Argus II · Grey Matter

Argus II is the epiretinal implant made by Second Sight Medical Products, the first retinal prosthesis approved in the United States, which gave a coarse sense of light and shape back to people blinded by retinitis pigmentosa and was then abandoned by its maker.

Argus II. Argus II is the epiretinal implant made by Second Sight Medical Products, the first retinal prosthesis approved in the United States, which gave a coarse sense of light and shape back to people blinded by retinitis pigmentosa and was then abandoned by its maker.

The system has three parts. A small camera on a pair of glasses films the scene, and a video processor worn on the body reduces each frame to a pattern of stimulation. A coil sewn onto the outside of the eye receives it by radio, and a fine cable carries it through the eye wall to 60 electrodes tacked against the retina. Each electrode excites the ganglion cells under it, and the person sees spots of light that the visual cortex has to read as a door, a window or a line on the floor. It was approved in Europe in 2011 and by the US regulator in February 2013, under an exemption for rare conditions, for adults with severe to profound retinitis pigmentosa who perceive little or no light, at about 150,000 dollars.

The picture is coarse. In the trial of 30 people behind its approval, nearly all located a bright square better with the system on, and the best acuity measured was 20/1260, far worse than the 20/200 that defines legal blindness.

The company left its patients. Second Sight stopped making Argus II in 2019 to concentrate on Orion, an implant on the visual cortex, wound down most of its operations in March 2020, and in August 2022 merged with a drug-implant company to become Vivani Medical.

More than 350 people had received it. IEEE Spectrum found recipients in 2022 without repairs, spare parts or the technical information needed for an MRI scan, which made the device the standing case for long-term duties in informed consent.

Argus II showed that a grid on the retina can give back usable light, and that an implant lasts only as long as the support behind it.

The implants stayed in the eyes after the company that understood them had gone.

Questions: How much can a person see through a retinal implant with sixty electrodes? At best a grid of sixty spots of light, and in practice less, because current from an electrode on the retina's surface also excites the axons passing beneath it, so many spots are drawn out into streaks. In the Argus II trial nearly everyone could find a bright square on a screen with the system on, more than half did better at telling the direction of a moving bar, and the best acuity measured was 20/1260. That is enough to find a door, a window or a line on the floor, and not enough to recognise a face. Why did the maker of Argus II turn to an implant on the visual cortex? Argus II only works when the retina's output cells and the optic nerve survive, which limits it to diseases such as retinitis pigmentosa that kill the photoreceptors alone. An implant on the visual cortex skips the eye and the nerve altogether, so it could serve people blinded by glaucoma, injury or optic nerve damage. Second Sight's Orion put 60 electrodes on the inner surface of the occipital lobe, was first implanted in January 2018 and reached six people in a feasibility study, and in 2019 the company stopped making Argus II to concentrate on it.