So the blind might see Wilmer Eye Institute taps into technology

September 15, 1996|By Jonathan Bor | Jonathan Bor,SUN STAFF

If the blind are ever made to see, they might recall with fascination the days when pioneering surgeons inserted electric probes into the eyes of human volunteers and, for an instant, illuminated the dark.

Such experiments, now in progress at the Johns Hopkins Wilmer Eye Institute, may be the rudimentary beginnings of a technology that will enable people blinded by the loss of light-sensing nerve cells to navigate without canes or guide dogs.

Though the achievement may be years away, Wilmer scientists believe they are on a path toward an electronic implant that would complete circuits destroyed by retinitis pigmentosa, a degenerative eye disease that afflicts about 100,000 people in the United States.

For now, in experiments that evoke the eerie excitement of discovery, ophthalmologists Eugene de Juan and Mark Humayun are finding answers to basic questions: Is the damaged retina useless? Can it be electrically stimulated to generate an image? And if so, at what level of detail?

So far, answers drawn from four years of human tests are encouraging.

Blind subjects have seen single circles of light -- like matches ignited in space -- when their retinas were stimulated with tiny probes carrying electric current. It's a hopeful sign that sophisticated technology could allow the diseased retina to perceive at least the outlines of objects.

Someday, these tests may seem quaintly historic, like the first telegraph transmission ("What hath God wrought?") in today's era of digital telecommunications.

Consider the words exchanged recently as de Juan, chief of retinal surgery at Hopkins, held electrodes to the retina of Brian Christensen, a fully conscious man who lost his last vestiges of vision 12 years ago.

"See anything yet?" said de Juan, hunched over a twin-lens microscope that gave him an expansive view of the retina.

"No, it's just a blur," Christensen replied.

"Can you see anything now?"

"Yes. Flash, flash, flash. It was like a white flash. Right over me."

"How big?"

"Like a circle, maybe the size of a quarter."

"You like it?'"

"Yeah."

In retinitis pigmentosa, the eye's working parts are intact except for crucial cells in the retina, a membrane in the back of the eye. These cells, called photoreceptors, are responsible for converting light to the electrical code that the brain "sees" as visual images.

Wilmer's researchers envision a chip, millimeters wide, that would sit on the retina and function much like photoreceptors. Early versions would probably work in concert with other electronic components worn outside the body -- say, a button-sized video camera fixed to a glasses frame.

In one version contemplated by the Wilmer team, the camera would capture images and project them to the light-sensing chip. The chip itself would be a grid, subdivided into components that are individually capable of detecting shades of light and dark. Like a plug into a socket, the implant would connect with the surviving neural pathway to the brain.

The idea may prove far-fetched. Neither Wilmer researchers nor the handful of researchers doing similar work elsewhere have any evidence that an implant could supply the brain with enough information to enable a blind person to walk around an apartment safely, much less to read a printed page. But there is a powerful precedent: cochlear implants for the deaf.

Just 20 years after they were introduced, these devices are enabling thousands of people to decipher conversation and, in some cases, to converse on the telephone. They are an encouraging example of electronics bringing sensory perception to people who have lost nerve cells to disease.

"There's an immediate and direct comparison," said de Juan. "The success of that implant was one of the things that really stimulated us."

Asking when the blind will see is much like asking when paraplegics will walk. Despite the almost cocky optimism that pervades the project, nobody wants to make bold predictions about so elusive a goal. But that doesn't stop the team from dreaming about what might happen.

"If I had to guess, I'd say it could be 10 to 15 years before we had something useful," said Robert Greenberg, a medical student and Ph.D. candidate who is the project's electronics expert. He does, however, envision an experimental device within five years -- one that could form the basis for a marketable implant.

Repairing the camera

In many ways, de Juan and his crew are trying to repair nature's camera.

A person's lens focuses light on a two-dimensional film, a concave membrane two-tenths of a millimeter thick and as fragile as wet tissue paper. This is the retina.

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