While staring directly at the sun is rightly discouraged, emerging research highlights the surprising benefits of specific wavelengths of sunlight on eye health. Intriguingly, these positive effects on vision and mitochondrial function can occur even without direct sunlight entering the eyes.
Background
Using long-wavelength red light has many therapeutic applications. Researchers are studying the benefits and limitations of natural versus artificial light. Sunlight emits a wide spectrum of wavelengths from 300 nanometers (nm) to 3000 nm. Different wavelengths have different impacts on physiology. For example, longer wavelength red light from 660-1000 nm increases mitochondrial function and ATP production. Shorter wavelengths from 400-450 nm have an opposite effect, reducing mitochondrial function and creating oxidative stress.
Humans have relied on sunlight and firelight for ages, and it is only relatively recently that electrical lighting has replaced these natural sources. Standard white Light-Emitting Diode (LED) lighting was introduced in the early 21st century and emits shorter wavelengths compared to natural sunlight or even older incandescent lighting. The dominant wavelength in LED lighting is blue at approximately 450 nm, and ranges of 420-450 nm are known to disrupt mitochondrial function in the absence of infrared.
The outer retina is abundant in mitochondria and is sensitive to the effects of aging. Studies have shown that exposure to long-wavelength light results in improved visual function via improved mitochondrial function. Therapeutic light applications are generally used on targeted tissues, but a new study shows that regional light exposure to the thorax has beneficial distal effects on vision.
The Study
An article published in Nature Scientific Reports studied light penetrance through the thorax and its impact on visual function in 40 individuals. Participants received 15 minutes of longwave 850 nm LED exposure on their backs. A subset of these participants also had their heads fully wrapped to block ocular light exposure. The 850 nm wavelength was chosen because it represented a similar range as that of natural sunlight passing through the thorax. Clothing layers reduced wavelength intensity but did not block the effect.
The participants completed color contrast sensitivity testing using a Chroma test before and 24 hours after exposure. Color contrast was chosen as the preferred test because, as one ages, the cone photoreceptors have reduced function due to mitochondrial decline. There was statistically significant improvement in protan (red-green) and tritan (blue-yellow) contrast thresholds after light exposure to the thorax, regardless of whether ocular exposure was blocked or not. This implies that sunlight exposure to the body can improve vision, independent of ocular input, but to different degrees.
Conclusions
The phenomenon in which targeting a single body part results in widespread physiological effects is known as the abscopal effect. In the context of long-wavelength light exposure, these systemic effects may be mediated through shifts in cytokine signaling and mitochondrial activity. The retina is one of the most mitochondria-dense tissues in the body, making it ideal for studying these mechanisms. However, it is important to recognize that sunlight influences a wide range of physiological processes beyond eye health.
Further research is essential to determine optimal dosing and therapeutic applications of light exposure. Additionally, the potential impact of standard household LED lighting, which lacks beneficial long-wavelength components, on visual and systemic health warrants deeper investigation.
