Noninvasive techniques for assessing the effect of environmental stressors on visual function

Visual acuity, a standard measure of visual function, is affected by a variety of physical and toxic stressors. In anesthetized animals, the acuity may be determined by the visualevoked potential (VEP). We compared two evoked potential methods: the steady-state VEP, elicited with a fixed stimulus, and the sweep VEP, elicited by a dynamic stimulus. The steady-state VEP is a conventional electrophysiological technique for determining acuity, although its signal-to-noise ratio declines at high spatial frequencies and introduces a source of error for acuity determinations. Moreover, it is unsuited for repeated or rapid measurements. The sweep VEP is elicited by a dynamic stimulus which sweeps through a series of spatial frequencies. Response amplitude is measured with a sensitive, synchronous filter. The sweep VEP can be completed in as little as 10 s and may be used for repeated measures. On the other hand, waveform data is lost with the sweep VEP. The two techniques yield fairly similar acuity measures, generally agreeing within a factor of two.