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R. T. Tzekov, M. Gibson, L. Zhu, A. Fawzi, R. Kubota; Dark- and Light-Adapted Intensity-Response Function ERG Characteristics in Rodents and Monkeys. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5814.
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To study the characteristics of dark-adapted and light adapted intensity-response functions in mice, rats and monkeys recorded under similar conditions.
A total of 28 albino (BALB/c), 6 pigmented (C57CL/6) mice, 2 albino rats and 12 cynomolgus monkeys were tested under similar dark and light-adapted conditions and similar series of light intensities. Scotopic sensitivity (a- and b-wave amplitude) was evaluated by applying 14-15 luminance steps stimuli (0.00003 to 333 cd.s/m²) and photopic ERG (b-wave amplitude) was recorded after 10 min light adaptation by applying 9 -10 stimuli (0.3 to 333 cd.s/m²). Oscillatory potentials were removed using digital filtration from all traces.
For all species, the dark-adapted intensity response b-wave amplitude function had 2 characteristics parts: an initial part, spanning 4 log units and a second part, covering 3 log units. Both parts could be fitted well with a sigmoidal function, but differed in top to bottom range, slope and variability. Fitting of the a-wave function demonstrated similar slope compared to the initial part of the b-wave. The light-adapted b-wave function fitted well through the full range of intensities for rodents, but only to ~30 cd.s/m² in monkeys ("photopic hill" phenomenon). Additionally, the Hill slope of the function was steeper in monkeys compared to rodents.
A- and b-wave ERG amplitudes were fitted well with sigmoidal type (Naka-Rushton) functions over a large range of stimulus intensities. The fitting parameters were similar between species for scotopic responses, but differed for photopic responses, reflecting differences in cell populations and topography.
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