A High-Density Retinal Prosthesis System with Automatic Equalization

Abstract

Purpose : For a retinal prosthesis to support a large field of view with a high resolution, a large number of microelectrodes are needed. We have developed a 4,000-pixel high-resolution imaging retinal prosthesis system. However, it will be time-consuming to individually set the weight parameters of the impedance of each microelectrode to its microenvironment of surrounding neural tissue by user feedback. This study targets to achieve an automatic tuning system to equalize the microenvironment effect to microelectrode current injection so user percept feedback can start with a better physical starting point.

Methods : By integrating electronic registers on the retinal chip to store tunable weights for each pixel, we implemented a high-density retinal prosthesis system with automatic equalization capability. The retinal prosthesis with 4,000 microelectrodes integrated with 4,000 wireless adjustable registers are implanted to 3 Lan-Yu minipigs in the subretinal space, and the tuning is conducted 4 weeks after the surgery. A uniform external lighting of 400 lux is used. ERG contact-lens electrodes on the cornea of the implanted eyes are used to record the artifacts from each microelectrode activated one at a time, and the tuning system wirelessly feedback to the implanted retina chip to adjust the weight registers associated to that microelectrode. The process repeats until the ERG electrode measures a preset value, and the equalization is achieved when all the microelectrodes measured the preset value under the uniform illumination.

Results : The wireless power transmission supplying the power required to operate the chip interferes with the ERG electrode measurement. This can be filtered out in our system, and the artifacts of the biphasic current injection from each microelectrode are successfully measured and wirelessly feedback to the implanted retina chip to adjust the weight registers. Equalizations of current injections from each microelectrode to its surrounding implant microenvironment of each implanted chip are achieved.

Conclusions : The automatic equalization system with the associated high-density imaging retinal prosthesis is verified in Lan-Yu minipig animal models. Automatic equalization can greatly reduce the time required to tune each microelectrode weight parameters to achieve a uniform electrical stimulation under a uniform illumination so user percept feedback can start with a better physical starting point.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.