Wireless, solar-powered bionic eyes benefit from sub-retinal placement

A team of Engineers from Stanford, and Glasgow, Scotland, have made some incredible advances on their earlier designs for a photovoltaic bionic eye. Their new paper, published in Nature Communications, describes how they can now create a pocket underneath the retina, and pop in a wireless visual processor that is fed by infrared pulses from an external camera. Ultimately, the hardware race for the coveted intra-eyeball space will face its greatest challenge from all-biological advances that threaten to cure photoreceptor-based blindness once and for all. When that happens, we will be left some powerful new hardware needing to adapt to a market — and that market will be everyone.
The common surgical need to fix detached retinas has led to some pretty cool tricks to manipulate the thin and fragile tissue deep inside the eye. Microbubble prods, thermal nudges, and laser bonds can be used to move things around, and stitch them back up. Sub-retinally placed hardware is more firmly attached than chips laid on the surface, and will remain in register with the cells it stimulates as the eye torques about. It is also better poised to access retinal circuitry at the front end, to provide for some natural bio-processing before signals are transmitted to the brain. The researchers were able to test implants having pixel sizes of 280, 140 and 70 μm in rats, and elicit strong cortical responses after IR stimulation. These characteristic “visually evoked potentials” are the hallmark signature that a light signal has made it to the brain. For babies, or test subjects that can not otherwise communicate what they are seeing, they work well.
Several other bionic implant designs have recently come to market. While their hardware resolutions are improving, it is difficult to match those performance increases at the level of actual perception. It is at once exciting to see so many new approaches to restoring vision, and also frustrating that no one method has emerged as the clear winner to be developed on a massive scale. Those waiting for a vision solution are understandably anxious. Regulatory bodies have done a good job in pushing through promising devices, but still, the pace must quicken.
Designs that manage to put the whole camera inside the eye are ideal because they permit natural eye movements and focusing mechanisms to be brought to bear. If, however, missing photoreceptors can be naturally replaced, a significant fraction of the full resolution of the original eye could potentially be restored. One such approach is being developed by optogenetics pioneer Ed Boyden, who spoke this past weekend at the GF2045 conference in New York. Ed’s plan is to treat patients who have compromised photoreceptors by converting the next cells up the the visual train, the bipolar cells, into light sensors.
Like photoreceptors, it is known that these bipolar cells also have the high-speed synaptic machinery, namely the “synaptic ribbons” that photoreceptors use to rapidly and accurately encode changes in light level. Adding the light detection machinery to bipolar cells may enable these patients to see at a level of detail that would not be possible with cameras or other sensor systems. When these methods succeed, all is not lost for the hardware consortium. Just as cochlear implant surgery may soon become an elective procedure used to augment natural abilities, elective eye implants should eventually be possible as well.
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One might ask why you would want to mess with something that works so well? Suppose you are a pigeon that, in order to navigate under any environmental condition, would benefit from an additional sense, let’s say, a magnetic sense. The best natural tooling, and greatest variety of raw materials at your disposal are probably those already found in and around the eye. Indeed evolution piggybacked magnetoreception in these creatures, and also polarization detection, mostly within the eye. Humans are not tuned in to magnetic fields but it has been recently discovered that our eyes do contain bits of the magnetosensitive protein, cryptochrome-2.
There is also mounting evidence that pigeons have magnetoreceptive components in the nose, beak, and perhaps even inner ear for detection of field direction, intensity and polarity. Although we needn’t limit ourselves anymore to all-natural precursors and construction methods, the dense sensory enervation, and fine motor enervation of the eye, still make it the prime position. Having tissue-compatible wireless access to this space now opens up unlimited opportunities for enhancement of our innate sensory abilities.


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