A Bionic Eye Implant for AMD?
Two years ago, 80-year-old Ray Flynn became the first patient to receive a “bionic eye” to treat the effects of age-related macular degeneration (AMD). The “eye,” a retinal prosthesis known as Argus II, has been used in both the United States and Europe to treat blindness caused by retinitis pigmentosa (RP)—a comparatively rare genetic eye disease.
Now a clinical trial will attempt to determine whether the Argus II can also be useful for people with non-neovascular (dry) AMD, a far more common condition.
How it works
Argus II is an electronic, software-driven system with two main parts—one external and the other implanted in the eye. Together these parts restore a degree of visual aptitude lost because of deteriorating light-sensitive cells that line the retina and send visual signals to the brain.
The external part of the Argus II system gathers visual data using a small camera mounted in the user’s eyeglasses and converts it to electrical pulses. The data is sent to the visual processing unit (VPU), a small console that can be worn on a belt or carried in a pocket.
Controls on the VPU allow the user to manipulate the software to adjust the signal that’s being sent—for instance, by enhancing the contrast. A transmitting antenna in the eyeglasses sends the processed signal wirelessly to a receiving antenna in the eye.
Inside the prosthetic eye, the electrical pulses are passed to an array of electrodes implanted on the retina during surgery. The pulses stimulate nerve cells that send the signals to the brain where they’re perceived as spots of light that the user learns to interpret.
What the user “sees” are patterns of brightness that represent visual images, such as the outline of a person or an object in front of the user.
Even though most of the cells that sense light have stopped functioning, light signals can be sent to the brain by neurons that are still viable. The neurons are able to transmit signals from the electrodes along the same path that had been used by signals from the natural light-sensing cells before they were damaged.
Argus II’s potential effectiveness was demonstrated in a clinical trial evaluating its use by 30 patients with advanced or severe retinitis pigmentosa. The trial showed that the system helped participants gain enough visual acuity to, for example, identify the location of objects and people.
Participants could also recognize movement; read large letters, words, and sentences; recognize the curb while walking on a sidewalk; and perform other tasks of everyday life that require sight.
That study led to FDA approval of the system in February 2013 as a humanitarian use device for patients with retinitis pigmentosa—approval that’s given to devices used to treat a very limited number of patients each year.
Approval means the developer, Second Sight Medical Products, has demonstrated that the device is safe and its use provides probable benefits that outweigh the risks. It remains to be proven whether Argus II will be effective for patients with AMD.
The primary difference between retinitis pigmentosa and AMD is the kind of vision that’s affected. RP leads to the deterioration of light-sensing cells on the retina—primarily the cells that make peripheral vision possible. As the disease progresses, people are still able to see what’s in front of them, but side vision deteriorates. So does the ability to see at night. Eventually the condition can lead to functional blindness.
AMD affects the light-sensitive cells in the macula, the central part of the retina. As the disease progresses, central vision dims, becomes blurred, and eventually can be blocked by dark spots that get larger and darker over time.
Flynn’s implant was the first step in a feasibility study to evaluate the safety and utility of Argus II in treating blindness in patients with dry AMD. The three-year study involves five patients with the disease.
Depending on the outcome, a larger trial will follow to meet the requirements for approval and marketing of Argus II. Only then might it be known whether vision with the implant offers improvement over the peripheral vision remaining in AMD patients.
Two weeks after surgery, the system implanted in Flynn’s eye was switched on. In tests that same day, Flynn was able to discern the outlines of people and objects. He also recognized patterns on a computer screen and was able to distinguish the orientation and movement of lines on the screen. To show it was the system at work, he accomplished these tasks with his eyes closed.
If clinical study results lead to the approval of Argus II for widespread treatment of dry AMD, the device will be costly. A single Argus II unit will sell for around $150,000. The surgery and other healthcare expenses are extra. But Medicare does provide coverage of the prosthesis for people with RP who are referred for treatment by their doctors.
Argus II is not the only prosthetic device for AMD treatment on the horizon. Basic research on retinal prostheses is ongoing at institutions such as Stanford University School of Medicine.
And a recent review in the Journal of the Chinese Medical Association identified at least three other systems currently undergoing clinical trials in Europe. Second Sight Medical Products is also developing other systems that can be used to address blindness associated with other causes.
What once was science fiction—made popular on the big screen by Star Trek: The Next Generation character Geordi La Forge, whose micro-implants enabled him to see—may one day become a reality for many people.