The Animal Model Pattern-Reversal EEP Study of A Contact-Lens-Shaped, Flexible Retinal Prosthesis

Abstract

Purpose: We previously reported a high-density flexible retinal prosthesis chip using a 180 nm mixed-signal CMOS Image Sensor technology with pixel array sensing image and generating bi-phasic electrical stimulations to enable the possibility of high visual acuity and cover a large field of view. The image-sensing retinal prosthesis is made into a contact lens shape conforming to the surface of a 25 mm eyeball for a better stimulation resolution and a lower stimulation threshold. The current study evaluates the efficacy of such contact-lens-shaped retinal prosthesis through in vivo experiments of pattern-reversal electrical evoked potential (pEEP) in the visual cortex using a rabbit animal model.

Methods: Pattern-reversal EEP experiments w. animal model are used to assess the potential visual acuity of the implanted high-density retinal prosthesis in the subretinal space. We surgically implanted stainless steel electrodes (1 mm OD) contacting the dura of the visual cortex of a rabbit model 2~3 weeks before the retinal prosthesis is implant in the subretinal space of the model and measure the electrically evoked potential. The electrical stimulation through the implanted microelectrode array (arranged in hexagonal array 30um in pitch) is grouped as stripe patterns in the perpendicular direction to the rabbit high-acuity horizontal stripe. The stripes are formed by selectively activating 2,500 electrodes with a pulse rate of 20 Hz to achieve the flicker fusion and the stripe pattern is reversed at 2Hz. The animal model is placed in a dark room and the pattern-reversal EEP measurements are repeated 100 times and recorded for each stripe width ranging from 750um to 30um.

Results: Recorded EEP data show that flicker fusion is formed with a pulse rate of 20 Hz, and the N1, P1, N2 peak signals can be measured for the stripe width between 750um to 30um with a signal-to-noise ratio up to 14.5dB. With a stripe width of 60um, the averaged EEP signal measured has an SNR of 8.7dB, and the average EEP signal amplitude falls within the background signal at a stripe width of 30um.

Conclusions: Pattern-reversal EEP experiments w. a rabbit animal model are used to assess the potential visual acuity of the implanted high-density retinal prosthesis in the subretinal space and the initial in vivo experiments show encouraging results toward achieving a visual acuity between 30um to 60um in the animal model.