Continuous Smartphone Screen Time Linked With Nearsightedness in Teens

By Lorraine L. Janeczko

August 11, 2021

NEW YORK (Reuters Health) - Teens who spend more continuous time on smartphone screens may become more nearsighted than those who take breaks, a population-based study from the Netherlands suggests.

"Dutch teenagers spent almost 4 hours per day on their smartphones," the authors write in Ophthalmology. "Episodes of 20 minutes of continuous use were associated with more myopic refractive errors, particularly in those with low outdoor exposure."

"Frequent breaks should become a recommendation for smartphone use in youth," they advise.

Corresponding author Dr. Caroline C. W. Klaver of Erasmus Medical Center in Rotterdam and her colleagues developed a smartphone application (the Myopia app; Innovattic) that records smartphone use and face-to-screen distance. With this app, they investigated the links between smartphone screen time, refractive error measured by the Myopia app, and self-reported time spent outdoors.

The 525 teenagers in the study ranged from 12 through 16 years of age, attended six schools, and were members of the Generation R birth cohort study. They underwent cycloplegic refraction and ocular biometry, and their smartphone use was measured over five weeks.

The authors examined relationships between smartphone use, continuous screen time of at least 20 minutes, and face-to-screen distance. They also compared spherical equivalent of refraction (SER) in diopters and the ratio of axial length to corneal radius (AL:CR), stratified by high vs. low (above or below median) outdoor exposure.

Overall myopia prevalence was 18.9%. On school days, total smartphone use averaged 3.71 hours per day and showed only a borderline-significant link with AL:CR ratio (beta=0.008; 95% confidence interval, -0.001 to -0.017) and none with SER.

Continuous use of at least 20 minutes without breaks averaged 6.42 episodes per day and was significantly linked with AL:CR ratio (beta=0.04) and SER (beta=-0.07).

When the teens' time outdoors was considered, continuous use remained significant only for those with low outdoor exposure (beta=0.007 for AL:CR ratio; beta=-0.10 for SER). Smartphone use over weekends, and face-to-screen distance, were not significantly linked with AL:CR ratio and SER.

Three eye doctors who were not involved in the study welcomed the research.

Dr. Aaron Zimmerman, a professor of clinical optometry and the chair of continuing education at The Ohio State University College of Optometry in Columbus, told Reuters Health by email, "This study supports previous work suggesting that prolonged use of digital screens is associated with increased risk of developing myopia. Spending more time outdoors, particularly for children and teenagers, seems to negate the effect of prolonged screen time."

"These findings do not surprise me," he added. "Although we do not know the exact level of risk associated with screen time and myopia, it is becoming increasingly clear that screen time is associated with myopia progression."

Dr. Zimmerman recommends educating patients about how spending less time on screens and more time outdoors, and taking frequent breaks from screens, to lower their risk of myopia progression.

"The importance of myopia as a growing global epidemic cannot be understated," Dr. Eric D. Gaier, a pediatric ophthalmologist at Massachusetts Eye and Ear and an assistant professor of ophthalmology at Harvard Medical School in Boston, said.

Dr. Gaier called this a well-conducted, important study, but noted that the study can't say anything about causality. "Likewise," he told Reuters Health by email, "stepping foot outside will not necessarily enable teens to avoid myopia that's potentially due to excessive continuous screen time."

"The approximately 4 hours per day the teenagers spent on their smart phones was probably in addition to their time on the tablets or laptops they used for homework and other things," noted Dr. Esen Akpek, a professor of ophthalmology at the Wilmer Eye Institute of Johns Hopkins University School of Medicine in Baltimore, Maryland.

"These results are important because we can now tell parents to make sure their children do not use these devices continuously for leisure," she told Reuters Health by email. "The results also apply to online learning. Children seem to spend too much time viewing these devices. Instead, they should go outdoors or do sports or other activities."

"Longer-term effects of these devices in relation to other ophthalmic issues - such as dry eye, cataract, and macular degeneration - are unknown," she cautioned.

The authors call for large related longitudinal studies.

Dr. Klaver did not respond to requests for comment.

SOURCE: Ophthalmology, online July 7, 2021.