Retinal circadian rhythms in mammals revealed using electroretinography

Light levels can change by up to ten orders of magnitude between midday and midnight. As a result, the visual system is faced with a large diurnal variation in functional demands. Two mechanisms exist to allow the retina to function under such varied conditions: adaptation and circadian rhythmicity. Adaptation occurs in response to the presenting light conditions and circadian rhythmicity allows the tissue to anticipate those light conditions. Circadian rhythmicity has been described at many points along the visual projection from its photoreceptive origins to the highest levels of visual processing. Electroretinography has proved a very useful tool in the assessment of retinal rhythms. It offers a noninvasive and quantitative assessment of the activity of first- and second-order cells in the retina and has been used by a number of researchers to describe diurnal and/or circadian rhythms and probe their mechanistic origins in several mammalian species. Here we review the various attempts to investigate these retinal rhythms, predominately by use of the electroretinogram, in several mammalian species.