Efficacy and reliability of long-term implantation of multi-channel microelectrode arrays in the optical nerve sheath of rabbit eyes

In addition to epiretinal and subretinal areas, the optic nerve (ON) is also a candidate location for implanting visual prosthesis to restore vision of patients with retinitis pigmentosa (RP). Since the ON receives all the signals from the retina, stimulating the ON may potentially evoke phosphenes over a wider range of visual field. In this study, we designed a 9-channel microelectrode array and implanted it between the dura mater and pia mater of rabbit ONs by lateral orbitotomy. We recorded the current thresholds and evaluated the efficacy of the array using electrically evoked potentials (EEPs). Spatial discrimination of approximately 20° was verified by EEP maps over visual cortex. A large area of the visual field (over 130° along horizontal meridian) could be activated by this microelectrode array. Visual evoked potentials (VEPs) and different pathological examinations were used to examine potential damage of ONs. One year post implantation, we did not notice significant damages to either the ONs or the microelectrode arrays. EEPs were successfully recorded up to 6months post implantations. However, further studies are still needed to reduce fibrous encapsulation of the microelectrode array, which resulted in a gradual elevation of current thresholds to elicit EEPs.