A 58-year-old man who has been blind for years now sees well enough to make out shapes, including the white lines of a crosswalk.
The advancement comes thanks to a technology called “optogenetics,” a kind of gene therapy that delivers light-sensing molecules into the eye. The molecules, called opsins, generate an electrical signal when exposed to a particular wavelength of light.
In healthy eyes, photoreceptors cells react to light by sending electrical signals to another type of cell, called ganglion cells. The ganglion cells transmit the signal to the brain.
The patient in the study was diagnosed at age 18 with an eye disease called retinitis pigmentosa, which causes the photoreceptor cells to die. Over time, his vision deteriorated, and when he enrolled in the study, he could make out light and darkness.
Luckily enough, if I may say so, it’s only the photoreceptors that degenerate, and the rest of the retina remains alive and functional,” says Bernard Gilly, co-founder of GenSight Biologics, the company that is developing the therapy. “What we are doing with optogenetics is to try to restore this function of converting light into an electric signal.”
To do this, the researchers injected a gene for an opsin directly into the eye. They chose a modified version of one found in algae, designed to respond to light in the red-orange part of the spectrum. Within 6 months, the ganglion cells in the patient’s eye had begun making the opsin protein. He was given goggles that translate the visible spectrum into a bright orange lights pattern to activate the opsins.
He still couldn’t see right away, though. First, he had to train his brain to interpret the signals coming from the goggles.
We see with our brains, not with our eyes.
When blindness strikes later in life, the brain already knows how to process the signals coming from the eyes. These neural pathways can be retrained to interpret new signals, such as those coming from opsins. But it takes work.
Photoreceptors in normal retinas respond to a broad spectrum of light wavelengths spanning the rainbow of visible colors. The opsin that GenSight used only responds to light in the dark orange/red part of the spectrum. The special goggles take in the visual field and translate that into amber points light that could trigger the opsin in the patient’s ganglion cells and signal to the brain.
“We founded this company, GenSight, to implement this approach,” says Jose-Alain Sahel, professor of ophthalmology at the University of Pittsburgh Medical Center and co-founder of GenSight. “A pharma company could work on the gene therapy, and a medical device company would be able to work on the goggles, but they would not be able to work on the gene therapy part. We thought we needed to build a very focused approach that comprises all these technologies integrated around the patient.”
The patient in the study spent months practicing with the goggles before he started to see anything. Even now, his vision is limited to making out high-contrast shapes, such as a black notebook on a white table. “It’s not like anyone thing is creating an image and projecting it onto the brain,” Sahel says. “The point is to send a signal that is meaningful to the brain. It may start like a starry sky with some constellations, but then with some training, you find out that this arrangement of dots corresponds to a door, or a different one corresponds to a window.”
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