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Partial sight restored for man who is blind thanks to optogenetics

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The optogenetics technique is combined with glasses that generate amber light

Sahel et al, Nature Medicine and StreetLab/Institut de la Vision

A man who is blind has had glimmers of vision restored thanks to a high-tech treatment using optogenetics, which involves genetically altering nerve cells so they respond to light.

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French firm GenSight Biologics has published results showing that the first recipient of its treatment can recognise different objects in lab tests. “It’s exciting to see the first publication on human optogenetics,” says Ed Boyden at the Massachusetts Institute of Technology in Boston, a co-inventor of optogenetics.

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Optogenetics has become a widely used lab tool, because it allows precision control over brain cells by altering them so they fire in response to light. It has led to many discoveries about the brain when used in animals – but is thought to have limited medical potential for treating brain disorders in people, because getting light inside the head requires implanting a fibre optic cable.

Several groups are trying to develop it as a treatment for blindness, though, because nerve cells in the eye are exposed to outside light. One targeted condition is retinitis pigmentosa, an inherited disease in which the retina, a disc of tissue at the back of the eye, gradually deteriorates and the light-detecting cells die.

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With GenSight’s therapy, the nerve cells underneath the light-detecting layer are injected with a gene originally found in algae, which makes them fire in response to amber light. To be able to see, the recipients need to wear goggles with cameras and processors that turn ordinary light into amber wavelengths, and boost the signal so it can be detected by the altered cells.

The first person to get this treatment, a 58-year-old man from Brittany in France, found that after about a year, he could see the black and white stripes of pedestrian crossings on the road.

Since then, he has become able to perceive objects like a phone, furniture or a door in a corridor. In lab tests, he was able to count and locate objects in front of him – but he can’t recognise faces.

The man’s vision may improve further, because it takes time for the brain to learn to process the unusual signals from the eyes, says José-Alain Sahel at the Vision Institute in Paris, who is working with the GenSight team. “What’s probably occurring is remodelling of the connectivity in the retina and the brain,” he says. The goggles also need adjusting in the lab while the wearer undergoes training, but this was disrupted by the covid-19 pandemic.

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Two people in the UK have received the same gene therapy but haven’t had any training, and so haven’t had any vision improvement yet. Four people have also recently received higher doses, which the team hopes will have greater benefits, says Sahel.

In its current form, the approach may not give good-enough vision to allow reading or recognising faces, says team member Botond Roska at the Institute of Molecular and Clinical Ophthalmology in Basel, Switzerland. “For that you need very high resolution.”

A US firm Bionic Sight, reported in March that four people who had been blind or nearly blind could now perceive light and motion of objects in front of them thanks to its optogenetic treatment, but hasn’t yet published a scientific paper on these findings.

Bionic Sight’s treatment delivers a different gene to GenSight’s, and also requires goggles. In a press release, Bionic Sight said that two people who received a higher dose of gene therapy had more of a rise in light sensitivity than the other two.

Even small improvements in vision may have a large impact for someone who is nearly blind, says Michel Michaelides at University College London, who is developing a different kind of gene therapy for blindness.

But targeting people with severe deterioration of their retinas, as is being done here, means it may be hard to restore them to full vision, he adds. “The field has gigantic challenges – but this is a chink of light.”

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Journal reference: Nature Medicine, DOI: 10.1038/s41591-021-01351-4

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