A blind man regained partial sight after undergoing a gene therapy known as optogenetics and using a pair of specialized goggles, according to a breakthrough case study published in Nature Medicine.
Why certain types of blindness have been so hard to treat
According to the New York Times, the human eye generates images when light hits the retina, where photoreceptor cells convert the light into electrical signals they send to neighboring ganglion cells. Those ganglion cells then use the optic nerve to send those signals to the brain, which converts the information into images.
However, roughly two million people worldwide suffer from a collection of progressive, hereditary diseases—together called retinitis pigmentosa—in which different gene mutations cause photoceptor cells to die off, eventually causing blindness.
While FDA has approved at least one medication aimed at a specific form of retinitis pigmentosa caused by a particular gene mutation, it's too costly an endeavor to develop gene therapies for all the various gene mutations that can cause the condition, the Wall Street Journal reports. Similarly, an alternative treatment—a microchip surgically implanted into the retina, which then relies on a video attached to a pair of glasses to activate remaining photoreceptive cells and generate highly pixelated images—is too invasive to be widely used.
"There's not a lot of hope for people who get a diagnosis of retinitis pigmentosa today," Todd Durham, VP of clinical and outcomes research at the Foundation Fighting Blindness. "When these folks lose the ability to see, they lose a lot of their independence and that brings with it a significant mental health burden. These are a very impactful set of conditions."
A new treatment using optogenetics
In 2005, however, researchers developed a new treatment, called optogenetics, that uses proteins derived from algae and other microbes that make "any nerve cell sensitive to light," the Times reports.
Originally, scientists used this treatment on mice to better understand how their brain circuitry worked. Specifically, they used a virus carrying the genes of these proteins to install the proteins in certain types of brain cells, which then used the new gene to create light-sensitive channels.
However, José-Alain Sahel, an ophthalmologist who works at the University of Pittsburgh and the Sorbonne in Paris, together with colleagues wondered if optogenetics could be used to add light-sensitive proteins to ganglion cells within the retina, the Times reports, thereby bypassing the need for photoreceptor cells altogether.
In their research, Sahel and his colleagues recognized that the optogenetic proteins developed so far were not sensitive enough to generate images using only regular light entering the eye—the researchers would have to add more light to make it work. As a result, Sahel and colleagues developed an optogenetic protein called ChrimsonR, which is sensitive only to amber light.
The researchers then used vector adenoviruses to deliver ChrimsonR genetic instructions to blind volunteers' retinas, where the ganglion cells over the course of a few months would learn to grow a sufficient amount of the protein. Next, the researchers planned to train participants on how to use a pair of specialized goggles that would convert visual information into amber light, so participants' ganglion cells would be able to recognize it. However, the researchers had time to train only one participant on how to use the goggles before Covid-19 temporarily suspended the project.
Seven months after the project was halted, that volunteer reached out and told the scientists that—after using googles regularly at home and on walks—he had been able to see the stripes of a crosswalk with the goggles. The man also reported that using the goggles had improved his daily life, making it easier for him to find plates or phones, or to notice furniture or a door.
After being brought in for examination, the scientists found the man was able to reach out and touch a notebook on a table and was able to correctly identify how many tumblers were placed in front of him 12 out of 19 times. And based on brain activity data, the man when using the googles appeared to activate parts the brain associated with vision.
'A major milestone'
"It's obviously not the end of the road, but it's a major milestone," Sahel said of the findings. According to the Times, Sahel and colleagues have founded a company called GenSight to move forward with this new treatment through clinical trials, in the hopes of eventually getting it approved by regulators worldwide.
For now, however, Sahel and his colleagues are enrolling more volunteers, testing higher doses of the virus, and revamping the goggles into thinner glasses, making them more comfortable and—hopefully—more informative for the user's retina.
Separately, Botond Roska, from the University of Basel and the Institute of Molecular and Clinical Ophthalmology Basel, noted that while the therapy didn't restore "normal vision," the technique "gives hope to restore vision that is meaningful."
Ed Boyden, a neuroscientist at MIT who helped pioneer the field of optogenetics, said the use of optogenetics to treat blindness surprised him. "So far, I've thought of optogenetics as a tool for scientists primarily, since it's being used by thousands of people to study the brain," he said. "But if optogenetics proves itself in the clinic, that would be extremely exciting."
Paul Bernstein, an ophthalmologist and retinal specialist at the University of Utah School of Medicine, said the new therapies being developed now "were just total science fiction when I started 26 years ago."
"These sorts of high tech approaches are bringing what was once a very distant horizon—restoring vision in these kinds of patients—much closer," he said. "It's really just amazing" (Zimmer, New York Times, 5/24; Molteni, STAT News, 5/24; Marcus, Wall Street Journal, 5/24; Kaiser, Science Magazine, 5/24).