I couldn’t imagine loosing any of my senses, least of all my sight. To go blind slowly over time must be one of the most challenging illnesses a person can have to face. Knowing that there is nothing that can stop a hereditary degeneration of your sight must be heartbreaking, to say the least. Just imagine having the memory of what a flower covered in morning dew looked like as a sunbeam touched the tip of the petal, or being able to recall how you used to look in a mirror but can no longer see yourself, to know that there are wonders beyond most peoples own imaginations that are possible to observe in a sunset and to have all of that knowledge, that discover, taken from you along with your independence has to be one of life’s most unfair consequences of genetic illnesses.
Like any disability that worsens over time you’d hold on to the hope that one day science will find a cure, but it would seem an unfathomable wish for them to cure blindness. This is why the news that came out this week of a microchip that has the potential to restore at least the basic functions of sight seems almost too good to be true.
Some forms of blindness are caused by a degeneration of the photo-receptors within the eye. These are the cells that allow us to interpret light signals into meaning, by building on signals received about colour and brightness. With this information our brain is then able to construct the images that allow us to perceive the world around us. Clever, clever nature.
In people with degenerative eye conditions such as retinitis pigmentosa (RP) the optic nerve is left mostly intact. There are two ‘treatment’ options available at the moment, the first involves forms of gene therapy and other protective factors, which have been shown to slow degeneration in people with this and similar conditions. However, this has to be received at an early enough stage of the degeneration. The second option is what this current research focused on, and sounds more like something from a science fiction film than reality. They invoke electrical stimulation of the surviving retinal networks to try to produce some form of visual experience in people who’s level of degeneration is beyond that which might be helped by the other form of ‘treatment’. More specifically in this case a microchip is implanted under the transparent retina to act as electronic man-made ‘replacement’ photoreceptors.
The chips are able to sense light and create signals from this at many pixel locations. This is achieved using “microphotodiode arrays” or MPDA’s. There are 1500 pixel generating arrays on a chip, and each acts independently as a light sensitive electrode, this is subsequently able to provide an electrical stimulus to the neurons nearby. In this way it is unique to other approaches, within each element is the electrode set allowing for the electrical stimulation of neurons to be caused by the reception of light. There are also photodiodes found within the chip which allow for varied amplifications to be transmitted based on the level of light reception.
With the chip in place within the eye, the photodiodes are able to capture an image each, several times a second, simultaneously.
Illustration from the original paper found here . It gives a better demonstration of the set up of the microchip with the electrodes and MPDAs, and also a nice picture of an eye is always a winner. (I can remember dissecting an eye in alevel bio, it was fascinating)
It’s enough to make your head hurt to think about, I mean really. There are 1500 elements able to transmit signals from the photodiodes, which are able to capture an image in a ridiculously small time frame and transfer this into meaningful information by way of electrical impulses to the bipolar cells that would have originally received information from the rods and cones of the eye. With the amount of current that is sent by each electrode determinable by the brightness recorded by each photodiode. Oh, did I also forget to mention that the chip that all of this occurs on is a mere 4mm square in size!
In this trial study of ‘the chip’ three people with hereditary degenerative blindness were given the implant. They were tested 7 to 9 days after the implant with some psycho-physical tests. If they achieved well on these they went on to be tested for recognition of everyday objects. Due to the electrical nature of the chip it was possible for two test conditions to be employed for all these tests, a chip ‘on’ and chip ‘off’ baseline condition, which allowed for statistically significant results to be acquired.
All three patients were able to detect single electrode single pulse simulations, the perception of this varied slightly between patients but they all reported seeing the stimuli.
They went on to distinguish letters from one another, patient one begin able to tell the difference between U and I, and patient three going further by successfully distinguish four letters presented at random. Patients were also tested on pattern recognition, two of the three were able to correctly distinguish the direction of grid patterns, showing that the chips have high spatial resolution capacities.
Patient two show better recognition in further tests, and interestingly was the only patient of the three to have the chip placed in a slightly different part of the eye. In these cases the patient, identified as Miikka, was able to name objects presented in an unknown dining table situation, including distinguishing between a fork and spoon, as well as an apple and banana. In subsequent optional tests he went on to read his name (a clip that many will have seen on the news) and pointed out the fact that they’d made a spelling mistake!
The fact that they’d only had the chips in place for just over a week and this was having an impact on their perception of light is impressive enough, but for one participant to go on to read their own name is quite incredible for a first trial.
It’s difficult to find fault in this study, you could say it only worked very successful on one subject, but that wouldn’t be fair at all. It seems promising that all of the patients were able to respond to light stimuli in the first instances. There are any number of individual differences that might account for the relative different levels of impact that the chip had on all three participants. One might try to say the media exaggerated the findings in some way but the majority of the reports I saw were very careful to give a full background of the type of blindness that this is appropriate for, as well as the fact that it is very new technology and that it doesn’t ‘restore full sight’.
No questioning then that the results are truly remarkable, and although the success wasn’t replicated in all three subjects, all involved had slight improvements above the level of vision that they had previous to the implant. This research is clearly going to continue to develop into something more and more complex throughout its research future and I hope it can go on to be offered to people with RP more widely in years to come.
It is not often that there is a developement of such magnitude that I’d feel comfortable ending on such a hopeful and positive note but I really do think that this will one day be able to improve the everyday lives of those who have degenerative eye sight. I hope that it’ll go on to allow them to regain the independence that has been taken from them by their conditions and also relieving some of the demands on the carers who have to become their replacement eyes at the moment.
The original paper is:
Subretinal electronic chips allow blind patients to read letters and combine them to words
Eberhart Zrenner, Karl Ulrich Bartz-Schmidt, Heval Benav, Dorothea Besch, Anna Bruckmann, Veit-Peter Gabel, Florian Gekeler, Udo Greppmaier, Alex Harscher, Steffen Kibbel, Johannes Koch, Akos Kusnyerik, Tobias Peters, Katarina Stingl, Helmut Sachs, Alfred Stett, Peter Szurman, Barbara Wilhelm, Robert Wilke.
and a full free PDF can be found here !