Age-related macular degeneration is the leading cause of blindness in North America, while retinitis pigmentosa causes approximately 1.5 million people worldwide to lose their sight every year. Individuals afflicted with retinal degenerative diseases such as these might someday be able to see again, however, thanks to a device being developed at California’s Stanford University. Scientists there are working on a retinal prosthesis, that uses what could almost be described as miniature solar panels to turn light signals into nerve impulses.
The system consists of a camera- and microprocessor-equipped pair of goggles, and a small photovoltaic chip that is implanted beneath the retina.
The output of the camera is displayed on a miniature LCD screen, located on the inside surface of the goggles. That screen is special, however – it emits pulses of infra-red laser light, that correspond to the images it’s displaying. Photodiodes on the chip register those pulses, and in turn stimulate retinal neurons. In theory, this firing of the neurons should produce visual images in the brain, as would occur if they had been stimulated by visible light.
“It works like the solar panels on your roof, converting light into electric current,” said Dr. Daniel Palanker, associate professor of ophthalmology. “But instead of the current flowing to your refrigerator, it flows into your retina.”
Palanker’s team has created a chip about the size of a pencil point, which is thinner than a human hair, and contains hundreds of the photodiodes. These were tested using retinas from both sighted rats, and rats that were blind in a fashion similar to human degenerative blindness – the retinal neurons were still present, but were generally inactive. While the chips in the blind retinas didn’t respond to visible light (unlike those in the sighted retinas), they did respond to the near-infrared light. “They didn't respond to normal light, but they did to infrared,” said Palanker. “This way the sight is restored with our system.”
The scientists are currently testing the technology on live rats, and state that it so far looks as if the electrical signals are indeed reaching the rats’ brains. They are now looking for a sponsor for human trials. Palanker notes that the system doesn’t allow for color vision, however, and that what vision is does provide would be “far from normal.”
While other retinal prostheses are also in development, these reportedly involve more in the way of hardware such as coils or antennas being implanted in the eye. Most of the technology used in the light-based Stanford system, by contrast, is located in the goggles.
A paper on the research was published this week, in the journal Nature Photonics.