Multi-electrode stimulation and recording in the isolated retina

As part of an exploration of the feasibility of an epi-retinal prosthesis, we developed an experimental method to electrically stimulate and record from retinal neurons using a micro-fabricated multi-electrode array. An isolated retina is placed on an array of 10 microm diameter disk electrodes with the ganglion cell side of the retina facing the electrode surfaces. The retina is bathed in oxygenated Ames' medium and warmed in order to sustain it in vitro for the duration of an experiment, typically 4-9 h. To reduce stimulus artifacts, the electrodes are grouped into two clusters - one used for stimulation and the other for recording--spaced several hundred microns apart, and electrodes are insulated with both silicon nitride and a 10 microm thick layer of polyimide. Stimuli are delivered to the array using an optically isolated current source stimulator, and the resulting responses recorded with an eight channel nerve response amplifier. Stimulation and recording are performed under computer control. A variety of physiologic measurements is described in order to illustrate the strengths and drawbacks of this method.