From implantable retinal pixels to visual cortex stimulation

July 07, 2016 //By Julien Happich
From implantable retinal pixels to visual cortex stimulation
French Startup Pixium Vision is moving fast in the field of vision restauration. The company is not only developing two distinct retinal-implant technologies to circumvent retinal degenerative diseases, it also hopes to be able one day to feed visual stimulation (from its proprietary bioinspired neuromorphic imaging sensor) directly to the visual cortex.

Created late 2011, the company has successfully carried out several clinical trials with its Pixium Vision implants IRIS I (with approximately 50 electrodes) and in February this year, it realized its first retinal implant of an improved version, IRIS II featuring 150 electrodes. IRIS is only the implantable part to be affixed outside the retina. It consists of tiny electrodes on the tip of a flexible circuit, an infrared photodetector cell, and a small ASIC in charge of multiplexing and mapping the IR signals received by the photodetector to the relevant electrodes. The electric signals then stimulate the ganglion cells whose terminations form directly the optic nerve fibres, sending the perceived signal to the brain.

The IRIS implantable device: electrodes are at the tip
of the flexible foil, controlled by the encapsulated ASIC.

A wearable part, in the shape of goggles equipped with a proprietary event-based camera, processes the visual information in front of the wearer and fires the encoded information to the IRIS through the eye. The ASIC is powered wirelessly through two inductive coils (one is in the goggle's casing).

IRIS was developed for patients with Retinitis Pigmentosa (RP), a genetic disease that affects about 1/4000 of the population and turns the patients blind by their forties. The surgery procedure takes about 2.5 to 3 hours, and patients can start seeing patterns and train their brains to make sense of that newfound vision within a couple of weeks after their operated eye has recovered from the operation, seeing hugely simplified black and white sceneries. Training procedures include identifying shapes, localizing light blocks on a screen, and in some cases, a complete software remapping of the signals to the electrodes may be necessary to cater for less receptive areas of the retina.

"Why only 150 electrodes?", I candidly asked Khalid Ishaque, Pixium Vision's CEO during an interview at their impressive R&D centre and headquarters in central Paris next to Institut de la Vision and Hôpital Quinze-Vingts.

"The electrodes are not the limiting factor here, but it is very complex to route all the signals from the ASIC to the electrodes on such a narrow flexible foil tip. We could not make the flexible foil much larger as it would make surgery more challenging, a larger slit in the eye would be riskier for sealing the scleral opening", Ishaque explained. Indeed, the ASIC and powering coil are hosted outside the eye ball.

"We already have ASIC design to manage over a thousand electrodes, but further shrinking the wires on that flexible foil is a challenge", he conceded, "but we can advance with IRIS to over a thousand electrodes within the next two to three years".

The company is expecting a CE mark for commercialization in Europe within the next few months.

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