Myopia Onset and Shifts Reduced With Increased Outdoor Time

An increase in time spent outdoors may decrease the risk of myopia onset or shifts in children, according to a study published in Ophthalmology. The duration of exposure and light intensity correlated with the protective effect of outdoor time.

Researchers conducted a prospective, cluster-randomized analysis of 6295 children (age range 6-9 years) from 24 schools. The team stratified participants into 1 of 3 groups using a 1:1:1 ratio: control group (n=2037, no changes in daily outdoor activity), group 1 (n=2329, additional 40 minutes of outdoor time daily) and group 2 (n=1929, additional 80 minutes of outdoor time daily). They performed cycloplegic examination, slit lamp evaluation, and intraocular pressure (IOP) and axial length (AL) measurement at baseline, and monitored participants throughout the 2-year study duration. The investigators also instructed the students to wear a sensory watch that provided data on luminance, UV intensity, and weather. 

The researchers noted cumulative myopia incidences of 24.9%, 20.6%, and 23.8% among the control group, group 1, and group 2, respectively. The team also observed less myopia shifts and AL length growth in groups 1 and 2 compared with the control group (-0.84 D and 0.55 mm; -0.91 and 0.57 mm; -1.04 D and 0.65 mm, respectively). Despite more targeted outdoor exposure time in group 2, the team determined that there were no significant differences in myopia incidence or myopic shift between groups 1 and 2. Researchers attribute this to the groups experiencing similar levels of outdoor time and light intensity despite goals of attaining 40 and 80 extra minutes of outdoor time in groups 1 and 2, respectively (group 1: 127±30 min/day; 3557±970 lux/min and group 2: 127±26 min/day; 3662±803 lux/min).    

“The long-term objective monitoring of outdoor exposure including outdoor time and light intensity in the present trial lent further evidence on effects of outdoor for myopia control and prevention by providing greater insights about outdoor time and light intensity,” according to the investigators. 

Study limitations include a lack of objective monitoring for compliance and a high loss to follow-up. 

Reference

He X, Sankaridurg P, Wang J, et al. Time outdoors in reducing myopia: a school-based cluster randomized trial with objective monitoring of outdoor time and light intensity. Ophthalmol. Published online June 30, 2022. doi:10.1016/j.ophtha.2022.06.024