Retina implant technology involves the use of microelectronics and microchip electrodes surgically implanted into the back of the eye (retina) to restore the function of the damaged light-activated cells found there.
These photoreceptor cells respond to light and convert it to an electrical signal which is passed to nerve cells in the eye, and then ultimately to the brain where it is perceived as vision.
A surprising finding is that in patients with retinitis pigmentosa and age-related macular degeneration where the photoreceptors have been damaged, often the nerve cells that relay the signal to the brain (the ganglion cells) are still intact after many years. Therefore, it is possible to directly stimulate these retinal nerve cells in these patients and produce signals that will be received by the brain and perceived as vision.
Scientists have looked at several different ways to stimulate retinal nerve cells including neurotransmitter release, magnetic, mechanical, and electrical stimulation. Most researchers are looking into electrical stimulation.
In order to work correctly, electronic retinal implants need to directly connect with retinal nerve cells, which are located above the photoreceptor cells in the eye.
Argus II Implant
The Argus II Retinal Prosthesis System consists of a miniature video camera that is housed in the patient’s glasses and this captures a scene. The video is sent to a small patient-worn computer (i.e., the video processing unit – VPU) where it is processed and transformed into instructions that are sent back to the glasses via a cable.
The Argus II Study Group comprises of 11 centres located throughout Europe, the United States and Mexico. A patient pilot study was initiated in Mexico in 2006, followed by a 30 patient trial in Europe and the United States. Follow-up for patients with the retinal prosthesis implanted ranged from a minimum of 3.5 years to almost 6 years, and cumulative subject-years of follow-up exceeds 125 years. The company responsible for marketing the implant is Second Sight. Argus II is approved for use in the European Economic Area (CE Mark) and is available in some European countries. On February 15th 2013, the FDA granted approval to Second Sight Medical Products to market the Argus II for patients with late-stage RP.
Retina Implant AG
Retina Implant AG is another company based in Germany that is developing their own retinal implant for patients with retinal degenerations. With their chip, they envisage that it should become possible again for a patient to move freely and independently without another person’s assistance. It is also conceivable that objects and faces could become recognisable again. A component of the early research into this implant was performed by the Tyndall institute in Cork and was funded by Fighting Blindness. One of the founders of Retina Implant AG, Professor Eberhart Zrenner was the keynote speaker at the Retina 2012 conference organised by Fighting Blindness in Dublin.
Professor Zrenner is based the University Of Tübingen and he delivered a fascinating and engaging talk entitled “What blind Retinitis Pigmentosa patients can see when using the new sub-retinal wireless implant Alpha-IMS.” Eberhart is also the co-ordinating director of an international team that are developing microchips to be surgically implanted beneath the transparent top membrane of the retina and into the macular region. This is the area of the eye where clear sharp central vision is formed. The heart of the retinal implant is approximately 3 x 3 mm2 large and consists of a silicon chip with 1,500 light sensitive elements. The chip senses light and transmits light signals back to the brain. The implant is controlled by a handheld, battery powered device which receives signals from a small device that is implanted under the skin behind the ear.
All components of the retinal chip must be biocompatible and demonstrate long term stability for many years. This is a huge technological challenge, which has led the team to explore the use of new materials and combinations. The components that are in contact with the surrounding tissue must be in a sealed protective layer to protect the device from the corrosive environment of the body. Eberhart explained that the retinal implants are well tolerated, and reassuringly remarked that although it is seven years since the first chips were implanted, they still look like new.
Eberhart then played some footage of one of the success stories of the retinal chip, a Finnish man named Miikka Terho, who was implanted with the retinal implant in 2010. Miika was able to distinguish between letters, a clock and amusingly his own name. When researchers placed letters reading MIKA in front of him, Miikka replied, “Do you think I’m a Formula 1 driver?”, as the research staff had confused the spelling of his name with fellow Finn, the race car driver Mika Hakkinen. Although the images generated by the retinal chip are in black and white and are not high resolution, most patients have trained their brain to interpret the images that they see. Eberhart then played more video clips showing how his patients are adapting; a woman points out her cutlery, her drink and her plate in a café; a young man can tell that his fiancé is smiling and laughing; a father plays with his young daughter and spots her bracelet which is reflective and easy to distinguish.
Professor Zrenner emphasised that although the development of retinal chip technology is still very much in its infancy, it has shown promising results. He expressed the certainty that the technology is already improving the mobility and quality of life of his patients. He concluded his presentation with a personal anecdote reminiscing about watching the first televised World Cup Final in 1954 where West Germany beat Hungary 3-2 in Switzerland. “Although it was black and white and the picture wasn’t very good…..it was still great!”
To read a feature in the Irish medical Times about Professor Zrenner’s work and his visit to Ireland, please follow this link: http://www.imt.ie/features-opinion/2012/11/far-sighted-view-on-retina-implant-technology.html
IRIS Retinal Implant System
In November 2013, the French company Pixium Vision attracted €15 million in new financing to help further development of the company’s retinal implant system. Pixium launched in 2011 and will use the new investment to fuel further development of IRIS, which is designed specifically to help treat degenerative eye conditions such as retinitis pigmentosa and macular degeneration.
There are several parts to IRIS, including an implant placed inside the eye and attached to the surface of the retina. As the company describes, a patient would then wear a special pair of glasses built with a minicamera and wireless transmitter, which is connected to a pocket computer. The computer transforms the image taken by the camera into a signal transferred back to the glasses, and in turn, onto the retinal implant, where it stimulates the optic nerve and generates ages. Over time and through a special rehabilitation program, the brain learns how to interpret the images.
Right now, Pixium’s first implant system–known as IRIS1–is in the midst of clinical trials in Europe, at sites in Paris, Hamburg and Graz according to their CEO, Bernard Gilly. Two additional centers will be added to the study in the coming months. Initial data is expected in 2014, and those results will form the basis of a CE mark submission, which will apply to the development of the company’s next-generation IRIS2 device.
Pixium is a spinout of the Vision Institute at the National Eye Hospital in Paris and Universite Pierre et Marie Curie.
Fighting Blindness Funded Research Project
2006 – “Improvement of stimulation electrodes for retinal prosthesis through electrophysiological investigations with cultured retinal cells and isolated retina.”
Project leader: Dr. John Alderman, Tyndall Institute, University College Cork.
One of the problems with electrical stimulation of the retina is that the electrodes need to be as small as possible to only stimulate a few nerve cells. Another problem is that nearby nerve cells can be stimulated as a side effect. Both of these problems lead to poor resolution. John’s team investigated the use of novel electrodes that have both negative and positive electrodes side by side (dipolar), to discover if this increases the resolution. At present most retina implants use monopolar stimulation. This important work in Cork contributed to the international effort to refine this implant technology.
For more information about retinal implants, please visit the following locations:
• Bionic Vision Australia – A partnership of Australian research institutions collaborating to develop an advanced retinal prosthesis based in Melbourne. (Epi-retinal implant)
• Boston Retinal Implant Project: A US based company developing two types of medical devices to help the visually-impaired.
• Artificial Retina Project – A number of researchers and institutions around the U.S. are collaborating with the Department of Energy on this project. (Epi-retinal implant)