Implantable chip could serve as a prosthetic retina for people who suffer from age-related blindness

Jun 24 2004

Researchers at the Stanford University School of Medicine have developed a prototype for a new kind of implantable chip they believe could be adapted to serve as both a prosthetic retina for people who suffer from a common form of age-related blindness and as a drug-delivery system that could treat conditions such as Parkinson’s disease.

Where other types of chips use electricity to stimulate nerves, this one instead tickles cells with minute amounts of chemicals. Because nerve cells normally communicate with each other by releasing chemicals known as neurotransmitters, the new device points to a more effective way of treating very delicate tissues, such as those in the eye and in the brain.

“People believed that a neurotransmitter device could not be done, in the sense that it wasn’t possible to deliver such small volumes of chemicals, but we show that it is possible and that further research along these lines should be done,” said Harvey A. Fishman, MD, PhD, director of the Stanford Ophthalmic Tissue Engineering Laboratory, who led the study. Fishman and his interdisciplinary team of colleagues report their findings in this week’s advance online issue of Proceedings of the National Academy of Sciences.

The team built a computer chip with four tiny openings, and used it to control the environment of neuron-like cells. The chip exuded droplets of chemicals using electro-osmosis. They then gauged the cells’ responses using fluorescent dye. The chip also withdraws fluid when needed, which could prevent a potentially toxic buildup of the chemicals.

“We’re very excited about the possibilities that are now available,” said Mark Blumenkranz, MD, professor and chair of the Department of Ophthalmology and a co-author of the study. The chip “may allow for graded responses to activation,” he added, enabling a more complex range of signals than the simple on/off capabilities of electrical devices.

Although the chip has many potential applications, both in medicine and research, the team is mainly concerned with devising a treatment for age-related macular degeneration, a condition that is the most common cause of blindness. In a healthy eye, vision occurs when light-sensitive cells in the retina convert light into electrical signals that the optic nerve then transmits to the brain. These cells receive nutrients and excrete waste through a thin layer of cells that covers them. In age-related macular degeneration, this life-giving layer degrades over time, leading to the eventual death of the cells beneath.

Patients with the disease typically lose central vision. In about 80 percent of those patients, some underlying cells remain alive although the cover layer has degraded, and they could potentially be treated with tissue transplants. For the remaining 20 percent of patients, however, a chip implanted on the retina could prove to be the best option. Rather than just four openings, such a chip would have thousands, each filling in for a lost light-sensitive cell that could then relay visual signals to the brain.

“It’s almost like an ink-jet printer for the eye,” Fishman said.

Because the chip can draw droplets of fluid in as well as out, it could also enable researchers to take samples in real time, giving them a chemical picture of what goes on in living tissues during certain processes. And it could deliver small amounts of drugs precisely where they’re needed, such as dopamine in the brains of patients with Parkinson’s disease. “It’s a very new way to interface with the brain,” Fishman said.

However, he estimated the device is still several years away from clinical trials. “We still have to look at how these chips interact with the body and ensure there’s no toxicity or clogging of microchannels and so forth,” he said. “There are a lot of potential pitfalls, as with any new technology, but the advantages are well worth the potential challenges.”

Other Stanford collaborators on the study were Mark Peterman, PhD, a former graduate student in applied physics, and Jaan Noolandi, PhD, senior research scientist in ophthalmology. Funding came from VISX Inc., a California-based company that specializes in the design, manufacture and marketing of proprietary laser vision-correction technologies.