  Clinical trials previously demonstrated the notable capacity to elicit visual
percepts in blind patients affected with retinal diseases by electrically
stimulating the remaining neurons on the retina. However, these implants
restored very limited visual acuity and required transcutaneous cables
traversing the eyeball, leading to reduced reliability and complex surgery with
high postoperative infection risks. To overcome the limitations imposed by
cables, a retinal implant architecture in which near-infrared illumination
carries both power and data through the pupil to a digital stimulation
controller is presented. A high efficiency multi-junction photovoltaic cell
transduces the optical power to a CMOS stimulator capable of delivering
flexible interleaved sequential stimulation through a diamond microelectrode
array. To demonstrate the capacity to elicit a neural response with this
approach while complying with the optical irradiance limit at the pupil,
fluorescence imaging with a calcium indicator is used on a degenerate rat
retina. The power delivered by the laser at the permissible irradiance of 4
mW/mm2 at 850 nm is shown to be sufficient to both power the stimulator ASIC
and elicit a response in retinal ganglion cells (RGCs), with the ability to
generate of up to 35 000 pulses per second at the average stimulation
threshold. This confirms the feasibility of generating a response in RGCs with
an infrared-powered digital architecture capable of delivering complex
sequential stimulation patterns at high repetition rates, albeit with some
limitations.
