Development of a Multi-Electrode Electroretinography System and Characterization of meERG Signals in Rat
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Multi-electrode electroretinography (meERG) is a new technique being developed in the Neural Engineering Vision Laboratory at UIC. The meERG is a simultaneous measure of potentials at several locations on the corneal surface in response to a photic stimulus. It is anticipated that analysis of these potentials will reveal spatial information about the health of the retina, and thus may prove useful in early diagnosis of eye diseases, such as glaucoma and diabetic retinopathy. While the meERG technique is being developed for clinical use, there is a great deal that can be learned in animal studies. In particular, the NEVL lab is working to characterize the sensitivity and specificity of the technique for detecting laser-induced retinal lesions in rats. The main goal of this thesis was to support this effort by improving the design of the stimulus source and the contact lens electrode array, and by doing the initial characterization of the meERG signals recorded from normally-sighted rats. With this in mind, the following aims were addressed. 1.2 Specific Aims I. To optimize a full-field, spatially-homogenous light-flash stimulus source suitable for use with rats. II. To improve the design and function of the rat-sized meERG Contact Lens Electrode Array (CLEAr Lens™), with the goals of increasing the yield of functional electrodes on each lens and improving the quality of the recorded signal. III. To record the meERG signal from normal rats and to characterize this relatively novel signal with regard to test-retest and inter animal variability and to quantify spatial differences in meERG potentials across the rat cornea Note: CLEAr Lens™ is a trademark of RetMap, Inc., a start-up company founded by NEVL alumni to facilitate development and distribution of meERG technology. A full-field light flash stimulus source for use in rats was optimized and characterized, and found suitable for the planned experiments (it is currently in routine use). The lens design, as well as the procedure for preparing the lens for recording, were both significantly improved; the lens preparation procedures developed here have been adopted for the human-version of the CLEAr Lens™ as well. The meERG responses were analyzed for spatial differences in amplitudes; the typical standard deviation of amplitudes across the corneal surface was 2-3% of the mean, indicating fairly uniform potnetials for normally-sighted rats. Inter-animal variability between a- and b-wave amplitudes was found to be high, but consistent with conventional ERG results. Regarding test-retest variability, a measure related to the spatial distribution of a-wave amplitudes was found to be significantly different in three of eight animals when comparing measurements made one week apart; this seems to indicate a degree of procedural variability inherent in this relatively new measurement.