6 August 2012
Retinitis pigmentosa (RP) is a degenerative eye disease that affects 200,000 people in the United States and Europe and has left 15 million people permanently blind worldwide. German biotechnology firm Retina Implant AG has developed a microchip that provides a useful degree of artificial vision in patients who have been blind for even long periods. The 3 x 3 mm (0.118 in) chip is implanted below the surface of the retina where it electrically stimulates the optical tissues. After successful clinical trials in Germany, the chip is now being tested in Hong Kong and Britain before moving on to planned trials in the U.S.
RP is a disease that mainly affects the retina – specifically, the photoreceptors in the macular layer. These receptors slowly degrade until the patient ends up blind. Though the disease is incurable, one bright spot is that the nerves of the retina remain functional. If these nerves can be stimulated, then some form of vision might be recovered. That’s the function of the retinal implant chip.
The device is a light-sensitive, externally powered microchip. This is surgically implanted beneath the transparent top membrane of the retina and into the macular region. This is the area of the eye where clear images are formed in normal-sighted individuals and where the implant is best protected against working loose. The chip is made up of 1,500 active microphotodiodes. Each of these has its own amplifier and electrode for stimulating the retinal nerves. In addition, there are 16 electrodes to stimulate the nerves directly and to test the interface between electrodes and neurons. Light falling on the microphotodiode array activates them and they stimulate the nerves, generating patterns on the retina with a resolution of 38 x 40 pixels.
This may not seem like much, but it does produce some degree of artificial vision. However, the vision is not like normal sight. It’s more in the form of lines and colors that the patient learns to interpret. The researchers say results in clinical trails have been better than expected. Provided contrast is strong enough, patients can identify objects, such as geometric shapes and fruit, observe people moving about the room, read numbers on dice and even read large letters and make out words on a screen.
Aside from giving sight, the chip has some advantages over alternative techniques, such as the Argus II Retinal Implant from California-based company Second Sight, which require eyeglass-mounted cameras and a transmitter. The subretinal chip is self-contained, works directly on the retina and only requires an external power source. Additionally, because the subretinal implants do not require a camera, eye-hand coordination is more easily restored.
So far, 26 patients who have been blind for over a decade have received the implant and the results have been published in the Proceedings of the Royal Society. The first clinical trials were carried out by Retinal Implant in Germany in 2005, but the company is now in its next phase of human clinical trials. These trials have been expanded to Britain and Hong Kong, with twelve patients receiving implants at King’s College Hospital and Oxford Eye Hospital in the U.K. and additional trials at the University of Hong Kong Eye Institute. Once FDA approval is granted, trials in the United States are scheduled at the Wills Eye Institute in Philadelphia, Pennsylvania.
As to continued development of the implant, the next step will be to increase the number of receptors, and thus increase resolution, as well as studying how such implants may help other degenerative eye conditions besides RP. However, they may be in a race against other, non-invasive approaches, such as the recent discovery of a chemical that makes cells in the retinas of blind mice sensitive to light, temporarily restoring some vision. Either way, the attack on RP from various fronts is good news for those suffering the disease.