Seasonal Variation in the Effect of Controlling Myopia Progression Using Orthokeratology.

Objectives: To investigate seasonal variations in the effect of controlling myopia progression using orthokeratology (Ortho-K) in Chinese myopic children.

Methods: One hundred sixteen myopic children aged 7 to 12 years who completed 1 year of Ortho-K treatment. Based on initial time wearing Ortho-K, subjects were classified as four groups: spring group (March-May), summer group (June-August), autumn group (September-November), and winter group (December-February). Axial length (AL) was measured every 3 months for 1 year by partial coherence interferometer. Axial elongation over time and between groups was compared.

Results: The effect of myopia control using Ortho-K was influenced by seasonal variation. After adjusting study groups (type of Ortho-K), age, AL, spherical equivalent refractive error (SER), and ocular parameters at the baseline, the mean axial elongation over 1 year wearing Ortho-K was 0.33±0.08 mm for spring group, 0.30±0.10 mm for summer group, 0.21±0.08 mm for autumn group, and 0.22±0.09 mm for winter group ( P <0.001). Statistically significantly higher mean axial elongation was observed in winter months than that in summer (0.09±0.06 mm vs. 0.05±0.05 mm, P <0.001).

Conclusions: In general, axial elongation in myopic children receiving Ortho-K in summer months was approximately 56% of that in winter. Initial time wearing Ortho-K in autumn/winter months, the effect of myopia control is better than in spring/summer. Our results indicated that seasonal variation should be taken into account in studies related to Ortho-K.