The challenges with current eye prosthetics
How sub-retinal implants will overcome blindness in the long run
Few disabilities are as frustrating and quality-of-life reducing as blindness. Losing an arm or a leg is a terrible thing as well, don’t get me wrong, but thanks to ever-improving prosthetics people are able to live self sufficient lives, or even compete at sport events like the Paralympics.
However, when it comes to blindness, we face several problems. The eye as a biological structure is complex, which can be said about the leg or the arm as well. However, what differentiates the former is the function it performs; while we can recapitulate the mostly mechanical functions of an arm, we have a hard time replicating the sensory function of the eye.
So why not use eye transplantations, like we do for kidneys or livers or even hearts?
Technically, it is not the eye itself that is the problem, but very specialized retinal cells that cover the back of the eye. These cells possess special light-sensitive proteins called photoreceptors, which detect light and transform it into electrochemical signals for the brain to process. The retina cells are embedded in a layered structure with several layers of neurons interconnected by synapses. Neurons and synapses are notoriously hard to regenerate, you might have heard of so-called “nerve damage”. While there are researchers working hard to find a solution to nerve damage, this is the reason why so far, the eye has been one of the most elusive organs to transplant.
However, one of the most common causes of blindness is a disorder called retinitis pigmentosa, where only retinal photoreceptor cells die off gradually, which leads to loss of vision, but does not cause damage to the neurons and synapses.
For those patients, artificial retinas are a viable treatment option. The artificial retina consists of an array of tiny electrodes, which take over from the damaged photoreceptors and generate electrical signals.
The person with the implant perceives these electrical signals as bright flashes called “phosphenes”. However, the phosphenes are too large and imprecise to provide the person with vision that is good enough for tasks such as walking unaided or reading. — Elife digest
In a recent publication in the journal Elife, scientists from France set out to identify the impact of visual compared to electrical stimulation of the retina at the primary visual cortex in the brain.
The primary visual cortex is the first layer of neurons in the brain that receive the electrochemical output signals from the “wires” coming from the eyes. By doing it this way, they could compare the signals that came from visual versus electrical stimulation and identify how these differ from each other. Then they adjusted the electrical stimulus to produce the same “pattern” of brain activation as the visual signals did.
This approach is called “reverse engineering”, a method that has been used in many different fields, from mechanics to business to crime solving to cracking software code.
Imagine being a detective at a crime scene, although the crime had been committed hours ago, by investigating knocked-over furniture, blood stains, foot- and fingerprints, DNA samples etc, you might get a good idea of what had happened, almost as if you had been present.
This is exactly the approach Roux S. and colleagues took to investigate what happened between the electric stimulus and visual cortex activation, and thus were able to improve significantly the accuracy and performance of artificial retinas in rats. The next step needed is to get this “reverse engineering” approach into non-human primates and ultimately humans.
While promising, scientists are still a long way to improve artificial retinas to a level that is almost equivalent to healthy eye function.
However, taking an engineering approach to treat disability has already improved countless lives, so we can be confident that it will overcome the biggest burdens accompanying blindness in the near future.
Source: Roux S. et al., Elife, 2016
This story is part of advances in biological sciences, a science communication plattform that aims to explain ground-breaking science in the field of biology, medicine, biotechnology, neuroscience and genetics to literally everyone. Scientific understanding has too many barriers, let’s break them down!
