How Would You Like Your Bionic Vision?

The eye is going bionic, and companies are competing fiercely to develop the best technologies that can restore vision to the blind. In this month's magazine we profile the company Second Sight, which has just brought its retina implant to market in Europe, and is hoping for FDA approval in the United States this year.

While Second Sight is ahead of the competition in commercializing its technology, it's not the only serious contender. The researchers behind Retina Implant AG of Germany recently stopped by the IEEE Spectrum office to show off their own gear, and to explain the details of how it works. Below is an image of the German company's delicate implant, which is currently undergoing clinical trials in Europe and the United States.

Both companies' devices are intended for patients with retinitis pigmentosa, a genetic disease that, in its most severe form, gradually robs people of their vision. The disease causes the retina's photoreceptor cells (the cells that respond to light) to die off, but it leaves the rest of the retina, the optic nerve, and the brain's vision centers perfectly intact. So companies are developing various types of implants that can take the place of those photoreceptor cells and send the visual data onward to the brain.

These devices don't come close to matching natural vision, but the rough black-and-white images they provide definitely help users navigate in the world.

While the two companies have the same basic idea, there are very interesting differences in their technical approaches.

The first major difference is in the image-capture process. Second Sight uses an external camera (mounted on a pair of sunglasses) to capture visual information, routes the info to a visual processing unit worn on a belt, and then sends the processed image to two antennae implanted around the eyes, where it's forwarded on to a 60-electrode array that stimulates the remaining retinal cells.

Brian Mech, a spokesman for Second Sight, says this approach allows them to "take advantage of the rapid evolution in camera and electronics technology." He says the company can upgrade the camera and the software inside the visual processing unit long after the surgery is over, and can keep improving the user's experience.

The researchers behind Retina Implant have taken a different approach. Instead of an external camera, they essentially built a camera into the eye itself, by constructing an implant that contains light-receiving photodiodes, amplifiers, and electrodes (the implant is shown in the image below). The array of 1500 tiny photodiodes on the implant turn the light signals they receive into electric signals, and an attached electrodes then send the signal up the optic nerve to the brain.  

After surgery, this system can't easily be upgraded. But Dr. Eberhart Zrenner, the founder of Retina Implant and a professor of ophthalmology, says his system has other advantages. With Second Sight's external camera, a user who wants to find an object has to move the camera lens around by moving the entire head, says Zrenner. "Our image receiver is right in the eye so that the patient can naturally gaze with his or her eyes, and find an object simply through eye movements," he says. "Vision therefore is very natural."

Another difference between the two companies arises in the surgical procedure for the implant, and the placement of all the parts. With Second Sight's system, all the implanted gear (the antennas that receive the external signal and power, as well as the electrode array) are implanted around the eye. 

With Retina Implant's system, the photodiode and electrode component is in the eye, but it's attached by a thin cable to a coil in a ceramic housing that's implanted under the skin behind the ear. That component, which is about the size of a silver dollar, receives power from a primary coil that sits outside the skin behind the ear, and which stays in place magnetically.

Retina Implant recently started a new round of clinical trials involving 25 patients, with hospitals in Germany, England, Hungary, and the United States (the Wills Eye Institute) taking part. Zrenner says the company hopes to get approval to sell its devices in Europe once the clinical results are in.

Of course both companies think their specific technology will give them an edge in the market. If they both get the regulatory approvals they're seeking, they'll soon get to battle it out. We look forward to a spirited competition.

Below, a video of a Retina Implant patient at a restaurant where she sees her beer waiting for her (oh happy day), and identifies her silverware.

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