Researchers from Adelaide University in Australia have carried out the first in-humans trial of a new type of treatment for a leading cause of blindness in working age adults – with promising results, they said.
Retinitis pigmentosa is a genetic condition where the retinal cells responsible for detecting light don’t work properly, resulting in progressive blindness. Current treatment options for later stages of the disease are limited and there’s no cure.
Now, a new approach to treating the disease is providing fresh hope. Working with researchers from the University of Washington, Adelaide University experts undertook a small pilot trial to see if a potential therapy based on a molecule could be tolerated safely by humans.
They found when the small molecule was injected into the eye, it revived some of the damaged retina cells, making them sensitive to light again. This happened even after the normal light-sensing cells had been lost.
What originally started as a very small trial to test the safety of the drug has now opened up the possibility of a completely new way of treating degenerative eye diseases, said Robert Casson, Professor and Principal Investigator, School of Medicine, Adelaide University.
“This is the first clinical trial of a photoswitch drug in humans. Unlike gene therapies, which target specific mutations, this approach could potentially be used across many different forms of retinal degeneration.
“It also avoids the need for genetic modification, which simplifies treatment and may reduce risks.”
Several participants involved in the trial reported short-term improvements to their ability to perform visual tests, including walking tasks. One participant with severely damaged retinal cells reported greater awareness of light perception within two days of receiving the treatment.
“We found that the treatment was well tolerated, with no serious adverse events and no evidence of harmful effects on the eye,” said Casson.
“We also saw early signals suggesting the drug may be having a biological effect – some participants reported changes in light perception, and brain imaging showed activity in visual areas of the brain after treatment. While this is certainly positive, it must also be stressed that these are preliminary findings and need to be confirmed in larger studies.”
Kiora Pharmaceuticals provided industry support for the study and the findings were published in Nature Medicine.
A larger phase 2 trial is currently under way to more rigorously assess whether this treatment can improve vision.
“More broadly, this work establishes a new platform for vision restoration that could be developed further for retinal diseases beyond retinitis pigmentosa,” said Casson.
Study details
Intravitreal photoswitch therapy in advanced retinitis pigmentosa: a phase 1 open-label trial
Robert Casson, Eric Daniels, Christen Barras et al.
Published in Nature Medicine on 14 April 2026
Abstract
A small azobenzene photoswitch molecule (KIO-301), designed to confer light responsiveness to retinal ganglion cells, was evaluated for safety and feasibility in a first-in-human, phase 1, gene-agnostic, open-label, dose-escalation clinical trial in individuals with advanced retinitis pigmentosa (RP). KIO-301 was administered by intravitreal injection to 12 eyes of six participants. The primary outcome was ocular and systemic safety over 30 days. Secondary and exploratory assessments included functional vision testing, visual acuity, kinetic visual field, functional magnetic resonance imaging and participant-reported outcomes. The primary safety outcome was met, with no serious adverse events or dose-limiting toxicities observed at any point. No drug-related intraocular inflammation occurred, and all ocular adverse events were mild and procedure-related. Exploratory assessments identified variation in light perception and functional vision measures in some participants. Light-evoked blood-oxygen-level-dependent signal changes in visual cortical regions were observed following dosing and showed a temporal pattern compatible with pharmacodynamic activity. Participant-reported quality-of-life scores varied over time. In this small, nonrandomised phase 1 study in individuals with late-stage RP, intravitreal KIO-301 demonstrated an acceptable safety and tolerability profile, supporting the feasibility of photoswitch therapy in advanced RP, and motivating further evaluation in larger trials.
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