A new round of clinical tests offers the promise of major advances in the U.S. Department of Energy’s (DOE) Artificial Retina Project—a collaborative, multi-institutional quest to help restore sight for people blinded by retinal diseases.

With approval from the U.S. Food and Drug Administration to move ahead with clinical trials, surgeons at the Doheny Eye Institute (University of Southern California Medical Center) are enrolling subjects blinded by retinitis pigmentosa (RP) to receive an Argus II—the latest model of an artificial retina. Other select implantation sites in the United States, Europe, and Latin America are also enrolling subjects for clinical trials.

Described as a group of inherited eye diseases that affect the retina, RP causes degeneration of the photoreceptor cells that enable sight by capturing and processing light. As the cells degenerate, patients experience progressive vision loss. The implant, manufactured by Second Sight Medical Products Inc., a private company, takes the place of the damaged photoreceptors. These devices are experimental and not yet commercially available.

The current clinical trial follows on the heels of earlier human implant tests that indicated the safety and long-term reliability of first-generation Argus I. During the testing phase, which began in 2002, six people received retinal prostheses. Each of these previously blind individuals has since been able to detect light, identify objects in the surrounding environment, and even perceive motion (see graph above). Although one implant had to be removed for unrelated health reasons, and one patient passed away, the remaining four patients continue to use the device at home.

To date, Argus I is the only retinal prosthesis developed worldwide that continues to work over a period of years, lasting an average of 3.6 years and a maximum of 5.3 years.

Extensive, preclinical testing preceded both human implant trials.

Another Step Forward

The second-generation retinal prosthesis incorporates revolutionary DOE national laboratory technologies. Designed to last a lifetime, the compact device contains 60 electrodes—nearly 4 times as many as the initial 16 electrodes—embedded in a tiny array. The array is surgically attached to the retinal surface and used in conjunction with an external camera and video-processing system to provide rudimentary sight to the implanted subjects.

Fitting neatly into the eye’s socket, the new prosthesis is only about a fourth the size of the original retinal implant, thereby dramatically reducing surgery and, potentially, recovery times.

“It’s aimed for patients with little or no light perception, hopefully to provide them with unaided mobility,” says Mark Humayun, a surgeon at Doheny who is leading the DOE effort. What’s key is that, like the Argus I, this device processes information in real time. “We can’t afford to have images coming back 5 to 10 seconds later when a person is trying to cross a street,” Humayun explains.

Leveraging DOE Know-How

A third implant model, under development, will incorporate cutting-edge, dual-use DOE technologies (see Lawrence Livermore National Laboratory). It will be even smaller and have 4 to 5 times more electrodes embedded in the array. Eventually, the DOE collaborators hope to produce a 1000-electrode device that potentially could restore enough sight to enable facial recognition and even the ability to read large print, in addition to unaided mobility (see graph above).

“This is a great example of how the unique talents and resources at the DOE national laboratories can be used to advance the development of instrumentation to help the blind to see,” says Dean Cole, program manager for the DOE Artificial Retina Project.

Clinical trials on the third model are expected to begin in 2011.

To date, participants in the clinical studies have had little or no light perception due to RP. Ultimately, however, millions suffering from dry, age-related macular degeneration, or AMD, also stand to benefit because the disease strikes the same photoreceptor cells as RP.

Other Projects Worldwide

Other efforts to develop retinal prostheses are ongoing in the United States, Germany, Japan, and elsewhere. These programs pursue many different designs and surgical approaches. Some show promise for the future but have yet to demonstrate practicality in terms of adapting to and lasting long term in a human eye. Thus far, Second Sight is the only company that has demonstrated visual acuity in preliminary testing of some implanted blind individuals.