The Hong Kong progressive lens myopia control study: study design and main findings.

To determine whether the use of progressive addition spectacle lenses reduced the progression of myopia, over a 2-year period, in Hong Kong children between the ages of 7 and 10.5 years.A clinical trial was carried out to compare the progression in myopia in a treatment group of 138 (121 retained) subjects wearing progressive lenses (PAL; add +1.50 D) and in a control group of 160 (133 retained) subjects wearing single vision lenses (SV). The research design was masked with random allocation to groups. Primary measurements outcomes were spherical equivalent refractive error and axial length (both measured using a cycloplegic agent).There were no statistically significant differences between the PAL and the SV groups for of any of the baseline outcome measures. After 2 years there had been statistically significant increases in myopia and axial length in both groups; however, there was no difference in the increases that occurred between the two groups.The research design used resulted in matched treatment and control groups. There was no evidence that progression of myopia was retarded by wearing progressive addition lenses, either in terms of refractive error or axial length.