It sounds like something from a science fiction novel: eye drops containing microscopic fragments of plant machinery that, when exposed to ordinary light, turn your eyes briefly photosynthetic. And yet this is exactly what researchers at the National University of Singapore have built — and in mice, it works remarkably well.
A Billion and a Half Sufferers
Dry eye disease affects an estimated 1.5 billion people worldwide, making it one of the most prevalent conditions on the planet.
It’s easy to dismiss as a minor inconvenience, but chronic dry eye causes persistent pain, corneal scarring, blurred vision, and light sensitivity, and has been linked to depression and anxiety. Current treatments target the underlying inflammation but are expensive, hard to access, and carry side effects with long-term use. A better solution has been stubbornly elusive.
The problem at the cellular level is a vicious, self-reinforcing cycle. When cells generate energy, they produce damaging byproducts called reactive oxygen species, essentially tiny molecular bullets that tear through membranes, disrupt proteins, and damage DNA. The body normally neutralises these with a molecule called NADPH. But in inflamed eyes, the defensive system collapses: reactive oxygen species destroy the very machinery needed to make NADPH, which generates even more damage, which activates immune cells, which cause more inflammation. Trying to break this cycle from within the existing system is a losing battle.
The Spinach Solution
Plants face a similar oxidative challenge — and solve it through photosynthesis. Powered by sunlight, plants generate NADPH through an entirely different biochemical pathway, completely bypassing the dysfunction that derails mammalian cells. The Singapore team wondered: what if you could transplant that plant machinery directly into human eye cells?
The active ingredient in their technology, called LEAF, is extracted from ordinary supermarket spinach. The key structures are thylakoids, the internal membranes within plant cells where photosynthesis actually occurs. Previous attempts to transplant thylakoids into animal cells had struggled: the structures are fragile, the extraction process typically damages them, and keeping them functional inside a foreign cell had required additional chemical support.
The team cracked the problem by developing a gentler extraction process that preserved the thylakoids’ NADPH-producing function while stripping away other parts of the plant cell that would interfere. The resulting nanoparticles, each roughly the size of a very small bacterium, produce NADPH steadily whenever they’re exposed to ambient light.
What Happened in the Lab
The results across several stages of testing were striking. In cell cultures, both corneal cells and immune cells readily absorbed the LEAF particles. Within 30 minutes of light exposure, levels of damaging reactive oxygen species dropped sharply. Aggressive immune cells calmed into an anti-inflammatory state. When tested in tears collected from actual dry eye patients, LEAF boosted NADPH levels roughly twentyfold and cut a key oxidative chemical by over 95%.
In a mouse model of dry eye disease, twice-daily drops for five days outperformed an existing approved drug treatment — reversing corneal damage and keeping eyes hydrated, all without triggering immune reactions in the eyes or elsewhere in the body.
Perhaps most reassuringly, the mice showed no sign that anything unusual had happened to them. They moved and behaved entirely normally, apparently unbothered by the fact that their eyes had temporarily acquired a capability no mammal evolved to have.
Practical Strengths
Beyond the headline science, LEAF has practical qualities that make it genuinely promising for eventual clinical use. It requires no external devices, no power source, and no complex delivery mechanism, just ambient light, which eyes receive naturally throughout the day. It is straightforwardly manufactured from widely available spinach, stable at room temperature for two weeks and for up to a year when frozen, and has produced consistent results across batches made independently in Singapore and China.
What Comes Next
The researchers are candid about what remains to be tested. Whether LEAF affects visual perception hasn’t yet been examined, and the jump from mouse models to human clinical trials is always the hardest step in medicine.
But the team’s ambitions extend beyond dry eye disease. The same approach could theoretically be adapted into a skin cream to treat inflammatory conditions, and they’re already exploring whether LEAF could deliver photosynthetic benefits to deeper organs and boost the function of mitochondria, the cell’s own energy-generating machinery.
The idea of human cells with limited photosynthetic abilities sounds almost surreal. But the underlying logic is straightforward: plants solved the oxidative stress problem billions of years ago. We’re just beginning to borrow the answer.