June 2, 2025
By Kevin Chan, OD, MS, FAAO, IACMM
Photo Credit: Dreamstime Photos
A recent study by Ding et al. (2025) investigated the impact of seasonal variations on axial length (AL) elongation in children undergoing orthokeratology treatment for myopia management. The objective of this study is to examine and understand whether seasonal differences affect the rate of axial elongation, thereby potentially influencing treatment efficacy of OrthoK for children.
This study was reported as the first to explore whether seasonal differences matter in clinical efficacy for children treated with OrthoK lenses. It represents a retrospective study of 600 children aged 7 to 13 years undergoing OrthoK lens wear for a minimum of one year. The children also had follow-up visits every three months during OrthoK treatment. Spherical equivalent of the subjects ranged from -0.75 to -5.00D, and with astigmatism <1.50D. The data were generally classified as ‘summer’ or ‘winter’ based on the six-month interval period between visits. AL data measured in each interval was obtained from the right eye for statistical analysis. Several relationships were explored:
- Are seasonal changes related to AL variations?
- Are age and initial AL a key factor in determining seasonal variations in AL?
- Which specific roles (if any) in seasonal changes might contribute to AL variations in children wearing OrthoK lenses?
Seasonal variations matter for OrthoK lens wearers – with caveats
Upon the first year of observation, children wearing OrthoK lenses showed an AL increase of 0.19mm (± 0.15 mm). Interestingly, though, the mid-year AL elongation was found to be reduced by 41.7% in the summer compared to winter (0.07 ± 0.09mm in summer and 0.12 ± 0.09 mm in winter). The result was found to be statistically significant, showing slower rates of AL elongation in the summer months compared to winter months. In addition, the seasonal-based pattern was maintained for three consecutive years of follow-up. Thus, seasonal variations appear to play a crucial role in the rates of axial length elongation among children treated with OrthoK lenses.
Another key finding in this study is that not only does AL growth vary seasonally, but the control of AL growth was also found to change seasonally; control of AL growth was found to be better in the summer than in the winter. For that, the authors hypothesized that increased exposure to sunlight and higher level of light intensity (yet not necessarily due to warmer temperatures) could contribute to better mitigation of AL elongation.
Young Age and Initial Axial Length Associated with Seasonal Variations
The study also showed that children aged 7 to 12 years were found to have slower rates of AL elongation in the summer compared to the winter. Nevertheless, the study found little seasonal-based impacts in children aged 13 years. The authors suggested that children generally experience a natural reduction of axial growth with age. It is plausible that the lack of seasonal difference in adolescents aged 13 or older was likely attributed to the gradual stability of AL with age, and thus improved inhibitory effects of axial growth by OrthoK treatment.
For children treated with OrthoK lenses and with the initial AL less than 26 mm, the study found clinically significant seasonal difference compared to those with longer initial AL greater than 26mm. It was hypothesized that longer AL positively correlates with higher levels of myopia. For children with higher myopia treated with OrthoK lenses, peripheral retinal myopic defocus may yield greater impact than those with lower myopia, regardless of seasonal variations in this study.
Limitations
This study highlights several limitations. First, there was no mention of how seasonal variations affect the changes of AL growth in regard to the multifactorial nature of myopia, including parental history of myopia, sleep time, or near-work demand. Second, no spherical equivalent (SE) data was collected upon the OrthoK treatment. Therefore, little is known about how refractive error data correlates with the seasonal differences.
Conclusions
The study concludes that treatment efficacy of OrthoK in controlling axial elongation may be influenced by seasonal factors, notably with greater treatment effects of AL growth in the summer compared to the winter. Nevertheless, the impact created by seasonality likely dwindles with increasing age and longer initial AL. Collectively, these findings suggest that seasonality plays an emerging role in guiding the interpretations of treatment efficacy by OrthoK. Furthermore, environmental factors, such as sunlight exposure and physical activity, should also be considered when evaluating and optimizing myopia control strategies in children.
Abstract
Seasonal Variation in Axial Elongation in Children with Orthokeratology Treatment
Wenzhi Ding, Chenpei Zhao, Xiaoxiao Li, Weicong Lu, Dongdong Jiang, Yuyin Tian, Lin Leng
Purpose
To investigate seasonal variations in changes of axial length (AL) among myopic children wearing orthokeratology (ortho-K) lenses.
Methods
The data of 600 children receiving ortho-K treatment, aged 7–13 years, were collected retrospectively. Data were classified as ‘summer’ or ‘winter’ based on the midpoint of the 6-month period between visits. For each interval, AL from the right eye was used for statistical analysis. Paired sample t-tests were used to compare the seasonal differences in AL. Furthermore, the relationship between seasonal differences in AL, age and initial AL was analysed using Pearson correlation and multiple regression analysis, respectively.
Results
The AL at 1 year after the initial ortho-K treatment was 24.96 ± 0.85 mm, representing an increase of 0.19 ± 0.15 mm. The semi-annual axial elongation was 0.07 ± 0.09 and 0.12 ± 0.09 mm for the summer and winter, respectively (p < 0.001). Linear regression analysis revealed that the control of axial growth in the summer was better than in the winter (β = −0.05, p < 0.001). A similar seasonal pattern was found among children aged 7–12 years as well as for those with an initial AL < 26 mm (but not in children aged 13 years).
Conclusions
The inhibition of axial growth by ortho-K treatment in the summer months is superior to that seen in the winter. Seasonal differences decrease with age and the initial AL.
