A short piece in the MIT Technology Review describes a new retinal implant designed to remain in place for long periods of time:
In retinal diseases such as acute macular degeneration and retinitis pigmentosa, the light-sensing cells of the retina may no longer work, even though the neurons that carry signals from these cells to the brain are still healthy. The Boston project uses an array of electrodes to stimulate these cells and reproduce a simplified visual image in the subject’s brain. A camera mounted on a pair of eyeglasses captures an image, which is rapidly processed by a microcontroller to produce a simplified picture. This is then wirelessly beamed to the implant, which activates 15 electrodes inside the eye. The implant also receives power wirelessly from the microcontroller.
[The] implant sits mostly outside the eye. The coil around the iris receives wireless power and image data from a microcontroller that can be carried on a belt. The coil transmits data to electronics inside a waterproof titanium case. The electronics controls an electrode array (not visible) connected to nerves in the back of the retina.
This device would be more bio-compatible than others, because it sits mostly outside the eye and therefore carries a reduced risk of inflammation and of a decline in performance with time. So far it has only been tested in pigs but human trials are planned for 2010.