Monday, May 14, 2012

Eye implant with lasers restores vision in blind people

By deepening our understanding of how the body works, we can create artificial tissues and organs that take over the body's function in the case of disease. When it comes to blindness, scientists are closing in on the development of a device that allows for restoring vision. In many forms of blindness, a dysfunctional retina is the cause of all the problems. Because it consists of light-sensitive cells, called cones and rods, the retina is required to convert incoming light into a neural signal that is consequently processed in the brain to generate vision. Scientists from Stanford University have developed an implant that mimics the function of the light-sensitive cells, generating the required electrical pulses to restore vision for blind people.

It consists of an array of many diodes that capture light. Three of them make up a single pixel, much in the same way as a digital screen, such as the one you are reading this on. Pixels are either 70µm or 140µm in size, eventually bringing the pixel density of the whole system to 178 or 55 pixels per mm², respectively. The device itself can be made in sizes 0,8x1,2mm or 2x2mm, which means the amount of pixels will not be nearly high enough to create perfect vision, but it is at least a step up from older implants. The whole array is only 30µm thick, but that is enough to absorb incoming light.
Individual pixels in the array.
While the array of photosensitive sensors is capable of catching light and turning it into a usable electrical signal to transport into the brain, the amount of required light is too high. Ordinary lighting conditions are too dim for the generation of a suitable electronic pulse, which is why the scientists devised a laser system to go along with the implant. Lasers can generate much higher light intensities with concentrated bundles. Therefore, using that as a surrogate for natural light, it is possible to come up with electrical pulses that are strong enough for the brain to turn into vision.

To get a laser to send pulses into a blind person's eye, the scientists made sunglasses containing a system of mirrors that direct the light beam into the retina, where the array of light sensors are located. A camera is built in and connected to the laser, so that incoming natural light is directing the laser beams. It makes the system mimic the way natural light falls on the retina, turning the camera view into actual vision with laser light.
Glasses with a video camera capture light, which is sent to an lcd. This pattern is copied by lasers that give light pulses that mimic the way light would fall onto the retina.
So far, the implant has only been tested in rat tissue. The scientists used healthy and dysfunctional retinas and put them into an experimental setup. They showed that it is possible to generate electrical pulses using the implant in both healthy and diseased tissue, indicating that their approach works. Obviously, it still needs to be tested for humans in combination with the laser glasses.

Fixing vision is a tremendously difficult task. The eye is a complex and delicate tissue, turning beams of light into electrical pulses, that consequently tell the brain something about our surroundings. While it is possible to mimic the electrical pulses, getting it right is incredibly hard. This new system developed at Stanford University is in several ways an improvement over old implants. It has a much higher resolution, and it does not require batteries: the diodes get their energy from incoming light. It would of course be better if we can simply find a way to restore the natural capabilities of the eye to catch light and turn it into electrical pulses. This is something that occasionally is possible using gene therapy.

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