What is the impact of smartphone screens on vision and with what consequences for future generations? This is the question asked by an Internet user, Renaudet Francis, on our page Facebook on the occasion of the Question of the week. Between assumptions and proven links, Science and Future sort it out.
A link " The trIt is difficult to prove scientifically“
Alicia Torriglia is director of research at theNational Institute of Health and Medical Research (Inserm). Interviewed by Science and Future, she warns that "The cause-effect link between exposure to screens and the evolution of vision is very difficult to prove scientifically" . " We still lack the perspective to properly measure this effect,” she insists.
Lack of resources, of perspective: faced with the famous blue light, that emitted by screens and which has been part of our daily lives for around twenty years, it is difficult to set up experimental protocols to demonstrate its harmfulness. There are many parameters to consider: who is looking at the screen? At what time of day or night? For how long? At what distance? lists the researcher. Nor can we do just any tests, whether on humans or animals."
While no one can yet fully affirm whether screens are harmful, or to what extent, some data nevertheless encourages us to limit our exposure to them.
A disruption of the circadian rhythm
The LEDs that make up our screens are diodes rich in blue light. In the spectrum of white light, the weakest wavelengths correspond to this blue light. Blue lights are the most harmful to the eye,” warns Alicia Torriglia.
But again, it all depends on the timing of the exposure. Throughout evolution, mammals' vision has developed so that they can see during the day in bright light, but also at night in the light of the moon. The retina, like the rest of the body, is subject to the circadian cycle. It is more sensitive at night because light is normally weaker there," explains the researcher. All our biological functions are subject to a circadian rhythm, a biological clock of approximately 25 hours, the synchronization of which is mainly done thanks to light.
Scrolling on your phone at night sends light onto your retina, disrupting this precious cycle.. “ The brain thinks it is daytime, and regulates its hormones accordingly, continues the researcher. In addition to decreasing sleep quality and alertness, a disruption of the circadian cycle can be linked to known general pathologies, such as cardiovascular diseases, diabetes, cancers, etc.
Read alsoHow Circadian Rhythms Regulate Our Health
Risks of early myopia and AMD?
In an article published in October 2021, we mentioned the risks of early AMD linked to exposure to blue light. AMD, or age-related macular degeneration, is a loss of vision in the center of the retina. It produces a black spot in the middle of the field of vision. If AMD is a disease of the elderly, it is from childhood that the destiny of our eyes is played out. Our eyes are in fact protected by the lens which filters part of the blue light thanks to the yellow tint it acquires with age. But children have a transparent lens, and therefore vulnerable.
We know that people who are very exposed to sunlight during childhood develop AMD at a younger age than others. Why? Because the Sun is also an emitter of blue light. In fact, just as our skin has a "sun capital", our eyes have a "light capital" and by exposing them, we gradually nibble away at this capital. Especially when it comes to blue light, since it is the most energetic of all, ahead of green, red or yellow. Does the blue light emitted by LEDs have the same effect as strong exposure? in the sun ? For now, there is no certainty: we will have to wait 20 to 30 years for the children who grew up in front of screens to age.
For myopia, the risks are more pronounced. There is not one incontrovertible proof, but a bundle of proofs", notes Alicia Torriglia. Globally, there are now more people with myopia than people with unimpaired vision, especially among the younger generations. The situation is already very worrying in Southeast Asia, particularly in South Korea. or up to 73% of 12-18 year olds are affected by myopia, according to a study. In France, the trends are also on the rise, with around a third of the general population (compared to 20% in the 1970s) affected and 42% for 10-19 year olds.
Experiments have been carried out on diurnal animals endowed, like humans, with rod and cone retinas. "To simplify, the results show that they become more myopic with exposure to blue light, and more hyperopic when exposed to red light.", explains the researcher. But here again, there are limits to these experiments, the results of which are not always transposable to humans.
Read alsoInsomnia: “The blue light from screens is not the problem, it’s our habits”
Blue light filters are ineffective ?
In an August 2023 article, We wrote that glasses and lenses treated to filter the blue light emitted by screens are not very useful. Opticians and companies that sell these anti-blue glare glasses promise to reduce up to 40% of the blue light perceived by the eyes in front of a screen. The lenses of these glasses often contain a chromophore [a chromatic film, editor's note] that reduces the amount of blue light that reaches the eye. Another approach is to coat the back and front surfaces of the lens with an anti-reflective interference coating that selectively reduces the transmission of a portion of the blue light spectrum.", explains the specialist.
But these glasses only filter 10 to 25% of blue light. A correction "minimal" for Alicia Torriglia, who nevertheless believes that "The real problem with these glasses is that people feel protected so they expose themselves more." "It's like with sunscreen," she illustrates.
To get more detailed answers, time is needed. It will give researchers the perspective they need to assess the effects of our exposure to screens. It's like all public health issues on any phenomenon: we have to wait until we have irrefutable proof to regulate and give recommendations.", regrets the researcher.
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