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M. Vezina, A. Patel; Non-Clinical Electroretinogram (ERG) Assessments in 5 Commonly Used Laboratory Species. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1295.
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To provide background information on the usefulness and limitations of the full field ERG in non-clinical studies conducted in multiple species.
The cumulative ERG data from non-clinical studies conducted over the past 8 years was compared from rats, rabbits, dogs, minipigs and non-human primates. The ERG protocol in most of these studies comprised 3-5 ascending light stimulus intensities in dark adapted scotopic conditions followed by a single flash and flicker stimulus in light adapted photopic conditions. Several of the studies involved the use of different colors of light stimulus as opposed to light intensities. In all cases, animals were anesthetized during recording and ERGs recorded bilaterally using corneal electrodes and a Ganzfeld dome. ERG data were evaluated in the context of clinical ophthalmology examinations, intraocular pressure (IOP) and histopathology.
The comparative results showed that ERG changes, mostly in the form of diminished a- or b-wave amplitude and/or prolonged implicit times, can often be detected several weeks prior to detection of changes by clinical ophthalmology examination and generally correlate well with subsequent histopathological evaluations. However, as a stand alone parameter in a non-clinical environment, the ERG can be misleading. There is considerable interspecies difference in retinal morphology and therefore in response to light stimuli and to a test compound. Individual variation is high at approximately 20-35% and varies by species, which must be considered in the study design. As well, many physical effects can affect the ERG indirectly, such as elevations in IOP, circulatory changes, body temperature, ocular inflammation and gross ocular changes, as well as cellular changes only detectable microscopically.
The ERG can be a valuable parameter for determining early onset of retinal damage in non-clinical studies and as such can be a vital marker in subsequent clinical trials. In animal studies, the ERG is often best evaluated in the context of complementary parameters such as clinical ophthalmology, tonometry and/or histopathology, the latter being the most important correlate with respect to safety evaluation.
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