Whereas Retina Implant's technology is just getting started in the U.S., another retinal implant–maker is already in FDA human clinical trials, which are expected to conclude in July 2014. Second Sight Medical Products sells its Argus II Retinal Prosthesis System in Europe—the first commercial implantation of their device took place October 29 in Pisa, Italy (pdf).
Second Sight's technology is fundamentally different, converting video images captured by a miniature camera—housed in a special pair of glasses worn by the patient—into a series of small electrical pulses transmitted wirelessly to an array of electrodes implanted on the retina's surface, rather than under it. These pulses are intended to stimulate the retina's remaining cells and create the perception of patterns of light in the brain. Epiretinal devices (overlying the retina) such as the Argus II preprocess an image before sending it to the retina. Because the camera does not create an exact simulation of normal retinal outputs, patients need time to learn how to process the information that their brain receives.
Although both Retina Implant and Second Sight's technologies are still relatively unproved, their potential is great. "As somebody who has to tell families that their child is going to lose all vision and not be able to do any of the things they had dreamed he or she would be able to do, I know that every little step you make, from absolute blindness to being able to see shapes to being able to count fingers and read words makes an incredible impact on a person's life," says Haller, who, in addition to being familiar with Retina Implant, has experience implanting Second Sight's retinal prosthetic devices.
Retina Implant and Second Sight's technologies may be the furthest along in terms of testing but they are not the only ones working on ways to treat, and even prevent, retinitis pigmentosa.
A sub-retinal implant under development by Optobionics in Glen Ellyn, Ill., most closely resembles the work of Retina Associates. Optobionics's Artificial Silicon Retina (ASR) microchip is designed as a stand-alone implant placed behind the retina to directly stimulate the remaining viable cells of the retina. Instead of an external power supply, the Optobionics chip has an array of micro-photodiodes that convert light energy to electrical signals, which stimulate retinal cells. Haller implanted several Optobionics sub-retinal chips as part of a study conducted at the Wilmer Eye Institute at Johns Hopkins in Baltimore throughout 2004 and 2005 while she was a surgeon there (pdf). The company's funding subsequently ran out, however. Only recently were Optobionics' co-founders able to acquire the rights to the ASR implant technology. They plan to reorganize a new company under the Optobionics name.
Neurotech Pharmaceuticals, Inc. in Lincoln, R.I., is developing a different type of implant. Their intraocular implant consists of human cells genetically modified to secrete a nerve growth factor they say is capable of rescuing and protecting dying photoreceptors. The implant does not replace retinal tissue but rather is a way to resuscitate damaged retinal cells.
At Weill Cornell Medical College of Cornell University in New York City, neuroscientist Sheila Nirenberg is leading a project to develop an artificial retina with the capacity to reproduce normal vision. Rather than increasing the number of electrodes placed in an eye to capture more information and send signals to the brain, Nirenberg's work focuses on the quality of the artificial signals themselves so as to improve their ability to carry impulses to the brain.
It will take some time to see which approach works best, Haller says, adding, "All of the treatments for retinitis pigmentosa are experimental right now, so there's no real comparison yet between what works and what doesn't."