One of the most extraordinary potentials of microelectronics is its promise to replicate the human senses - sight, smell, touch and hearing.
Earlier this month a totally blind person had an IC implanted in his eye which allowed him to make out objects and even correct the spelling of his name.
The implant came from the German firm Retina Implant.
Some eye diseases destroy the eye's photoreceptors, but leave its layers of image processing neurons intact.
By sliding an IC containing a photodiode array under the neuron layer, between the neurons and the damaged photoreceptors, the implant can both receive images focused by the eye's existing optical system, and inject signals directly into the original neurons.
The chip, which is 3mm across and 50µm thick, has a 70µm pitch 40x40 photodiode array, plus a corresponding electrode array.
According to the company, photodiodes of this size cannot produce sufficient power to directly stimulate neurons, so the chip includes signal conditioning, and has to receive power from an external source.
This is provided along a cable that exits through the side of the eyeball and is led to an inductively coupled power receiver under the skin near the subject's ear.
"Assigned to each pixel field are two photocells, one amplifying circuit and a stimulating electrode," says Retina Implant, "the microchip yields a visual field of about 12°, allowing mobility and object recognition in space."
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