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Retina Implant AG is developing a retinal prosthesis by means of which a good number of blind persons should be able to partly regain sight. So far the development of the implants was undertaken by a German Ministry for Education and Research funded research consortium out of which the Retina Implant AG was founded.

The core of the implant is a microchip of about 3 mm diameter and about 50 µm thickness, in which 1,500 pixels are arranged. The size of one pixel is around 70 x 70 µm², yielding a visual field of 12° and allowing mobility and object recognition in space. Assigned to each pixelfield are two photocells, one amplifying circuit and a stimulating electrode. Each one of the photocells absorbs the light falling into the eye and transforms it into electrical energy. This energy serves to control external source energy, adduced in order to stimulate the intact nerve cells in the retina. The nervous impulses from these cells are then led via the optic nerve to the visual cortex where they finally lead to impressions of sight.

The chip gets implanted beneath the retina..

Where exactly is the implant located?

The following figure illustrates the site of the implant within the eye schematically:

Diagram of the chip

The chip is placed underneath the retina, exactly at the place where in normal-sighted persons the light-sensitive photoreceptor cells are found. Thus we can be sure that the electric impulses emitted by the implant are really transmitted to the same nerve cells that in persons with a healthy retina receive information from the photoreceptors. In this manner, the original, natural information processing network is being used along the natural pathway.

Energy supply of the retinal implant

In order to overcome the stimulus thresholds for a successful stimulation of retinal nerve cells, a special integrated amplification into the chip is necessary. Otherwise, no visual impression would be possible with no other source of energy than normal daylight. In the first clinical trial series, the necessary energy is transmitted across fine wires from outside. In the second clinical trial series, planned over a time-span of at least 6 months, the supply of energy takes the form of high frequency.

Prototype of an active implant

The components are attached to a highly flexible polyimide ribbon. With the exception of the stimulating chip, the entire implant is embedded in silicone. The entire length of the implant measures ca. 100 mm, the width 3 mm and the thickness 0,1 mm. Only the right half of the implant rests beneath the retina; the left, thicker part is sewn from the outside onto the eyebulb and is covered by the conjunctiva.

What can be achieved with the help of the implant?

Even a spatial resolution of 1° visual angle constitutes a significant improvement of the patient’s quality of life, since he is able to orient himself in space and to recognize and distinguish at least larger objects.

In summary, after implantation of the chip the patient’s visual ability should meet the following criteria:

• Orientation in space
• visual field: 8° - 12°
• Capacity to see without visual aids (except glasses): at least ability to count fingers, at best ability to recognize faces.
• Ability to recognize the letters of the alphabet with additional visual aids.
• Ability to see in surround brightness from 10 Lux to 100.000 Lux.

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Other technologies

So far there exist no products that can restore sight in patients with degenerative retinal diseases.

Retina Implant’s approach is medium-term the most promising because all crucial elements such as implantability, biocompatibility, spatial resolution and technical realization have been successfully tested, whereas this is not entirely the case in other developments (see also Science-Publication by Prof. Zrenner).

The following supporting, but not healing therapies are available or being developed:

In development are retinal prostheses (on the retina: Intelligent Implants, Bonn, Prof. Rizzo, Boston, Second Sight, Los Angeles; under the retina: Optobionics, Chicago), Prostheses on the optic nerve (Prof. Veraarts, Belgium), Prostheses in the cortex (Prof. Dobelle, New York, Prof. Norman, Salt Lake City), surgical procedures, pharmacological therapies with growth factors as well as gene therapy approaches.

It is important to emphasize tht gene technology, transplantation and growth factors can only be applied in cases where the photoreceptors are still intact. A possible stem cell therapy is not in sight for the next few years. In existing blindness or in advanced photoreceptor degeneration the only possible therapy is the artificial electronic chip.

Among these different approaches retinal implants are the furthest developed and also appear to be the most promising in the long run.

The following table lists the different retinal implants being developed, contrasting their principle advantages and drawbacks.