Continuous smartphone use tied to refractive error in teens

A recent study involving Dutch teenagers has found that a higher number of episodes of >20 minutes of continuous smartphone use may lead to more myopic refractive errors. Such association does not exist in those with high outdoor exposure.

“This study suggested that frequent breaks should become a recommendation for smartphone use in teenagers,” the researchers said.

A total of 525 teenagers aged 12–16 years from six secondary schools and from the birth cohort study Generation R participated in this cross-sectional population-based study. A smartphone application (Myopia app; Innovattic) was designed to measure smartphone use and face-to-screen distance, as well as to pose questions regarding outdoor exposure.

Participants underwent cycloplegic refractive error and ocular biometry measurements. The researchers used linear mixed models, with smartphone use, continuous use, and face-to-screen distance as determinants and spherical equivalent of refraction (SER) in dioptres (D) and axial-length-to-corneal radius (AL:CR) as outcome measures, stratified by median outdoor exposure.

The mean age of participants was 13.7 years, and myopia prevalence was 18.9 percent. Total smartphone use during school days was 3.71 hours/day on average and was borderline significantly associated with AL:CR ratio (β, 0.008, 95 percent confidence interval [CI], –0.001 to 0.017), but not with SER. [Ophthalmology 2021;128:1681-1688]

Continuous use had an average of 6.42 episodes of 20-minute use without breaks per day and was significantly associated with SER (β, –0.07, 95 percent CI, –0.13 to –0.01) and AL:CR ratio (β, 0.004, 95 percent CI, 0.001–0.008). Stratifying for outdoor exposure confirmed such association only for teenagers with low exposure (SER: β, –0.10, 95 percent CI, –0.20 to –0.01; AL:CR ratio: β, 0.007, 95 percent CI, 0.001–0.013).

Notably, smartphone use during weekends, as well as face-to-screen distance, did not significantly correlate with SER and AL:CR ratio.

“Although the association between screen time and myopia was debatable for a long time, recently, the results of many studies support the presence of such an association,” the researchers said. [Senses and Sciences 2014;1:82-83; Ophthalmic Physiol Opt 2020 Mar;40:216-229; Int J Environ Res Public Health 2020;17:1056; Br J Ophthalmol 2019;103:1803-1809; Prev Med 2020;132:105988]

In addition, previous studies identified reading distance as a risk factor for myopia and reported positive associations for 30, 20, and 33 cm. [PLoS One 2015;10e0134514; Invest Ophthalmol Vis Sci 2008;49:2903-2910; Int J Med Sci 2015;12:633-638]

“The sensitivity analysis in [the present] study showed that a 1-cm-shorter face-to-screen distance was associated with –0.03 D (95 percent CI, 0.02 to –0.08) more myopia, but this association failed to reach statistical significance,” the researchers said. “Face-to-screen distance was not correlated with smartphone use in our study.”

Earlier studies also did not find a link between reading distance and reading time, which adds to the discrepancies in the associations with refractive error for continuous smartphone use and face-to-screen distance. [PLoS One 2015;10e0134514; Invest Ophthalmol Vis Sci 2008;49:2903-2910]

“Future large longitudinal studies will allow more detailed information on safe screen use in youth,” the researchers said.