A team of scientists at UC Berkeley used a breakthrough gene therapy to help blind mice gain sight, and some on the team think the same therapy could eventually be used to help cure blindness in humans.

A month after the team injected a gene for a green-light receptor into the eyes of blind mice, they showed signs of gaining sight, such as being able to identify and navigate around obstacles nearly as easily as mice without vision problems. The results of the study were published in Nature on March 15.

The once-blind mice who received the gene therapy were also able to detect motion and changes in brightness, recognize patterns, and see enough detail on an iPad to distinguish letters. The gene, called a medium wavelength cone opsin (MW-ospin rd1) and delivered by an inactivated virus that's injected into the eye, has the potential to restore vision enough to move around without assistance, read, or watch video.

"We actually think that within three years this could be in humans," said Ehud Isacoff, a UC Berkeley professor of molecular and cell biology and one of the authors of the study, referring to how soon the treatment could be tested in clinical trials. "The only thing that needs to be done in order to achieve that at this point is to work out the details of the delivery mechanism of the gene."

This isn't the first time that gene therapy has been used to restore vision in subjects that were once blind, even by this team of scientists at Berkeley. In 2017, a team at University of Oxford showed that it was possible to restore vision in humans using gene therapy injected into the eyes. The same year, the UC Berkeley team used another form of gene therapy, delivered the same way but using a different gene, to help blind mice gain sight.

Still, this was an exciting result for the researchers. "It was really thrilling and really felt like we were on to something," said Michael Berry, one of the authors.

The way that diseases like macular degeneration and retinitis pigmentosa work is that they kill off some photoreceptor cells in the retina of the eye, known as rods and cones, that are sensitive to light. But these conditions spare other cells that are typically insensitive to light, like bipolar and the retinal ganglion cells. This gene therapy injects a gene into the eye through an inactivated virus, targeting the retinal ganglion directly and making them light sensitive. The UC Berkeley team made 90 percent of the ganglion cells light sensitive during their recent trials.

Blind mice who got the gene therapy in the experiment were also able to see a broader range of light. In previous experiments by this team of researchers, like the one in 2017, the gene therapy only allowed mice to see LED lights with high levels of intensity, but mice in this most recent study could see dimmer lights, like ones from computers and iPads.

If the results in the mice can be replicated in humans, it has the potential for world-changing impact. According to 2014 research published in The Lancet, about 170 million people worldwide have age-related macular degeneration, which causes vision impairment. That's 1 in 10 people over the age of 55. And 1.5 million worldwide have retinitis pigmentosa, which is the most common form of inherited blindness and leaves most people who have it blind by the age of 40, according to healthfundingresearch.org.

"I have friends with no light perception, and their lifestyle is heart-wrenching," John Flannery, a UC Berkeley professor of molecular and cell biology who is a member of the team of scientists that researched the gene therapy in mice, said in a statement about the research.

"They have to consider what sighted people take for granted. For example, every time they go to a hotel, each room layout is a little different, and they need somebody to walk them around the room while they build a 3D map in their head. Everyday objects, like a low coffee table, can be a falling hazard. The burden of disease is enormous among people with severe, disabling vision loss, and they may be the first candidates for this kind of therapy."