Apr 12 2021

Progress on Bionic Eye

Some terms created for science fiction eventually are adopted when the technology they anticipate comes to pass. In this case, we can thank The Six Million Dollar Man for popularizing the term “bionic” which was originally coined by Jack E. Steele in August 1958. The term is a portmanteau of biological and electronic, plus it just sounds cools and does roll off the tongue, so it’s a keeper. So while there are more technical terms for an artificial electronic eye, such as “biomimetic”, the press has almost entirely used the term “bionic”.

The current state of the art is nowhere near Geordi’s visor from Star Trek TNG. In terms of approved devices actually in use, we have the Argus II, which is a device that include an external camera mounted on glasses and connected to a processor. These send information to a retinal implant that connects to ganglion cells which send the signals to the brain. In a healthy eye the light-sensing cells in the retina will connect to the ganglion cells, but there are many conditions that prevent this and cause blindness. The photoreceptors my degenerate, for example, or corneal damage does not allow light to get to the photoreceptors. As long as there are surviving ganglion cells this device can work.

Currently the Argus II contains 60 pixels (6 columns of 10) in black and white. This is incredibly low resolution, but it can be far better than nothing at all. For those with complete blindness, being able to sense light and shapes can greatly enhance the ability to interact with the environment. They would still need to use their normal assistive device while walking (cane, guide dog or human), but would help them identify items in their environment, such as a door. Now that this device is approved and it functions, incremental improvements should come steadily. One firmware update allows for the perception of color, which is not directly senses but inferred from the pattern of signals.

One limitation of this technology, even though the pixel density is extremely low, stimulation of one pixel can at times trigger an adjacent ganglion cell, so the user would see an elongated line rather than a square. Here comes the slight incremental advance – a new study uses computer models to analyze how the healthy human eye works in order to apply that knowledge to the prosthesis. Specifically, they modeled the waveform of the activating signal. By duplicating this waveform they can more precisely target the desired ganglion cell without cross-stimulation. This would allow for more precise stimulation, reducing cross stimulation artifacts, and may allow for eventually higher pixel count implants. I know this is minor, but these kinds of basic advances are what incremental technological progress is made of.

This technology is very difficult, however, and is taking years to develop. For example, a German company has been working on their own version, the Alpha IMS, for 16 years. They were boasting an implantable device that used light that entered the eye, rather than an external camera, and boasted 1,500 pixels. That is enough to see a fuzzy but recognizable image of a person or object. There are lots of articles written about the amazing potential of this bionic eye – but in 2019 the company shut down. They cited two reasons for shutting down, the oppressive regulatory environment of Europe, and the fact that their device, “did not lead to the concrete benefit in everyday life of those affected, which we had sought.”

The reason for the failure might be that vision is about much more than pixels. Our eyes are not just cameras, they process visual information from the retina to various brain regions. Visual perception is a complex constructed phenomenon. What might a more mature version of a bionic eye look like, then? In May of 2020 another company published a proof of concept study of their bionic eye which is designed much like a human eye and uses an array of perovskite nanowires as sensors. This eye is more designed for robots than as a human prosthetic, however. This is all about the sensing device, and does not contain the technology for interfacing with the human visual system, which is a critical component.

The Argus II technology is certainly one way to go – stimulating the ganglion cells which are already connected to the visual cortex. The brain-machine interface there is the electrodes used to stimulate the ganglion cells. It remains to be seen what the ultimate limitation of this approach will be. Right now it’s 60 pixels, and while this is probably not the ultimate limit, we don’t know what the ceiling is.

Another way would be to take the Geordi’s visor approach – jack directly into the brain. This would require a fairly mature brain-machine interface that we do not currently have. The advantage here is that the light sensing device could then be anything – it won’t need to fit in the eye or interface with the retina. It could be the pair of new pervoskite nanowire eyes, or a visor, or something else. That would then connect to the visual cortex through nanowire or some other electrodes, and the ultimate resolution limit would be determined by the connections to the cortex. This could be more limited that the ganglion cell route, depending on how mature this technology is. The optic nerve is comprised of axons from the ganglion cells, so connecting to that is the same as connecting through the ganglion cells themselves. In this technology we are talking about bypassing that route.

In any case, there is no easy way to do this. True artificial vision, something coming close to current healthy human vision, is a long way off. The primary limiting factor is not making an artificial eye (which we arguably already have) but in the interface with the brain. Getting high resolution information to the visual cortex is going to take advanced brain-machine interface technology that is at least decades away, and may be closer to a century or more. But limited vision is already possible now, and any incremental improvement is likely to improve the experience for the user.

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