Innovative Retinal Implant Could Help Restore Partial Vision

The implant array conforms to the outer wall of the eye, using a specially designed surgical technique that fixes the bulk of the prosthesis to the outer surface of the sclera, and drives a micro-fabricated polyimide-stimulating electrode array with sputtered iridium oxide electrodes that is implanted in the subretinal space. The polyimide-implanted device consists of a 15-channel stimulator chip, secondary power and data receiving coils, and discrete power supply components.

The completed device is encapsulated in titanium, except for the reference electrode and the thin electrode array. In vitro testing was performed to verify the performance of the system in biological saline using a custom RF transmitter circuit and primary coils. Stimulation patterns as well as pulse strength, duration, and frequency were programmed wirelessly using custom software and a graphical user interface. Patients who received the implant wear a pair of glasses with a camera that sends images to a microchip attached to the eyeball. The glasses also contain a coil that wirelessly transmits power to receiving coils surrounding the eyeball. When the microchip receives visual information, it activates electrodes that stimulate nerve cells in the areas of the retina corresponding to the features of the visual scene. The electrodes directly activate optical nerves that carry signals to the brain, bypassing the damaged layers of retina. The wirelessly operated, minimally invasive retinal prosthesis was tested in preclinical chronic implantation studies in Yucatan miniature pigs, which have roughly the same size eyeballs as humans. Wireless operation was verified both in vitro and in vivo for more than seven months. The study was published in the October 2009 issue of IEEE Transactions on Biomedical Engineering.

"Anything that could help them see a little better and let them identify objects and move around a room would be an enormous help,” said Shawn Kelly, a researcher in MIT's Research Laboratory for Electronics and a member of the retinal implant project at the U.S. Veterans Affairs (VA) Center for Innovative Visual Rehabilitation (Boston, MA, USA).

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