The Rate of Myopia Progression in Chinese Children is Slower in Summer than in Winter

Abstract

Purpose: : To characterize seasonal variations in myopic progression in Chinese children

Methods: : Data are presented for 98 children who wore single-vision spectacles in two clinical trials conducted at Zhongshan Ophthalmic Center for the Vision CRC Myopia Control Study. Children were 6-16 yrs old in the first trial and 6 to 12 yrs in the second. Refractive error and axial length data were obtained 6-monthly by cycloplegic autorefraction and partial coherence interferometry respectively. Progression rates were defined for the first and second 6 months of the 12 months studied. Data were classified in terms of summer, winter or other months, based on the mid-month of the 6-month period between visits; June through September as summer; December through March as winter. Guangzhou has 8 weeks of summer school holidays during July/August and one month of winter holidays during January/February.

Results: : The mean 6-month spherical equivalent progressions were -0.25±0.24D, -0.42±0.24D, and -0.57±0.33D for summer, other, and winter months, respectively (p<0.001) and for axial elongation 0.12± 0.11mm, 0.20±0.11mm and 0.25±0.12mm (p<0.001). Post-hoc analysis showed data for each season were different to each other at the p=0.05 level, with the exception of axial length for other months versus summer (p=0.085).

Conclusions: : The children exhibited less than half the myopia progression and axial elongation in summer months as they did in winter. These results demonstrate the importance of taking into account the time of year when conducting studies of myopia progression and clinical trials of potential treatment strategies for myopia. Ambient light levels and higher levels of outdoor activities in summer versus winter may be contributing factors to these substantial differences in rates of myopia increase and their relative influences need to be determined.

Clinical Trial: : ChiCTR, TRC 00000029

Keywords: myopia