Vision occurs when light enters the eye, is picked by photoreceptors and transmitted through the optic nerve to the vision centers of the brain for interpretation. An interruption anywhere in this circuit would cause blindness. The first place an interruption of the circuit could occur is in the cornea where the light is let into the eye. The cornea becomes opaque with age or injury. This is an easily solved problem, as it does not involve nerve cells. The cornea can be replaced with either an artificial lens or a transplant. There is not even an issue of needing to match tissue. If the person is not blind due to the cornea solving the problem becomes a little more difficult. The next part of the eye where problems may occur is the retina.
The retina is made of several layers of tissue. The top layer contains cones and rods. These are the photoreceptors, which transfer light to the ganglia. There is also a layer of lateral inhibitors, which help the ganglia determine the edges of pictures. Due to lateral inhibitors, the ganglia are only turned on at the edges of light and dark. The ganglia transmit this data to the brain through an optic nerve. The mind takes this information and turns it into a picture by filling in the blank spots. Damage to the optic nerve or the brain itself may also cause blindness.
A group of researchers with the plan of using electrodes to excite nerve cells has developed a device, which has a camera and an ultrasound instead of photoreceptors. They are mounted on a pair of glasses to give them a location similar to the one the brain is expecting. These are connected to a computer attached at the hip, which transmits signals to the brain via cables that end in electrodes implanted in various parts of the vision center in the brain. This system would bypass any problems that did not originate in the brain itself. This version will actually be on sale in other countries with in the year. The device still has some problems, as it does not provide good sight or depth perception yet. (1).
Another group is working on a less invasive technique that would only help those who were missing the rods and cones. Without these receptors, there is no way to turn on the ganglia. The ganglia are still there and capable of transmitting signals but they have no cells to excite them. This device to be implanted on the retina of the eye will transmit signals to the ganglia. The device receives its signals and power from a small laser mounted on a pair of glasses. The laser is attached to a camera mounted on the glasses. Unfortunately, the group has not yet developed a device, which is biologically inert enough to stay in the eye permanently. (2).
This merger of technology and the nervous system will help to improve vision of the blind. The ability to merge technology and nerves to get understandable input has implications in the other senses as well. It means that we maybe able to repair other senses in similar ways. This could mean hearing for the deaf and even touch for the paralyzed. More importantly if electrical signals can be transmitted to the brain there is no reason why neural signals can not be transmitted to the electronic leading to prosthetics that can be moved like a real limb. It may even eventually lead to a way to reconnect the brain and the spinal cord with a computer.
2) Reseachers Trying to Produce Artificial Vision System , Another news story which I found in several newspapers which all said exactly the same thing I am not sure which one was quoting which.
3) Eye and Retina , A page that gives information on the structure of the eye.
4) Central Visual Pathways , A page that describes the path that vision takes after it leaves the eye and the related structures.