Areal summed corneal power shift is an important determinant for axial length elongation in myopic children treated with overnight orthokeratology

Abstract

BackgroundThe myopia control effect of orthokeratology (OK) varies among individuals. The variation might relate to the proposed ‘areal summation effect’ of lens-induced visual signals. The current study evaluated the areal summed corneal power shift (ASCPS) in myopic children treated with OK lenses and assessed whether the ASCPS achieved at early post-OK visit can predict the lens long-term effect on the axial length (AL) elongation.MethodsStudy participants were 130 myopic children treated with OK lenses (age range, 8 to 15 years) in a prospective study. Corneal topography and AL were measured at baseline and 1, 3, 6, 9 and 12 months after OK lens wear. The ASCPS was derived from corneal topographic measurements and defined as the change in the areal summed corneal relative refraction at the follow-up visit from baseline. The impact of the ASCPS achieved at the 1 month post-OK visit on the 12 months AL elongation was examined using multivariate linear regression analysis.ResultsBaseline age of the study participants was 11.8 ± 1.8 years and their mean spherical equivalent was −3.00±0.92 D. The ASCPS was 6.90±6.09 D*mm at the 1 month visit and remained stable throughout the follow-up period (p=0.5508, repeated-measures analysis of variance). Greater 1 month ASCPS was associated with slower AL elongation at the 12 months visit (β=−0.007, p=0.001).ConclusionsThe ASCPS achieved at early post-OK visit is predictive for the lens long-term effect on the myopic AL elongation. The parameter is potential in guiding the OK lens practice to slow down axial growth in myopic children.

The Spatial Distribution of Relative Corneal Refractive Power Shift and Axial Growth in Myopic Children: Orthokeratology Versus Multifocal Contact Lens

“…AL elongations of the OK and MFCL groups, 0.19 mm and 0.27 mm respectively, were consistent with the previous study (Paune et al, 2015). Our results suggest that the spatial distribution of the RCRPS, rather than the total amount (Zhong et al, 2015;Hu et al, 2019), is critical in slowing myopia progression. First, AL elongation was not related to the peak values, and the significantly greater peak values in MFCL subjects did not lead to smaller AL elongations.…”

“…Subtracting the apex value from each point of the CRPS then derives the relative CRPS (RCRPS) that is related with the myopic shift in defocus on the peripheral retina ( Kang and Swarbrick, 2013 ). Some studies have suggested that RCRPS is strongly associated with AL elongation ( Zhong et al, 2014 , 2015 ; Lee et al, 2018 ; Hu et al, 2019 ). However, existing studies used only simple measures, such as the maximum value of either the whole map ( Lee et al, 2018 ) or along some axes ( Zhong et al, 2014 ), or the summed value within a certain area ( Zhong et al, 2015 ; Hu et al, 2019 ).…”

“…Some studies have suggested that RCRPS is strongly associated with AL elongation ( Zhong et al, 2014 , 2015 ; Lee et al, 2018 ; Hu et al, 2019 ). However, existing studies used only simple measures, such as the maximum value of either the whole map ( Lee et al, 2018 ) or along some axes ( Zhong et al, 2014 ), or the summed value within a certain area ( Zhong et al, 2015 ; Hu et al, 2019 ). Neither maximum nor summed value provides information on the spatial distribution of the RCRPS because lenses with different spatial distributions of RCRPS may have similar maximum and summed values.…”

The Treatment Zone Size and Its Decentration Influence Axial Length Grow in Children With Orthokeratology Treatment

“…24 With a decentered treatment zone or a smaller treatment size, the reverse zone which has positive RCRPS moves closer to the apex. This could lead to a larger summed RCRPS within a 4 mm area, which agrees with the study by Yang et al 38 Given the same pupil size, TZD, and a smaller TZS, the summed RCRPS within the pupillary zone would be much greater in corneal power pro les, which would agree with the larger pupil size often associated with smaller axial growth. 18 We speculate that a smaller TZ and a higher decentered one will move the mid-peripheral ring inside the pupil if it is of the appropriate size, inducing higher optical changes that may be bene cial for myopia control in the subjects receiving orthokeratology treatment.…”

“…[34][35][36] Cho et al 37 hypothesized that the greater the corneal reshaping effect, the greater peripheral myopic defocus, the higher the regulation e cacy in retarding myopia progression. Yang et al 38 suggested that areal summed corneal power shift (ASCPS) in a 4 mm area was a potential predictor of axial elongation in orthokeratology treatment. Wang et al 19 agreed that a maximum value of posttreatment corneal relative power (PCRP) resulted in a higher probability of effective axial elongation control.…”