Episodes of continuous smartphone use in teenagers is associated with more myopic refractive errors, particularly in those with low outdoor exposure, according to findings published in Ophthalmology.

Researchers conducted a cross-sectional, population-based study investigating the association between smartphone use and axial length and refractive error in teenagers. The study included teenagers between 12 to 16 years old (n=525) from 6 secondary schools and from the birth cohort study, Generation R. Participants used the Myopia App, a smartphone application designed to measure smartphone use and face-to-screen distance, as well as to pose questions about outdoor exposure at regular intervals.

Investigators measured participants’ cycloplegic refractive error and ocular biometry. Mean daily smartphone use was calculated in hours per day, and continuous use was measured in the number of episodes of 20 minutes on screen without breaks. Mean outcome measures were spherical equivalent of refraction (SER) in dioptres and axial length corneal radius (AL/CR) ratio.

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The study found 18.9% prevalence of myopia. Total smartphone use was 3.71 hr/day on average on school days, and it was only borderline significantly associated with AL/CR (β=0.008), and not with SER. On average, continuous use was 6.42, 20-minute episodes  without breaks each day, and it was significantly associated with SER (β=-0.07) and AL/CR (β=0.004). Continuous use remained only significant for teenagers with low outdoor explosure (β=-0.10 for SER; β=0.007 for AL/CR) when stratifying for exposure. Smartphone use on weekends was not significantly associated with SER or AL/CR, nor was face-to-screen distance. 

The study explains that there is a long-running debate regarding the association between screen time and myopia, but that recent results suggest that one does exist, citing some examples.

“Exposure to screen time before the age of 1 was associated with myopia (prevalence ratio 4.02) among 26,433 preschool children in China,” the researchers note. “Irish school children who spent >3 hr/day on a screen were more often myopic 317 (odds ratio 3.70), and 1 hour increase in computer use was associated with myopia (odds ratio 1.005) in our former study among 9-year-old children.”

The main study limitation was its cross-sectional nature, which hinders casual interpretation of data. The researchers suggest that future studies use a longitudinal design with a larger sample size.


Enthoven CA, Polling JR, Verzijden T, et al. Smartphone use associated with refractive error in teenagers; the Myopia app study. Ophthalmol. Published online July 7, 2021. doi:10.1016/ j.ophtha.2021.06.016.