Childhood age, time outdoors, and the risk of juvenile-onset myopia

Abstract

Purpose : Several longitudinal studies have demonstrated that children who spend more time outdoors have a lower risk of myopia onset. We wanted to investigate whether this protective effect was consistent across a range of ages in childhood.

Methods : Subjects were children participating in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error study who were non-myopic at baseline visits between the ages of 6 and 12 years (n = 549 to 1854 per age group). Children with incident myopia developed refractive errors of at least -0.75 D in all meridians as measured by cycloplegic autorefraction. Children’s time outdoors (hrs/wk) was assessed at baseline by a survey given to their parents. The risk of myopia onset by 14 years of age was estimated using discrete time survival models as a function of time outdoors adjusting for sex, ethnicity, number of myopic parents, and time spent reading.

Results : The proportion of children who became myopic by 14 years of age was highest for younger baseline ages of 6-8 years (17-19%), decreasing to 7.3% at a baseline age of 12 years. Having 2 compared to 0 myopic parents was consistently associated with increased risk of myopia onset but time spent reading was unrelated to the risk of myopia onset. The protective effect of time outdoors was inconsistent across the range of baseline ages. More time spent outdoors (10 more hrs/wk) significantly reduced the risk of myopia onset for children at baseline ages of 7, 8, 9, and 10 years (OR = 0.69 to 0.81 (95% CI = 0.55-0.86 to 0.67-0.98)). Time outdoors was not associated with a reduced risk of myopia onset for baseline ages of 6, 11, or 12 years (OR = 0.74 to 1.0 (95% CI = 0.52-1.0 to 0.83-1.3)).

Conclusions : The age at which non-myopic children experience increased time spent outdoors appears to influence whether or not that exposure is protective against future myopia onset. The range of ages when increased time outdoors is effective in lowering the risk of myopia onset may be narrower than previously thought. The reason for the lack of effect at the extremes of our age range is unknown. At younger baseline ages it may involve low statistical power or a greater genetic component to risk. Lack of effect at older ages may indicate greater difficulty in preserving emmetropia when the eye is larger and closer to the criterion level of myopia.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.