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Sun 1 Apr 2007 03:32 PM

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Chip has potential to aid vision

Retina Implant GmbH, the University Eye Hospital in Tübingen and other partners claim to have developed a chip that allows some blind people to perceive initial impressions of vision again.

Retina Implant GmbH, the University Eye Hospital in Tübingen and other partners claim to have developed a chip that allows some blind people to perceive initial impressions of vision again. This treatment method, which is currently at the research stage, is suitable for blind people whose optical nerves and associated regions of the brain are still intact, as is the case, for instance, with the inherited retinal disease RP.

In the newly-developed retinal chip, tiny light-sensitive photodiodes take over the function of the photoreceptor cells (rods and cones) which have perished by converting light into electronic signals and steering these signals to the nerve cells in the retina.

A tiny microelectronic chip, which has been implanted directly under the retina of initially seven blind patients since autumn 2005, replaces the photoreceptor cells which have perished and is intended to return part of the patients' vision.

According to a statement from Retina Implant, all of the patients tolerated the implant, which was operatively placed under the retina by PhD Helmut Sachs or Professor Karl-Ulrich Bartz-Schmidt, well. There were no detachments of the retina, inflammations, rejection reactions, severe bleeding or the like.

The power supply cable laid by PhDs Dorothea Besch and Florian Gekeler under the facial skin and the scalp also caused no problems. Swellings of the retina were able to be treated well. The new operational method, executed through the choroid coat of the eye, can be considered to be safe.

The core of the implant is a microchip, approximately 3 mm x 3 mm in size, in which about 1500 pixel fields are arranged, including circuitry for amplification, brightness adjustment and safety switching. A field of view of twelve degrees is created, which is already sufficient to enable mobility and the orienting recognition of objects. Each pixel cell is assigned one photodiode, an amplification circuit and a stimulation electrode. Each photocell takes the light entering the eye and converts it into the electrical energy which is required to electrically stimulate the intact nerve cells in the retina. The nerve impulses from these cells are relayed to the brain via the optical nerve and ultimately lead to impressions of vision there.

The implant is placed under the retina in the area where the light-sensitive sensory cells are located in healthy persons. This ensures that the electrical charges emitted by the implant are actually transmitted to the same nerve cells in the retina which are supplied with information from the photoreceptors in people with intact retinas. The retina's information processing network is thus used in a natural way.

A kind of tongue is located at the tip of the implant, on which an additional 16 small electrodes are mounted; these are activated individually or in groups via direct electrical stimulation in order to check how the nerve cells react. This test serves to specifically generate perception of light and to find the optimal electronic setting for the conveyance of the perception. Independent of the chip function, further important information is gained via the direct stimulation. Visit:
www.retina-implant.de

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