British Journal of Ophthalmology
Published online June 19, 2020
Several studies have found outdoor time to be associated with reduced myopia prevalence in children. It remains unclear if this effect is mediated directly by being outside or if hormonal changes, such as increased vitamin D from sun exposure, might be responsible. Given the high prevalence of myopia in children with a history of premature birth, Chou et al. set out to evaluate the potential role of both time outdoors and serum vitamin D levels in altering myopia risk among school-aged children born prematurely, some of whom had retinopathy of prematurity (ROP). They found that myopia prevalence was inversely associated with time spent outdoors. However, they did not find a relationship with vitamin D levels; in fact, the majority of participants were deficient in vitamin D irrespective of time spent outdoors.
For this prospective study, the researchers enrolled 99 children (99 eyes) born before 37 weeks’ gestation. The mean age at assessment was 6.8 years. The children were assigned to the myopic or nonmyopic group, based on cycloplegic refraction results. The eye with the lower spherical equivalent was evaluated.
The authors looked for potential relationships between myopia status and prespecified factors, including time spent outdoors, time spent on near-work activities, and serum concentration of 25-hydroxyvitamin D. Exposure times to different activities were estimated from information given by parents in a questionnaire.
The results showed that the mean time spent outdoors was significantly greater for children without myopia (n = 76) than for those with myopia (n = 23): 0.9 versus 0.7 hours per day, respectively. After adjusting for age and gender and incorporating demographic and other variables (e.g., ROP severity, vitamin D level, near-work time, parents’ myopia status) into a multivariable logistic regression model, more time spent outside (hours/day) correlated with lower risk of myopia (odds ratio [OR], 0.13). However, mean serum vitamin D concentrations were similar for the two groups. More than half the study population (57%) was found to have vitamin D insufficiency, defined as 30-50 nmol/L.
In other findings, no significant between-group difference was seen in time spent on near-work activities or watching television. Type I ROP was associated with a higher risk of myopia (OR, 3.82), and mean axial length was significantly greater in myopic children.
The authors cautioned that their study was limited by semiquantitative data on exposure times. For children born preterm, they recommend extending outdoor time as a noninvasive intervention to possibly minimize myopia.
The original article can be found here.