There are many other groups worldwide working on the problem of a retinal prosthesis, but Shepherd’s approach is to modify the electrode array and stimulation technology that were developed for the cochlear implant. “The cochlear implant is a mature technology,” said Shepherd. “We thought we could take advantage of the knowledge of 30-plus years of research and apply it to a different sensory system using tried-and-true materials that have already been shown to be safe to use in clinical research.”
Visual prostheses currently under development in different labs are designed to restore vision by stimulating nerve cells at different sites along the visual pathway. These include the retina (the eye’s light sensor), optic nerve (the connection from the eye to the brain) and visual cortex in the brain. But Shepherd believes that stimulating just behind the retina, rather than along the optic nerve or in the visual cortex, takes advantage of the eye’s built-in circuitry for transforming light into an image.
|Longtime NIH grantee Dr. Robert Shepherd is now director of the Bionics Institute of Australia and head of the medical bionics department at the University of Melbourne.
Seeing into the future. A graphic of the next-generation bionic eye developed by Shepherd’s team
Image: Bionics Institute
“This means the natural organization of the eye and the central visual pathway is doing some of the heavy lifting of creating an image perception,” says Shepherd. “We’ve found that neural pathways in the eye are still intact, even after as many as 20 years of blindness.”
The device Shepherd’s team is developing includes an external video camera, a vision processor, power supply and an implanted stimulator. The stimulator connects to an electrode microarray surgically implanted behind the retina between two layers of the eye, the sclera (the white part) and the choroid (a blood vessel layer). This is a called a suprachoroidal implant. Based on extensive preclinical studies already performed by the group, Shepherd theorizes that it will provide a safer and simpler surgical implant procedure, as well as a more mechanically stable location, compared to subretinal or epiretinal implants.
This prototype bionic eye has been successfully implanted in three blind volunteers in Australia, who had lost their vision due to retinitis pigmentosa, a condition that causes progressive vision loss often starting in adolescence. Because there are only 24 electrodes in the microarray while the retina contains millions of neurons, the device provides low-resolution vision, what is sometimes called “shape vision.” It doesn’t allow the user to see a detailed visual scene, but it can be helpful for navigation. Wearing the device, one volunteer was able to walk through a room and avoid obstacles without her guide dog for the first time in 20 years.
At the end of the lecture, Shepherd screened a video of one of the participants who admitted that what she was seeing wasn’t like regular vision, but she was learning to trust what she saw. “It’s been amazing,” said Dianne Ashworth. “The more I’ve been doing it, the more natural it feels.”
Up next for Shepherd’s team is a fully implantable device using 44 electrodes to improve image resolution, along with another piece of technology to aid in the patient’s depth perception. They expect to implant this device in an additional 3 to 6 patients. Shepherd hopes that additional steps will occur in the near future for good restoration of vision in blind or visually impaired people. He emphasized the importance of multidisciplinary research in achieving these technological advances: “This work is only successful because of an effective research team including eye specialists, scientists and engineers who are focused on developing the technology.
“In 5 years, I think there will be 2 or 3 visual prosthetic devices that will be considered the standard of care for conditions such as end-stage retinitis pigmentosa, and we’ll also be expanding the research into other areas of vision pathology,” he concluded.