The Effect Of Corneal Orthokeratology On Corneal Morphology And Ocular Axis

Purpose:To discover cornea morphology change and explore the relationship between the axial length elongation and the distribution of peripheral relative power(PRP)on cornea in myopic children undergoing overnight orthokeratology.Methods:Fifty five children,aged between 8 to 12 years of age,met the inclusion criteria and were enrolled in this study.Axial length and corneal topography were assessed before and 1 year after the start of orthokeratology.The corneal topography was divided as central treatment zone and reverse zone by lens design.The central points with changes less than OD was defined as the central treatment zone.The changes points between OD were defined as the reverse zone.Corneal curve、corneal thickness and corneal optical density was compared before and after orthokeratology.Topography of the axial power was divided into thirty-six 10-degree sections.PRP was calculated as the difference between central and peripheral corneal powers,and a maximal PRP value(PRPmax)was found for each section.The modulation of the PRPs over the 360 degrees was fitted into a model that is composed of three components M,fl and f2.Mean reflects the baseline spherical equivalent,fl reflects the corneal asymmetry associated with orthokeratology lens decentration,and f2 reflects the corneal astigmatism.PRP= mean*(1+ f1 Amp*sin(x+phasel)+f2Amp*sin(2x+phase2)).Multiple logistics regression was applied to identify potential explanatory variables with a statistically significant contribution to axial elongation.Logistic regression was applied to analyze the relationship between axial length growth and model parameters.Results:Corneal curve、center corneal thickness and lens decentration was stable within a week(P<0.05).There is no significant change between corneal optical density after orthokeratology.The mean axial length significantly increased from 24.81 mm at baseline to 25.00 mm 1 year after treatment.However,the distribution was not normal,with a 45 having less than 0.30 mm(success)and 10 having greater than 0.30mm(failure)in axial length elongation.The M component was not significantly different between the success and failure groups(3.37 vs.2.91D,p =0.06).However,F1 and F2 were significantly larger in the success group(1.17 vs.0.64D for fl,p = 0.02;0.85 vs.0.35D for f2,p = 0.03).The odds of having a successful myopic control were significantly associated with the modulation amplitude of PRP.Subjects with a large PRP modulation tend to have small axial length elongation and a larger axial length elongation was more likely to be associated with a small PRP modulation.Conclusions:Corneal morphological changes were a short-term effect after orthokeratology,and the morphological changes of cornea were mostly stable within a week.The probability of having a successful myopia progress control is related to the amplitude of modulation of PRP over the 360 degrees of corneal peripheral zone.An even ring more likely leads to larger axial length growth。An uneven reverse zone increases the chance of having a successful myopic control in children treated with overnight orthokeratology.