Scientists from the University of California have announced a possible alternative option to electronic eye implants for those who have lost their sight: gene therapy. Virus-delivered genes for green opsin gave blind mice sight enough to determine patterns on an iPad, they found, with the therapy possibly ready for clinical trials in three years’ time.

Currently, around 170 million individuals in the world suffer from age-related macular degeneration, with around 10% of all those over 55 suffering from the problem. The only option for such people at present is an eye implant linked to a video camera on some glasses, with an image equivalent to only a few hundred pixels.

There are also over 250 different genetic mutations responsible for retinitis pigmentosa, the most common form of inherited blindness. Almost all of these kill the retina’s photoreceptor cells, but leave other layers of retinal cells unaffected, including the retinal ganglion cells. The new experiment succeeded in making the ganglion cells light-sensitive in around 90% of blind mouse cases.

The scientists created a virus targeting the retinal ganglion cells, filling it with the gene for a light-sensitive receptor, the green cone opsin. Opsin is usually only expressed by cone photoreceptor cells, making them sensitive to green-yellow light. When injected into the eye, the virus made the ganglion cells light-sensitive and able to send signals to the brain that were interpreted as sight.

The researchers are now testing variants of the science, to potentially restore colour vision entirely and better increase adaptation and acuity.