| Part 1 Change in Corneal Refractive Power along Specific Axes and Its Effect on Axial Elongation in Orthokeratology Treated ChildrenPurpose. To investigate the distribution of corneal refractive power change along three axes (nasal, temporal, and inferior) after orthokeratology (OK). To assess the correlations of the maximum power change along three axes versus axial growth.Methods. Thirty-two Chinese children aged from 9 to 14 were fitted with OK. Inclusion criteria:corrected visual acuity was no worse than 20/20; spherical equivalent refractive error (SER) was between -0.50D and -4.50D in both eyes; with-the-rule astigmatism was less than -1.50D; anisometropia was less than 1.50D; no strabismus at near or distance; no ocular surface disorder affecting tear film or active inflammation; no previous use of contact lens, spectacles other than single-vision spectacle. Uncorrected visual acuity (UCVA), axial length, fluorescein staining test with lens in situ and corneal topography were assessed before enrollment,3 months, and every 6 months after lens delivery. Corneal refractive powers along the nasal, temporal and inferior axes were collected over an 8mm diameter ring in 1mm steps using the sagittal power map (N1～N4, T1～T4, I1～14). The maximum power change along each axis was defined as maxN, maxT, and maxI. Within-subject standard deviation (Sw), test-retest repeatability (TRT), and coefficient of variation (COV) were calculated for corneal apex (Apex), maxN, maxT, and maxI, respectively. The subjects were divided into 2 subcategories, level 1 and level 2, according to whether the value was below or above the average maximum power change along each axis. The correlations of the maximum power changes versus 2-year axial elongation were analyzed using Pearson correlation.Results. There was no significant difference in Apex, maxN, maxT, and maxI among the 3 sets of repeated data (p>0.93, repeated-measures ANOVA). TRTs were 0.06D, 0.27D,0.18D, and 0.44D for Apex, maxN, maxT and maxl, respectively. COVs were 0.05%,0.22%,0.16%, and 0.36% for Apex, maxN, maxT and maxI, respectively. Twenty-seven subjects completed the 24-month study. The baseline age, SER, AL, and apical corneal power were 10.37±1.18 years,-2.57±0.90 D,24.50±0.60 mm, and 43.46±1.02 D, respectively. There were no significant differences in these variables between the two subgroups of N level, T level, and I level. After OK treatment, statistically significant steepening (p<0.05, Bonferroni test) was observed at the nasal 2mm and 3mm, temporal 3mm, and inferior 2mm,3mm, and 4mm locations compared with the apical center. AL increased significantly throughout the 24-month observation period (p<0.001, repeated-measures ANOVA). Changes in corneal refractive power significantly affected axial elongation (nasal, p=0.001; temporal, p=0.011; inferior, p=0.001; repeated-measures ANOVA). Two-year axial elongation in patients with larger corneal power changes (level 2) was reduced by 54%-69% compared with those with smaller corneal power changes (level 1). Maximum power changes along the three axes were negatively correlated (p<0.05, Pearson correlation) with 2-year axial growth. Conclusions. The repeatability of Apex, maxN, maxT and maxl measurements are fairly acceptable after OK treatment. Corneal relative peripheral power along nasal, temporal and inferior axis significantly increased from the baseline. Subjects with larger magnitude of corneal relative peripheral power change along specific axes after OK treatment experienced slower axial elongation.Part 2 Corneal Power Relative Myopia Shift and Its Predictive Effect on Axial Elongation in Orthokeratology treated childrenPurpose. To investigate the distribution of average corneal ring power after OK lens. To assess the correlation of corneal power relative myopia shift (CPRMS) versus axial elongation.Methods. Eighty-eight myopic children aged between 7 and 12 were fitted with OK lens. Inclusion criteria:corrected visual acuity was no worse than 20/20; SER was between -0.50D and -4.50D in both eyes; with-the-rule astigmatism was less than-1.50D; anisometropia was less than 1.50D; no strabismus at near or distance; no ocular surface disorder affecting tear film or active inflammation; no previous use of contact lens, spectacles other than single-vision spectacle. UCVA, cycloplegic autoreraction, AL, fluorescein staining test with lens in situ, and corneal topography were assessed before enrollment,3 months, and every 6 months after lens delivery. Corneal axial refractive power at the apex and the average powers on the rings of 0.5-7.2mm diameter (0.1mm interval) were measured using Pentacam. The average ring power of 0.5-7.2mm after OK treatment were compared with corneal apical power (one-way ANOVA, post hoc Bonferroni correction). Corneal apical power and average ring powers were put into MATLAB and corneal power relative myopia shift (CPRMS) was calculated using spline interpolation method (0.01mm spline width). SER, AL, corneal apical power, axial growth, corneal apical power change (CAPC), and CPRMS at every visits were compared (repeated-measures ANOVA, post hoc Bonferroni correction). The average ring powers of 0.5-7.2mm diameter were compared with corneal apical power after OK treatment (one-way ANOVA, post hoc Bonferroni correction). Partial correlations of 2-year axial growth versus scotopic pupil diameter, baseline SER, CPRMS, and CAPC were tested in pairs, with age and gender as control factors. The correlation of CAPC versus CPRMS was tested by Pearson correlation. Results of p<0.05 was considered as significant difference.Results. The baseline age, gender (M/F), SER, AL, corneal apical power of the completed cases (64 subjects) were as following:9.6±1.7years,23/41,-2.88±0.96D, 24.53±0.61mm, and 43.47±1.03D, which were found no significant difference compared with the dropouts (24 subjects). For the 64 completed subjects, SER was reduced from -2.88±0.96D to -0.20±0.85D after 3 months, no significant difference was found between any two latter visits (p≥0.453, post hoc Bonferroni correction); 2-year axial growth was 0.37±0.27mm, AL at 18- and 24- month visits were significantly different from the baseline (p<0.05, post hoc Bonferroni correction); CAPC was 2.86±1.01D after 3 months, no significant difference was found between any two latter visits (p≥0.229, post hoc Bonferroni correction); CPRMS was 10.84±5.28D·mm after 3 months, no significant difference was found between any two latter visits (p>0.999, post hoc Bonferroni correction). Corneal apical power was reduced from 43.47±1.03D to 40.61±1.23D after 3 months. The average ring power increased from the center to the peripheral, reaching the peak of 42.80±1.01D on the 5.8mm ring. Ring powers of 2.8-7.2mm were significantly larger than corneal apical power (p<0.05, post hoc Bonferroni correction). Scotopic pupil diameter was not significantly correlated to 2-year axial growth (p=0.169, partial regression); baseline SER was positively correlated to 2-year axial growth (p=0.042, r=0.298, partial regression); CPRMS was negatively correlated to 2-year axial growth (p<0.001, r=0.624, partial regression); CAPC was negatively correlated to 2-year axial growth (p<0.001, r=0.592, partial regression). CAPC was positively correlated to CPRMS (p<0.001, r=0.916, Pearson correlation).Conclusions. Corneal average ring power decrease in the central part after OK treatment and increased from the central to the peripheral cornea. Both CPRMS and CAPC were negatively correlated to axial growth. CAPC was positively correlated to CPRMS. |
