Boston University researchers (from left) Yueming Li, Chen Yang, and Ji-Xin Cheng are collaborating on a retinal prosthesis they hope will offer much higher acuity and improved field of vision compared to past technologies.

Retinal Disease

Could a Retinal Prosthesis Restore Sight for People with Age-Related Macular Degeneration?

Boston University–developed technology could one day bring hope to millions with the incurable disease that’s one of the nation’s leading causes of blindness

In the first stages of age-related macular degeneration, patients can often see just fine. But then colors start dimming, reading becomes tougher; as the eye disease progresses, their central vision may turn blurry, or fade altogether.

Eventually, the disease could leave people legally blind. Treatments can slow the deterioration, but for the nearly 200 million people globally with age-related macular degeneration (AMD), there’s no cure.

In her lab at Boston University, chemist and engineer Chen Yang is testing and refining a flexible retinal prosthesis that she hopes could one day be implanted in the eye to help restore sight in people with severe AMD and a range of other retinal degenerative diseases. Using a thin, soft polymer- and nanocarbon-based film, the prosthesis turns light into ultrasound to stimulate the healthy parts of the eye undamaged by disease.

“Lost vision has a huge impact on quality of life,” says Yang, a BU professor of chemistry and of electrical and computer engineering. “There is a critical need for so many patients—they need an alternative solution.”

Around 1.5 million people in the US are estimated to be in AMD’s later stages; it’s reportedly the most common cause of sight loss in those aged over 60. One of the most famous people with late-stage AMD is the actor Dame Judi Dench. In a 2023 interview with the UK’s Sunday Mirror, the Oscar-winning star of stage and screen said she could no longer watch television or read scripts. “I can’t see on a film set anymore,” she said.

Some of the BU team’s patents for its prosthesis technology have already been licensed to a French company, Axorus, which is developing a contact lens to restore sight for people with the disease. Yang also plans to found a start-up to help commercialize the technology in the United States.

“For diseases that don’t have a cure, we’re really passionate about developing methods to treat them,” says Yang, who’s also studying ways to apply the science behind her technology to other neurological disorders and diseases, including epilepsy and depression. “Our next step [with the prosthesis] is to get a first human study, validate the safety of the technology, then move on to a clinical trial for patients who are blind.”

Converting Light to Sound, Then to Sight

The retina is where the action happens in the eye—its cells transforming light into the signals your brain turns into images. Yang says it’s structured a bit like a lasagna, containing layers of cells with different jobs to do. “We have a layer called the photoreceptor—that’s the layer that’s sensitive to light.” It’s also the one that AMD attacks, Yang says: “When patients become blind, that layer is gone.”

The prosthesis is designed to take that layer’s place. To do so, it takes advantage of a phenomenon known as the photoacoustic effect, which is when sound waves are produced by a material when it absorbs light.

“The implant will convert each pixel of light to a very tiny ultrasound,” a sound wave, says Yang. “Then this ultrasound will stimulate the rest of the ‘lasagna,’ those layers that have mechanosensitive proteins on their membrane, so they generate an electrical signal, which is then propagated to the brain.” According to Yang, the mechanosensitive layers—which turn physical input into an output signal—still function, even in severe AMD. 

The team recently examined its prosthesis in test retinas and animal models, publishing the results in Nature Communications. They found the implant—a flexible, photoacoustic film—“efficiently generated acoustic waves,” which sparked the rest of the retina into activity, leading to “visual restoration.”

It’s not the first time a retinal prosthesis has been tested: Yang says a few previous efforts by other groups made it to clinics and patients, but have since been discontinued. “It’s very challenging to develop positive, satisfying patient outcomes,” she says. One of the discontinued versions, according to Yang, offered only 60 pixels (many smartphone cameras have millions of pixels, and some have estimated your eye to have the resolution equivalent of hundreds of millions). It was also rigid, making surgery difficult and minimizing the field of vision it could restore.

“Our technology is made of polymer, so we can make large implants relatively easily. And it’s soft, so the surgical procedure is easier,” says Yang, who’s also affiliated with BU’s centers for neurophotonics and photonics. She expects it to offer much higher acuity and improved field of vision compared to past technologies.

“It’s Possible to Give Artificial Vision”

Yang didn’t start out trying to find a solution to blindness. She was first trained as a chemist and experimented with nanomaterials—tiny substances that measure less than 0.0001 mm—analyzing their ability to control cellular activity.

“I realized if we’re able to control neuron cell activity, it opens doors for us to treat diseases,” says Yang. One of those diseases was AMD.

At BU, she teamed up with Ji-Xin Cheng, a BU College of Engineering distinguished professor who’s a precision medicine pioneer and expert in potential applications of the photoacoustic effect. Yang also started collaborating with Serge Picaud, a vision neuroscientist at Sorbonne Université and the Institut de la Vision in France. Both were coauthors on the recent Nature Communications study. The students in her lab have been drawn from fields as diverse as chemistry, optical engineering, mechanical engineering, and neuroscience.

“Solving problems like this requires contributions from researchers with different backgrounds,” says Yang. “We’re very fortunate to have that environment at BU.”

She hopes the retinal prosthesis technology will be in clinics and helping patients within the next few decades. Yang says one of those other recent products took over 20 years to reach the market and that her team has been working on its prosthesis and the technology behind it for around seven years.

“The science part we have—it’s possible to give artificial vision,” says Yang. “It’s going to be a long trajectory, but we’re highly motivated. If we can do something to help [people who’ve lost their sight], that’s what we want to spend our time on.”

Yang’s retinal prosthesis research is funded by the National Institutes of Health and Axorus.