In an open, uncontrolled study, an international team led by Sahel and Roska published results in the New England Journal of Medicine involving ten people blinded by advanced retinitis pigmentosa. Each participant received a single intravitreal injection of a gene therapy vector delivering the gene for light-sensitive protein ChrimsonR into retinal ganglion cells, combined with a custom-developed light-stimulation goggle system.
Safety was the study's primary endpoint. The authors assessed the treatment as safe within the limits of this small study and call for further research on safety and efficacy.
Ten participants in open, uncontrolled study
Ten people blinded by advanced retinitis pigmentosa were actually enrolled. Three dosage groups of three participants each were planned, along with an expansion group at the highest tolerated dose. The authors defined clinical significance as a 0.6 logarithmic unit decrease in light threshold, roughly a fourfold increase in light sensitivity, based on literature findings rather than pre-specified in the protocol. Retinitis pigmentosa is a genetic disease leading to degeneration of light-sensitive retinal cells, often rendering people legally blind in young adulthood; a subset with specific mutations may be amenable to gene therapy.
34 adverse eye events
Nine of the ten participants experienced 34 total adverse eye events, including 23 mild and 10 moderate ones. Researchers classified temporary central retinal artery occlusion immediately after injection as a serious event; it resolved within minutes after administration of the medication Iopidine.
What some participants could do with the goggles
Some participants better detected object presence with the goggles, determined position, and reached for objects, but normal vision or reading did not return. Multiple participants improved at recognizing objects, finding door openings, and following lines with the goggles, though the treatment did not restore normal vision. Researchers led by Marlene Behrmann found electroencephalography evidence that visual signals reached the visual cortex; four participants showed consistent improvements over months to years in several everyday vision tasks. Four participants showed clinically meaningful improvement.
Study funding
GenSight Biologics financed the study as industry sponsor. According to company statements, José-Alain Sahel and Botond Roska are company co-founders. Author disclosures are available on NEJM.org. Sahel stated the results are exploratory and require confirmation.
Comparison: from rat nerve cells to the human eye
The Sahel and Roska team previously tested the approach in a 2021 case report of a single blind patient. Using a ChrimsonR-encoding vector and custom goggles, he detected, localized, counted, and touched objects with the treated eye and activated goggles. The underlying technique stems from basic research for which the Nobel Assembly at the Karolinska Institute awarded the 2026 Nobel Prize in Physiology or Medicine on October 5, 2026, to Karl Deisseroth, Peter Hegemann, and Georg Nagel. Deisseroth demonstrated the procedure in 2005 in rat nerve cells and had it working in living mouse brains two years later.
Through estimated study completion in October 2027
According to ClinicalTrials.gov, the PIONEER study was active in February 2026 but not enrolling new participants; it began in September 2018 with primary and final completion estimated for October 2027. Expanded trials are expected in 2027 and 2028, with possible regulatory approval between 2029 and 2031.