What are retinal implants?

Retinal implant technology has the same basic premise as cochlear implants, which allow tens of thousands of deaf people around the globe to hear sounds. Both implants bridge the "missing link" between the damaged organ and the brain. Cochlear implants detect sounds in the ear and transmit them to the brain's auditory nerve, and retinal implants detect light signals and transmit them to the optic nerve.

There are two kinds of retinal implants, subretinal and epiretinal.

Subretinal devices, like the Optobionics chips now in human trials, are only 2 millimeters in diameter and are composed of tiny electrodes that are powered by 3,500 microscopic solar cells. In the Optobionics chips, light coming into the eye both powers the device and is transmitted to the brain as an image by the device.

There is some speculation as to whether solar cells can generate an electrical pulse strong enough to be picked up by the brain as an image. Optobionics says 10 years of study and animal trials lead them to believe the solar cells are sufficient.

But a group of German researchers at the University of Tuebingen said their research shows solar cells aren't enough, so they have developed a subretinal implant with an outside power supply.

The other type of implants, epiretinal devices, go on top of the damaged retina, and are far more complicated than subretinal chips. At Johns Hopkins University, researchers have developed an implant system where a video camera captures images, a chip processes the images, and an electrode array transmits the images to the brain.

The Johns Hopkins chips, which drew the attention of blind musician Stevie Wonder, garnered a lot of media attention last year when they were implanted into patients for about 45 minutes. During that time, patients said they could see some colors and the outlines of letters.

Who are retinal implants good for?

As it turns out, not Stevie Wonder. That's because his blindness is not caused by a gradual breakdown of the retina, but from complications at the time of his birth.