Big plans for a nano-based artificial retina
Open your eyes and uncountable photons stream into and through them, smacking against the retina — a postage-stamp-sized patch of lightsensitive cells at the back of each eye — where they are almost instantaneously converted into electrical impulses sent to the brain.
When everything is working, it's a sight to behold.
In diseases like retinitis pigmentosa and age-related macular degeneration, however, the retina’s photoreceptor cells — its critical rods and cones — degenerate and die. Light signals aren’t detected and vision is impaired, perhaps lost altogether. For decades, researchers have labored to create an artificial retina that might restore sight. Though progress has been made, the technology is limited and comparatively crude, consisting of a tiny, eyeglass-mounted camera that beams data wirelessly to a watch battery-sized electronic array implanted inside the user’s eye. Electrodes in the array stimulate existing retinal cells, resulting in the brain “seeing” rough patterns of blacks, whites and grays. Resolution is insufficient for functional vision; it’s a shadow of the real thing.
A collaborative team of doctors, scientists and engineers from the Jacobs Retina Center at UCSD’s Shiley Eye Institute and UC San Diego Jacobs School of Engineering envisions a different remedy — one that exploits the small wonders of nanotechnology.
Gabriel A. Silva, PhD
Leaping beyond current micro-electronic technologies, researchers at the Jacobs Retina Center and in the UCSD Departments of Bioengineering and Electrical Engineering are bundling together infinitesimally tiny optoelectronic nanowires, 50 to 100 per retinal cell. (These wires can be 0.2 to 5 micrometers in diameter and 1 to 50 micrometers in length. By comparison, the typical human cell is 10 micrometers wide.) Each nanowire can detect approximately 50 percent of passing photons and transmit that data directly to biological retinal neurons that have attached themselves to the artificial retina.
“We can easily fit thousands of these nanowires into an artificial retina, which means resolution is not an issue,” said William R. Freeman, MD, Distinguished Professor of Ophthalmology and director of the Jacobs Retina Center. “We can make more megapixels of visual information than the brain has ever seen or the retina could handle.”
A cultured cortical neuron grows atop an array of photonic nanowires, which chan be 0.2 to 5 micrometers in diameter. A typical human cell is 10 micrometers wide.
Image by assistant project scientist Massoud Kraichem, PhD, UCSD Department of Ophthalmology
It’s not simply progress writ amazingly small, added Gabriel A. Silva, PhD, an associate professor of bioengineering and ophthalmology and project co-leader. At this scale, the physics and chemistry of the interface between the device and biology involves fundamental molecular interactions that do not occur at larger microscales, he said. Many current technical hurdles become irrelevant.
For example, because the nanowires require relatively little energy to function, Silva said much less heat is generated and external batteries may not be needed or, if required, could be small enough to be implanted alongside the eye and changed just once or twice a year.
William R. Freeman, MD
Distinguished professor of Ophthalmology
Every aspect of this nano-based retinal prosthesis is designed to help get it to the millions of Americans suffering from degenerative retinal disease faster. The surgical implantation techniques, for example, are minimally invasive and well-tested. The wires themselves are made of inert materials that do not provoke an immune response. “They don’t corrode. There’s nothing for enzymes to digest,” Freeman said.
Freeman said a nano-based artificial retina would be complementary to related biological research, such as exploratory efforts to rebuild retinas using stem cells. While that approach may one day yield meaningful results, Freeman said it’s easier and faster to engineer a device to meet specific needs than it is to manipulate live cells or develop drugs.
“Right now, we’re still doing animal studies, but things are moving pretty fast. I think we’ll be in clinical trials in five years with a first- or maybe a second-generation device.”