Vision is the primary mechanism humans and many other animals have for sensing the world around them. The human eye is a remarkable biological structure – approximately 100 million photoreceptor cells in the retina are spaced about one three-hundredth of a millimeter apart to sense incoming light, which is focused by the lens of the eye. The hemispherical shape of the retina also offers some benefit in focusing light from a wide field of view. Signals from the photoreceptor cells are then processed and sent to the brain for analysis through the optic nerve.

This complex structure makes the eye an excellent image-sensing device, but also makes it rather difficult to reproduce artificially – a task that could prove useful in robotics, prosthetics, and electronic devices like cameras. Current digital cameras cannot match the resolution or field of view of the human eye for the same size device, but utilize widely-used silicon-based manufacturing technologies (the same as those used for microchips and in computers and cell phones). These techniques are cheap, fast, and can be easily automated, but are limited to flat products. Now, engineers from The Hong Kong University of Science and Technology and UC Berkeley have built an artificial eye with a structure that closely resembles the human eye and may even have the ability to surpass its image sensing capabilities.

The front side of the “electrochemical eye” (EC-EYE) device consists of a lens, an aperture which mimics the human iris, and an aluminum shell filled with an electrically-charged liquid analogous to the gel-like vitreous humor in the human eye. In the back, a silicone eye socket is used to make contact between the sensing components and the wires used to send the electrical activity to a computer for processing. The only remaining piece is the main innovation in this work- the actual sensing devices themselves, which are made of tiny electrically sensitive nanowires space one two-thousandth of a millimeter apart, even closer than the photoreceptors in the human eye. Incoming light particles cause electrical reactions on individual nanowires, which can be picked up and processed by the computer. The response rate of these nanowires is even faster than photoreceptor cells, approximately one twenty-fifth of a second. The authors interfaced the EC-EYE with a computer and demonstrated that the device is capable of “seeing” the letters A, E, I, and Y with higher resolution than flat image sensing devices using a ten-by-ten grid of pixels.

While the new device represents an important step forward in artificial vision devices, there are numerous challenges facing the widespread adoption of EC-EYE. Conventional cameras and all other silicon-based devices are easy to fabricate. The curved shape of the EC-EYE and the need for precise nanowire growth (where the constituent material is deposited from a gas on the top of the growing wire) and alignment may make this more difficult to automate. More importantly, the hardest part of any new electrical device is actually getting the signals to a computer where they can be analyzed. Despite having thousands of closely spaced nanowires, the larger wires used to interface with the computer limited the authors to 100 pixels in practice. Certainly, this number can be increased, but the alignment becomes more challenging as a result. The authors explored other interfacing techniques in the paper, and some allowed for more closely-spaced wires, but each presented its own difficulties. This will be the major challenge in commercializing this device. It’s also difficult to see how such a device could potentially be used in prosthetics until this issue is solved, along with the issue of actually interfacing the device with the brain or optic nerve. Even so, the EC-EYE shows promising initial results that surpass other image-sensing devices, and given the right interface, may even surpass the human eye itself.

Managing Correspondent: Andrew T. Sullivan

Press Articles: “Biomimetic eye prototype brings cyborgs closer to reality,” Slash Gear

“Artificial eye has the potential to outperform human visionhttps://physicsworld.com/a/artificial-eye-has-the-potential-to-outperform-human-vision/,” physicsworld

“Scientists Have Made the Most Powerful Bionic Eye Ever,” Popular Mechanics

Original Journal Article: “A biomimetic eye with a hemispherical perovskite nanowire array retina,” Nature

Image Credit: Pixabay