Sudden loss of vision on one side may not be due to complete dysfunction of one eye. In this condition, a person loses half of their visual field in both eyes, as if looking through glasses with one side of the lenses darkened. This impairment is called homonymous hemianopia. Imagine how much harder it becomes to perform everyday tasks if you can't see from one side: driving a car or bicycle, reading, playing sports, cooking on a stove with multiple burners, or caring for children or elderly relatives—all of these activities become extremely inconvenient or even impossible.

Until recently, there was no effective treatment for hemianopia. Patients had to learn to live with a drastically reduced quality of life. Some therapeutic methods existed, but even after months of neurorehabilitation training, only moderate vision recovery could be achieved.

The problem lies in the fact that the brain coordinates the work of visual areas to perform various functions, including motion detection. Normally, these areas exchange information through perfectly synchronized electrical rhythms—oscillations. A stroke can disrupt this synchrony, leaving a person "half-blind."

However, there is now hope. In a scientific study led by Estelle Raffin, Michele Bevilacqua, and colleagues from the Swiss Federal Institute of Technology in Lausanne (EPFL), a placebo-controlled, double-blind clinical trial of a new therapy showed promising results.

In the study, 16 patients who had lost vision after a stroke underwent two blocks of 10 daily training sessions aimed at stimulating the edge of their blind visual field. At the same time, one of two types of cross-frequency transcranial brain stimulation was applied.

The results showed significant improvement in vision, even among those who had suffered from hemianopia for a long time. External stimulation of brain oscillations helped restore synchrony between the brain's visual areas. As project lead Friedhelm Hummel from the Neuro-X Institute at EPFL explains, the team used an innovative treatment strategy based on coordinated bifocal non-invasive electrical stimulation of the brain's visual system, inspired by the brain's natural physiology.

An additional achievement was the identification of factors associated with treatment response—potential biomarkers for patient stratification, meaning the ability to determine who is most likely to benefit from EPFL therapy.

During the study, cross-frequency bifocal transcranial alternating current stimulation (cf-tACS) was used to synchronize brain oscillations between the mediotemporal area and the primary visual cortex. By stimulating these areas with different frequencies of electrical signals, the researchers recreated the brain's natural communication pattern. More specifically, cf-tACS with a direct pattern sent high-frequency gamma waves to the motion-sensitive area and low-frequency alpha waves to the primary visual cortex, mirroring the natural flow of information during visual processing and helping to restore disrupted communication after a stroke.

Patients who received cf-tACS with the direct pattern showed significantly greater improvement in motion perception compared to the control group. Brain scans and electroencephalography confirmed the restoration of communication between the mediotemporal area and the primary visual cortex, and EEG recorded improved synchrony between these regions.

While laboratory improvements were impressive—some patients noted measurable expansion of their visual fields—real-life examples are even more telling. One participant shared that he was finally able to see his wife's right hand while she was driving and he sat in the passenger seat.

Visual training will likely remain an important part of hemianopia treatment, but the EPFL study demonstrates that external brain stimulation using cf-tACS is a promising way to improve vision and, at the same time, the quality of life for patients.