Intensive outdoor activity for 1 week increases choroidal thickness in Japanese schoolchildren: a prospective observational study

Background Outdoor activity is important to prevent myopia progression among schoolchildren, and maintaining the choroidal thickness is important to retard myopia progression. However, no research has reported the effects of short-term intensive outdoor activities on the choroidal thickness. This institution-based prospective observational study aims to assess the impact of outdoor activity for 1 week during a camp program to study ocular parameters including the choroidal thickness. Methods The intensive outdoor activity program included an average of 6.15 +/- 2.98 h of daily time spent outdoors during the camp on subsequent days for 1 week at a low-altitude mountain camp. Twenty-four children participated in this program. Results The main outcome was the change in the choroidal thickness compared with baseline. The data were measured at the beginning and end of the program over the course of 1 week and the changes analyzed. The mean age of the participants (50% female) was 11.5 +/- 0.5 (standard deviation) years, and the mean changes were as follows: the refractive error became more positive, the axial length decreased, and the choroidal thickness (mu m) increased, respectively, by 0.21 +/- 1.35 diopters (P = 0.742), -0.01 +/- 0.02 mm (P = 0.241), and 30.7 +/- 20.3 mu m (P < 0.001). Conclusion The results suggested that intensive outdoor activity for only 1 week increased the choroidal thickness in Japanese schoolchildren.