Abstract
Purpose:
Myopia is predominantly caused by increase of the eye ball’s axial length in childhood. Various studies reported an association between time spent outdoors, near work, and risk of myopia in children. The aim of this study was to investigate whether environmental exposures already influence axial length in children who are just learning to read.
Methods:
The Generation R Study is a multi-ethnic population-based birth-cohort study in Rotterdam, the Netherlands, which includes a total of 6690 children. Visual acuity (LEA charts) and axial length (IOL master) were obtained at the research center at age 6. Cycloplegic refraction was evaluated in those with LogMAR acuity > 0.1 and in those already receiving ophthalmologic care. Data on ethnicity, time spent outdoors and near work activities were obtained by questionnaire. In groups varying in duration of time spent outdoors (<1 hour, 1-2 hours, or >2 hours per day) and near work (<15 min, 15-30 min and >30 min per day) we investigated the association with axial length using linear and logistic regression analysis adjusting for age, gender, ethnicity and height.
Results:
The prevalence of myopia was 1.9% (129 children), and varied from 0.9% in Dutch to 3.2% in non-western immigrants. Axial length ranged from 19,27 mm to 25,05 mm with a median of 22,35 (SD 0,73). 4059 children completed the questionnaires. Time spent outdoors was significantly associated with axial length (22,41 mm for < 1 hr. outdoors vs. 22,33 mm for > 2 hrs., P<0.001). Playing outside < 1 hrs./day increased the risk of more than average axial length by 34% (OR 1.34, 95% CI 1,14-1,58). Time spent on near work was not significantly associated with axial length (P=0.14).
Conclusions:
Time spent outdoors already influences axial length in children who have just started to read. Parents of children at risk of myopia progression should be made aware of the protective effect of outdoor exposure in very young children.
Keywords: 605 myopia •
677 refractive error development •
757 visual development: infancy and childhood