A Brighter Future for Retinal Implants

Biomedicine

A Brighter Future for Retinal Implants

(Page 2 of 2)

Tuesday, September 29, 2009
By Duncan Graham-Rowe

Bionic eye: Images are fed to the Argus II implant chip from a camera via a wireless induction loop, with the receiver attached to the outside of the eyeball.
Second Sight

There is hope that the resolution and granularity of these devices can be improved further and that the devices can be made more self-contained. At last week's symposium, Eberhart Zrenner, director of the Institute for Ophthalmic Research at the University of Tübingen, in Germany, presented the results of a trial involving a patient who was able to read eight-centimeter-high letters, albeit with the assistance of a large magnifying device called a dioptre lens. This was achieved using a 3-millimeter-diameter implant made up of roughly 1,500 electrodes, each connected to a photocell. These photocells are used both to sense light and to power the electrodes, which means no external power or camera is needed.

Although Zrenner's device is compact, it is only designed for semichronic implantation, and it is unable to last within the body for long periods of time, says Mark Humayun, a retinal surgeon at the University of Southern California who is involved in the Argus II trials. What's more, Humayun says that reading text has been demonstrated before, albeit with considerably larger letters. "It translates into little useful reading vision, not only because letters are too big, but because it often takes 30 seconds to recognize a single letter," he says.

Cosendai says that, for now, the field is taking small steps and trying not to overstate the potential. Initially, he says, retinal implants will be used to merely help people navigate and orient themselves.

The signal-processing side of these implants remains a key technical challenge, says Cosendai. A patient's brain often needs to be retrained to adapt to the new stimulation.

Rolf Eckmiller, another researcher in the field at the University of Bonn, says that much remains to be done. "Progress has been made, but we have so far underestimated the amount of work involved," he says.

Seeing shapes and edges may help many people become more mobile, Eckmiller says, but it's a big leap to restoring full vision or even the ability to recognize faces or to read. "There's a difference between seeing and recognizing a banana, and seeing something that might be a banana," he says. Currently our understanding of the signals required to make this leap is lacking, he says.