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S. Viswanathan, A. J. Weber, V. E. Malinovsky, C. D. Harman; Comparison of Progressive Changes in the Photopic Negative Response and the Transient Pattern Electroretinogram of the Cat Following Retrograde Degeneration of Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2849. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The pattern electroretinogram (PERG) and the photopic negative response (PhNR) are ERG potentials that originate from the electrical activity of the retinal ganglion cells. We compared the time course of changes in the PERG and PhNR in a feline model of retrograde degeneration of retinal ganglion cells secondary to severe optic nerve (ON) crush.
Full-field flash ERGs (750ms red-610nm flashes of 0.56 - 75 ph cd/m2 delivered on a rod-saturating blue-440nm background of 75 sc cd/m2) and PERGs from the central retina (0.016 - 2 cpd square wave gratings, counterphase modulated at 1Hz with 98% contrast and 50 cd/m2 mean luminance) were recorded from 13 anesthetized adult cats over 8 weeks following severe unilateral ON crush. The PhNRVmax, calculated from the intensity response function and the amplitude of the PERG N95 potential from eyes with ON crush were normalized to their respective control eye values and studied as a function of time. Optical coherence tomography (OCT) measurements were performed to document progressive changes in average retinal nerve fiber layer (RNFL) thickness.
PhNRVmax, PERG amplitudes, and RNFL thickness showed progressive reductions following ON crush. Each parameter was fit with an exponential decay function of the form y=a.e-bx. The value of the exponent b for both the PhNRVmax and RNFL was 0.032, whereas the exponent for the PERG amplitudes ranged from 0.044-0.05 for the various stimulus spatial frequencies, indicating that to achieve a 50% reduction in PhNRVmax and PERG amplitude it took approximately 31 and 11 days, respectively, with a proportionate reduction in RNFL thickness occurring around 26 days.
PERG amplitudes reduce at a faster rate than PhNRVmax indicating that different ERG parameters can be potentially useful as objective tests for tracking ganglion cell health at different stages of a disease process. While the PERG could serve as an indicator of early dysfunction of retinal ganglion cells and may not necessarily serve as a good indicator of structural loss, the PhNRVmax could serve as a test of ganglion cell function that is a better predictor of structural loss.
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