Seasonal variation in myopia progression and axial elongation: An evaluation of Japanese children participating in a myopia control trial

Purpose: To investigate the seasonal variations in myopia progression and axial elongation in Japanese children. Methods: Ninety-two children who were enrolled in a myopia-control trial and wearing single vision or progressive addition lenses were included in the analyses (mean ± SD age 11.4 ± 1.7 years, mean spherical equivalent refractive error -4.40 ± 1.38 D). Refractive error and axial length were measured every 6 months for 1.5 years by non-cycloplegic autorefraction and partial coherence interferometer, respectively. Myopia progression and axial elongation for each 6-month interval were calculated by subtracting the measure at the end of the interval from that at the beginning. Seasons were classified as summer, winter or others, based on mid-day of the 6-month period between visits. Results: Myopia progression was not significantly influenced by the season. After adjusting study groups (type of spectacles), years and age at the baseline, the mean (±SE) myopia progression was 0.35 ± 0.04 D for summer, 0.28 ± 0.06 D for winter and 0.38 ± 0.04 D for the others. In contrast, axial elongation was significantly influenced by the season, and the mean axial elongation was 0.137 ± 0.010 mm for summer, 0.170 ± 0.013 mm for winter and 0.163 ± 0.008 mm for the others. The seasonal variation in axial elongation, however, was smaller than that previously reported overseas. Conclusions: In Japanese children myopia progression did not slow in summer. Although axial elongation slightly decreased in summer, myopia progression seems to be fairly stable throughout the year.