How the visual implant chip works?

The German vision implant chip consists of 1500 sensors, each of which sends a stronger current when more light falls on it and a weaker current when no light falls on it (and no current at all if no light enters the eye). The whole assembly is only 20 microns thick. That's 20 millionths of a meter, or 20 thousandths of a millimeter (1/5000th of an inch). Behind the thin chip there are 16 electrodes to power the device and to allow for testing. The surgeon lifts the eyeball with a steel tube and slips the chip underneath with tiny wires. The battery pack is inserted behind the ear. It has a magnet that holds a recharging device to the ear when power runs low.

Each of the 1500 sensors on the chip is separately wired to the electrodes that send the signal to the optic nerve which the optic nerve then sends to the brain. The chip is sensitive to light falling over a range of about 11 degrees (180 degrees would be complete left to right vision). It only allows the user to see straight ahead. The recipients have had the implant in just one eye.

It is also important to understand that the implanted chip does not exactly offer high-resolution vision. The image produced by the chip is just 38 by 40 pixels, and it is in black and white, not color. Users may see the images as black and yellow, however.

Just how good were the results?

Even this little bit of vision, however, can make a tremendous difference if you were previously blind. Sitting at a table, one of the recipients of the chip was able to point to a fork, a cup, and a plate as well as a banana and an apple without having to feel for them first. He was able to select a triangle, a circle, a rectangle, and a square from a sheet of paper on which all four shapes had been printed. He was able to tell time when the minute hand was at 3, 6, 9, or 12, and he could read most of the letters M, I, K, A, T, U, L, Z, C, V, N, O, E, S, K, and H, in that order, on a vision chart. Reading shapes and shades was much easier for him than reading letters.
 
The retinal implant is a tremendous advance, but it's not a complete cure. The German researchers believe that the longer someone has been blind, the harder it will be to recognize subtle differences in shapes, such as those even in block letters. The advantage of this device over its predecessors, however, is that it at least transmits the images falling on the chip in the same configuration as they are transmitted in a healthy eye. Previous devices required long periods of training to get users accustomed to the bizarre distortions of images that the device was able to transmit to the brain.