Researchers at the Institute for Bioengineering of Catalonia have developed photoswitchable eye drops for blindness that restored light perception and visually guided behaviour in blind animal models, with no gene therapy, no implants, and no specialised equipment required. The results, published in the Journal of the American Chemical Society, point toward a treatment approach that could reach patients currently excluded from every existing option.
A problem that affects 200 million people and costs $400 billion a year
The conditions in focus, age-related macular degeneration (AMD) and retinitis pigmentosa (RP), together affect roughly 200 million people worldwide and carry an estimated $400 billion annual cost in healthcare expenses and lost productivity. When the photoreceptor cells in the retina die, the visual system loses its ability to convert light into neural signals. The deeper retinal circuitry often remains intact, but those surviving neurons have nothing to respond to.
Existing interventions each have a ceiling. Gene therapy works only for patients with specific genetic mutations, a small fraction of those affected. Retinal prostheses are invasive, expensive, and require training to use. Optogenetics and earlier light-responsive drugs have reached clinical trials, but restoring reliable vision at ordinary light levels has proved harder than early results suggested.
The IBEC team worked in the field of photopharmacology, which builds a light-sensitive molecular switch directly into a drug’s structure so the compound’s activity changes when light hits it. Their molecules, called prosthe6, are designed to fill in for the photoreceptors that disease has destroyed.
How photoswitchable eye drops for blindness work in practice
‘Our goal was to restore vision using a molecular mechanism that is as close as possible to how the healthy retina works,’ said Rosalba Sortino, a co-first author of the study. ‘Instead of bypassing retinal processing, we aimed to reactivate it right at the same level of the retinal circuit as the lost photoreceptor cells.’
Prosthe6 compounds target ON-bipolar neurons, which normally receive signals from photoreceptors and relay them deeper into the retinal network. In blinded zebrafish larvae, the compounds restored saccadic eye movements. In mouse models of both AMD and retinitis pigmentosa, they restored something harder to fake: the instinctive preference for darker environments that sighted mice have and blind mice lose.
After receiving prosthe6, blind mice spontaneously avoided bright areas again, with no training, at light levels comparable to being indoors or outside on a cloudy day. Two compounds, prosthe6-12 and prosthe6-15, stood out. Both worked when applied as ordinary eye drops rather than injections, a practical advantage that could matter considerably for patients and clinicians.
‘These molecules do not cure blindness, because they do not address the cause of photoreceptor degeneration,’ said Pau Gorostiza, co-leader of the study. ‘But they are remarkably effective at restoring sight, and they do so using a very simple and potentially patient-friendly approach.’
Who could benefit, and what comes next
One practical advantage of the approach is that it does not require knowing which mutation caused the photoreceptor loss. That means it could, in principle, reach the large number of patients who do not qualify for gene therapy because their condition lacks a targetable genetic cause. The treatment is also reversible.
The research has been running for more than ten years across multiple Spanish universities and research institutions. The team is now working with Eyelumina, a spin-off company in formation, to secure the investment needed for translational development and future clinical trials, according to the Institute for Bioengineering of Catalonia. That commercial structure is a necessary step: without it, results that work in mice stay in mice.
Gorostiza was direct about the road ahead. ‘Turning this into a therapy is a long and laborious process,’ he said. The photoswitchable eye drops for blindness have cleared a credible scientific bar, but the gap between animal models and a licensed treatment remains wide. Eyelumina’s formation marks the point at which the laboratory work begins its translation into something a patient could one day pick up at a pharmacy.
The American Chemical Society published the full study under the title ‘Restoration of saccadic eye movements and visually guided behavior in ambient white light with photoswitchable small molecules’.
