A New Method to Analyze the Relative Corneal Refractive Power and Its Association to Myopic Progression Control With Orthokeratology

Efficacy of orthokeratology lens with the modified small treatment zone on myopia progression and visual quality: a randomized clinical trial

BACKGROUND

To evaluate the long-term effectiveness of orthokeratology (ortho-K) lenses with small treatment zone (STZ) or conventional treatment zone (CTZ) in controlling axial elongation in children with myopia as well as the impact on visual quality. We also sought to determine the effect of retinal visual signal quality on axial elongation.

METHODS

This is a prospective randomized controlled study. A total of 140 participants (age ranging from 8 to 12 years) were randomly assigned to wear either STZ or CTZ ortho-K lenses. STZ ortho-K lenses design was achieved by changing the depth of reverse zone and the sagitta height of the optical zone. Using the IOL-Master 500, axial length (AL) was measured at baseline and after 6, 12 and 18 months of ortho-K treatment. Spherical aberration (SA) and corneal topographic parameters were obtained by the Pentacam anterior segment analyzer at baseline and the 1-month follow-up visit, and optical qualities were assessed by optical quality analysis system-II (OQAS-II) at baseline and after 1 month of lens wearing. Optical quality parameters mainly included the modulation transfer function (MTF) cutoff, Strehl ratio (SR), objective scattering index (OSI), and predicted visual acuity (PVA).

RESULTS

A total of 131 participants completed the study, including 68 in the STZ group and 63 in the CTZ group. The STZ group had significantly reduced AL elongation compared to the CTZ group after treatment (12 months: 0.07 ± 0.11 mm vs. 0.14 ± 0.12 mm, P = 0.002; 18 months: 0.17 ± 0.15 mm vs. 0.26 ± 0.16 mm, P = 0.002). The topography in the STZ group showed a smaller treatment zone (TZ) diameter (2.50 ± 0.23 mm vs. 2.77 ± 0.18 mm, P < 0.001), a wider defocus ring width (2.45 ± 0.28 mm vs. 2.30 ± 0.30 mm, P = 0.006), and larger values of total amount of defocus (119.38 ± 63.71 D·mm2 vs. 91.40 ± 40.83 D·mm2, P = 0.003) and total SA (0.37 ± 0.25 μm vs. 0.25 ± 0.29 μm, P = 0.015), compared with the CTZ group. Objective visual quality decreased in both groups (P < 0.001). This was evidenced by a greater decrease in MTF cutoff (- 14.24 ± 10.48 vs. - 10.74 ± 9.46, P = 0.047) and SR values (- 0.09 ± 0.07 vs. - 0.06 ± 0.07, P = 0.026), and an increase in OSI value (0.84 ± 0.72 vs. 0.58 ± 0.53, P = 0.019). PVA9% decreased significantly in the STZ group but not the CTZ group. A statistically significant negative correlation was found between the changes in total SA and MTF cutoff values (r =  - 0.202, P = 0.025). AL changes were associated with sex, change of MTF cutoff value, increment of total SA and TZ area.

CONCLUSIONS

Compared with CTZ ortho-K lenses, STZ ortho-K lenses significantly inhibited axial elongation in children with myopia while moderately reducing their objective visual quality. Axial elongation was affected by retinal visual quality, and it may be a possible mechanism for ortho-K slowing myopia progression. Trial registration This trial is registered at Chinese Clinical Trial Registry on November 5, 2019 with trial registration number: ChiCTR1900027218. https://www.chictr.org.cn/showproj.html?proj=45380.

Altering optical zone diameter, reverse curve width, and compression factor: impacts on visual performance and axial elongation in orthokeratology

PURPOSE

To investigate the effects of modifications in back optical zone diameter (BOZD), reverse curve width (RCW), and compression factor (CF) on refractive error changes and axial elongation in myopic children undergoing orthokeratology (ortho-k) over a 12-month period.

METHOD

In this retrospective study, data from 126 myopic children undergoing ortho-k fitting were analyzed. Subjects were categorized into four distinct groups based on lens design parameters: Group A (BOZD 6.0 mm, RCW 0.6 mm, CF 0.75 D); Group B (BOZD 6.0 mm, RCW 0.6 mm, CF 1.25 D); Group C (BOZD 5.4 mm, RCW 0.9 mm, CF 1.25 D); and Group D (BOZD 5.0 mm, RCW 1.1 mm, CF 1.25 D). The study evaluated uncorrected visual acuity (UCVA), corneal topography, and axial length (AL) at intervals, using Linear Mixed Models (LMMs) for time-based changes, and ANOVA or Kruskal-Wallis tests for group differences in AL elongation. A multivariable regression analysis identified factors independently associated with AL elongation.

RESULTS

Within the first day and week, all four groups displayed significant improvements in UCVA and alterations in corneal curvature, which subsequently stabilized. Although UCVA variations between groups were subtle, Group D had less corneal curvature change than Groups A and B initially and exhibited significantly less AL elongation after one year. No significant difference in corneal curvature change or AL elongation was observed between Group C and the other groups. Multiple regression analysis indicated that older baseline age, greater baseline spherical equivalent refractive error, and smaller BOZD were associated with less AL elongation.

CONCLUSION

The study reveals a positive correlation between BOZD and axial length growth over the 12-month period. A pure 0.5 D CF increment demonstrates a nonsignificant impact. This study provides new ideas into optimizing the parameters of ortho-k lenses.

Relative corneal refractive power shift and inter-eye differential axial growth in children with myopic anisometropia treated with bilateral orthokeratology

PURPOSE

To investigate the relationship between relative corneal refractive power shift (RCRPS) and axial length growth (ALG) in bilateral myopic anisometropes treated with orthokeratology.

METHODS

A total of 102 children with myopic anisometropia in this prospective interventional study were randomly assigned to the spectacle group and orthokeratology group. Axial length (AL) and corneal topography was measured at baseline and the 12-month follow-up visit. ALG was defined as the difference between the two measurements, and RCRPS profiles were calculated from two axial maps obtained.

RESULTS

In the orthokeratology group, the ALG in the more myopic eye (0.06 ± 0.15 mm) was significantly smaller than that in the less myopic eye (0.15 ± 0.15 mm, p < 0.001), and the interocular difference in AL significantly decreased following 1-year treatment, from 0.47 ± 0.32 to 0.38 ± 0.28 mm (p < 0.001). However, in the spectacle group, the ALG was similar between the two eyes, and the interocular difference in AL did not change significantly over one year (all p > 0.05). The interocular difference in ALG in the orthokeratology group was significantly correlated with the interocular difference in RCRPS (dRCRPS, β=-0.003, p < 0.001) and the interocular difference in baseline AL (β=-0.1179, p < 0.001), with R2 being 0.6197.

CONCLUSION

Orthokeratology was effective in decreasing the magnitude of anisometropia. The interocular variation in RCRPS is an important factor accounting for the reduction of interocular ALG difference in anisomyopic children post-orthokeratology. These results provide insight into establishing eye-specific myopia control guidelines during orthokeratology treatment for myopic anisometropes.

Machine learning-based nomogram to predict poor response to overnight orthokeratology in Chinese myopic children: A multicentre, retrospective study

PURPOSE

To develop and validate an effective nomogram for predicting poor response to orthokeratology.

METHODS

Myopic children (aged 8-15 years) treated with orthokeratology between February 2018 and January 2022 were screened in four hospitals of different tiers (i.e. municipal and provincial) in China. Potential predictors included 32 baseline clinical variables. Nomogram for the outcome (1-year axial elongation ≥0.20 mm: poor response; <0.20 mm: good response) was computed from a logistic regression model with the least absolute shrinkage and selection operator. The data from the First Affiliated Hospital of Chengdu Medical College were randomly assigned (7:3) to the training and validation cohorts. An external cohort from three independent multicentre was used for the model test. Model performance was assessed by discrimination (the area under curve, AUC), calibration (calibration plots) and utility (decision curve analysis).

RESULTS

Between January 2022 and March 2023, 1183 eligible subjects were screened from the First Affiliated Hospital of Chengdu Medical College, then randomly divided into training (n = 831) and validation (n = 352) cohorts. A total of 405 eligible subjects were screened in the external cohort. Predictors included in the nomogram were baseline age, spherical equivalent, axial length, pupil diameter, surface asymmetry index and parental myopia (p < 0.05). This nomogram demonstrated excellent calibration, clinical net benefit and discrimination, with the AUC of 0.871 (95% CI 0.847-0.894), 0.863 (0.826-0.901) and 0.817 (0.777-0.857) in the training, validation and external cohorts, respectively. An online calculator was generated for free access (http://39.96.75.172:8182/#/nomogram).

CONCLUSION

The nomogram provides accurate individual prediction of poor response to overnight orthokeratology in Chinese myopic children.

Relationship between myopia control and amount of corneal refractive change after orthokeratology lens treatment

BACKGROUND

To evaluate the relationship between amount of corneal refractive change (CRC) after wearing orthokeratology (Ortho-K) lenses and axial length (AL) growth.

METHODS

We retrospectively enrolled 77 patients (77 eyes) aged 8-14 years who wore Ortho-K lenses more than 12 months. We divided the patients into 2 subgroups: spherical equivalent (SE) ≤ -3.0 D and SE > -3.0 D subgroup. The sagittal and tangential curvature maps and corneal topographic data within the 8-mm diameter ring at the baseline and during follow-up visits after wearing Ortho-K lens were recorded in addition to the area, height, and volume of the CRC region. The AL data were recorded at the baseline and during follow-up visits. Multivariate linear regression was conducted to analyze associations between the area, height, and volume of the CRC region, AL elongation, and SE.

RESULTS

The average change in the CRC region was 9.77 ± 0.60 D in height, 16.66 ± 3.61 mm2 in area, and 87.47 ± 8.96 D*mm2 in volume on the tangential diagram after wearing Ortho-K lenses for 3 months. The AL showed a change of 0.19 ± 0.14 mm after 1 year of Ortho-K lens wear (P < 0.05). At 1 year, AL elongation was negatively correlated with the area (P = 0.019) and volume (P < 0.001) of the CRC region. At 1 year, for every 1-mm2 increase in the area and every 1-D*mm2 increase in the volume of the CRC region, the average AL elongation decreased by 0.01 mm and 0.002 mm, respectively, in the multivariate analysis. In patients with SE ≤ -3.0 D, AL elongation was negatively correlated with the CRC-region volume (β = -0.002, P = 0.018), and in patients with SE > -3.0 D, AL elongation was negatively correlated with the CRC-region area (β = -0.017, P = 0.016).

CONCLUSIONS

The AL elongation-control efficacy of Ortho-K lenses may be related to the area and volume of the CRC region.

Comparison of two different orthokeratology lenses and defocus incorporated soft contact (DISC) lens in controlling myopia progression

BACKGROUND

To compare axial elongation in 8-11-year-old myopes wearing orthokeratology (OK) lenses with different back optic zone diameters (BOZD), defocus incorporated soft contact (DISC) lenses, and single-vision soft contact lenses (SCLs).

METHODS

A total of 122 children (aged 8-11 years) with spherical equivalent refraction (SER) between - 1.00 D and - 4.00 D were enrolled in this prospective study and randomly assigned to four groups: 5.0 mm-BOZD OK, 6.2 mm-BOZD OK, DISC, and single-vision SCLs. Children in each group were further divided into subgroups stratified by the average baseline SER: low myopic eyes (SER: - 1.00 D to - 2.50 D) and moderate myopic eyes (SER: - 2.50 D and over). Axial length (AL) was measured at baseline and after one year.

RESULTS

The 5.0 mm-BOZD OK, 6.2 mm-BOZD OK, and DISC groups exhibited significantly slower AL elongation than the SCL group. The proportion of slow progressors (AL elongation ≤ 0.18 mm/year) in the first three groups was 42%, 23%, and 29%, respectively. Furthermore, one-year AL elongation was significantly smaller in the 5.0 mm-BOZD OK group compared with the 6.2 mm-BOZD OK group. Regardless of SER, children in the 5.0 mm-BOZD OK and DISC groups showed comparably slower AL elongation than those in the SCL group. However, fitting with 6.2 mm-BOZD OK lenses significantly retarded AL elongation in moderate myopic eyes, but not in low myopic eyes.

CONCLUSIONS

Overall, 5.0 mm-BOZD OK lenses, 6.2 mm-BOZD OK lenses, and DISC lenses were effective in retarding AL elongation in 8-11-year-old myopes compared with single-vision SCLs, but for children with SER less than - 2.50 D, fitting with 5.0 mm-BOZD OK lenses and DISC lenses yielded better myopia control efficacy compared to wearing single-vision SCLs or 6.2 mm-BOZD OK lenses.

Two-Dimensional Peripheral Refraction and Higher-Order Wavefront Aberrations Induced by Orthokeratology Lenses Decentration

Purpose

The purpose of this study was to explore two-dimensional peripheral refraction and higher-order aberrations (HOAs) induced by orthokeratology lens decentration.

Methods

Two-dimensional peripheral refraction and HOAs in a rectangular field (horizontally 60 degrees and vertically 36 degrees) were obtained using an open-view Hartmann-Shack wavefront sensor. The peripheral field was divided into 8 regions according to a combination of superior (UZ) or inferior (LZ) and a value, 1 (T25 to T30), 2 (T20 to T25), 3 (N20 to N25), or 4 (N25 to N30). The decentration of the lens was evaluated based on the change of power in the front of the tangential corneal map. All measurements were taken at the baseline and 1 month after lens fitting.

Results

In total, 134 myopic children (age = 12.47 ± 1.70 years, SER = -2.44 ± 1.10 diopters [D]) were recruited. In general, horizontally asymmetrical change was observed in relative peripheral refraction (RPR), spherical aberration (SA), and horizontal coma. The root-mean square of higher order aberration (RMSHOA) and vertical coma demonstrated radial symmetrical change and vertically asymmetric change, respectively. Relative peripheral myopia was significantly increased after the treatment, with more myopic refraction in the temporal side. RPR changes in UZ2, UZ3, UZ4, LZ1, and LZ2 were related to the amount of lens decentration (r ≈ 0.4, P < 0.05). All HOAs increased after lens fitting (around 0.03 um, 0.02 um, 0.04 um, and 0.41 um for SA, horizontal COMA, vertical COMA, and RMSHOA in the periphery region).

Conclusions

RPR and HOAs are related to lens decentration, which might contribute to the efficacy of orthokeratology.

Translational Relevance

The study found a decentration-related optical feature after 1 month of lens wear, which is a suggested protective factor in myopia treatment. The findings might provide new insights for customized contact lens myopia treatment based on optics.

Efficacy of the Euclid orthokeratology lens in slowing axial elongation

PURPOSE

The Euclid Emerald lens designs for orthokeratology have been available in global markets for over 20 years and is used extensively by clinicians for slowing myopia progression in children. This paper comprehensively reviews data from published studies of the efficacy of this lens.

METHODS

A comprehensive systematic search was performed in March 2023 using Medline with the following search terms: orthokeratology AND myopi* AND (axial or elong*) NOT (review or meta).

RESULTS

The original search identified 189 articles, of which 140 reported axial elongation. Of those, 49 reported data on the Euclid Emerald design. Unique axial elongation data could be extracted from 37 papers-14 of which included an untreated control group. Among these, the mean 12-month efficacy-the difference in axial elongation between orthokeratology wearers and controls-was 0.18 mm (range: 0.05-0.29 mm), and the mean 24-month efficacy was 0.28 mm (range: 0.17-0.38 mm). The orthokeratology wearers in 23 studies without an untreated comparison group showed similar axial elongation to those in the 14 studies with a control group. For example, the mean 12-month axial elongation for the studies with controls was 0.20 ± 0.06 mm compared with 0.20 ± 0.07 mm for the studies without controls.

CONCLUSIONS

This extensive body of literature on a single device for myopia control is unique and demonstrates the efficacy of this design in slowing axial elongation in myopic children.

A machine learning-based algorithm for estimating the original corneal curvature based on corneal topography after orthokeratology

OBJECTIVE

To estimate the original corneal curvature after orthokeratology by applying a machine learning-based algorithm.

METHODS

A total of 497 right eyes of 497 patients undergoing overnight orthokeratology for myopia for more than 1 year were enrolled in this retrospective study. All patients were fitted with lenses from Paragon CRT. Corneal topography was obtained by a Sirius corneal topography system (CSO, Italy). Original flat K (K1) and original steep K (K2) were set as the targets of calculation. The importance of each variable was explored by Fisher's criterion. Two machine learning models were established to allow adaptation to more situations. Bagging Tree, Gaussian process, support vector machine (SVM), and decision tree were used for prediction.

RESULTS

K2 after one year of orthokeratology (K2after) was most important in the prediction of K1 and K2. Bagging Tree performed best in both models 1 and 2 for K1 prediction (R = 0.812, RMSE = 0.855 in model 1 and R = 0.812, RMSE = 0.858 in model 2) and K2 prediction (R = 0.831, RMSE = 0.898 in model 1 and R = 0.837, RMSE = 0.888 in model 2). In model 1, the difference was 0.006 ± 1.34 D (p = 0.93) between the predictive value of K1 and the true value of K1 (K1before) and was 0.005 ± 1.51 D(p = 0.94) between the predictive value of K2 and the true value of K2 (K2before). In model 2, the difference was -0.056 ± 1.75 D (p = 0.59) between the predictive value of K1 and K1before and was 0.017 ± 2.01 D(p = 0.88) between the predictive value of K2 and K2before.

CONCLUSION

Bagging Tree performed best in predicting K1 and K2. Machine learning can be applied to predict the corneal curvature for those who cannot provide the initial corneal parameters in the outpatient clinic, providing a relatively certain degree of reference for the refitting of the Ortho-k lenses.

The correlation between modifications to corneal topography and changes in retinal vascular density and retinal thickness in myopic children after undergoing orthokeratology

Purpose

This study aimed to investigate the relationship among changes in corneal topography, retinal vascular density, and retinal thickness in myopic children who underwent orthokeratology for 3 months.

Method

Thirty children with myopia wore orthokeratology lenses for 3 months. Using optical coherence tomography angiography (OCTA), the retina was imaged as 6 × 6 mm en-face images at baseline and 3 months after orthokeratology. Cornea data was acquired by topography and analyzed by customer MATLAB software. The cornea was divided into 3 zones and 9 sectors. The relative corneal refractive power shift (RCRPS) was used in this study. Changes in retinal vascular density (RVDC) and retinal thickness change (RTC) were associated with RCRPS by using spearman test. Statistical significance was set at p < 0.05.

Result

A significant correlation was observed between the RVDC and the RCRPS in many regions (the r was 0.375 ~ 0.548, all p value <0.05). Significant positive correlations were found between RVDC in inner and outer temple regions with RCRPS at inner and outer nasal sectors. There were no significant correlations between RTC and RCRPS in other sectors except in the central cornea and the outer nasal retina (r:0.501, p:0.006). At baseline and 3 months after wearing the orthokeratology lens, no significant differences in the retinal microvasculature or thickness (p > 0.05) were observed at any regions.

Conclusion

The correlation between the cornea and the retina was observed after orthokeratology. Cornea changes may affect regional retinal responses accordingly，which may explain how orthokeratology delays myopia progression partially.

Orthokeratology lenses with increased compression factor (OKIC): A 2-year longitudinal clinical trial for myopia control

PURPOSE

To investigate the effectiveness of orthokeratology (ortho-k) lenses and corneal changes with increased compression factor for myopia control over a 2-year period.

METHODS

Young participants (age: 6-<12 years), with low myopia (0.50-4.00 D) and low astigmatism (≤1.25 D), were recruited and allowed to choose to wear either single-vision spectacles or ortho-k lenses (randomly assigned to compression factor of either 0.75 or 1.75 D). Axial length and cycloplegic refraction were measured at six monthly intervals for two years by a masked examiner. The myopia control effectiveness was determined by axial elongation.

RESULTS

A significant number of control (63 %) dropped out, mainly due to concern about myopia progression (58 %). A total of 75 participants (mean age: 9.3 ± 1.0 years; control: n = 11, ortho-k [0.75 D]: n = 29, ortho-k [1.75 D]: n = 35) completed the study. Considering ortho-k groups only, the mean axial elongation of participants wearing ortho-k lenses of conventional compression factor (0.75 D) and increased compression factor (1.75 D) were 0.53 ± 0.29 and 0.35 ± 0.29 mm, respectively, over the 2-year study period. The between-group differences in corneal health were not significant at all visits.

CONCLUSION

Participants wearing ortho-k lenses of increased compression factor further slowed axial elongation by 34%, when compared with the conventional compression factor without compromising corneal health. Further investigations are warranted to confirm the potential mechanism of an increased compression factor for improved myopia control effectiveness.

The effect of back optic zone diameter on relative corneal refractive power distribution and corneal higher-order aberrations in orthokeratology

PURPOSE

To compare axial elongation, relative corneal refractive power (RCRP) distribution within the pupillary diameter, and corneal higher-order aberrations (HOAs) in myopic children wearing orthokeratology (ortho-k) lenses with different back optic zone diameters (BOZD).

METHODS

Children aged 8-11 years were fitted with 5.0 or 6.2 mm-BOZD ortho-k lenses (groups A and B, respectively). Axial length (AL) and corneal topography were measured at baseline and during the annual visit. RCRP and corneal HOAs were compared between the two groups after one-year treatment. Multivariate linear regression analysis was performed to determine the association between AL elongation and RCRP parameters, corneal HOAs, and other variables between the groups.

RESULTS

After one-year treatment, axial elongation was slower in group A than in group B, with a difference of 0.15 mm. Children in group A showed smaller treatment zone size, smaller 3/4X value (describing the distance from the apex RCRP profile rising to its three-quarter-peak level), greater RCRP sum value within the pupillary area, and higher increases in corneal total HOAs and horizontal coma (Z₃¹). AL elongation was significantly correlated with baseline age, baseline spherical equivalent refraction (SER), treatment zone size, and 3/4X value.

CONCLUSIONS

Ortho-k lenses designed with smaller BOZD increased myopia control efficacy, induced a steeper distribution of the RCRP profile within the pupillary diameter, and induced greater increases in corneal total HOAs and horizontal coma (Z₃¹). Lens-induced RCRP profile within pupillary diameter, rising to its three-quarter-peak level at a smaller distance, may show a better myopia control effect.

Development and Validation of a Simple Nomogram for Predicting Rapid Myopia Progression in Children with Orthokeratology Management

PURPOSE

To develop and validate an ideal nomogram and an online calculator for predicting rapid myopia progression risk in children managed with orthokeratology (ortho-k).

METHODS

Data of children undergoing ortho-k treatment at Shanghai Children's Hospitals between January 2018 and April 2021 were retrospectively assessed. Potential predictors were screened using univariable analyses and a bidirectional stepwise procedure based on Akaike's information criterion. The final model was constructed using multivariable logistic regression and validated using an internal validation cohort. A nomogram and an online calculator were used to present the final model.

RESULTS

In this retrospective study with 1051 eyes of 560 myopia patients, the training cohort included 735 eyes, and the validation cohort included 316 eyes. Among 11 potential predictors of rapid myopia progression considered, the following four variables identified as independent predictive factors were included in the nomogram: age (odds ratio [OR], 0.69; 95% confidence interval [CI], 0.61-0.79), baseline spherical equivalent (OR, 1.53; 95% CI, 1.31-1.79), pupil diameter (OR, 0.56; 95% CI, 0.32-0.97), and horizontal visible iris diameter (OR, 0.57; 95% CI, 0.33-0.97). The mean concordance statistics for the training and validation cohorts were 0.705 (95% CI 0.664-0.747) and 0.707 (95% CI 0.639-0.774), respectively. The online calculator is publicly available (https://hycalculatoronline.shinyapps.io/dynnomapp/).

CONCLUSION

This study developed a simple-to-use nomogram and online calculator that predicted rapid myopia progression risk in children treated with ortho-k, who will likely benefit from early intervention and improved surveillance.

Effect of treatment zone decentration on axial length growth after orthokeratology

Objective

To study the effect of treatment zone (TZ) decentration on axial length growth (ALG) in adolescents after wearing the orthokeratology lenses (OK lenses).

Materials and methods

This retrospective clinical study selected 251 adolescents who were fitted OK lenses at the Clinical College of Ophthalmology, Tianjin Medical University (Tianjin, China) from January 2018–December 2018 and wore them continuously for >12 months. The age of the subjects was 8–15 years, spherical equivalent (SE): −1.00 to −5.00 diopter (D), and astigmatism ≤ 1.50 D. The corneal topography were recorded at baseline and 1-, 6-, and 12-month visits, and the axial length (AL) were recorded at baseline and 6-, 12-month visits. The data of the right eye were collected for statistical analysis.

Results

The subjects were divided into three groups according to the decentration distance of the TZ after wearing lenses for 1 month: 56 cases in the mild (<0.5 mm), 110 in the moderate (0.5–1.0 mm), and 85 in the severe decentration group (>1.0 mm). A significant difference was detected in the ALG between the three groups after wearing lenses for 6 and 12 months (F = 10.223, P < 0.001; F = 13.380, P < 0.001, respectively). Among these, the 6- and 12-month ALG of the mild decentration group was significantly higher than that of the other two groups. Multivariable linear regression analysis showed that age, baseline SE, and 1-month decentration distance associated with the 12-month ALG (P < 0.001, P < 0.001, and P = 0.001, respectively).

Conclusion

The decentration of the TZ of the OK lens affected the growth of the AL in adolescents, i.e., the greater the decentration, the slower the ALG.

Treatment zone decentration promotes retinal reshaping in Chinese myopic children wearing orthokeratology lenses

PURPOSE

To investigate whether the treatment zone (TZ) decentration in orthokeratology (OK) lenses affects retinal expansion in Chinese children with myopia.

METHODS

Children aged 8 to 13 years (n = 30) were assessed over 13 months comprising 12 months of OK lens wear followed by discontinuation of lens wear for 1 month. Corneal topography was measured at 0, 1, 3, 6, 9, 12 and 13 months. TZ decentration of the OK lens was calculated, and subjects were subdivided into a small decentration group (group S) and a large decentration group (group L) based on the median value of the weighted average decentration (d_ave ). Central axial length (AL) and peripheral eye lengths (PELs) at the central retina, as well as 10°, 20° and 30° nasally and temporally were measured at 0 and 13 months under cycloplegia. Second-order polynomial (y = ax²  + bx + c) and linear fits (y = Kx + B) were applied to the peripheral relative eye length (PREL), and the coefficients 'a' and 'K' were used to describe the shape of the eye.

RESULTS

Mean AL growth for one year was 0.28 ± 0.17 mm. In a multiple linear regression model, AL elongation was related to the baseline age (β = -0.41, p = 0.01) and the d_ave (β = -0.37, p = 0.03) (R²  = 0.34, p = 0.002). When compared with smaller d_ave (0.45 ± 0.15 mm), a larger d_ave (0.89 ± 0.17 mm) was associated with slower ocular growth (central: 0.20 ± 0.13 mm vs. 0.35 ± 0.17 mm, p = 0.009; 10° nasal: 0.26 ± 0.18 mm vs. 0.45 ± 0.21 mm, p = 0.02; 10° temporal: 0.17 ± 0.14 mm vs. 0.32 ± 0.19 mm, p = 0.02) and more oblate retina shape ('a': -0.13 ± 0.02 vs. -0.14 ± 0.02, p = 0.02; K_nasal : 0.35 ± 0.11 vs. 0.39 ± 0.09, p = 0.02; K_temporal : -0.42 ± 0.08 vs. -0.46 ± 0.08, p = 0.004).

CONCLUSIONS

Greater TZ decentration with the use of OK lenses was associated with slower axial growth and a more oblate retinal shape. TZ decentration caused local defocusing changes, which may inhibit myopic progression. These findings may have important implications for improving optical designs for myopia control.

The treatment zone decentration and corneal refractive profile changes in children undergoing orthokeratology treatment

Background

To confirm the association between treatment-zone (TZ) decentration and axial length growth (ALG) in children who underwent orthokeratology; and to explore the association between TZ decentration and relative corneal refractive power (RCRP) profile, which was known to be significantly associated with ALG retardation.

Methods

Four hundred myopic children of age 12 years participated in the study, with 200 wearing orthokeratology lenses and the other 200 wearing single-vision spectacle as the controls. Cycloplegic refraction was performed at baseline. Axial length was measured at baseline and 12 months after initial lens wear, and ALG was defined as the difference. In the ortho-k group, TZ decentration and the RCRP map were calculated from the topography map obtained at the 12-month visit. RCRP were summed within various chord radii from the cornea center, and the association to TZ decentration, spherical equivalent (SE), ALG were analyzed with linear regressions.

Results

Compared to the controls, children wearing orthokeratology lenses had significantly smaller ALG over 1 year (0.1 ± 0.15 mm vs. 0.32 ± 0.17 mm, p < 0.001). ALG was significantly and negatively associated with summed RCRP within the central cornea of 2 mm in radius. The mean TZ decentration was 0.62 ± 0.25 mm, and the mean direction was 214.26 ± 7.39 degrees. ALG was negatively associated with the TZ decentration magnitude (p < 0.01), but not the direction (p = 0.905). TZ decentration caused an asymmetrical distribution of the RCRP with the nasal side plus power shifting towards the corneal center. For chord radius ranging 1-2 mm, the association between TZ decentration and the summed RCRP were significant, and the proportion of variance accountable increased with chord radius. For chord radius beyond 1.5 mm, the association between baseline spherical equivalent (SE) and summed RCRP was significant. The portion of variance accountable by SE increased and peaked in 2.5 mm chord radius.

Conclusions

A larger TZ decentration was associated with a larger summed RCRP in the central cornea. It may be one of the possible reasons why TZ decentration is beneficial to retarding myopia progression.

The Effect of Lens Design on Corneal Power Distribution in Orthokeratology

SIGNIFICANCE

This study will enhance our understanding of the effects of orthokeratology lens design on corneal profile, the results of which may be useful in developing future orthokeratology lens designs.

PURPOSE

This study aimed to evaluate the effect of lens design on corneal power distribution after orthokeratology using mathematical methods.

METHODS

Sixty-five subjects were enrolled in this prospective study and assigned to four groups: Euclid with 6.2-mm back optic zone diameter (aged <14 years), Euclid with 6.2-mm back optic zone diameter (aged ≥14 years), double tear reservoir lens with 5.0-mm back optic zone diameter, and double tear reservoir lens with 6.0-mm back optic zone diameter. Manifest refraction and corneal topography were checked at baseline and 1 day, 1 week, 2 weeks, and 1 month after lens wear. Relative corneal refractive power change was calculated by a polynomial function and a monomial function. The maximum relative corneal refractive power change (Ymax) and the corresponding distance from the corneal center (Xmax) were analyzed. Relative corneal refractive power change over time and between groups was compared using repeated-measures analysis of variance.

RESULTS

Refractive reduction and central corneal flattening were seen at all follow-up visits after orthokeratology lens wear, being fastest in the 5.0-mm back optic zone diameter group (P < .001). The cornea steepened in an aspheric way toward the midperiphery and peaked at approximately 2 to 3 mm off the apex. Overall, Ymax was not different among the four groups, but Xmax was smallest in the 5.0-mm back optic zone diameter group (P < .001). At 1/2 Xmax, relative corneal refractive power change of the 5.0-mm back optic zone diameter design was significantly higher than that of the other three groups (P < .001). The power exponent of the monomial of the 5.0-mm back optic zone diameter design was greater than that of the other three groups (P < .001).

CONCLUSIONS

An orthokeratology lens design with smaller back optic zone diameter might yield a faster myopic reduction and a smaller aspheric treatment zone.

Group-Based Trajectory Modeling to Identify Factors Influencing the Development of Myopia in Patients Receiving Orthokeratology

Purpose

To analyze the factors influencing the progression of myopia in adolescents receiving orthokeratology.

Methods

This prospective cohort study collected the data of 378 myopia patients receiving orthokeratology. The follow-up time was 12 months ranging from December 2015 to December 2019. The group-based trajectory modeling (GBTM) was used to identify similar developmental trajectories in the levels of uncorrected visual acuity and changes of axial length elongation. Univariate and multivariate logistic regression analyses were conducted to explore the influencing factors of myopia development in patients wearing orthokeratology.

Results

There was no factor having effect on visual acuity (left) and visual acuity (right) in different trajectories (all P>0.05). The corneal curvature K1 (left) (OR=0.382, 95% CI: 0.188–0.776), corneal curvature K2 (left) (OR=0.362, 95% CI: 0.187–0.699), degree of spherical refraction (left) (OR=0.139, 95% CI: 0.082–0.235) and spherical equivalent (left) (OR=7.276, 95% CI: 3.724–14.215) were factors associated with the changes of axial length elongation (left). The corneal curvature K1 (right) (OR=0.260, 95% CI: 0.116–0.585), corneal curvature K2 (left) (OR=0.272, 95% CI: 0.121–0.610) and degree of spherical refraction (right) (OR=0.129, 95% CI: 0.068–0.244) were correlated with the changes of axial length elongation (right). All P<0.05.

Conclusion

Orthokeratology is a promising method for controlling the progression of myopia. The corneal curvature, degree of spherical refraction and spherical equivalent were factors influencing the changes of axial length elongation in myopia patients wearing orthokeratology. The findings might give a reference for the application of orthokeratology in clinic.

Change in Corneal Power Distribution in Orthokeratology: A Predictor for the Change in Axial Length

Purpose

To investigate the correlation between the change in spatial corneal power distribution and axial length (AL) elongation during orthokeratology (Ortho-k) treatment using mathematical methods.

Methods

Seventy-six subjects aged from eight to 13 years were fitted with Paragon CRT ortho-k lenses. Manifest refraction and corneal topography were checked at baseline and one day, one week, two weeks, one month, three months, six months, nine months, and one year after lens wear. AL was measured at baseline and the six-month and one-year follow-up visits. Relative corneal refractive power change (RCRPC) was calculated by a polynomial function and a monomial function. Factors including age, baseline spherical equivalent refractive error (SER), power exponent and RCRPC were tested against one-year AL growth in a stepwise multiple linear regression model.

Results

A total of 67 subjects completed the one-year study, with nine dropouts. The SER significantly reduced after the first month of lens wear (P < 0.001). AL significantly changed over time (P = 0.0003) with the annual growth being 0.32 ± 0.18 mm. Power exponent and RCRPC were stable throughout the follow-up visits (all P > 0.05). Change of AL was significantly correlated with baseline age (standardized β = −0.292, P < 0.001) and power exponent (standardized β = 0.691, P < 0.001), but not with the other factors being analyzed. The regression equation using baseline age (X₁) and power exponent (X₂) as functions for 1-year AL change (Y) was Y = 0.438-0.034X₁ + 0.309X₂, with R² being 0.752.

Conclusions

The asphericity of the treatment zone may affect axial elongation in children undergoing ortho-k therapy.

Translational Relevance

Because the ortho-k lens design may affect myopia control effect in children undergoing ortho-k therapy, future ortho-k lenses should consider applying these designs to obtain a better myopia control effect in children.

The treatment zone size and its decentration influence axial elongation in children with orthokeratology treatment

BACKGROUND

To investigate whether the treatment zone size (TZS) and treatment zone decentration (TZD) will affect the axial elongation in myopic children undergoing orthokeratology treatment.

METHODS

A self-controlled retrospective study was conducted on 352 children who met the inclusion criteria. Axial length was measured before and at 12 months after the initial lens wear. Corneal topography was measured at baseline and at each follow-up after lens wear. The Corneal topography obtained from the 12-month visit was used to quantify TZS and TZD for each subject. Cycloplegic refraction was required for all children before fitting the orthokeratology lenses.

RESULTS

Axial elongation was significantly associated with age, baseline spherical equivalent (SE), TZS, and TZD with univariate linear regression. In groups with both small and large TZS, axial elongation was significantly decreased with large TZD (both P < 0.01). In groups with both small and large TZD, axial elongation was significantly decreased with small TZS (P = 0.03 for small TZD, P = 0.01 for large TZD). Age, SE, and TZD were significantly associated with axial elongation in multiple regression (all P < 0.01).

CONCLUSION

Relatively smaller TZS and larger TZD may be beneficial in slowing myopia progression in children with orthokeratology treatment.

Development and validation of a prediction model for axial length elongation in myopic children treated with overnight orthokeratology

PURPOSE

To develop and validate a standardized prediction model aiming at 1-year axial length elongation and to guide the orthokeratology lens practice.

METHODS

This retrospective study was based on medical records of myopic children treated with orthokeratology. Individuals aged 8-15 years (n = 1261) were included and divided into the primary cohort (n = 757) and validation cohort (n = 504). Feature selection was primarily performed to sort out influential predictors by high-throughput extraction. Then, the prediction model was developed using multivariable linear regression analysis completed by backward stepwise selection. Finally, the validation of the prediction model was performed by evaluation metrics (mean-square error, root-mean-square error, mean absolute error and R ad 2 ).

RESULTS

No significant difference was found between primary and validation cohort (all p > 0.05). After the feature selection, the crude model was adjusted by demographic information in multivariable linear regression analysis, and five final predictors were identified (all p < 0.01). The interaction effect of age with 1-month change of zone-3 mm flat K was detected (p < 0.01); hence, two final prediction models were developed based on two age subgroups. The validation proved an acceptable performance.

CONCLUSION

An effective multivariable prediction model aiming at 1-year axial length elongation was developed and validated. It can potentially help clinicians to predict orthokeratology efficacy and make valid adjustments. The influential variables revealed in this model can also provide designers directions to optimize the design of lens to improve the efficacy of myopia control.

The Association between Fourier Parameters and Clinical Parameters in Myopic Children Undergoing Orthokeratology

Purpose: To explore how Fourier parameters are associated with axial length growth (ALG) and clinical parameters in children who underwent orthokeratology.Materials and Methods: A total of 267 children received orthokeratology. Baseline cycloplegic autorefraction was performed. Axial length was measured at baseline and one year after the lens dispatch, and the difference was defined as ALG. Corneal topography was performed at the same two visits. Central treatment zone (CTZ) was identified from the difference between the two tangential maps, and its center distance to corneal center was defined as decentration. A relative refractive corneal power (RCRP) map was derived by subtracting the center value from every point on the one-year axial map. It was decomposed into 3 Fourier components: a mean (F0), a single-cycle sinewave (F1), and a double-cycle sinewave (F2). Linear regressions were used to reveal the association between ALG and these parameters.Results: At baseline, the age was 10.18 ± 1.48 year, spherical equivalent (SE) was - 3.10 ± 1.15D, astigmatism was 1.17 ± 0.58D, and axial length was 24.69 ± 0.81 mm. The mean ALG was 0.181 ± 0.22 mm. In multiple regression, ALG was negatively associated with F1 (p < .001), not F0 and F2. Amplitude-wise, F0 and F1 were correlated with decentration (p < .01) and SE (p < .01), and F2 was associated with astigmatism (p < .001). Direction-wise, F1 was correlated with decentration (p < .001) and F2 was associated with astigmatism (p < .001).Conclusions: Among Fourier parameters, F0 and F1 were negatively associated with ALG in myopic children undergoing orthokeratology. Their associations to SE and CTZ decentration may partially explain the effect on ALG retardation.

Blur Detection Sensitivity Increases in Children Using Orthokeratology

Purpose

To investigate changes in blur detection sensitivity in children using orthokeratology (Ortho-K) and explore the relationships between blur detection thresholds (BDTs) and aberrations and accommodative function.

Methods

Thirty-two children aged 8–14 years old who underwent Ortho-K treatment participated in and completed this study. Their BDTs, aberrations, and accommodative responses (ARs) were measured before and after a month of Ortho-K treatment. A two forced-choice double-staircase procedure with varying extents of blur in three images (Tumbling Es, Lena, and Street View) was used to measure the BDTs. The participants were required to judge whether the images looked blurry. The BDT of each of the images (BDT_Es, BDT_Lena, and BDT_Street) was the average value of the last three reversals. The accommodative lag was quantified by the difference between the AR and the accommodative demand (AD). Changes in the BDTs, aberrations, and accommodative lags and their relationships were analyzed.

Results

After a month of wearing Ortho-K lenses, the children’s BDT_Es and BDT_Lena values decreased, the aberrations increased significantly (for all, P ≤0.050), and the accommodative lag decreased to a certain extent [T(31) = 2.029, P = 0.051]. Before Ortho-K treatment, higher-order aberrations (HOAs) were related to BDT_Lena (r = 0.463, P = 0.008) and the accommodative lag was related to BDT_Es (r = −0.356, P = −0.046). After one month, no significant correlations were found between the BDTs and aberrations or accommodative lags, as well as between the variations of them (for all, P ≥ 0.069).

Conclusion

Ortho-K treatment increased the children’s level of blur detection sensitivity, which may have contributed to their good visual acuity.

Is It Possible to Predict Progression of Childhood Myopia Using Short-Term Axial Change After Orthokeratology?

OBJECTIVES

To investigate changes in axial length in children undergoing orthokeratology (OK) and evaluate short-term axial change in predicting post-OK myopia progression.

METHODS

In this retrospective study, the subjects included 70 myopic children aged 8 to 15 years wearing OK contact lenses for more than 3 years. Axial length changes at 0.5, 1, 2, and 3 years relative to the baseline were measured. Patients were evaluated for age, spherical equivalent refraction (SER), pupil size, and half-year axial change using repeated analysis of variance and multivariate linear regression analysis to predict half to 3 year-axial elongation (AE, seventh-36th month post-OK).

RESULTS

The axial length grew significantly during the 3 years; the mean annual axial growth was 0.20±0.12 mm. The half-year axial change was 0.04±0.12 mm. The univariate linear analyses showed that half to 3-year AE was correlated with baseline age (r=-0.393, P<0.001) and half-year axial change (r=0.379, P=0.001), but not pupil diameter (P=0.692) or SER (P=0.673). In a multiple linear regression model, the half to 3-year AE was related with the baseline age (standardized β=-0.312, P=0.007) and half-year axial change (standardized β=0.293, P=0.01). The model was fair (adjusted R=0.21) and statistically significant (F=10.24, P<0.001).

CONCLUSIONS

It is practical to predict long-term AE with half-year axial change for children with OK correction. Therefore, this may aid in fast and timely measures in children who are predicted to have rapid myopia progression.

The Role of Back Optic Zone Diameter in Myopia Control with Orthokeratology Lenses

We compared the efficacy of controlling the annual increase in axial length (AL) in myopic Caucasian children based on two parameters: the back optic zone diameter (BOZD) of the orthokeratology (OK) lens and plus power ring diameter (PPRD) or mid-peripheral annular ring of corneal steepening. Data from 71 myopic patients (mean age, 13.34 ± 1.38 years; range, 10-15 years; 64% male) corrected with different BOZD OK lenses (DRL, Precilens) were collected retrospectively from a Spanish optometric clinic. The sample was divided into groups with BOZDs above or below 5.00 mm and the induced PPRD above or below 4.5 mm, and the relation to AL and refractive progression at 12 months was analyzed. Three subgroups were analyzed, i.e., plus power ring (PPR) inside, outside, or matching the pupil. The mean baseline myopia was -3.11 ± 1.46 D and the AL 24.65 ± 0.88 mm. Significant (p < 0.001) differences were found after 12 months of treatment in the refractive error and AL for the BOZD and PPRD. AL changes in subjects with smaller BOZDs decreased significantly regarding larger diameters (0.09 ± 0.12 and 0.15 ± 0.11 mm, respectively); in subjects with a horizontal sector of PPRD falling inside the pupil, the AL increased less (p = 0.035) than matching or outside the pupil groups by 0.04 ± 0.10 mm, 0.10 ± 0.11 mm, and 0.17 ± 0.12 mm, respectively. This means a 76% lesser AL growth or 0.13 mm/year in absolute reduction. OK corneal parameters can be modified by changing the OK lens designs, which affects myopia progression and AL elongation. Smaller BOZD induces a reduced PPRDs that slows AL elongation better than standard OK lenses. Further investigations should elucidate the effect of pupillary diameter, PPRD, and power change on myopia control.

The Effect of Relative Corneal Refractive Power Shift Distribution on Axial Length Growth in Myopic Children Undergoing Orthokeratology Treatment

PURPOSE

To quantify the spatial distribution of relative corneal refractive power shift (RCRPS) to investigate its association with axial length growth.

METHODS

Eighty myopic children were randomly assigned for fitting with type A or B lenses. Axial lengths and corneal topographies were measured at baseline and the 1-, 6-, and 12-months follow-up visits. Treatment-zone decentrations and sizes were derived from tangential maps. RCRPSs were computed by taking the difference between after-treatment and baseline axial maps and then subtracting the apex value. Values at the same radius were averaged to obtain an RCRPS profile, from which four distributional parameters were extracted: the peak value (Rmax), the location where the profile first reached its half peak (X50), and the powers summed within 4- and 8-mm diameter areas (Sum4 and Sum8, respectively). Linear mixed models were used to analyse the correlation between the AL growth and the distributional parameters.

RESULTS

At baseline, no significant differences were observed between the two groups. After treatment, Axial length growth was significantly smaller in subjects fitted with type-B lenses (0.15 ± 0.16 vs 0.25 ± 0.22 mm, P = .028). Smaller treatment-zones (1.56 ± 0.14 vs 1.75 ± 0.13 mm, P < .01), smaller X50 values (1.56 ± 0.39 vs 1.98 ± 0.28 mm, P < .01), and greater Sum4 values (11.83 ± 6.47 vs 8.14 ± 5.06 D, P = .01) were also observed in subjects wearing type-B lenses. Among the distributional parameters, only X50 was significantly associated with AL growth in the multiple regression analysis (P = .005).

CONCLUSION

The spatial distribution of RCRPS is critical in retarding AL growth, and the ones reaching peak within a shorter distance from the apex may provide better myopia control.