Which age group might benefit most from orthokeratology?

Paper title: Protective Role of Orthokeratology in Reducing Risk of Rapid Axial Elongation: A Reanalysis of Data From the ROMIO and TO-SEE Studies

Authors: Pauline Cho (1), Sin-Wan Cheung (1)

1. School of Optometry, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China

Date: Jan 2017

Reference:  Cho P, Cheung SW. Protective Role of Orthokeratology in Reducing Risk of Rapid Axial Elongation: A Reanalysis of Data From the ROMIO and TO-SEE Studies. Invest Ophthalmol Vis Sci. 2017 Mar 1;58(3):1411-1416. [Link to open access paper]

Orthokeratology (OrthoK) as myopia control for children has featured in several previous studies and meta-analyses. Two such prospective cohort studies of OrthoK have been re-analysed to combine their data with the aim of assessing the ability of orthokeratology to reduce axial elongation in children.

The retardation of myopia in orthokeratology (ROMIO)¹ study was a randomised control trial involving children with low myopia and low astigmatism that found a 46% slowing effect for axial lengths in children aged 6 to 12yrs. There were also fewer young children (7-8yrs) who experienced rapid axial elongation when wearing OrthoK lenses than those wearing single vision spectacles.

The toric orthokeratology-slowing eye elongation (TO-SEE)² study was a non-randomised trial with children aged 6 to 10yrs who also had low myopia, but with moderate to high astigmatism. There was a slowing effect found of 56% for the OrthoK group compared to spectacle wearers. The odds of faster myopic progression were nearly 15 times greater for single vision spectacle wearers than for OrthoK lens wearers.

The purpose of the study was to revisit the data to determine the relative risk (RR) of myopia progression for those not wearing OrthoK lenses and the number needed to treat (NNT) with OrthoK to prevent one rapid progressing child. The reanalysis included 136 children from across both studies.

OrthoK lenses were worn by 72 children (37 in the ROMIO study and 35 in TO-SEE) and 64 wore single vision spectacles in the control group (41 in ROMIO and 23 in TO-SEE). The myopia control effect was evaluated for young children (6 to 8yrs) and older children aged 9 to 12yrs.

Axial elongation was classified as rapid for changes of 0.36mm or more per year and non-rapid for changes less than 0.36mm.

• Over 24 months, the axial length growth for 6-8yr olds was found to be 0.46±0.22mm when OrthoK was worn and 0.81±0.27mm for the single vision control group.
• For 9-12yr olds, 24-mth axial growth was 0.28±0.26mm when wearing OrthoK and 0.52±0.22mm for the control group.

The younger group were shown to have the largest and fastest progression after 24 months. However, the myopia control effect was also more pronounced for the younger children wearing OrthoK.

The overall relative risk of fast axial progression was reduced by OrthoK treatment compared to wearing single vision spectacles, most significantly for younger children (6-8 years).

The 2-year need-to-treat value for younger OrthoK wearers was 1.8

• This means that by treating two young children with OrthoK over a 2yr period, one child would be prevented from experiencing rapid myopic progression.
• The 2-year NNT for the older OrthoK wearers was 11.8 and statistically insignificant.

OrthoK was found to be effective in reducing the speed of axial length growth, especially in young myopic children. Although we might expect to see faster progression in younger children and therefore a greater myopic control effect from treatment, there were still fewer children with fast axial progression and more with slower progression after a 2-year period of wear.

Eye care practitioners can be reassured that offering OrthoK to younger children can provide a real myopia control benefit from age 6-8yrs old, when axial elongation can be most rapid.

1. A reduction in axial length values (measured shortening) was seen for 14% of the older age group after 2yrs of OrthoK lens wear that was not found for the younger ones. The reason for this is not clear. Previous studies have found that this effect could occur when initially fitted with OrthoK and is thought to be a result of central corneal thinning due to tissue redistribution^1-5 and choroidal thickening.^6-8 Further research into choroidal thickening over time could provide answers as to why this was still apparent after 2yrs, what the relationship is to axial length, if it could be permanent or if a return to longer axial lengths is seen once OrthoK is stopped.
2. The original 2 studies featured in this reanalysis had concentrated particularly on children either with low myopia of 0.50D to 4D and low astigmatism up to 1.25DC (ROMIO study) or children with myopia between 0.75 and 5D and with astigmatism up to 3DC (TO-SEE study). The results from this study may not hold true for children with higher myopia - this has yet to be studied.

Title: Protective Role of Orthokeratology in Reducing Risk of Rapid Axial Elongation: A Reanalysis of Data From the ROMIO and TO-SEE Studies

Authors: Pauline Cho, Sin-Wan Cheung

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.

[Link to open access paper]