The post-COVID lifestyle has been vastly different from that of previous generations. Buying groceries and consumer products is a click away, and a lot of work can be done while perched on the couch. A study published in the peer-reviewed Journal of the American Planning Association reports that people spend an hour less on outdoor activities than before. A new study shows that children who spend more time indoors are more likely to develop myopia or nearsightedness. Turns out, a missing color in indoor lighting may hold a key to preventing it.
New research led by scientists at Cincinnati Children’s and the University of Alabama at Birmingham examined indigo light, one of the seven broad colors of natural sunlight. However, indigo light is scarce in standard white LED lighting. Research on tree shrews, whose visual systems are quite similar to humans, revealed that exposure to indigo light completely prevents myopia.
“The model of myopia we use in the tree shrew is fairly extreme,” says corresponding author Richard Lang, PhD, director of research in the Division of Ophthalmology at Cincinnati Children’s. “So, if indigo light can suppress myopia in these tests, then it should also be quite effective in humans.”
Setting up the Experiment
Myopia develops when the incoming light from objects focuses in front of the retina, producing a blurry image of a distant object. Glasses can correct blurry vision, but myopic eyes are prone to other severe eye problems later in life. Tree shrews that were used in the experiment used tiny spectacles designed for them to produce a strong signal that encouraged myopia in one eye, leaving the other one as a control. The researchers exposed the animals to several wavelengths of light and tracked changes in their eyes, which were detected using a biometer that measured eye shape and axial length. An attached autorefractor monitored changes in refraction over time.
Indigo Light Prevents Myopia
Previous experiments in mice showed that violet light near 380 nanometers could reduce myopia, along with opsin 5 (OPN5), a light-sensing receptor required for a more pronounced protective effect. However, light at that wavelength didn’t produce a similar effect, as their eye lenses, which were more like human eyes, blocked most wavelengths below 400 nanometers.
Tree shrews and humans don’t transmit a lot of light in the ultraviolet range, so the researchers explored slightly longer wavelengths that could stimulate OPN5. Indigo light (419-446 nanometers) did better at preventing myopia than other wavelengths. The findings add to the idea that our eyes have not evolved to work under LEDs, which generally peak around 450 nanometers and provide ample long-wavelength light for normal vision. However, they contain relatively little indigo light, which activates nonvisual opsins associated with biological processes beyond forming images. Our eyes evolved outside in the full-spectrum light provided by the Sun. Staying indoors deprives us of many of the wavelengths needed for normal refractive development. The crux of the paper explores how this one lifestyle change can make us more prone to myopia.
Designing Lights that Prevent Myopia
While spending more time outdoors is a possible strategy to reduce myopia in children, but it is difficult to switch from an indoor, tech-dependent lifestyle. A better way out is to redesign indoor lighting to mimic the full spectrum of sunlight; in fact, Cincinnati Children’s became the first pediatric hospital to install a full-spectrum lighting system in its neonatal intensive care unit. The effects of that system are still being studied.
Specialty lamps designed to cope with botched sleep-wake cycles and jet lag are being widely sold, but products that tackle myopia are still rare. Tree shrew experiments give a good view into the benefits of indigo light, but it is yet to be seen if indigo-enriched indoor lighting can actually prevent myopia in children. In a way, the researchers want to make artificial light more complete and comparable to the natural light that humans have evolved under for thousands of years.
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