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Alan Kwok-Hei Mok1,2, Cindy Sin-Ting Chung1
1Eye’ni, Hong Kong, People’s Republic of China; 2Department of Anatomy, LiKaShing Faculty of Medicine, The University of Hong Kong, Hong Kong, People’s Republic of China

Objectives: To investigate retrospectively the difference in myopia progression, over about 7 years, between two groups of Hong Kong Chinese myopic children who wore overnight orthokeratology lenses or single-vision spectacles.
Methods: A total of 238 records of children wearing overnight orthokeratology lenses or single-vision spectacles from Eye’ni optical shop (Hong Kong) between January 1999 and December 2009 were reviewed. Refractive and central corneal curvature data with 6-year or a longer follow-up period of 70 patients were retrieved: 34 children (15 boys and 19 girls, aged 9.2 ± 1.8 years) wore orthokeratology lenses and 36 (20 boys and 16 girls, aged 10.2 ± 2.0 years) wore spectacles. Myopic progression was determined as the change of myopia from the baseline to the final visit.
Results: No statistically significant differences (P > 0.05) in age, central flat corneal curvatures, baseline refractive error, or follow-up period were observed between the two groups. Average myopic progression of the overnight orthokeratology contact lens cohort 
(-0.37 ± 0.49 D) was significantly less (< 0.001) than of the single-vision spectacle group (-2.06 ± 0.81 D) over about 7 years.
Conclusion: Our preliminary 7-year data support the claim that overnight orthokeratology contact lenses may be a feasible clinical method for myopic progression control. Prospective and randomized investigations are warranted to overcome the limitations of this retrospective study.