Associations of near work time, watching TV, outdoors time, and parents' myopia with myopia among school children based on 38-year-old historical data

PURPOSE

To study the prevalence and risk factors of myopia with data from a questionnaire study conducted in 1983 among Finnish school children.

METHODS

School children (n = 4 961) from the 1st, 5th and 8th grades of school (7-, 11- and 15-year-olds) in Central Finland were screened for vision followed by a questionnaire, which was returned by 4 352 (87.7%) participants. Myopia was categorized based on the questionnaire. Items concerned daily time spent on near work and outdoor activities, excluding time spent at school, watching TV and parental myopia and the associations of myopia with these factors were studied.

RESULTS

The prevalence of myopia was 3%, 15% and 27% among the 7-, 11- and 15-year-olds, and if daily near work at home was ≤1 hr, myopia prevalence was 0.5%, 3.3% and 17.6%, respectively. The adjusted risk of myopia for each daily near work hour was OR 1.476 (95% confidence interval 1.099-1.984, p = 0.010), OR 1.346 (1.170-1.584, p < 0.001) and OR 1.206 (1.076-1.352, p = 0.001), in the 3 age groups, respectively. The adjusted risk of myopia for each daily hour spent outdoors was OR 0.764 (0.648-0.900, p = 0.001) in the 11-year-olds and OR (0.840, 0.743-0.950, p = 0.005) in the 15-year-olds. Outdoors time prevented myopia at different levels of near work, although less at the highest levels, and near work increased risk of myopia with the level of outdoors time. If the ratio between near work and outdoors time was ≤0. 5 or >1.5, the prevalence of myopia was 1.4% versus 5.6%, 6.3% versus 24.7% and 15.9% versus 36.9%, among the 7-, 11- and 15-year-olds, respectively. The higher prevalence of myopia among the 11- and 15-year-old girls than boys was explained by more near work and less outdoor time among the girls. Having two myopic parents roughly doubled the risk of myopia compared to if one myopic parent in the 11- and 15-year-olds.

CONCLUSIONS

Myopic parents, greater near work time, less outdoors time, a higher near work/outdoors ratio, and being a girl increased the risk of myopia. Myopia was rare in the 7- and 11-year-olds if daily near work at home did not exceed one hour or if the near work/outdoors ratio was not higher than 0.5. Outdoors time was associated with the prevalence of myopia at all levels of near work, although the association was weaker at the highest level.