Behavioral assessment of photovoltaic subretinal prosthesis in rats with retinal degeneration

Abstract

Purpose : Assessment of prosthetic vision using behavioral responses in awake animals is a challenge for many prosthetic approaches. Here we take advantage of the wireless nature of photovoltaic stimulation and measure characteristics of prosthetic vision using behavioral responses in rats with retinal degeneration.

Methods : Pigmented rats (n=9) were implanted subretinally with photovoltaic arrays. Among them, 6 animals had global retinal degeneration (RCS rats) and 3 were Long Evans (LE) rats that developed local degeneration above the implant. Stimulation was performed with 4 LED panels surrounding the cage, emitting 880nm radiation. Animal behavior in response to stimulation was recorded on video and analyzed by the experimenter.

Results : Implanted RCS rats reacted to prosthetic stimulation by startling (freezing) response, similar to the fear response in conditioning paradigms. This response was absent in the age-matched non-implanted RCS as well as in implanted LE rats, indicating that it is mediated by the implant and that remaining natural vision in LE rats negates startling response. With this method, we found stimulation thresholds of 0.17mW/mm² with 10 ms pulses at 2 Hz. To assess contrast sensitivity, we applied a continuous train of pulses at 20 Hz, and modulated the pulse duration within 2 seconds long segments. We found responses to both increase and decrease in light intensity, with Michelson contrast of 12%.

Conclusions : Behavioral studies in awake, freely moving animals enable quantitative assessment of prosthetic vision, and reveal higher contrast sensitivity than with VEP measurements, as well as the presence of not only ON but also OFF responses.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.