A look behind Second Sight's Argus II eye prosthetic that is giving new hope to blind patients
Roughly 100,000 Americans are affected by retinitis pigementosa (RP), a degenerative retinal disease that often results in complete blindness in both eyes. There is no effective treatment for this condition. But there may be new hope for the blind. The Argus II is a retinal prosthetic from Second Sight Medical Products Inc. (Sylmar, CA) designed for patients with RP. Approved by FDA in February, the Argus II is a system featuring a head-mounted digital camera that communicates with an implant attached to the eye. Once implanted, the device allows patients to recover a semblance of their vision.
The Argus II Retinal Prosthesis System’s external equipment.
The Argus II
is the result of more than 20 years of research conducted by Second Sight’s CEO, Robert Greenberg, and his team. The genesis came during Greenberg’s time as a graduate student at Johns Hopkins University in 1991. Greenberg was helping to conduct early patient testing. At one point the research team inserted an electrode into a patient’s eye—resulting in the patient seeing a spot of light. Adding a second electrode produced two spots of light. “For me that was the life-changing moment,” Greenberg says. “I realized that if a blind person can see two spots of light; the rest of it was just engineering.”
The engineering challenge was to incorporate enough sensors (60 total) to yield a more complete field of vision and fit them into a small enough area while also protecting them from the fluids inside the eye and without damaging the retina.
Although a 20-year development time wasn’t anticipated, it was really a matter of having technology available that would facilitate Second Sight’s actual goals. The camera used in the Argus II, for example, is essentially a cellphone camera.
The first model of the device, the Argus I, was based on similar principles as a cochlear implant. The device went behind the ear, ran a cable to the eye, then put an electrode array inside the eye. Six patients were implanted with clinical trials, and while patients reported utility from the device (there are still two patients actively using the Argus I today), Greenberg and his team realized what they had was not the ideal. “It was quite an invasive procedure. It took four surgeons working eight hours to implant,” Greenberg recalls. The Argus II, by contrast, can be implanted by a single surgeon in a two-hour outpatient procedure done under general anesthesia.
The Argus II’s implant is surgically placed in and on the eye.
After allowing a week for healing, patients have their implants, which are powered by wireless induction between the headset and implant, activated. Using a combination of ophthalmology tests and what Second Sight calls a “visual rehabilitation kit,” patients have their device calibrated and are trained using simple tasks, like putting together large puzzle pieces, to see with their new implant and relearn hand-eye coordination. The Argus II affords patients a view that is analogous to a pixelated, black-and-white TV. Patients have very good edge detection abilities and can distinguish objects, but still have trouble perceiving depth because of the lower resolutoin of the images. Some of the most successful patients are able to read large letters and even words.
However, there does tend to be variance in how well the Argus II works for patients. “So far we’ve identified potential variables that could impact performance—retinal health, age at which they went blind, how long they’ve been blind,” says Greenberg. “We haven’t been able to definitively identify any predictors of good performance, but some data suggest that patients with slightly better residual vision, as measured by ERG or flash detection tests, tend to do better. In terms of the maximum benefit we’ve seen, the most common thing we hear is orientation and mobility improvement— the ability to find a door or follow along a sidewalk or crosswalk.”
The Argus II’s upgradable software package could be an avenue for combatting some of these variances as well as introducing new features into the device. The issue of depth, for example, can be addressed by adding image processing and zooming capabilities into the software. “We’ve developed an image processing system where we can zoom in and we were actually able to achieve 2200 vision in a completely blind patient,” Greenberg says. Other enhancements include the ability to see color using frequency modulation.
“I would love to make our software open source,” Greenberg says. “During clinical trials we tried to do a little bit of that. One thing we did do in trial is open a small window where we had all of the safety features built into the core and let researchers build on that so that they have some control over the stimulation.” It’s the same sort of semi-open source API model employed by Apple, allowing developers access to work with only certain components of the programming. However, “to make it broadly open source is unfortunately not possible in a regulated environment.”
Still, Greenberg is grateful for the stringent FDA oversight, which he says made the Argus II a better product. “FDA insisted on very extensive reliability testing because they didn’t want any device failures in patients,” he says. “They wanted us to really prove that the device was robust and would last in the patient. That was a significant barrier, but looking back I’m thankful they set the bar that high. Even though the development time was longer it was a good thing actually for the patients. In clinical trials we’ve only had one device failure and it was attributed to surgical error. Even that device lasted four years before it failed.”
With the Argus II already available in Germany, the UK, Netherlands, and Saudi Arabia, Second Sight is currently looking to expand its offerings in Europe and the Middle East. With the recent FDA approval, Second Sight has set a launch time for the Argus II for later in 2013. Since the approval was announced more than 1000 patients have contacted the company expressing interest in receiving the implant. “Ultimately, we’d like to use Argus II technology in the visual cortex—using similar technology to help the 7.8 million patients who are blind from all causes.”
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