Arnow T L, Geisler W, Longbotham H
Division of Engineering, University of Texas, San Antonio 78249.
Biomed Sci Instrum. 1993;29:327-34.
The effects of laser damage in the eye have been studied with an electrophysiological measure, the Visual Evoked Potentials (VEP). The VEP is generated by placing surface electrodes at the back of a subject's head, and having the subject watch a pattern of alternating light and dark bars. The spatial frequency of the bar pattern, measured in cycles per degree, increases as the bars become finer. The bar pattern changes in time, as the light bars become dark, and visa versa. The rate of this change is the temporal frequency, measured in Hertz. The VEP amplitudes referred to in this paper are a sum of the first three even harmonics of the temporal frequency (since the pattern change two times for every temporal cycle). As spatial frequency increases, a point will be reached where the subject will no longer be able to resolve the bars, and the VEP amplitude will become indistinguishable from noise. This spatial frequency is a measure of visual acuity. A computer model has been developed to simulate vision loss from lesions on the retina. It has been checked against experimental data from Rhesus monkeys with burns made under laboratory conditions. Vision was checked before and after the burns with VEP at a temporal frequency of six Hertz. This model divides the visual field into concentric rings centered about the visual axis. Each ring contributes to the VEP by an amount that depends on its eccentricity, or radius in degrees, as well as the spatial frequency.(ABSTRACT TRUNCATED AT 250 WORDS)
已通过一种电生理测量方法——视觉诱发电位（VEP），对眼睛中的激光损伤效应展开了研究。VEP是通过在受试者头部后方放置表面电极，并让受试者观看明暗交替条纹的图案来产生的。条纹图案的空间频率以每度周期数来衡量，随着条纹变得更细，该频率会增加。条纹图案会随时间变化，亮条纹变暗，反之亦然。这种变化的速率就是时间频率，以赫兹为单位进行测量。本文中所提及的VEP振幅是时间频率的前三个偶次谐波之和（因为对于每个时间周期，图案会变化两次）。随着空间频率增加，会达到一个点，此时受试者将无法再分辨条纹，VEP振幅将变得与噪声难以区分。这个空间频率就是视力的一种度量。已开发出一个计算机模型来模拟视网膜损伤导致的视力丧失情况。该模型已根据在实验室条件下对恒河猴造成烧伤的实验数据进行了验证。在烧伤前后，使用六赫兹的时间频率通过VEP来检查视力。此模型将视野划分为以视轴为中心的同心环。每个环对VEP的贡献量取决于其偏心率或度数半径，以及空间频率。（摘要截选至250词）
