in the iris to detect torsion and to enable correction for false rotation. Torsion is detected by cross-correlation of each segment and estimated from the outcome of the correlation coefficients. All transformations are established by predefined stored transformation matrices thus making real time calculations for transformation unnecessary. After corrections for eccentricity and 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).
到目前为止，仅能在实时状态下检测水平和垂直眼球运动；扭转性眼球运动必须从经过多次处理的录像带中计算得出，而且每次检测都需要相当长的时间。我们开发了一种用于常规临床检查的实时双目红外视频眼动仪，它能够以12赫兹的带宽（25赫兹刷新频率）对水平、垂直和扭转性眼球运动进行实时图形可视化显示。现在获取三维眼球运动就如同以前用眼震电图检测水平分量一样容易。与之前描述的系统不同，我们只分析视频帧中对检测所有三种眼球运动至关重要的那些部分。这导致数据大幅减少，同时分析速度加快。通过对偶数视频场的几条水平和垂直线进行迭代分析来检测黑色瞳孔中心。该算法搜索强度最小的区域。然后计算水平和垂直眼球旋转并转换为菲克坐标。基于瞳孔中心，在虹膜中定义四个同心段以检测扭转并校正错误旋转。通过各段的互相关检测扭转，并根据相关系数的结果进行估计。所有转换均由预定义的存储转换矩阵完成，因此无需进行实时转换计算。在对偏心率进行校正并假设被测试对象的注视完美的情况下，所有三个维度的精度似乎在0.3度至1.0度范围内。在60×40度（水平×垂直）的视野内，所有校正后的线性度在4%至9%以内。
