A clinical test of a technique called optogenetics has enabled a 58-year-old man to see for the first time in 40 years.

After receiving an injection of light-sensitive proteins into his retina, and with the help of image-enhancing goggles, he can now see images and moving objects.

The study, published this week in Nature Medicine, is the first successful clinical application of optogenetics, which uses flashes of light to control gene expression and neuron firing.

The technique is being investigated as a potential treatment for pain, blindness and brain disorders.

The trial, run by French company GenSight Biologics, enrols people with retinitis pigmentosa (RP), a degenerative disease that kills off the eye’s photoreceptor cells.

In a healthy retina, photoreceptors detect light and send electrical signals to retinal ganglion cells (RGCs), which then transmit the signal to the brain.

GenSight’s optogenetic therapy skips the damaged photoreceptor cells entirely by using a virus to deliver light-sensitive bacterial proteins into the RGCs, allowing them to detect images directly.

“It’s a big step for the field,” John Flannery, a neurobiologist at the University of California, Berkeley, told Nature. “The most important thing is that it seems to be safe and permanent, which is really encouraging.”

Flannery added: "Because the retina contains around 100 times more photoreceptors than RGCs, the resolution of images detected by RGCs will never be as good as natural vision. But Flannery says it is exciting that the brain can interpret images accurately.”

But some scientists say that more research is necessary.

“It’s interesting, but it’s an N of 1,” said Sheila Nirenberg, a neuroscientist at Weill Cornell Medical College in New York City, to the journal.

Nirenberg said that she looks forward to seeing whether the other people in the trial, including some who were injected with higher doses of the protein, have similar results.

Neuroscientist Karl Deisseroth from Stanford University in California, who co-developed optogenetics as a laboratory technique, said the study is important because it is the first time that its effects have been shown in people. “It will be interesting to try this with more light-sensitive opsins” that might not require goggles, he added.

But Deisseroth thinks that optogenetics will be most useful as a research tool that leads to therapies rather than a therapy itself.

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