At the National University of Singapore, researchers have done something nature itself has achieved only once: they've engineered human cells to harness light the way plants do. The innovation sounds almost fantastical—eye drops containing spinach-derived photosynthetic machinery that could heal dry eye disease by allowing the cornea to generate its own protective molecules in response to ordinary light.
Dry eye disease affects over 1.5 billion people worldwide, making it one of the most prevalent eye conditions globally. What might sound like a minor irritation is anything but. The disease causes corneal scarring, chronic pain, blurred vision, and light sensitivity so severe it has been linked to depression, anxiety, and reduced workplace productivity. The economic cost in the United States alone reaches $3.84 billion annually.
Current treatments, such as Restasis and Xiidra, work by targeting inflammation through specific molecular pathways. But they come with significant drawbacks: high costs and adverse side effects that limit how long patients can tolerate them. A team led by Associate Professor David Leong Tai Wei from NUS's Department of Chemical and Biomolecular Engineering took a radically different approach. Rather than fighting inflammation directly, they asked: what if we gave the eye's own cells the power to defend themselves?
At the heart of dry eye disease lies a destructive cycle driven by reactive oxygen species—chemically aggressive molecules generated by inflammation that damage cells faster than the eye can repair itself. Healthy eyes produce an antioxidant called NADPH that neutralizes this damage, but in inflamed eyes, the system becomes overwhelmed. The NUS team's breakthrough was to transplant functional photosynthetic machinery directly into corneal cells, allowing them to produce NADPH independently whenever exposed to ambient light.
They engineered a particle they call LEAF—Light-reaction Enriched thylAkoid NADPH-Foundry—by extracting thylakoid grana, the light-harvesting structures inside spinach plant chloroplasts. The team stripped away the components that consume NADPH while preserving the machinery that generates it, creating a nanosized package roughly 400 nanometers across. Prepared using a patented mechanical and chemical extraction method, these particles are small enough to be readily absorbed by cells and remarkably produce about 20% more NADPH than unpackaged thylakoids.
In preclinical studies, the eye drops—delivered at doses so low they don't interfere with color perception—reversed corneal damage to near-healthy levels within just five days. Most strikingly, they outperformed Restasis, the gold-standard existing treatment. The findings, published in the journal Cell, represent something unprecedented: a mammalian organ acquiring a functional form of photosynthesis to heal itself.
The concept echoes nature's only known example: the sacoglossan sea slug, which ingests chloroplasts from microalgae and can photosynthesize to survive starvation. The NUS researchers recognized that the human eye, uniquely among most organs, absorbs visible light regularly—making it an ideal candidate for this kind of biological engineering. What they've created isn't science fiction but a practical, light-activated solution that harnesses biology's most ancient energy-conversion system to combat a disease affecting billions.