Break Through! Implanted Chip Will Let Blind People See

Three blind people in Germany have been fitted with an optical sensor chip implanted behind the retina that has allowed them to see shapes and objects just days after the procedure.

The chip has been developed by a joint effort of the Institute for Ophthalmic Research, Univertsei Tübingen, Germany and Retinal Implant AG, also in Germany, specifically for people who have lost or who are losing their sight by retinitis pigmentosa.

What is retinitis pigmentosa?

Retinitis pigmentosa, also known as RP, is an inherited condition of chronic inflammation in the retina, the light-sensing tissue in the back of the eye. The retina has about 120 million rods that help detect shapes and motion. It has about 6 million cones that detect color. Most of the cones are concentrated in the center of the eye known as the fovea centralis, where they are very densely packed into a region just 0.3 mm (about 1/100 of an inch) across. If anything happens in that area of the eye, color perception may be lost.

There are at least nine different genes that, if any one of them goes wrong, can cause problems with rods in the retina that detect shape and motion. There are over 100 genes that can be mutated and cause loss of function in the color-detecting cones. Because there are so many different genes that can cause the same problem, people with RP can have very different experiences of the disease. Some go blind in childhood. Some retain partial sight all the way through life. Some people develop tunnel vision, and others develop night blindness. At some point in life, however, many people with RP become totally blind.

The nature of the disease, however, is that people have some life experience with sight, so their brains can detect shapes, sounds, and colors if sight is restored. The nerves to the retina continue working even though they don't receive any new visual information. This makes people RP prime candidates for prosthetic vision implants such as the chip recently developed in Germany.

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.

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Where will researchers go from here?

The next development in the technique probably will be implanting multiple chips so the user can have a wider field of vision. They will to make sure that images are stable over time and they will continue to develop devices that work inside the body, not outside it, and that will accommodate eye-hand coordination. This technology is not likely ever to accomplish complete restoration of sight, but it will bring some people from a state of total blindness to enough vision to read and accomplish daily tasks by sight.