Purpose: To determine the relative risk of rapid progression and number needed to treat (NNT) in younger and older children using combined data from the retardation of myopia in orthokeratology (ROMIO) and toric orthokeratology-slowing eye elongation (TO-SEE) studies.
Methods: Data from 136 subjects of two studies, ROMIO and TO-SEE, were retrieved (72 orthokeratology [ortho-k]: 37 ROMIO, 35 TO-SEE; 64 control: 41 ROMIO, 23 TO-SEE) and the myopia control effect on younger (6-8 years) and older (9-12 years) subjects evaluated. The rate of axial elongation was classified as not rapid (axial elongation = <0.36 mm/year) or rapid (axial elongation >0.36 mm/year).
Results: Cumulative frequency curves showed that the younger subjects in the control group had the greatest and most rapid axial elongation at the end of 24 months. In the younger subjects, ortho-k lens wear significantly reduced the risk of rapid progression by 88.8% (P = 0.002). The 2-year NNT for the younger ortho-k subgroup was 1.8, suggesting that treating just two younger subjects with ortho-k would prevent one subject from experiencing rapid progression over a 2-year period of treatment. The 2-year NNT for the older ortho-k subgroup was 11.8, which was statistically insignificant (P = 0.197).
Conclusions: Orthokeratology significantly reduced risk of rapid progression in younger subjects. Treating just two 6- to 8-year-old subjects with ortho-k instead of single-vision spectacles could prevent one subject from developing rapidly progressing axial elongation during this critical 2-year period.