Spatial differences in corneal electroretinogram potentials measured in rat with a contact lens electrode array.

PURPOSE: It has been known for several decades that the magnitude of the corneal electroretinogram (ERG) varies with position on the eye surface, especially in the presence of focal or asymmetric stimuli or retinal lesions. However, this phenomenon has not been well-characterized using simultaneous measurements at multiple locations on the cornea. This work provides the first characterization of spatial differences in the ERG across the rat cornea. METHODS: A contact lens electrode array was employed to record ERG potentials at 25 corneal locations simultaneously following brief full-field flash stimuli in normally sighted Long-Evans rats. These multi-electrode electroretinogram (meERG) responses were analyzed for spatial differences in a-wave and b-wave amplitudes and implicit times. RESULTS: Spatially distinct ERG potentials could be recorded reliably. Comparing relative amplitudes across the corneal locations suggested a slight non-uniform distribution when using full-field, near-saturating stimuli. Amplitudes of a- and b-waves were approximately 3 % lower in the inferior quadrant than in the superior quadrant of the cornea. CONCLUSIONS: The present results comprise the start of the first normative meERG database for rat eyes and provide a basis for comparison of results from eyes with functional deficit. Robust measures of spatial differences in corneal potentials will also support optimization and validation of computational source models of the ERG. To fully utilize the information contained in the meERG data, a detailed understanding of the roles of the many determinants of local corneal potentials will eventually be required.

Corneal Potential Maps Measured With Multi-Electrode Electroretinography in Rat Eyes With Experimental Lesions.

Purpose: Conventional full-field flash electroretinography (ERG) yields a single response waveform that can be useful in the early detection and diagnosis of many diseases affecting the retina. It is an objective measurement that probes the entire retina. However, localized areas of dysfunction have relatively small influence on ERG amplitudes compared to normal ranges. Here we evaluate the use of corneal potential maps obtained in response to full-field flash stimuli for sensitivity to local areas of retinal damage. Methods: A contact lens electrode array was used to record 25 ERG waveforms simultaneously following saturating full-field flash stimuli (multi-electrode electroretinography, meERG) in rats. Waveforms were evaluated for a-wave and b-wave amplitudes; these values were normalized and further evaluated for spatial differences across the corneal surface. Cluster analysis and a support vector machine approach were used to classify meERG responses from healthy eyes and eyes with central (photocoagulation) or peripheral (cryocoagulation) experimental lesions. Results: A normative normalized corneal potential map was obtained from healthy eyes (n = 26). Corneal potential maps from eyes with experimental lesions (n = 13) could be classified with sensitivity and specificity of approximately 80% based solely on the normalized spatial distribution of corneal potentials, that is, with no knowledge of absolute amplitudes. Conclusions: Corneal potential maps obtained in response to full-field flash stimuli are altered in eyes with scotomas in the central and far-peripheral retina. The meERG approach yields useful spatial information following a single brief flash, analogous to body-surface potential maps used to evaluate heart and brain.