Researchers at the University of Washington say a novel experimental therapy rooted in decades of academic research has reached a key clinical milestone, offering early hope for people with advanced retinitis pigmentosa (RP).

Results from a first-in-human study of the therapy, known as KIO-301, were published April 14 in Nature Medicine.¹ The treatment is a light-activated small molecule designed to restore some degree of vision by making surviving retinal cells responsive to light—even after the eye’s photoreceptors have been lost.

The underlying science was developed in part at the University of Washington (UW) Department of Ophthalmology. Russell N. Van Gelder, MD, PhD, chair of the department and a co-author of the study, helped pioneer the approach using compounds called molecular photoswitches.

“These are essentially nanometer-scale light switches that can turn drug activity on and off with light,” Dr. Van Gelder explained. “It is very gratifying to see the first steps in translating this remarkable technology to clinical use.”

KIO-301 works by targeting voltage-gated potassium channels in retinal ganglion cells, which play a key role in neuronal signaling. The drug contains a light-reactive azobenzene group that enables these cells to respond to light and send visual signals to the brain, bypassing damaged photoreceptors.

The phase 1 study, known as ABACUS-1, enrolled six participants with late-stage RP and evaluated 12 treated eyes. Led by Dr. Robert Casson at the University of Adelaide, the trial primarily assessed safety—and met its main endpoint. Researchers reported no serious adverse events, dose-limiting toxicities, or treatment-related inflammation or structural damage to the retina.

While the study was not designed to definitively measure effectiveness, early signals of clinical activity were observed. Participants demonstrated improvements in light perception and functional vision tests, alongside changes in visual cortex activity seen on functional MRI scans. Patients also reported improvements in quality of life during the study period.

Researchers caution that these findings are preliminary. Larger, controlled trials will be required to determine whether the therapy can deliver consistent, meaningful improvements in everyday vision.

One potential advantage of KIO-301 is its mutation-agnostic design. Unlike gene therapies that target specific genetic defects, this approach could be applicable to a broad range of patients with retinal degeneration.

“For people with advanced retinal degeneration, the need for mutation-independent restorative therapies is enormous,” Dr. Van Gelder said. “This publication reflects over 20 years of work aimed at turning a powerful concept into something that may ultimately help patients.”

Building on the phase 1 results, developers have launched ABACUS-2, a randomized phase 2 trial that will evaluate higher doses and focus more closely on functional vision outcomes.

Reference

1. Casson RJ, Daniels E, Barras C, et al. Vision restoration using a light-responsive small-molecule photoswitch (KIO-301) in advanced retinitis pigmentosa: the ABACUS-1 phase 1/2 clinical trial. Nat Med. Published April 14, 2026. doi:10.1038/s41591-026-04317-6