Bionic eye

physicists and eye doctors have designed an optoelectronic retinal prosthesis system that can stimulate the retina with resolution corresponding to a visual acuity of 20/80.

The researchers hope their device may someday bring artificial vision to those blind due to retinal degeneration. They are testing their system in rats, but human trials are at least three years away.

Currently, there is no effective treatment for most patients with related macular degeneration (AMD), the major cause of vision loss in people over age 65, or retinitis pigmentosa (RP), the leading cause of inherited blindness.

However, if one could bypass the photoreceptors in the eye and directly stimulate the inner retina with visual signals, one might be able to restore some degree of sight.

To that end, the researchers directly stimulate the layer underneath dead photoreceptors in the eye using a system that consists of a tiny video camera mounted on transparent "virtual reality" style goggles, a wallet-sized computer processor, a solar-powered battery implanted in the iris and a light-sensing chip implanted in the retina.

In operation, an image is first captured by the video camera, then sent to the computer for processing. The processor then wirelessly sends the captured image to an infrared LED-LCD screen mounted on the goggles. The transparent goggles reflect an infrared image into the eye and onto the retinal chip stimulating its array of photodiodes.

Currently the researchers are testing two chip designs in parallel because they aren't yet sure which will be best.

One design uses electrodes that protrude up from the chip like pillars. One side of each pillar is a light-sensing pixel and the other side is a cell-stimulating electrode. The pillars allow retinal cells greater access to nutrients and let researchers affect specific cell layers by controlling the height of the pillars. But pillars expose more cells to current, potentially heating tissue and increasing the chance for "cross-talk" where many electrodes affect one cell.

The second design has electrodes recessed into pores, which localises currents and makes stimulation selective, perhaps allowing the researchers to stimulate single cells.

The retinal chips have already been implanted in rats and have not been rejected. The next step will be longer tests in rats, as well as tests in larger animals for which models of retinal dystrophy exist. The researchers are currently shipping chips to Harvard Medical School for tests in which the chips will be implanted into pigs.