Towards a Bionic Eye III

Roberto Saracco July 23, 2018 Blog 987 Views

Biologic synthetic tissue mimicking the human retina. Credit: Restrepo-Schild/Oxford University

Following on challenges to create a bionic eye, an issue is the material compatibility of the implant. So far implants are made of hard materials, they are rigid and may subject to wear and tear the surrounding tissues. Flexible electronics is clearly moving in the direction of allowing circuits into soft and stretchable materials, like living tissue.

Students at Oxford University demonstrated (in the lab) in 2017 a soft artificial retina consisting of soft materials embedding micro water droplets. The enclosure of the droplets act as a micro lens and when photons hit an electrical signal is generated that is then picked up by the optical nerve.
The prototype is more a proof of concept than a real artificial retinal but it shows a way to the future. For the time being the idea has been patented and studies are going on to move into a trial phase.

Alternative ways to restore vision are also being considered. These involve bio-engineering. stem cells and direct brain connectivity (cortical visual prostheses).

Alternative ways of restoring visual function. In this figure the graphical depiction of the visual pathways and electrical stimulation targets for developing a visual prosthesis. Small arrays of electrodes can be implanted epiretinally, subretinally or suprachoroidally to stimulate retinal ganglion cells and generate phosphenes. Similarly, the axons of these cells can be stimulated as they pass along the optic nerve, using “cuff-style” electrodes. The lateral geniculate nucleus can be accessed using conventional deep-brain stimulation electrodes, or newer-generation devices incorporating a “tuft” of microelectrodes. Lastly, the visual cortex may be stimulated directly using surface or penetrating micro-electrodes. Image credit: Philip M. Lewis et Al.

At Monash University professor Arthur Lowery has been working on the idea of coding visual images in ways that can be directly transmitted to the brain, using electrodes to stimulate the visual cortex(cortical visual prostheses).
In this way there is no need for an eye and it might be a solution for those cases where the issue is not the retina but the optic nerve. Also, it may allow recovery of vision lost because of a stroke affecting the optic chiasm. However, it should be noted that our vision system is quite complex, with vision distributed in several parts of the brain. By stimulating the optic nerve we are basically relaying on the whole brain visual processing mechanism, whilst by stimulating the visual cortex we are not engaging the other parts of the brain visual system. That can lead to a situation where one person can see an object but does not understand it. Examples in literature exist where people having suffered from a stroke can see objects but no longer understand them, or, the other way round, where people no longer see objects but nevertheless can perceive them and appreciate the implication (blindsight). Skipping the optic nerve as proposed by these researches, can lead to the same awkward situations.

https://vimeo.com/144756116