In the previous post I considered some recent advances that help in repairing the “optical part” of the eye”. More challenging is fixing the sensorial part, the retina. In the last decade results have been achieved in both epiretinal and subretinal implant. The former are easier to implant (the surgery requires from 1 to 4 hours, the latter is more complex requiring up to 10 hours. With epiretinal implant the number of electrodes is more limited (60 with ARGUS, 150 with IRIS – Intelligent Retinal Implant System), with subretinal the technology has reached 1,600 electrodes (hence potentially more resolution. So far human implants have been approved with epiretinal procedures since these are reversible.
- ARGUS – Bionic eyes have been in the making for several years now, aiming at restoring vision to people that lost retinal capabilities (as an example those suffering from retinitis pigmentosa, a hereditary disease). Technological progresses have made the implant of a chip on the surface of the retina more effective. Basically the bionic eye is a whole system including a video camera (that nowadays can be so tiny to be embedded without being noticed in a normal pair of glasses) a computer that convert the image into signals that are transmitted via radio to the implanted chip on the retina. This chip, in turns on receiving the radio signals convert them into voltage spikes that are carried by the optical nerve to the brain. The largest part of the system, making it noticeable, is the external coil used to power the implant (pointed by the arrow in the photo).
The bionic eye is already a reality, as an example read the article reporting on the Flaum Eye Institute, University of Rochester, surgeons who have implanted a bionic eye to William Heidt, one of the several thousand patients that have their sight restored (up to a certain -very limited- point; they can see light and dark, shapes of objects to the point of being able to navigate in a room avoiding obstacles, single letters can be read but they have to be very large font 3cm at 30cm distance, and some are able to read words, again written in large font).
For those of you that are interested in the actual implant you can click here to see the photo of the implant as it is implanted in the eye (not for the faint of heart!).
The technology is still not delivering at the level where complete sight is restored (although for a blind person it is a significant step forward) and we might expect significant progress in the next two decade that would achieve the goal.
There are many hurdles that need to be overcome. One of them is creating an electrical spike that mimics the one of a human nerve to trick the brain into seeing what is been detected by an artificial optical sensor.
- An article on Nature Communications (July 12th, 2018) reports on the work of researchers at Osaka University on exploiting nano materials to create electrical spikes that are mimicking the ones of natural synapses. The study is addressing the evolution of neuromorphic networks that are mimicking neuronal circuits of the brain. So far they have been shown to be functionally equivalent but are not able to reproduce the same density of neuronal networks with all their synaptic interactions, hence only a limited subset of functionalities can be mimicked. The research team has chosen to move from silicon based neuromorphic circuits to carbon based ones, using nanotechnologies and nanotubes. These latter are in the size range of synaptic interfaces (actually even smaller) and promise to deliver very dense neuronal circuits matching the ones in the brain. As a side effect of this study is the capability to create artificial spikes that perfectly mimic, also as physical dimension, the one of synapses and therefore could be used for a much accurate interface at retinal level with the optical nerve, potentially expanding the range of signals that can be exchanged in parallel.