Next-generation artificial retina focuses on clinical trials

PORTLAND, Ore. — A second-generation artificial retina chip called the Argus II Retinal Prosthesis System is beginning clinical trials.

The new retina chip was designed at the University of California at Santa Cruz and fabricated by Second Sight Medical Products. The project was funded by the Artificial Retina Project at the U.S. Energy Department.

The Argus II works by implanting the artificial retina chip directly inside the eye atop the old retina. (It only works for patients whose retina has degenerated, but still have intact nerves connecting to the brain--a condition brought on the disease retinitis pigmentosa and by age-related macular degeneration.) The artificial retina has an array of electrodes that stimulates optic nerve cells, sending an image to the brain's vision centers. The plasticity of the brain's vision processing capabilities enable it to adapt to the artificially generated signals.

A tiny wire connects the artificial retina to a circular antenna mounted around the pupil on the inside front of the eye. A video camera mounted on a pair of eyeglasses wirelessly transmits images to a belt pack containing a microprocessor that processes the video signal, then transmits it to the antenna in the eye, which in turn sends signals down the wire to directly stimulate optic nerves with the implanted electrode array.

The electrode array was cast using a 1.2-micron CMOS process on a 5.5x5.25 millimeter die consuming 42 milliwatts. It achieves 4-bit resolution for each of the 60 implanted electrodes. Both power and data are supplied to the chip wirelessly.

The major challenges overcome by the new chip included "minimizing the size and power requirements of the implanted device, optimizing power delivery and managing reliable communication and data transmission between implanted and external components," said engineering professor Wentai Liu at the University of California at Santa Cruz.

The first generation Argus I contained just 16 electrodes, enabling patients to detect motion, sense patterns of light and dark and to count large objects. The new model increased the array to 60 electrodes while reducing the surgical implant time has from six to two hours.

Currently, ten patients are scheduled to receive the implant in the U.S., with several more patient trials planned in Mexico, Switzerland, France and England.

The Artificial Retina Project was the brain-child of an ophthamologist and bioengineer, Mark Humayun, who pioneered the original project. The project is is now part of a DoE consortium of three universities, six national laboratories, and the commercial company, Second Sight LLC (Sylmar, Calif.)

Six patients with retinitis pigmentosa have received the Argus I. After the conclusion of successful testing of Argus II during a three-year clinical trial, a third generation device--the Argus III with 200 electrodes--will be tested and considered for approval by the U.S. Food and Drug Administration for implantation.

Argus II is about four times smaller than Argus I, but still uses a sealed package. Argus III will replace the package with a much smaller bare die with a special coating only a few microns thick on a flexible substrate that allows the electrode array to conform to the curve of the inner eye.

The ultimate goal of the Artificial Retina Project is a long-lived implant with enough resolution to enable patients to walk unassisted, recognize faces and read large print.

Along with DoE, additional funding was provided by the National Science Foundation and the National Institutes of Health.