The first contact lenses for depression — Could they replace medication?

Contact lenses are generally used to improve vision. Here, the idea is more subtle: Thanks to light, using the eye as a gateway to the brain brings about targeted electrical impulses that are almost as invisible as the device that produces them.

A team of researchers at Yonsei University in South Korea has developed a flexible, transparent lens designed to stimulate the retina and influence, via visual circuits, certain areas of the brain involved in mood regulation. The study, published in Cell Reports Physical Science, concerns a technology that is still experimental: for the moment, it has only been tested on animal models, with promising results after three weeks of treatment. The road to the eventual use on human beings remains long and will require extremely rigorous clinical trials.

From retina to brain

The retina is part of the central nervous system, and communicates directly with the brain. It's from this anatomical relationship that the researchers' hypothesis was born: to stimulate the eye to reach, in a less invasive way, the circuits linked to mood.

The lenses were designed with ultra-thin electrodes made of gallium oxide and platinum, materials chosen to ensure that the device remains flexible, transparent and adapted to the surface of the eye. Stimulation is based on a principle known as "temporal interference": two electrical signals circulate separately and are only activated at the point where they meet, thus concentrating the effect on the desired area.

The image used by the researchers themselves is a simple one: two weak beams of light which, when superimposed, create a more intense spot. With electricity, something similar happens. The electrodes remain on the lens, while the useful stimulation is concentrated deeper down, in the retina.

Promising results, but handle with caution

During laboratory tests, animals treated with these lenses showed an improvement in certain behavioral, neuronal and biological signals associated with depression. After three weeks, researchers observed an effect comparable to that of fluoxetine, the active ingredient in Prozac, as well as a restoration of connectivity between the hippocampus and prefrontal cortex, areas involved in emotional and cognitive processes.

Changes were also observed in biomarkers: a drop in inflammatory molecules in the brain, a reduction in blood corticosterone levels and an increase in serotonin levels compared to the control group. These are interesting data because they affect several levels at once: behavior, brain activity and biological response.

Caution is still called for, however. Animal experiments are used to determine whether a lead is relevant, safe and potentially effective. To develop a treatment that can be used in humans, further steps are required: tests on larger animals, long-term safety assessments, clinical trials, comparison with therapies already available and vigilance against possible side effects. A device applied to the eye and linked to brain stimulation will have to overcome extremely stringent controls.

A still distant frontier

This work falls within the field of neuromodulation, i.e. the use of electrical or magnetic stimuli to modify nervous system activity. Today, techniques such as transcranial magnetic stimulation are already available for certain mood disorders that are resistant to conventional treatments, or, in very specific cases, more invasive approaches. The advantages of a contact lens are obvious: it would be small, portable and, in theory, easier to use.

Researchers imagine future applications in anxiety, addiction and cognitive decline. For the time being, we remain in the field of preclinical research, where a good idea still has to prove that it's safe, stable and genuinely useful in everyday life.

In this research, the eye is seen as much more than just a surface to be corrected with a lens. It becomes a potential gateway to the brain. An everyday, flexible and transparent object is transformed into a small bioelectronic device. At first glance, it seems insignificant. In reality, it raises a huge question about how certain therapies could evolve in the coming years.

Source: Cell Reports Physical Science