A synthetically engineered gene therapy designed to restore some retinal function in people with severe vision loss has been shown to bring sustained improvement in visual function out to 3 years, to a point where patients can make out objects on a table or walk down a hallway, according to new research presented at the Association for Research in Vision and Ophthalmology (ARVO) 2026 Annual Meeting.

The treatment, MCO-010, is a protein designed to infuse light-sensitive proteins, called multi-characteristic opsins, into otherwise dormant retina cells of patients with retinitis pigmentosa (RP). MCO-010 is delivered with a gene therapy vector into bipolar cells in the retina by an intravitreal injection that can be given in the office, whereas other gene therapies require placement below the retina in a procedure done in an operating room.

“This is one of the first optogenetic trials to achieve its primary endpoints,” Vinit Mahajan, MD, PhD, a vitreoretinal surgeon who directs the Molecular Surgery and Omics Laboratory at Stanford University , who presented 3-year results of the REMAIN phase 2b/3 trial of MCO-010.

MCO-010 is engineered to detect different color wavelengths of light, Mahajan added. “This single engineered opsin is doing the job of four natural opsins in the human eye,” he said.

Eyes treated in the study had “very, very low vision” in the range of hand motions or light perception, Mahajan said, with Snellen equivalents ranging from 20/1700 to 20/3000. “You cannot do standard gene therapy or cell therapy in these patients because there are no cells to rescue,” he said. “They’ve lost their photoreceptors; they’ve lost their retinal pigment epithelium cells.”

REMAIN 3-Year Results

REMAIN is an extension trial of the phase 2b RESTORE trial, in which patients had a statistically significant improvement in best-corrected visual acuity (BCVA) at 1 year of.337 LogMAR (P = .021 ) in the high-dose group and.382 LogMAR in the low-dose group (P = .029) compared with that in the sham group — the equivalent of three lines of improvement on the Snellen chart.

In REMAIN, the 3-year BCVA improvement was.264 LogMAR in the high-dose group and.453 LogMAR in the low-dose groups, Mahajan said. REMAIN enrolled 18 patients in the treatment group and nine in the sham group. BCVA in a “handful” of REMAIN patients improved by six lines, Mahajan said.

“The patients that actually had the best improvement actually began with better vision and better retinas,” Mahajan said. RESTORE found patients who had RP for 30 years or less responded more favorably to the treatment at week 52 than those who had the disease longer.

REMAIN also found improvement in BCVA correlated with retinal transduction and expression of multi-characteristic opsin, based on fluorescein autofluorescence imaging, and less retinal thinning as measured with optical coherence tomography.

Safety outcomes were similar between the one- and three-year results, Mahajan said. No serious adverse events emerged, and cases of mild ocular inflammation were treated successfully with topical corticosteroids, he said. After receiving the intravitreal injection, patients received three weeks of oral steroids to control inflammation.

Patients also demonstrated improvement in secondary endpoints, such as being able to identify objects in front of them on a table and navigating spaces, he added.

“So even though these retinas have lost their photoreceptors and their retinal pigment epithelium cells, some of the cells are still intact,” Mahajan said. “Some of that retinal circuitry is still there and the goal was to make these bipolar cells light sensitive, to basically get those bipolar cells to act like a photoreceptor, generate a sense of light and then generate an electrical current that goes to the brain.”

MCO-010 is “gene-agnostic,” Mahajan said, meaning it targets damaged retinal pigment epithelium cells regardless of the underlying genetic mutation. “This is about any retinal disease where you have severe photoreceptor loss,” he said. “We can start thinking about not just retinitis pigmentosa but about age-related macular degeneration-geographic atrophy, Stargardt disease and, as a retina surgeon, even some of the cases of retinal detachment where patients have lost photoreceptors. It’s something that we can really imagine expanding to other patients with very severe low vision.”

Answering a ‘Critical Question’

The 3-year REMAIN results are encouraging “particularly because durability is a critical question for any retinal restorative therapy,” said Stephen Tsang, MD, PhD, a medical geneticist and professor of ophthalmology, pathology, and cell biology at Columbia University in New York City. “For patients with advanced retinal degeneration and severe vision loss, even modest gains in functional vision can be life-changing, especially when those gains improve independence in daily living.”

The potentially gene-agnostic nature of optogenetics is particularly promising for patients who either do not have a molecular diagnosis, have mutations without an approved gene-specific therapy, or who are already beyond the stage where photoreceptor rescue is feasible, he said.

“If the safety and durability signals continue to hold up, this technology could become an important treatment approach for late-stage inherited retinal degeneration — a group of patients who currently have limited therapeutic options,” he said.

This study was funded by Nanoscope Therapeutics. Mahajan reported acting as an adviser to Nanoscope. Tsang reported having no relevant financial relationships.

Richard Mark Kirkner is a medical journalist based in Philadelphia.