Objective:This study illustrates how multifocal visual evoked components are derived from multichannel bipolar recordings when analyzed topographically. In addition to the wave shapes of the evoked potentials, the latencies(ms) and wavelengths(mV) of the components are also influenced by the cortical site of the recordings. Methods: Multifocal VEPs were recorded from different parts of the visual field(up to 30 o of eccentricity) of both eyes stimulated separately in fifty normosensoric subjects. The pseudorandom alterhated stirmulus array was produced with a multichanel roland consults system (Retiscan, Wiesbaden/Brandenburg, Germany). The stimulus consisted of 60sectors,each with 16 checks,8 white( ＞ 130 cd/m2) and 8 black( ＜ 2 cd/m2). For electrode placement we used a bipolar(occipito-occipital) arrangement. The visual evoked wave shapes were reconded simultaneously from a row of four scalp electrodes placed along the sagital midline and four scalp electrodes placed along the transversal axis of the occipital cortex. Each of the eight electrodes could be used as the negative or the positive electrode. Results:These studies showed that different recording channels displayed different averaage peak latencies and armplitudes ranging over the occipital cortex.During recording of the mVEPs along the sagital axis, one could observe a reduction in the maximum amplitude compared to the transversal axis. On the other hand, we found differences in the electrode location of the evoked components when different retinal areas were stimulated. Conclusion: The multifocal VEP demonstrated good correlation with the topography of the visual field wben recording from bipolar occipital sites along the sagital midline. The bipolar recording site, the inion(negative electrode), and 2 cm or 4 cm superior(sagital) or 4 em between the left and the right site(transversal) to the inion seemed to produce more reliable results. For more accurate assessments of objective visual field defect, one should evaluate the superior, inferior and the lateral hemifields separately.%目的:阐明多焦视诱发电位成分是如何从多通道双极记录中得出和进行地形学分析的.并研究不同的视皮层记录位置对多焦视诱发电位的波形、潜伏期(ms)和振幅(mV)的影响.方法:采用多通道罗兰电生理系统(Retiscan,Wiesbaden/Brandenburg,Germany)分别测量50位正常人双眼不同视野的多焦视诱发电位(visual evoked potential,VEP)(最大的离心率为30°).两眼分别给予刺激.伪随机改变的刺激由多通道罗兰系统产生.刺激图形由60个刺激扇形组成,每个扇形又含16个方格,8个白色方格(＞130 cd/m2)和8个黑色方格(＜2 cd/m2).各个刺激单元的刺激翻转由一个伪随机序列控制.电极放置参照双极枕叶电极放置法,同时从4个前-后矢状中线及4个水平连线(横贯枕叶视皮层)上的皮肤电极上记录视觉诱发电位波形.上述电极可以是正极或负极.结果:在记录的枕叶皮层区,不同记录通道所记录的VEP显示了不同的平均峰潜伏期和振幅值.在矢状中线上记录到的mVEP,其最大振幅值小于水平线上的记录值.另外,刺激视网膜不同部位所诱发的电位在头皮的位置是不同的.结论:双极枕叶电极在矢状中线上记录到的mVEP与视野地形图记录的有良好的相关性.双极记录位置:负极在枕骨粗隆,而正极在枕骨粗隆矢状轴上2 cm或4cm或正极在枕骨粗隆水平左、右4 cm时,记录得到的VEP结果更具可比性.为了更准确地评估客观视野缺损,可进行上下1/2或者水平1/2的多焦VEP记录.
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