Children hold electronic devices much closer to their faces than adults, putting them at risk for myopia as a result of chronic hyperopic defocus, findings from a new study show.
Rates of myopia are increasing around the world and are especially high in East Asia. The prevalence was shown to be 96% in a 2012 study of 5083 university students in Shanghai, for whom mean spherical equivalent was –4.10 diopters, reported Renfeng Xu, MD, PhD, from the University of Nebraska Medical Center in Omaha during her presentation at the virtual Association for Research in Vision and Ophthalmology (ARVO) 2020 Annual Meeting.
Two main hypotheses explain the increase in myopia: first, near work could cause chronic hyperopic defocus associated with accommodative lag; and second, time spent indoors could deprive the retina of luminance necessary for eye development.
Schools in China are already acting on both hypotheses, Xu reported. They have built classrooms with transparent walls and roofs that allow more luminance from the sun. And they have installed metal bars on desks to prevent children from bringing their eyes too close to their work.
Yet it's not clear whether either approach will help. Observational studies have supported both hypotheses, but the results are ambiguous. "Unfortunately, these two factors typically co-occur as children engage in near-viewing activities," Xu said. "These data couldn't tell us which one is the dominant factor."
Another problem is that previous research has relied on questionnaires and telephone interviews with parents, who don't always know exactly what their children are doing and often can't remember accurately what they do know.
For their study funded by the National Institutes of Health and ARVO, Xu and colleagues used a commercially available software program, VisionApp, to gather objective data. The app uses the light sensor on the phone to measure lighting levels and the front camera to estimate the viewing distance from the width of the user's face.
Smartphone App to Measure
To assess children's behavior, the researchers gave the Google Pixel smartphones with the app installed to 20 children ranging in age from 6 to 12 years. Ten of the study participants were myopic and 10 were emmetropic (normal eyesight).
The children watched a movie on the YouTube Kids platform with room lights on at 226 lux, and a movie with lights off at 0.1 lux. They read 8-point text and 16-point text. And they played the video game Minecraft.
The researchers used a ruler to validate the app's estimates of viewing distance. They found a very close correlation, even when the phone was rotated. And they found that its measurement of light levels were consistent with those of a photometer, an instrument used to measure the diverse aspects of the light intensity.
The mean viewing distance across all tasks and subjects was 24 cm. That dropped to 21 cm when the children read small text, and increased to 27 cm when they watched a movie in the dark or played the video game. Over a 5-minute period, the mean standard deviation of viewing distance was 4.8 cm. The viewing-distance range has been reported to be 40 to 50 cm in adults.
VisionApp could help determine what is causing myopia, said Lisa Ostrin, OD, PhD, from the University of Houston in Texas.
"This is one of the first software programs to objectively measure where someone is looking and how far away" they are looking, she told Medscape Medical News. "It's definitely a step in the right direction, and I think more studies like this, using objective measures, are going to help answer this question."
One limitation of the app is that it only measures how children use the phone, not how they use other electronic devices or do other 'near work,' such as reading or writing on paper, she pointed out.
But other devices are being developed to address these challenges. RangeLife, which has a 940 nm laser and a sensor mounted on spectacles, was developed by Ostrin and her colleagues to calculate the distance from the spectacles to an object by measuring the time between the emission of a signal and the signal's return to the sensor after it is reflected from the object.
The principle behind the commercially available Clouclip device is similar.
Research conducted in Ostrin's lab so far supports the finding Xu reported — that children hold their devices closer to their faces than adults — but it also suggests differences in behavior for print and electronic media, Ostrin said.
And animal studies have suggested that interrupting periods of near work can alleviate the risk for myopia.
A drawback to devices mounted on spectacles is that children don't always want to wear them. "The child has to be excited to wear the glasses or they won't be compliant," Ostrin acknowledged. But "a lot of children enjoy being in research studies. And we found a lot of children who don't wear glasses would like to wear glasses."
Future studies should compare Asian and white children, myopic and emmetropic children, and children who have and have not been treated for myopia, Xu suggested, noting that only longitudinal studies will show a correlation between viewing behavior and myopia.
"Please stay tuned and we will have reports of our ongoing research later," she said.
In the meantime, clinicians will likely get questions from parents that are difficult to answer. "There is a lot of concern about whether electronic devices are affecting children's eyes, even though nearsightedness was increasing before the advent of these devices," Ostrin said. "I am conflicted about giving parents advice when it's not evidence-based."
She does, however, recommend that children spend as much time as possible playing outside.
Association for Research in Vision and Ophthalmology (ARVO) 2020 Annual Meeting.
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