The prevalence of myopia (nearsightedness) is increasing worldwide and rates over 90% have been reported in Asia. In Denmark myopia has increased from 13% in 2007 to 25% in 2020. The increase is worrying because of the sight-threatening conditions associated with high degrees of myopia such as retinal detachment, macular atrophy, and macular neovascularisation. Thus, we conducted a 1:1 randomised clinical trial to investigate the myopia control efficacy and safety of orthokeratology lenses (OKL) in Scandinavian children with a control group using single-vision spectacles (SVS). For secondary outcomes, we investigated the association between baseline relative peripheral refractive error (RPR) and myopia progression in both study groups, change in RPR in the OKL group and its association with treatment efficacy, and the correlation between cycloplegic spherical equivalent refractive error (SEQ) and axial growth in order to relate the results to clinical assessments for myopic patients. The study subjects comprised 60 myopic, ethnically Scandinavian (Danish) children aged 6 to 12 years with myopia of 0.5 to 4.75 dioptres spherical and up to 2.5 D regular astigmatism in both eyes.
We found that axial growth was significantly smaller in the OKL group compared to the SVS group at all follow-up visits. There were no treatment-requiring or vision-threatening adverse events during the study. RPR changed significantly from baseline to 6-month follow-up in the OKL group. Baseline RPR was not correlated to axial growth in either the OKL or the SVS group. Initial change in RPR was not correlated to the myopia control effect of the OKL. In the SVS group, the correlation between changes in SEQ and axial length at 12-month follow-up was 1 D = 0.55 mm for all subjects, 0.60 mm for male subjects, and 0.53 for female subjects. The correlation is higher in Danes compared to other ethnic groups.
In conclusion, we found that OKL effectively reduced the progression of myopia without severe adverse events. We found that OKL induced relative peripheral myopic defocus, which may contribute to the altered axial elongation. However, neither the degree of RPR change (OKL group) nor the baseline RPR was associated with the myopic progression. Finally, we estimated the correlation between changes in SEQ and axial length which can be used when monitoring myopic progression in ethnically Danish OKL patients in a clinical setting.