Liquid Crystal Lens Filters out Light that Causes Seizures

In people who experience photosensitive epilepsy, seizures can be triggered by visual stimuli, like video games, that are displayed at certain wavelengths. Lenses made with cholesteric liquid crystal (CLC), a material that is sensitive to changes in temperature as well as the electrical field, could help block these harmful wavelengths through thermal control.

The CLC lenses are the result of a collaboration between the University of Glasgow and the University of Birmingham. “The project shows how collaboration between different disciplines such as engineering, neuroscience, and mathematics can bring about potential discoveries that could transform the lives of patients affected by various diseases,” professor Rami Ghannam at the University of Glasgow said.

The highly tunable CLC lenses can dynamically change their stopband in response to small changes in temperature. An electronic system is built into the lens for controlling the temperature in real time. At room temperature, the stopband of the lens is outside the visible spectrum, and the lens functions like conventional glass. As the temperature rises to 36.5 degrees Celsius (C), or 97.7 degrees Fahrenheit (F), the lens blocks the light that is within the wavelength range known to cause photosensitive epilepsy. The wavelength of the block band is controlled by variations in the temperature of the lens.

Researchers used cholesteric liquid crystal (CLC) materials to develop reconfigurable color-filter lenses. The lenses can cut off specific wavelengths of light that cause seizures in people with photosensitive epilepsy. Courtesy of Xia, Yuanjie et al. Cell Reports Physical Science, Volume 5, Issue 9, 102158, doi: 10.1016/j.xcrp.2024.102158.

The researchers used CLC materials with opposite handedness to achieve maximum cutoff of the target wavelength at the stopband. They developed a dual-layer CLC lens configuration, in which left-handed and right-handed CLC layers were cascaded to block more than 98% of light in the 660 nm to 720 nm wavelength range — the range that affects the most patients with photosensitive epilepsy.

Traditional treatments for this disease include colored glasses whose optical properties are fixed and cannot be adjusted. However, only a few scenarios are likely to trigger photosensitive epilepsy, making the continual use of conventional colored glasses inconvenient for most patients. The CLC-based, tunable color filter lens for epilepsy treatment can switch its working mode to adapt to different environments.

The team developed and tested a prototype of the CLC-based lens. “The prototype shows how a discrete circuit installed in the frame of a pair of glasses can power these lenses and be used in situations where certain wavelength light is likely to trigger a seizure, such as while watching TV or playing computer games,” University of Birmingham professor Zubair Ahmed said. “The circuit heats up the lenses to a comfortable temperature for wearers, that will also cut out more than 98% of light with a wavelength that can cause seizures.”

In tests of the prototype, the researchers found that it was functional at room temperatures of up to 26 C, or 78.8 F. The lenses demonstrated outstanding optical tunability and were able to vary the reflection band by modulating the temperature. At room temperature (around 25 C, or 77 F), the reflection band of the CLC lens exceeded 720 nm, which is beyond the visible spectrum. At this temperature, the lenses exhibited good transmittance within the visible spectrum and had the same appearance as normal lenses.

However, if the environmental temperature exceeded 26 C (78.8 F), a portion of the reflection band fell within the visible spectrum, which could affect the patient’s experience. To support the use of the CLC lenses at temperatures higher than 26 C, chiral dopants with high helical twisting power could be introduced to modify the thermal sensitivity of CLC materials. The working temperature of the lenses could be calibrated to the needs of the individual.

The researchers plan to reduce heating and cooling time in the prototype, possibly by refining the lens structure or incorporating advanced electrodes with enhanced thermal conductivity to accelerate temperature changes. Further exploration of CLC materials with higher temperatures could also provide a solution to shortening the time to heat and cool the lens, by allowing larger stopband shifts with smaller temperature changes. A built-in temperature sensor could be incorporated in the CLC cell to monitor the temperature of the CLC material in real time.

“We are now developing this prototype further to improve its performance before we take this into human studies,” Ghannam said.

Despite its shortcomings, the prototype demonstrated that it is feasible to use CLC lenses to filter certain wavelengths of light that are harmful to people with photosensitive epilepsy. The lens exhibited tunability of temperature variation, showing its potential as an adaptable, responsive means to filter damaging light.

“This is a hugely exciting project that . . . demonstrates the potential for the use of liquid crystal lenses that can be modulated to cut out specific wavelengths of light,” Ahmed said.

The research was published in Cell Reports Physical Science (www.doi.org/10.1016/j.xcrp.2024.102158).