Work in the field of retinal prostheses is at various stages of development. Of the dozen projects currently active, the furthest along is USC’s Argus II. In the late 1990s, the USC researchers formed a Sylmar, Calif.–based company called Second Sight, which has since commercialized the implant. In the first generation of the device, a camera on a pair of glasses wirelessly sends video signals to a receiver implanted inside the head. The signal is then sent by wire to 16 electrodes attached to the retina. Five patients who were once totally blind still use that version of the device. In the second generation of the device (Argus II), the video data is transmitted wirelessly to a coil that surrounds the eye’s iris (but is not visible to onlookers), which in turn routes the data to a chip attached to the side of the eyeball. The chip processes the data and sends pulses via a thin cable to electrodes implanted on the retina. At least 13 people have been outfitted with the new version, which contains 60 electrodes.
The MIT-Harvard team’s system, which is still being tested on animals but may move to human clinical testing in three years uses similar RF transmission technology, but the electrode array is placed in subretinal space where the Stanford researchers place their photovoltaic chip.
The Stanford group is not the only one to attempt photovoltaic conversion. Optobionics Corp., of Glen Ellyn, Ill., got as far as Phase 2 clinical trials using a 5000-microphotodiodes chip. But the firm went bankrupt before trials could continue. According to Palanker, the ambient light Optobionics relied on is insufficient to drive an implant.
Palanker says he has ”no clue” when a version of the Stanford system approved for clinical use will be available. The group is perfecting the system in animal experiments and developing image-processing software for the implant.
