Spatiotemporal aspects of pulsed electrical stimuli on the responses of rabbit retinal ganglion cells.

Implanted intraocular microelectrode arrays are being used to provide sight to individuals who are blind due to photoreceptor degeneration. It is envisioned that this retinal prosthesis will create the illusion of motion by stimulating focal areas of the retina in a sequential fashion through neighboring electrodes, much like the rapid succession of still images in movies and computer animation gives rise to apparent motion. Using a high-density microelectrode array, we examined the extracellularly recorded responses of rabbit retinal ganglion cells to a bar-shaped electrode array that was stepped at 50 microm increments at different rates across the retina and compared these responses to the responses generated to a similarly shaped light stimulus that was stepped across the retina.

In vitro activation of retinal cells: estimating location of stimulated cell by using a mathematical model.

Activation of neurons at different depths within the retina and at various eccentricities from the stimulating electrode will presumably influence the visual percepts created by a retinal prosthesis. With an electrical prosthesis, neurons will be activated in relation to the stimulating charge that impacts their cell membranes. The common model used to predict charge density is Coulomb's law, also known as the square law.

Responses of rabbit retinal ganglion cells to electrical stimulation with an epiretinal electrode.

Rational selection of electrical stimulus parameters for an electronic retinal prosthesis requires knowledge of the electrophysiological responses of retinal neurons to electrical stimuli. In this study, we examined the effects of cathodal and anodal current pulses on the extracellularly recorded responses of OFF and ON rabbit retinal ganglion cells (RGCs) in an in vitro preparation. Current pulses (1 msec duration), delivered by a 125 microm electrode placed on the inner retinal surface within the receptive field of a RGC, produced both short-latency (< or =5 msec) and long-latency (8-60 msec) responses.

Thresholds for activation of rabbit retinal ganglion cells with relatively large, extracellular microelectrodes.

Purpose: To investigate the responses of retinal ganglion cells (RGCs) to electrical stimulation, using electrodes comparable in size to those used in human studies investigating the feasibility of an electronic retinal prosthesis.

Methods: Rabbit retinas were stimulated in vitro with current pulses applied to the inner surface with 125- and 500-mum diameter electrodes while the responses of RGCs were recorded extracellularly.

Results: Both short-latency (SL; 3-5 ms) and long-latency (LL; >/=9 ms) responses were observed after electrical stimulation within the receptive field of an RGC.

Differential recovery of the electroretinogram, visually evoked cortical potential, and electrically evoked cortical potential following vitrectomy: implications for acute testing of an implanted retinal prosthesis.

To determine the extent to which electrophysiologic tests of the afferent visual pathway are affected by vitrectomy, the procedure was performed in 15 eyes of 11 adult Dutch-belted rabbits. An electroretinogram (ERG), visually evoked cortical potential (VECP), and electrically evoked cortical potential (EECP) were obtained preoperatively and sequentially after surgery. For electrical stimulations, biphasic impulses were delivered to the retina.

Thresholds for activation of rabbit retinal ganglion cells with an ultrafine, extracellular microelectrode.

Purpose: To determine electrical thresholds required for extracellular activation of retinal ganglion cells as part of a project to develop an epiretinal prosthesis.

Methods: Retinal ganglion cells were recorded extracellularly in retinas isolated from adult New Zealand White rabbits. Electrical current pulses of 100- micro s duration were delivered to the inner surface of the retina from a 5- micro m long electrode.