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October 23, 2019

Bionic Eyes

Back in the 1970's we had Steve Austin the bionic man who could run at speeds of over 60 mph, had bionic limbs with the pulling power the equivalent of a bulldozer and a bionic eye with a 20:1 zoom lens and infrared capabilities. In reality we are still some way from a real life version of the bionic man but we are a step closer in creating a bionic eye 

The bionic eye, also called a visual prosthesis is an experimental visual device intended to restore functional vision in those suffering from partial or total blindness. Many devices have been developed, usually modelled on bionic ear devices, a type of neural prosthesis in use since the mid-1980s. The idea of using electrical current to provide sight dates back to the 18th century.  

Who gets a bionic eye? 

The ability to give sight to a blind person via a bionic eye depends on the circumstances surrounding the loss of sight. For retinal prostheses, which are the most prevalent visual prosthetic under development, patients with vision loss due to degeneration of photo-receptors are the best candidate for treatment. Candidates with the most success are those where the optic nerve was developed prior to the onset of blindness. Persons born with blindness may lack a fully developed optical nerve, which typically develops prior to birth, however though neuro-plasticity it is possible for the nerve, and sight, to develop after implantation. 

Spearheaded by world leading eye hospitals Moorfields and Manchester, bionic eye implants have already given blind people sight. 

To date, only people with degenerative retinal diseases have been eligible to receive a bionic eye. Three approved retinal bionic eyes have been approved include the Argus II developed in the USA, the Alpha-AMS in Germany, and the IRIS V2 in France. 

There have also been trials with retinal implants that have mainly been used for people with retinitis pigmentosa. This device may have a safer surgical profile than existing bionic eyes as it is implanted at the back of the eye rather than inside the eye. 

Implants placed on either the optic nerve or directly into the brain may be able to provide benefit to people with a broader range of conditions, such as trauma or glaucoma. Devices for these particular conditions are still in the research phase but are expected to enter human clinical trials in the near future. 

How it works 

The bionic eye implant receives its visual information from a miniature camera mounted on glasses worn by the patient. The images are then converted into electrical pulses and transmitted wirelessly to an array of electrodes attached to the retina. The electrodes stimulate the remaining retina's remaining cells which send the information to the brain. 

Dr Jonathan Fielden, from NHS England, said: "This highly innovative NHS-funded procedure shows real promise and could change lives. 

"The NHS has given the world medical innovations ranging from modern cataract surgery, new vaccines and hip replacements, now once again the NHS is at the forefront of harnessing ground-breaking science for the benefit of patients in this country." 

What recipients actually see 

We know from the experience of patients on a trial in Melbourne that activity on the electrodes is seen as a series of bright flashes rather than as a steady perception. The world is thus flashing bursts of light arranged to represent the basic shape – like the height and width – and approximate location of an object in front of the camera.  

Recipients need to use these irregular flashes to interpret the camera image. The field of view (the extent of the observable world) is small – about 30 degrees wide or one hand span at arm’s length – so recipients need to have a good memory to put the whole image together. 

Improvements to the external camera and video processing are able to assist here. For example, distance-sensing cameras can highlight obstacles such as a rubbish bin on the sidewalk, and thermal cameras can highlight human shapes. Right now, the best outcomes rely heavily on patient engagement and rehabilitation. 

Can image quality be improved? 

 One way to improve image quality is to increase the number of implanted micro-electrodes and make them smaller, allowing them to target selective neurons for more independent “pixels” and greater resolution. There are newer nanotechnology materials that might allow the electrodes to be small enough to produce high-acuity resolution. 

Another technique is to refine the electrical stimulation patterns to better force the stimulation to activate smaller-sized clusters of neurons. We can also artificially increase the resolution by creating “virtual electrodes” where electrical current is shared between two or more electrodes. These new stimulation methods could improve stability, reduce blurriness and possibly even provide rudimentary control over colour. 

Ultimately, researchers are seeking to understand and mimic the neural code the retina uses to communicate with the brain. If the firing patterns of photoreceptors could be replicated, the correct message would be transmitted to the brain. The resulting vision would become significantly more natural. 

Combining these techniques, the level of vision attainable might allow patients to independently navigate around without the use of a guide dog or cane. It could be possible to recognise everyday objects or even emotions on faces of loved ones. As to which approach is ultimately feasible, only time will tell. One thing that is certain is bionic eyes will get better over time. 

Posted by RBME Team