The more time spent engaging in near work and the less time spent outdoors, the more likely a child is to develop myopia, according to researchers. The risk was also more elevated for girls as well as any child whose parents have myopia, according to a Finnish study published in Acta Ophthalmologica.
The study shows associations between near work, outdoor time, and parental myopia with myopia prevalence in school aged children. The researchers reanalyzed data collected in a 1983 questionnaire in Central Finland. Original questionnaire data included all schoolchildren (n=4961) in the first, fifth, and eighth grades—ages 7, 11, and 15—who were screened for visual acuity according to Finnish law on basic health services.
Of the 4961 surveys distributed, 4344 (87.6%) were completed and returned.
The questionnaire collected data on sex, near and distant vision, vision quality without spectacles, age of spectacle receipt, and the purpose of the spectacles; additional questions included those on daily time spent doing homework, reading, and other near work, as well as time spent watching TV and time spent outdoors. Parents were asked about their education and vision, among other items.
Myopia prevalence was 3.2%, 15.4%, and 27.2% among 7-, 11-, and 15-year-olds, respectively. The prevalence of children in these same age groups who had spectacles that improved distance, but not near vision, was 2.7%, 10.3%, and 22.7%.
In 13.7% of cases, the child had a father who had myopia; mothers had myopia in 26.3% of cases, 1 parent had myopia in 30.4% of cases, and both parents had myopia in 4.8% of cases. Myopia in parents was not associated with myopia in children in the 7-year-old group. In the 11- and 15-year-old groups, however, this association was significant and both father and mother myopia was associated with a higher level of basic education.
Myopia prevalence was not significantly different between 7-year-old boys and girls. It was, however, twice as high among girls than among boys in the 11- and 15-year-old groups and was the highest in 15-year-old girls, at 35%.
Among all children, mean daily near work time was 2.28±1.04 hours. TV viewing time was 1.63±0.86 hours, and outdoors time was 2.54±1.00 hours. Children with myopia spent significantly more time participating in near work and less time in outdoor activities compared with children without myopia. However, among 7-year-old girls, the differences between children with and without myopia were statistically nonsignificant.
Results of a binary logistic regression model showed that among 11- and 15-year-old children, myopia risk was increased with more daily near work time and decreased with more daily outdoor time. This difference was the primary driver explaining the difference in myopia prevalence by sex.
Myopia predictors were studied through multiple logistic regression models. Sex, time spent on near work, time spent on outdoor activities, and parent myopia were all used as predictors in models. Among 7-year-olds, near work significantly increases myopia risk. The opposite effect was found for outdoor hours, although this effect was nonsignificant.
Neither parental myopia nor sex were statistically significant predictors of myopia in the 7-year-old age group.
Among 11-year-olds, near work and outdoor time demonstrated similar significant but opposite associations with myopia risk. Compared with boys, girls were at nearly double the risk for myopia; having 1 and 2 parents with myopia increased this risk by 1.66- and 3.29-fold, respectively.
Odds ratio (OR) for near work time was highest in younger children, but OR for outdoor time demonstrated little change by age.
Near work time was less than outdoors time in 56.7% of all children, with a prevalence of myopia of 9.5% vs 21.6% in the remaining children.
In order to determine if spending more time outdoors prevents myopia in children doing either less or more near work, researchers divided the near work and outdoor time variables into 3 categories: <2 hours, 2 to 3 hours, and >3 hours. Multiple logistic regression models were computed separately for each age group. Researchers found that age, sex, time spent on near work and outdoor activities, and parental myopia were all used as predictors of myopia.
In all 3 near work categories, less outdoors time increased myopia risk. A comparison of OR values suggests that the positive influence of increased amount of time outdoors diminished in children who had higher levels of near work time.
Study limitations include the definition of myopia, based solely on “anamnestic information obtained by screening for poor distant and good near vision prior to a questionnaire,” the exclusion of time spent on near work and outdoor activities at school, reducing the total time for each activity, and the use of 40-year-old questionnaire data in the current study.
“More time spent in near work and less time spent outdoors independently increased the risk of myopia,” the researchers explain. “If daily near work time, excluding near work at school, did not exceed 1 hour, the prevalence of myopia was rare among the 7- and 11-year-olds, and the same held true if the ratio between near work and outdoors did not exceed 0.5.”
“The influence of outdoors time in preventing myopia was seen at all levels of near work time, although it was less marked at the highest levels,” the research concludes.
Pärssinen O, Kappinen M. Associations of near work time, watching TV, outdoors time, and parents’ myopia with myopia among school children based on 38-year-old historical data. Acta Ophthalmol. Published online July 21, 2021. doi:10.1111/aos.14980