When the Argus retinal prosthesis was first implanted into patients, it made headlines for bringing back elements of vision to those that had lost their sight. Now the system is giving medical professionals a fascinating insight into the plasticity of the human brain, with users learning to integrate computer-generated images with their everyday vision.
The Argus II, made by California-based Second Sight, works by gathering imagery from a camera built into a pair of glasses worn by the patient. The information is passed to an electrode array implanted into the patient's retina, at rear of the eye.
The electrical signals from the array are then sent down the optic nerve, allowing the patient to effectively 'see' a computer-generated visual representation of the world around them.
First used on patients with retinitis pigmentosa, who were completely blind, last year saw the system also implanted into patients with a condition called macular degeneration. While retinitis pigmentosa patients see nothing at all, those with macular degeneration still retain their peripheral vision, while their central vision is lost -- an outer ring of vision remains, but at the centre images are blurred beyond recognition, if they're visible at all.
When Second Sight began work on macular degeneration, there were questions over whether patients would be able to cope with the two types of vision, one from their eyes, one from the Argus system.
"One of the big things we were curious about when we implanted the patients was would they be able to integrate their natural vision with the artificial vision, or would they get confused or be bothered by the flicking lights in the middle? What we found, somewhat surprisingly, is they loved it and they were able to use both," Dr Robert Greenberg, Second Sight's chairman, told ZDNet.
"What we don't know yet is how they're doing that: they could be fully integrating that, which is one possibility -- the brain can figure it out and use both, or our best guess is that when they're trying to focus on something centrally, the brain switches and uses central vision, and when they're trying to walk around, the brain switches to the patients' own peripheral vision. Either way, the brain is incredible plastic and can adapt."
The company is now testing a second system designed to restore sight to patients whose optic nerve has been damaged, the Orion. Instead of outputting electrical signals to the retina, the Orion will send them directly into the visual cortex, an area at the back of the brain involved in processing information received from the eyes.
"The eye really is an extension of the brain, it's directly connected -- brain tissue becomes the retina as we develop in utero. The biologically environments are quite similar. All the things we know, such as which bio-compatible to use, really carried over," Greenberg said.
While the two systems are broadly similar in terms of hardware, some adjustments had to be made, including flattening out the electrode array to accommodate the more gentle curve of the brain compared to the eye. "Both the [Argus II and Orion] devices cover the small amount of visual space, but in the eye, the electrode is quite small, but the visual area in the brain is quite a bit larger, so we have to make the array cover a bigger area to correspond to the same amount of visual space," Greenberg said. In addition, the company chose to lay the electrode grid on the surface of the brain rather than try to access deeper structures for safety reasons, which meant a higher level of current was needed.
The Argus was designed for conditions where the retina is damaged or degenerating, initially retinitis pigmentosa and macular degeneration. However, the Orion could potentially be used for a far wider range of conditions -- by circumventing the eye and optic nerve behind it and sending data directly to the brain, the can Orion restore a degree of sight for any illness where there is damage to the eye itself, or to any point along the nerve or the neuronal way stations along it.
Last year, Second Sight tried a pilot system with a blind volunteer, who agreed to have an off-the-shelf neural stimulator with eight electrodes installed directly onto their visual cortex to see if the concept behind the device would work in practice, and what frequencies and currents would work best.
"The good news was that it confirmed a lot of our assumptions and showed we were on the right track," Greenberg said. With the volunteer able to see the impulses from the array as lights, the company is now developing the prototype Orion into a final version, as well making some adjustments to the software and applying for FDA approvals. The aim is to start the first implantations on human patients later this year.
It's not uncommon for surgeries involving the brain, like the implantation of the Orion, to be done while the patient is awake and conscious so surgeons make sure that the procedure isn't touching into structures of the brain that it shouldn't -- for example, by asking a patient to keep talking while they operate, surgeons can see if they're affecting parts of the brain that involve language.
While the company debated whether the patient would need to be woken up to check that the device was positioned in the best place for their visual field, the similar size of the device and visual cortex means patients won't have to undergo that.
While Orion implantations will be performed by neurosurgeons, who prefer to keep patients in overnight, the surgery's minimally invasive nature and short duration -- around an hour and a half -- may mean eventually implantees can go home on the same day.
While both the Argus II and Orion implants restore some of patient's lost vision, allowing them to read a clock or see the outline of the objects or people around them, it's not by any means a complete cure for blindness: patients will see a flickering black and white image, not the full-colour, video-type view of the world they're used to.
Improving the quality of the imagery is Second Sight's main priority, and the company intends to bring colour vision to the Argus system and improve the picture quality through a software upgrade: "Just like the iPhone - you download a new OS and get new functionality".
"One of our big R&D efforts over the last year that's starting to show some promise now is working to improve the resolution of the Argus by modifying software... We have over 200 Argus II patients now implanted, they're all software upgradeable. We could hopefully improve the vision that all these patients have with a software update," Greenberg said. "And we're hoping a lot of what we're doing with the Argus will carry over to the Orion."
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