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G.R. Rubin, M.S. Loop, T.W. Kraft; Assessment of Rod and Cone Function Using Flicker ERG in RCS Rats . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4735.
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© ARVO (1962-2015); The Authors (2016-present)
Critical flicker frequency (CFF) is the threshold frequency for which a flickering light is indistinguishable from a non–flickering light of the same mean luminance. CFF is related to light intensity, with cone cells capable of achieving higher CFF than rods. The significant difference between rod and cone CFF allows us to distinguish and quantify the scotopic and photopic performance. This simultaneous measure of rod and cone function leads to an informative approach to characterizing retinal degeneration.
We used sinusoidal flicker ERG to obtain CFF values, over a wide range of light intensities, in RCS dystrophic (RCS–p+) and wild type rats. Recordings were made at PN23, PN44, and PN64.
The CFF curve in control animals increased in proportion to the log of intensity, with a gentle slope over the lowest 4 log–unit intensity range. The slope of the CFF curve dramatically increased for higher intensities, indicating a rod–cone break. The rod driven CFF for RCS was significantly lower across all experimental days. Cone CFF was reduced by PN44. By PN64 there was no longer a discernable rod–cone break.
CFF derived from sinusoidal flicker ERG is an effective diagnostic tool for fully and simultaneously assessing functionality of rod and cone circuits in the retina. These CFF/ERG data show that RCS exhibits significant early degeneration of the rods, followed soon after by degeneration the cones. With this data in hand, rod and cone function can be independently accessed using flicker ERG and a few select background intensities.
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