It’s become conventional wisdom that kids who spend more time outdoors have lower rates of myopia. That relationship gains further credence from a recent Chinese study showing that a large amount of time spent outdoors may reduce the risk of myopia by 31%; however, extra hours outside don’t appear to mitigate myopia progression, new research in BMC Ophthalmology suggests. The study also found that a higher level of outdoor time is a protective factor for children with myopic parents.
The study included 1,388 first-, second- and third-graders. Out of the initial group, 1,294 students (about 93%) returned for follow-up.
Children underwent noncycloplegic refractometry every six months and axial length (AL) measurements every year. At the conclusion of the study, students completed a questionnaire about their near work activity and time spent outdoors, and their parents answered a questionnaire regarding their background and history of myopia.
Some key highlights of the study:
- Children with initial but no myopia at the end of the investigation spent more time doing outdoor activities compared with those with new-onset myopia (1.92 hours/day vs. 1.81 hours/day).
- Elongation of AL in children with a high level (more than 2.5 hours/day) of outdoor time (0.22mm/year) was lower than those who spent less (1.5 or fewer hours/day) time outdoors (0.24mm/year).
- The proportion of subjects experiencing rapid myopia progression (-0.5D/year or less) was 16.7%, 20.2% and 31.5% among children with no myopic parent, one myopic parent and two myopic parents, respectively.
- AL elongation in children among different numbers of myopic parents was significantly different.
- A high level of outdoor time was a protective factor for children with one myopic parent.
- Children with new-onset myopia had a higher proportion of two myopic parents than those with initial and final non-myopia (51.5% vs. 34.3%).
“We found that a high level of outdoor exposure had a remarkable influence on the risk of new myopia for children even with one myopic parent. Therefore, it is suggested that time spent on outdoor activities for children with myopic parents should be increased,” the researchers wrote in their paper.
Jiang D, Lin H, Li C, et al. Longitudinal association between myopia and parental myopia and outdoor time among students in Wenzhou: a 2.5-year longitudinal cohort study. BMC Ophthalmol. January 6, 2021. [Epub ahead of print].