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Ashutosh Jnawali, Krista Beach, Sudan Puri, Ostrin Lisa; Pattern Electroretinogram in Guinea Pigs: A Measure of Visual Function. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5528.
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© ARVO (1962-2015); The Authors (2016-present)
Guinea pigs are increasingly being used as a model of myopia; however, their visual function has not yet been fully characterized. Here, visual function was assessed noninvasively with pattern electroretinogram (pERG) and behaviorally with an optokinetic paradigm to determine spatial frequency discrimination. Findings were compared with theoretical limits of spatial vision calculated from ganglion cell density.
pERGs were elicited in normal young guinea pigs (n=6) using 1.05 Hz alternating square wave gratings from 0.05 to 0.5 cycles per degree (cpd) at 100% contrast. Waveforms were qualitatively analyzed for the presence of positive and negative peaks. Behavioral evaluation of spatial frequency discrimination was performed using an optomotor instrument with spatial frequencies from 0.3 to 1.5 cpd at 100% contrast for clockwise and counterclockwise directions. Guinea pigs (n=4) were then sacrificed and eyes enucleated. Ganglion cells were immunolabeled with antibodies against RNA binding protein with multiple splicing, imaged (Delta Vision Elite), and counted (ImageJ) across the entire retina. The spatial frequency limit was determined from peak ganglion cell density.
A characteristic positive peak was identified in all animals, with a subsequent negative trough in half of the animals. Responses were greatest for the spatial frequency of 0.05 cpd. Behavioral tests showed a spatial frequency cut-off of 0.9 cpd for gratings drifting in the temporal to nasal direction for each eye. The region of maximum ganglion cell density, or visual streak, extended horizontally above the optic nerve head, with a peak ganglion cell density of 1621 ± 129 cells/mm2. The calculated upper limit of spatial resolving power was 2.1 cpd.
pERG recordings were elicited in guinea pigs; however, the origins of the waveforms have yet to be determined. The location of visual streak was identified anatomically, superior to the optic nerve head. This study is the first to demonstrate pERG responses in the guinea pig. Future studies will be aimed at optimizing pERG protocols and determining the retinal origins of the pERG response so that it can be used to objectively and noninvasively assess retinal function in disease models.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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