Was outdoor time or physical activity more closely linked to new childhood myopia?

Details

Time spent in “sports/outdoor activity” had previously been negatively associated with new myopia in childhood. The researchers investigated time outdoors and physical activity separately.

Participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) underwent noncycloplegic autorefraction at ages 7, 10, 11, 12 and 15. At each visit, they were classified as myopic (≤−1 diopters) or emmetropic/hyperopic (≥−0.25 diopters); the number assessed ranged from 4,837 to 7,747. Physical activity at age 11 was measured objectively with an accelerometer worn for one week. Outdoor time was assessed through a parental questionnaire when the children were 8–9 years old. The researchers used Cox regression to examine variables associated with new myopia.

Using all available data, both outdoor time and physical activity were associated with new myopia, with a larger effect for outdoor time. Results were similar when analyses were restricted to children classified as either nonmyopic or emmetropic/hyperopic at age 11. Among children who were nonmyopic at 11, the hazard ratio for new myopia was 0.66 (95% confidence interval 0.47–0.93) for high versus low outdoor time, and 0.87 (95% confidence interval 0.76–0.99) per standard-deviation-unit increase above average in moderate/vigorous physical activity.

Outdoor time predicted new myopia independently of physical activity level. The researchers suggested that the stronger association for outdoor time meant the previously reported link with “sports/outdoor activity” mainly reflected information about time outdoors rather than physical activity.