People with a severe form of blindness were able to make out the outlines of objects and find a doorway again, thanks to an experimental gene therapy. Scientists did not repair the damaged cells of the eye; instead, they taught other retinal cells to perceive light. Ten people took part in the clinical trial, and seven of them saw their sensitivity to light improve.
All the participants suffered from retinitis pigmentosa, a group of inherited diseases that gradually destroy the retina's photoreceptors, the specialized light-sensitive cells. Around 1.5 million people worldwide live with these conditions. The disease begins with a person seeing less well in the dark, then losing peripheral vision, and eventually may lead to complete blindness. A universal treatment is hard to create, because the disease is caused by mutations in different genes, and correcting a mutation does not necessarily bring back photoreceptors that have already died.
An international team of researchers led by Jose-Alain Sahel of the University of Pittsburgh and Botond Roska of the Institute of Molecular and Clinical Ophthalmology in Basel chose not to restore the photoreceptors but to bypass them. The scientists turned their attention to the retina's ganglion cells, the nerve cells that normally receive already processed visual information and pass it on to the brain. Many of these cells survive even in the late stages of retinitis pigmentosa.
The researchers used optogenetics, a technology that uses the genes of light-sensitive proteins to make cells respond to light. Each patient received an injection into one eye of a modified, harmless virus. The virus delivered into the ganglion cells the gene for the ChrimsonR protein, which works as a switch that responds to light. As a result, the ganglion cells were able to perceive light signals directly.
The treatment had two parts. In addition to the injection, patients wore special glasses fitted with a camera and a light projector. The glasses captured the surroundings, processed the image and projected patterns of light directly onto the retina. The treatment proved safe for all ten participants, which was the main goal of the first and second phases of the clinical trials. In seven people, sensitivity to light increased: in some it doubled, and in others it rose more than 60-fold. Six of them achieved clinically meaningful improvements, and some were able to distinguish objects and orient themselves in space, which they could not do before.
Optogenetics is based on proteins of green algae that help them respond to light. These proteins, channelrhodopsins, work as tiny gates in cell membranes: under the action of light they open and let charged particles through, changing the cell's electrical activity. Scientists have learned to insert the genes of these proteins into other cells, including neurons, and to control them with light. For this work, Karl Deisseroth, Peter Hegemann and Georg Nagel were awarded the 2026 Nobel Prize in Physiology or Medicine.
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