"Smartphone use associated with higher myopic refractive errors in teenagers", finds Study

An early onset of myopia results in higher degrees of myopia in adulthood. This can lead to visual impairment and even blindness due to retinal complications later in life. The rise in myopia prevalence in the last decade is caused by many lifestyle and behavioural changes. For instance, spending less time outdoors is an established risk factor; the role of prolonged near work is still debated but many reports conclude an association.

In the last years, researchers have speculated that smartphone use is an additional risk factor for myopia. Time spent on smartphones adds considerably to the total hours spent on near work among teenagers.

Smartphone use is prone to underreporting and therefore difficult to determine by questionnaire. For the current study, Clair A. Enthoven and team developed a smartphone application (the Myopia app) that registered smartphone use and face-to-screen distance electronically to allow for objective measurements. Authors assessed the association between smartphone use, outdoor exposure and refractive error as measured by the Myopia app and self-reported outdoor exposure.

A smartphone application (Myopia app) was designed to objectively measure smartphone use and face to screen distance, and to pose questions about outdoor exposure at regular intervals. Participants underwent cycloplegic refractive error and ocular biometry measurements. Mean daily smartphone use was calculated in hours per day; continuous use in the number of episodes of 20 minutes on screen without breaks. Linear mixed models were conducted with smartphone use, continuous use, and face to screen distance as determinants, and spherical equivalent (SER) and the ratio of axial length and corneal radius (AL/CR) as outcome measures stratified by median outdoor exposure.

Teenagers aged 12 to 16 years old from two cohorts were enrolled in the study; participants of the Myopia App Study (MAS), and the Generation R study. The MAS participants were recruited from six secondary schools in semi-urban areas in the Netherlands. Generation R was a large, prospective population-based birth-cohort in which 9778 pregnant mothers were enrolled between 2002 and 2006. The app and ophthalmic measurements were performed between November 2018 to December 2019 in both cohorts.

• The teenagers were on average 13.7 (0.85) years old, 54% of them were girls. The teenagers spent on average 3.71 (1.70) hr/day on their smartphone on schooldays and 3.82 (2.09) hr/day on non school days with an average face to screen distance of 29.1 (6.25) cm.

• Myopia prevalence was 8.9%. During schooldays, total smartphone use was on average 3.71 (1.70) hr/day, and was only borderline significantly associated with AL/CR (β=0.008, 95%CI=-0.001, 0.017) and not with SER.

• Continuous use was on average 6.42 (4.36) episodes of 20 minutes use without breaks/day, and was significantly associated with SER and AL/CR (β=-0.07, 95%CI=-0.13, -0.01; β=0.004, 95%CI=0.001-0.008, respectively).

• When stratifying for outdoor exposure, continuous use remained only significant for teenagers with low exposure (β=-0.10, 95%CI=-0.20, -0.01 and β=0.007, 95%CI=0.001-0.013 for SER and AL/CR, respectively).

• Participants with myopia had a more negative SER, larger AL/CR and axial length, compared to participants without myopia.

• Smartphone use during weekends was not significantly associated with SER and AL/CR, nor was face to screen distance.

• Variables that differed between the MAS cohort and Generation R were age (p=0.02), ethnic background (p<0.001), and outdoor exposure during schooldays (p=0.01).><0.001), and outdoor exposure during schooldays (p=0.01). Differences between children included in the analysis and those excluded regarding sex, SER, myopia, axial length and AL/CR were not observed.

In this study, authors used a mobile application to determine smartphone use in relation to refractive error. They showed that those with more episodes of continuous use had a more myopic refractive error. This association disappeared in teenagers with high outdoor exposure, suggesting that outdoor exposure may moderate this effect.

Smartphone use is a relatively new behaviour among our youth. In this study, smartphone use was 3.71 hr/day during schooldays according to our Myopia app, which is comparable with the 4 hr/day among 19-year-old university students from the United States measured with the app Moment.

Authors observed a particular association with continuous use; SER was -0.07 D more myopic and AL/CR 0.005 larger for each extra episode of 20 minutes continuous use. SER was -0.10 D more myopic and AL/CR 0.008 larger for each hour of daily smartphone use, but this association was not significant (p=0.22 for SER and p=0.07 for AL/CR). Continuous near work may be a more important risk factor than time spent on near work, suggesting that regular breaks during near work (including smartphone use) will help prevent teenagers from myopia.

Researchers concluded, "Our study showed that Dutch teenagers use their smartphone almost 4 hours per day. A higher number of episodes of >20 minutes continuous use was associated with more myopic SER and a larger AL/CR. This association was not present in teenagers with high outdoor exposure, suggesting that outdoor exposure moderates the association. This study suggests that frequent breaks should become a recommendation for smartphone use in teenagers. Since smartphone use is becoming increasingly popular, awareness of the potential negative consequences of prolonged smartphone use is warranted. The 20-20-2 rule as recommended earlier remains good advice. Future large longitudinal studies will allow more detailed information on safe screen use in youth."

Source: Enthoven CA, Polling JR, Verzijden T, Tideman JWL, Al-Jaffar N, Jansen PW, Raat H, Metz L, Verhoeven VJM, Klaver CCW, Smartphone use associated with refractive error in teenagers; the Myopia app Study, Ophthalmology (2021),

doi: https://doi.org/10.1016/ j.ophtha.2021.06.016.