Migration of neural retina through a perforated membrane implanted in the subretinal space of RCS rats: implications for prosthetics

Abstract

Abstract: : Purpose: Close proximity between prosthetic chip stimulating electrodes and target cells is necessary for a high resolution retinal interface. We reported previously that neural cells from cultured retina grew through a perforated membrane. We report here on in vivo results with an animal model of photoreceptor degeneration (RCS rat). Methods: Five albino RCS rats received implants at age 65 days. Mylar film (0.8x1.5mm in size, 13 um thick) with perforations 15–40 um in diameter was placed into the subretinal space near the optic disc. Rats were sacrificed at 5, 7, and 9 days after surgery. Enucleated eyes were fixed in glutaraldehyde/paraformaldehyde, and prepared for light and transmission electron microscopy. Results: Robust migration of neural retina through the perforations was seen as early as day 5 after surgery. Several layers of the retina were seen histologically to be involved with this migration including neuronal elements of the inner plexiform, inner nuclear, and outer plexiform layers. Muller processes and blood vessels growing into the pores have been observed. Conclusions: We have shown that inner retinal cells migrate rapidly through an implanted perforated subretinal membrane. If such growth would occur (and prove to be stable) through a perforated prosthetic chip, it effectively eliminate distance between the target neurons and electrodes located at the perforations. This would reduce electrode erosion, power requirements and cross–talk that limit the density of stimulus pixels on prosthetic chips (and thereby limits resolution).

Keywords: retina • age–related macular degeneration • retina: proximal (bipolar, amacrine, and ganglion cells)