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METHODS FOR MONITORING THE EFFECTS OF ENVIRONMENTAL TOXINS ON THE VISUAL SYSTEM.
Citation:
Geller, A M. METHODS FOR MONITORING THE EFFECTS OF ENVIRONMENTAL TOXINS ON THE VISUAL SYSTEM. Presented at International Society of Ocular Toxicology, Kiawah Island, SC, 9/30-10/5/2000.
Description:
A high percentage of neurotoxic compounds adversely effect the visual system. Our goal is to apply the tools of vision science to problems of toxicological import, exposure-related alterations in visual physiology, psychophysical function, and ocular development. Methods can be divided into two broad classes ? those that measure the overall integrity of the visual system and those that localize toxic insult to particular elements or structures in the visual pathway. In the former class, psychophysical (behavioral) measurements of color vision, contrast sensitivity, visual acuity, and absolute and increment thresholds require an intact visual pathway from retinal input to cortical processing plus the ability to learn the task and generate responses. Behavioral measurements have utility in that they directly measure what the organism sees; a decrement in performance is an adverse outcome. Visual cortical evoked potentials (VCEP) also require an intact visual pathway. Evoked potential recordings often correlate with psychophysical measures of visual function. Methods will be discussed for using VCEP data to extrapolate to contrast and luminance thresholds. In addition, evoked potential and psychophysical tests can be done in awake animals and similar procedures can be carried out in animals and humans, aiding in cross-species extrapolation.
Tests that localize toxic insult to particular parts of the visual system include the electroretinogram (ERG), ultrasound and refractive measurement of the dioptric elements of the eye, and histological preparation. Our laboratories concentrate on electrophysiological and structural measures. The ERG can be used to examine the physiology of each of the retinal lamina, depending on the design of the stimulus and recording conditions and the portion of the elicited waveform examined. Quantitative models of the ERG waveform have been developed to elucidate the biochemical aspects of visual transduction in rods and cones as well as in bipolar cells. Effects of toxic exposure on development of the dioptrics of the eye require assessment of the axial dimensions of the eye, objective refraction, and consideration of effects on the retina, since eye growth signals are largely driven by visual input.
Examples of these methods will be discussed in reference to a range of environmental toxicants and human and animal models.
This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.