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T. Ban, S. Rahmani, J. R. Hetling; Computational Model Correlates Local Retinal Activity With Spatially-Variant Corneal Potentials in Rat. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2893.
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In vivo mapping of retinal activity requires either local stimulation and one recording location on the cornea (e.g. the multifocal ERG) or full-field stimulation and recording from multiple locations on the cornea (source modeling). Both approaches are influenced by the relationship between local retinal activity and the spatial distribution of resulting corneal potentials. In the present study, hexagonal areas of retinal activity are simulated in a computational model of a rat eye, and the resulting corneal potentials evaluated. Implications for source modeling and the multi-focal ERG are discussed.
A detailed 3-D FE model of a rat eye was constructed in ANSYS EMag. Anatomical structure and conductivities were obtained from the literature and the model was validated by comparison to multi-electrode electroretinogram (meERG) data. Hexagonal areas of retinal activity (subtending ~7 degrees of visual angle) were simulated as sinusoidal charge separations across the retina. Parameters investigated include position and size of the hexagons, and amplitude of the simulated activity. The resulting potential distributions at the cornea surface were evaluated.
Potential distributions at the cornea were strongly influenced by position of local retinal activity. For four peripheral locations of a fixed-size hexagon, 2-3 fold differences in potential across the cornea were typical. Hexagons located in the periphery contributed substantially less to the corneal potentials than centrally-located hexagons. Corneal potentials scaled linearly with amplitude of local retinal activity but non-linearly with size of hexagon.
Simulation results suggest that position of an ERG recording electrode will determine the relative weights of local areas of retinal activity contributing to the recorded potential. The non-uniform spatial summation of retinal contributions at defined corneal locations may be exploited to perform source modeling of retinal activity using potentials recorded from an array of corneal electrodes.
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