Weekly exposure to deep red light (650–900 nm wavelength), when delivered in the morning, can enhance color vision in the aged human retina, according to a new study.

Researchers at University College London (UCL; United Kingdom) conducted a study on the effects of deep red light in humans, building on previous findings in mice, bumblebees, and fruit flies that showed significant improvements in the function of the retina's photoreceptors when their eyes were exposed to 670 nm deep red light. For the study, 20 participants (34-70 years of age, 13 female) were exposed to three minutes of deep red light between 8am and 9am. Color vision was tested before and after exposure, and again three hours post exposure. Ten participants were also tested one week post exposure.

The results revealed that on average, there was a significant 17% improvement in participant’s color vision following just a single three minute 670 nm exposure, which lasted for a whole week; in some of the older participants there was a 20% improvement, also lasting a week. However, when the test was conducted a in the afternoon--a few months on from the first test to ensure any positive effects had been 'washed out'--zero improvement was seen. The study was published on November 24, 2021, in Scientific Reports.

“Mitochondria have specific sensitivities to long wavelengths, and morning exposure is absolutely key to achieving improvements in declining vision. A simple LED device once a week recharges the energy system that has declined in the retina cells, rather like re-charging a battery,” said senior author Professor Glen Jeffery, PhD, of the UCL Institute of Ophthalmology. “We demonstrate that one single exposure to long wave deep red light in the morning can significantly improve declining vision, which is a major health and wellbeing issue, affecting millions of people globally.”

In humans around 40 years old, cells in the eye's retina begin to age, partly since the mitochondria, whose role is to produce adenosine triphosphate (ATP, a molecule that carries energy within cells), also age. Since mitochondrial density is greatest in the retina's photoreceptor cells, the retina ages more rapidly than other organs. Deep red light exposure partially restores ATP generation ability by reducing nanoscopic interfacial water viscosity around the ATP rota pumps, thus improving their efficiency. 

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