Smart goggles and gene therapy are about to be tested as a cure for blindness. This is one of the first ever uses in people of optogenetics, a technique that involves changing the DNA of nerve cells so that they can be controlled by light.
This technique has been a powerful laboratory tool for understanding how brains work in animals, but has been seen as impractical for use in humans  because of the need to put a wire into the brain through a hole in the head.
But 12 people in the UK are now about to have an optogenetic treatment for , a rare inherited condition in which the eye’s light-sensitive cells slowly die, eventually causing blindness. Because light can reach nerve cells in the retina of the eye without any need to drill a hole in the skull, sight loss disorders could be prime targets for optogenetic therapies.
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The new treatment, developed by French firm , targets nerve cells in the retina that aren’t normally sensitive to light. The idea is that by genetically modifying these to detect light, they can compensate for the cells that die off as the disease progresses.
To make these cells sensitive to light, they will be injected with a gene that normally helps single-celled algae to detect light. The same gene is often used in optogenetic lab studies. Each patient will receive one injection, in only one eye.
suggests that, after about six weeks, this injection should make the cells able to detect red light.
Seeing red
If successful, this would only boost detection of red light, which isn’t likely to improve vision very much on its own. So the trial volunteers will wear special goggles that have cameras and light sources that together convert other colours into red light. The hope is that this will give them improved vision, albeit in black and white.
The big unknown is how much of a benefit this will give. of University College London predicts people’s sight will be “rudimentary”. Because the nerve cells being changed are normally involved in improving or refining visual information that is sent to the brain, using them to detect light will reduce clarity compared with a healthy eye.
But José-Alain Sahel, GenSight co-founder, says: “We hope the patients will regain, after training​, useful vision that will allow them to have autonomy, for example recognising objects, detecting people and large obstacles, possibly better.”
Eye to safety
For the first trial, the firm is recruiting people who are not yet totally blind – they should be able to count the number of fingers on a hand held 50 centimetres away. The first patient will get an injection into one eye within the next two months, says the company, and .
Although many improvements have been made in gene therapies in recent years, such trials are still closely monitored for adverse effects, after a US teenager died in 1999 when a gene therapy for a liver condition provoked a massive immune reaction.
Eyes are seen as a safer target, though, as they are relatively isolated from the immune system, and any side effects are likely to be limited to the eye. Although retinitis pigmentosa is rare, GenSight says the same approach might also help people with age-related macular degeneration, which is the commonest cause of blindness in rich nations.
Another trial of an optogenetic treatment for retinitis pigmentosa began in 2016. The approach is similar but people will become receptive to blue light, not red, and they will not wear goggles.
