Spatial Distribution of Rat Oscillatory Potentials Evaluated using the Multi-Electrode Electroretinogram

Oscillatory potentials (OPs) are a component of the corneal electroretinogram signal that reflects inner-retinal activity. Features of the OPs have been shown to be affected by disease states that involve changes in retinal circulation, such as diabetic retinopathy or retinopathy of prematurity. The multi-electrode electroretinogram (meERG) is a developing technique which records ERG potentials at several locations on the cornea simultaneously, with the promise of detecting regional dysfunction at the retina. The goal of this study was to characterize oscillatory potential (OP) amplitudes as a function of location on the cornea, in Long-Evans rats. Variation of OPs across electrode positions and radial eccentricity were analyzed, and variances of repeated measures across animals were evaluated for nine rats at 6 and 7 weeks of age. Specific Aim 1 – OP amplitudes across electrode positions were analyzed. The spatial variance of the OP amplitudes was found to be typically in the range of 10-30% of the mean amplitude, and was typically smaller than the spatial variance of the a-wave and b-wave amplitudes in the same responses. This may imply a different spatial distribution of the cell types that give rise to these three components. Specific Aim 2 – Variation of OP amplitudes as a function of radial eccentricity on the cornea was examined. The SOP amplitudes were found to be similar between the A, B, C and M rings, consistent with the low spatial variance described under Specific Aim 1. Specific Aim 3 – The variation of OP amplitudes between animals was evaluated. Large differences in mean OP amplitudes were found, similar to between-animal differences found in other ERG components. The utility of the meERG approach lies in the ability to measure spatial differences within an animal, so between-animal differences in mean amplitudes are not a challenge to this approach. Specific Aim 4 – Variation of OP amplitudes for repeated measures was examined. Significant differences were found in OP amplitudes for the same test performed one week apart in the same animal, but relative spatial differences were preserved.