July 2015
Volume 56, Issue 8
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Visual Psychophysics and Physiological Optics  |   July 2015
Central and Peripheral Corneal Power Change in Myopic Orthokeratology and Its Relationship With 2-Year Axial Length Change
Author Affiliations & Notes
  • Yuanyuan Zhong
    Department of Ophthalmology and Vision Science Eye and ENT Hospital, Fudan University, Shanghai, China
  • Zhi Chen
    Department of Ophthalmology and Vision Science Eye and ENT Hospital, Fudan University, Shanghai, China
  • Feng Xue
    Department of Ophthalmology and Vision Science Eye and ENT Hospital, Fudan University, Shanghai, China
  • Huamao Miao
    Department of Ophthalmology and Vision Science Eye and ENT Hospital, Fudan University, Shanghai, China
  • Xingtao Zhou
    Department of Ophthalmology and Vision Science Eye and ENT Hospital, Fudan University, Shanghai, China
  • Correspondence: Xingtao Zhou, Department of Ophthalmology and Vision Science, Eye and ENT Hospital, Fudan University, 19 Baoqing Road, Xuhui District, Shanghai, China; doctzhouxingtao@163.com
  • Footnotes
     YZ and ZC contributed equally to the work presented here and should therefore be regarded as equivalent authors.
Investigative Ophthalmology & Visual Science July 2015, Vol.56, 4514-4519. doi:10.1167/iovs.14-13935
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      Yuanyuan Zhong, Zhi Chen, Feng Xue, Huamao Miao, Xingtao Zhou; Central and Peripheral Corneal Power Change in Myopic Orthokeratology and Its Relationship With 2-Year Axial Length Change. Invest. Ophthalmol. Vis. Sci. 2015;56(8):4514-4519. doi: 10.1167/iovs.14-13935.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: We assessed the relationship between axial length (AL) change and corneal refractive power change induced by orthokeratology (ortho-k) contact lens wear.

Methods: A total of 88 myopic children aged 7 to 12 years were fitted with ortho-k lenses for overnight wear. Axial length was measured before enrollment and every 6 months after initiation of lens wear up to 24 months. Corneal apical refractive power and the mean power of each concentric ring from 0.5 to 7.2 mm in diameter at 0.1-mm intervals were measured using the Pentacam HR, and compared before and after 3 months of ortho-k lens wear. Summed corneal power change (SCPC) was defined as the sum of relative corneal power change within the central 7.2-mm diameter corneal region. Age, baseline spherical equivalent refractive error (SERE), and SCPC were tested against 2-year AL growth in a stepwise multiple linear regression model.

Results: Of the 88 myopic children who were successfully fitted with ortho-k lenses, 64 completed the 2-year follow-up period. These completed test subjects experienced a mean axial growth of 0.37 ± 0.27 mm. Spherical equivalent refractive error and corneal apical refractive power decreased from baseline values of −2.88 ± 0.96 diopters (D) and 43.47 ± 1.03 D to −0.20 ± 0.85 D and 40.61 ± 1.23 D, respectively, after 3 months of lens wear. The mean SCPC was 10.84 ± 5.28 D·mm after 3 months. Axial elongation was significantly correlated with SCPC (standardized β = −0.573, P < 0.001) and baseline age (standardized β = −0.403, P < 0.001), but not with baseline SERE (β = 0.081, P = 0.396). The regression model using SCPC and baseline age to predict axial elongation was acceptable (adjusted R2 = 0.56) and statistically significant (F2,61 = 41.09, P < 0.001).

Conclusions: Axial elongation in children undergoing ortho-k therapy is negatively correlated with the age of the wearer and summed corneal power change from the central to the mid-peripheral cornea. We speculate that axial elongation is influenced by the extent to which the retinal defocus profile is altered with ortho-k lens wear. (http://www.chictr.org number, ChiCTR-TNRC-11001210.)

The prevalence of myopia in East Asian adolescents, from 53.1% to 96.5% reported by epidemiologic surveys, is the highest in the world.14 Excessive axial length (AL) elongation in high myopia is associated with higher risk of developing sight-threatening complications, such as glaucoma, cataract, retinal degeneration, and retinal detachment.57 
The mechanism underlying myopia development is an ongoing debate. In animal models, some visual experiences, such as hyperopic defocus induced by negative lenses on the whole retina, are known to stimulate axial growth.8 More recent studies have suggested that the peripheral retina, in addition to the central retina, influences refractive development in animals.9,10 These results have important clinical implications as studies involving human subjects suggest that greater amounts of inherent peripheral hyperopic defocus may be associated with early onset of myopia in children.11 Although the authors of the same study group did not find a significant correlation between baseline peripheral hyperopic defocus and subsequent myopia progression in the same cohort,12 growing evidence suggests that AL elongation in children is slower with optical treatments that reduce the peripheral hyperopic defocus often measured in myopes. Whereas conventional bifocal spectacles13 and progressive addition spectacle lenses14 demonstrated only modest myopia control, they also have minimal effects on peripheral defocus. In contrast, dual-focal and multifocal soft contact lenses with a distance-center and near-periphery design, and orthokeratology (ortho-k) lenses exhibited a more effective reduction in peripheral hyperopic defocus, along with a stronger myopia control effect in children.1518 
Modern myopic ortho-k lenses are designed for overnight use, with a reverse geometry back surface design to reshape the cornea during sleep and correct refractive error on lens removal. Using optical coherence tomography and confocal microscopy technology, researchers have established that the central corneal epithelium becomes thinner, while the mid-peripheral cornea becomes thicker, mainly in the stroma, after ortho-k lens wear.19,20 These characteristic morphological corneal changes also correlate with refractive power changes: central corneal flattening corrects axial myopia, whereas mid-peripheral corneal steepening may act to reduce relative peripheral hyperopia.21,22 
Another important aspect of ortho-k lens use in myopes is its potential to reduce myopia progression in children. For example, Cho and Cheung23 reported in their 2-year randomized clinical trial (the ROMIO study) that axial elongation in Asian children wearing ortho-k lenses was on average decreased by 43% compared to those wearing single-vision spectacles. Other studies conducted on subjects of different ethnicities also have reported a decrease in axial elongation of 32% to 55% with ortho-k in comparison with single-vision spectacle or soft contact lens control groups.2428 Although this treatment effect is believed by many to be caused by lens-induced mid-peripheral corneal steepening and consequent myopic shift on the peripheral retina,24 to our knowledge no direct evidence is available to confirm this hypothesis. On the other hand, some factors have been shown to influence axial growth in children undergoing ortho-k therapy. For example, in a recent study, we found that the subjects with greater peripheral corneal power change at some locations along specific axes experienced less axial growth.29 That study, however, limited by the topographer being used, did not continuously measure corneal power in the area of interest associated with ortho-k treatment. The current study used the Pentacam HR (Oculus, Inc., Wetzlar, Germany) system to capture corneal topography data in a more detailed manner, and mathematical software to calculate the summed corneal power change from the apex to mid-periphery after ortho-k lens treatment. 
The main aim of this study was to assess the correlation between 2-year AL change and summed corneal refractive power changes induced by ortho-k contact lens wear. 
Methods
Study Design
This longitudinal, prospective study was conducted at Fudan University, Eye and ENT Hospital (Shanghai, China) between June 2011 and August 2013. This study adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Ethical Committee Review Board of Fudan University Eye and ENT Hospital. 
Subjects
Chinese children who desired ortho-k treatment underwent a series of prescreening ocular examinations, including anterior segment biomicroscopy, cycloplegic manifest refraction, keratometry (ARK-510A; NIDEK, Aichi, Japan), and binocular vision assessment. The inclusion criteria were: age between 7 and 12 years; spherical equivalent refractive error (SERE) between −0.50 and −4.50 diopters (D) in either eye; with-the-rule astigmatism no greater than −1.50 D; anisometropia no greater than 1.50 D; monocular corrected distance visual acuity (CDVA) no worse than 20/20; no active inflammatory or ocular surface diseases; no strabismus at near or distance; no previous use of contact lenses, spectacles other than single-vision spectacles, or any other myopia control modalities (Table 1). Only data of the right eye were analyzed. Detailed explanation of all possible risks was made to subjects' parents, and they signed the written informed consents before the study. 
Table 1
 
Inclusion and Exclusion Criteria
Table 1
 
Inclusion and Exclusion Criteria
After baseline measurements, eligible subjects were fitted with spherical 4-zone ortho-k lenses (Hiline; Marco Vision, Taiwan, China) in both eyes. The lens material was fluorosilicone acrylate (Boston XO), with an oxygen permeability (Dk) of 100 × 10−11 (cm2/sec; mL O2/mL · mm Hg). Lens fitting was performed following the manufacturer's fitting guidelines. In brief, for the first trial lens selection, cycloplegic manifest refraction, horizontal visible iris diameter (IOLMaster; Carl Zeiss, Jena, Germany), corneal flat-K (keratometric value along the flattest meridian restricted to a 3-mm diameter ring; ARK-510A; NIDEK) and corneal eccentricity (over a 10-mm chord diameter; Pentacam HR) were collected to determine the back optical zone radius (BOZR) and the alignment curve (AC) radius. The overall diameter of the lenses ranged from 10.6 to 10.8 mm, the back optic zone diameter (BOZD) was 6.0 mm, and the reverse curve (RC) width was between 0.6 and 0.8 mm. Lens fitting evaluations using fluorescein were performed 1 and 2 hours after lens insertion. Over-refraction was performed before the final lenses were ordered. After lens delivery, subjects were provided with Boston rewetting drops (Bausch & Lomb, Rochester, NY, USA) for daily lens rewetting and lubricating, Boston Simplus multi-action solution (Bausch & Lomb, USA) for daily lens cleaning, rinsing, and disinfecting, and Menicon Progent intensive cleaner (Menicon, Nagoya, Japan) for lens cleaning every 2 weeks. Manuals on lens wear and care procedures were given to the parents. Subjects were required to wear ortho-k lenses every night during the first month. Upon stabilization of refractive error correction, they were instructed to wear their lenses for 6 nights per week with a minimum of 8 hours per night, and not to wear any type of lens on the seventh day. They were instructed to return for study visits 1 day, 1 week, 1 month, 3 months, and every 6 months after lens delivery until 24 months. Those who failed to show up at any of these time points were considered dropouts and excluded from final analysis. At all follow-up visits, subjects were requested to register between 9 and 11 AM, approximately 2 to 4 hours after lens removal. Parents were requested to log their children's wearing schedule and provide this log to the researchers at every face-to-face follow-up visit. Subjects were reevaluated for compliance, visual acuity, corneal topography, and ocular health during every visit. Should they show an unaided visual acuity worse than 20/20, or significant decentration of treatment zone on corneal topography, prescriptions were modified until the manufacturer's recommended “bull's eye” pattern was seen on corneal topography and a visual acuity of 20/20 was reached. Subjects who required lens modifications beyond 3 months from enrollment were excluded from the study analysis. In cases of lens damage, a new lens of the same parameters was prescribed and delivered to the subjects within 1 week. 
Measurements
Refraction.
Cycloplegic manifest refraction was performed before enrollment. Cycloplegia was induced 20 minutes before refraction measurements with 0.5% tropicamide/0.5% phenylephrine eye drops (multidose bottle; Santen, Tampere, Finland). Three drops were administered at 5-minute intervals. 
Axial Length.
Axial length was measured with the IOLMaster at the time of enrollment, and 6, 12, 18, and 24 months after lens delivery. The first five readings with signal-to-noise ratio above 3 and intrasession differences of no greater than 0.02 mm were selected and averaged for data analysis. 
Corneal Topography.
During topography measurement, the Pentacam uses a blue LED slit beam to illuminate a section of the cornea and anterior chamber, and the subject was instructed to fixate on a target in the center of the slit beam. The Pentacam detects the most anterior point of the cornea, the corneal apex, and uses this point as the center of the Scheimpflug camera's rotation point as well as the center of the topography map. It is reasonable to compare curvature and elevation measurements taken before and after procedures that reshape the corneal surface as long as the subject fixated on the same target on both scans. The actual shift in corneal apex after ortho-k treatment in the current study was less than 0.1 mm on average (range, 0.02–0.16 mm; mean ± SD, 0.08 ± 0.05 mm; by comparing the apex position relative to the pupil center in the Pentacam raw data spreadsheet), which had a slight effect on comparisons between the pre– and post– ortho-k topography maps. 
Corneal topography was measured at the time of enrollment and at every follow-up visit after lens delivery until 24 months. Previous study has shown that corneal topography usually stabilizes within 1 month after initiation of ortho-k lens wear.30 Thus, the 3-month topographic outputs were taken as representative of the post–ortho-k topography. Corneal axial refractive power was derived from the axial radius of curvature using an assumed refractive index of 1.3375. To optimize reliability of the Pentacam HR readings, we evaluated the quality of topography maps with the Pentacam HR software and only those with an acceptable quality score as defined by the instrument software (no significant eye movement, blinking, and so forth) were included in the analysis. The mean corneal refractive power of each concentric ring (around the corneal apex) from 0.5 to 7.2 mm diameter at 0.1-mm intervals was automatically calculated by the Pentacam HR software for both pre– and post–ortho-k conditions. 
Previous studies suggest that the posterior corneal curvature remains unchanged3133 or slightly flattened34 during ortho-k treatment. Thus, it was assumed that refractive changes after ortho-k lens wear were limited to changes in the anterior cornea. As previously suggested by other studies, to compare the shape of image shells before and after ortho-k treatment, central refraction was subtracted from peripheral refraction values to derive relative peripheral refraction.17,18 By analogy, in this study, the peripheral corneal power values were normalized to the central corneal power to calculate the relative peripheral corneal power for pre– and post–ortho-k conditions, respectively.29 Then, pre– and post–ortho-k apical corneal powers were transformed to zero value to compare the relative peripheral corneal powers. Summed corneal power change (SCPC) was defined as the sum of relative corneal power change within the area of 7.2 mm diameter. 
For the calculation of SCPC, pre– and post–ortho-k topographic data were imported into MATLAB (Version 7.9; MathWorks, Natick, MA, USA). Spline interpolation method with 0.01 mm spline width was applied to “smooth” the pre– and post–ortho-k corneal power curves. Every spline value of the transformed pre–ortho-k curve was subtracted from that of the transformed post–ortho-k curve to calculate the power difference (pi). All the mean differences within the chord of 7.2-mm diameter around the corneal apex were added up to determine SCPC. These calculations were performed using the following mathematical formula:    
Statistical Analysis
Data were analyzed using SPSS (version 20.0; IBM, Armonk, NY, USA). The Kolmogorov-Smirnov test was used to test the normality of the data. The baseline variables including age, sex, SERE, AL, and corneal apical power of the 64 subjects completing the study and those of the 24 dropouts were compared using independent t-tests except for sex, which was compared using χ2 tests. Corneal apical power, SERE, AL, and SCPC for the 64 subjects who completed the study were compared at each visit using repeated-measures ANOVA. The central and peripheral corneal refractive powers before and 3 months after ortho-k treatment were compared using paired-sample t-tests. 
Factors including age, baseline SERE, and SCPC were tested against 2-year AL growth in a stepwise multiple linear regression model. The F probability test with P values of 0.05 and 0.1 was set for selecting each variable's enter and exit criteria in the model, respectively. 
Results
A total of 88 subjects were successfully fitted with ortho-k lenses within 1 month from study enrollment. During the follow-up period, 24 subjects were discontinued from the study for various reasons (Fig. 1). Consequently, 64 subjects completed the 2-year follow-up study; the dropout rate was 27%. 
Figure 1
 
Follow-up flow chart and details of dropouts.
Figure 1
 
Follow-up flow chart and details of dropouts.
The baseline demographics of the 64 completed subjects and the 24 dropouts are shown in Table 2. There were no significant differences in age, sex, SERE, AL, or corneal apical refractive power between the two groups. For the 64 children who completed the 2-year study, SERE significantly reduced from −2.88 ± 0.96 to −0.20 ± 0.85 D after 3 months of lens wear (P < 0.001) and did not significantly change during the later follow-up visits when compared in pairs (P ≥ 0.453, post hoc Bonferroni correction). Corneal apical power change was 2.86 ± 1.01 D after 3 months of lens wear and stabilized during the later follow-up visits (P ≥ 0.229, post hoc Bonferroni correction, Table 3). Lens decentration (distance between the approximate center of treatment zone and corneal apex) was consistently less than 0.5 mm in all cases. Axial length did not significantly change from baseline until 18 months into the study (0.31 ± 0.22, P = 0.047). The overall increase in AL over 2 years was 0.37 ± 0.27 mm (P = 0.005). 
Table 2
 
Baseline Variables (Mean ± SD) of the Completed Cases and the Dropouts
Table 2
 
Baseline Variables (Mean ± SD) of the Completed Cases and the Dropouts
Table 3
 
Baseline and Follow-up Data (Mean ± SD) of the Right Eyes of 64 Subjects Who Completed the Study
Table 3
 
Baseline and Follow-up Data (Mean ± SD) of the Right Eyes of 64 Subjects Who Completed the Study
The mean corneal refractive power of the rings from 0.5 to 7.2 mm diameter before and after ortho-k treatment are displayed in Figure 2A. After ortho-k treatment, refractive power significantly decreased in the central 5.5-mm area (P < 0.013), remained unchanged between the chords of 5.6 - and 6.3-mm diameter (P = 0.063–0.081), and increased between the chords of 6.4- and 7.2-mm diameter (P = 0.014–0.038), in comparison with baseline values. After 3 months of lens wear, SCPC was 10.84 ± 5.28 D·mm (Fig. 2B, highlighted in gray) 
Figure 2
 
(A) Means and standard errors of corneal refractive power at 0.1-mm steps between the chord of 0.5 and 7.2 mm diameter centered on corneal apex before and after orthokeratology (ortho-k) lens wear. *Significant decrease in corneal power after ortho-k. **Significant increase in corneal power after ortho-k. °No significant change in corneal power after ortho-k. (B) Curves showing relative peripheral corneal power before and after ortho-k lens wear. The areal difference between the two curves, highlighted in gray, is defined as SCPC.
Figure 2
 
(A) Means and standard errors of corneal refractive power at 0.1-mm steps between the chord of 0.5 and 7.2 mm diameter centered on corneal apex before and after orthokeratology (ortho-k) lens wear. *Significant decrease in corneal power after ortho-k. **Significant increase in corneal power after ortho-k. °No significant change in corneal power after ortho-k. (B) Curves showing relative peripheral corneal power before and after ortho-k lens wear. The areal difference between the two curves, highlighted in gray, is defined as SCPC.
Stepwise multiple linear regression analysis, including baseline age, SERE, and SCPC as potential predictive factors, showed that axial elongation was significantly correlated with SCPC (standardized β = −0.573, P < 0.001) and baseline age (standardized β = −0.403, P < 0.001) of the subjects, but not with baseline SERE (β = 0.081, P = 0.396). The regression equation using SCPC and baseline age to predict axial elongation was acceptable (adjusted R2 = 0.56) and statistically significant (F2,61 = 41.09, P < 0.001). The regression equation using SCPC (X1) and baseline age (X2) as functions for 2-year axial growth (Y) was Y = 1.309 − 0.029X1 − 0.065X2. In brief, a higher summed corneal power change and an older starting age of ortho-k treatment were associated with less axial growth in this 2-year study. 
Discussion
Numerous studies have shown that, compared to single-vision spectacle or contact lens control groups, ortho-k contact lens–treated children experience on average 41.7% less axial growth over a 2-year period.2328 However, the variability of myopia control effect among ortho-k–treated subjects is substantial, raising questions as how to screen for the best candidates for this treatment modality. This study found that AL growth was slower in children who started ortho-k lens wear at an older age and who experienced a greater summed corneal power change during ortho-k treatment. 
Cho et al.27 first reported in their 2005 LORIC study that 2-year AL change in ortho-k lens–treated children is negatively correlated with their baseline SERE, with initial higher myopia associated with less axial growth. However, the same authors did not find a significant correlation between these two factors in their later randomized trial (ROMIO study).23 Other studies have investigated the relationship between baseline SERE and axial elongation in children undergoing ortho-k therapy, and controversy exists. As with the LORIC study, Kakita et al.26 and Hiraoka et al.24 found a negative correlation between baseline SERE and axial growth, whereas Santodomingo-Rubido et al.28 did not find a significant correlation between these two factors. In the current study, the contribution of SERE at baseline was much less than that of SCPC in the stepwise multiple linear regression analysis, suggesting that SCPC is a superior predictor for axial elongation to baseline SERE. Summed corneal power change is more likely to be influenced by differences in ortho-k contact lens design, fitting philosophy, and corneal reaction to the ortho-k reshaping process. Therefore, SCPC may be possibly more closely related to the actual visual input, changes in the retinal image shell, and potentially the rate of eye growth, than the change in SERE. The direct influence of corneal power change on refraction across the visual field, however, was not tested in the current study, and warrants further investigation. 
Although it has been suggested that the myopic eye often is characterized by peripheral hyperopic defocus in humans, the impact on axial elongation is not clear.11,12,35 In contrast, animal models have convincingly shown that refractive development is modulated by the sign of imposed optical defocus and that even peripheral hyperopic defocus can promote axial elongation, with the converse being true for peripheral myopic defocus.3638 
In agreement with these animal experiments, optical treatment modalities that appropriately manipulate the effective focus on the peripheral retina in humans could slow myopia progression in children. According to Smith,39 the effectiveness of a treatment is influenced by the extent of the visual field that is manipulated. Accumulating evidence has indicated that this may be true for ortho-k treatment. For example, Chen et al.40 found that in the ortho-k group, children with larger pupil size experienced slower axial elongation compared to those with smaller pupil size, whereas this correlation was not found in the single-vision spectacle lens group. The authors proposed that the pupil might work as a diaphragm to modulate the retinal area receiving myopic defocus induced by ortho-k lens wear. Another study from our group29 investigated the correlation between AL growth and change in peripheral corneal power at 2, 3, and 4 mm away from the apex along the nasal, temporal, and inferior axes after ortho-k lens wear. Results showed that axial elongation was slower in subjects with greater change in refractive power at some of these locations. The current study tested this correlation further by taking the area and extent of corneal power change into account. The advantage of this method over our previous analysis mentioned above is that it documented the corneal power change in a nearly continuous manner across the cornea, and as a result, has minimized missing data in the area of interest. 
Post–ortho-k corneal refractive power significantly decreased within a chord of 5.5-mm diameter around the apex, compared to the pre–ortho-k cornea (Fig. 2A). The definition of the treatment zone in ortho-k, however, remains controversial. While some authors restrict it to the central flattened area (approximately 5.5 mm diameter),21 others prefer to include the mid-peripheral steepened annulus as well.41 In our study, the post–ortho-k corneal refractive power increased slightly, but significantly (by approximately 0.1 D) between the chord of 6.4 and 7.2 mm diameter, but the corneal power change beyond this chord diameter is not known because of the measurement limit of 7.2 mm imposed by the Pentacam HR software. Future updates in equipment and software are required to understand the corneal power change from the apex to the lens edge. 
Another important finding of the current study is that baseline age carries as much weight as corneal power change in the prediction of axial growth following ortho-k treatment. This is in agreement with many previous studies that found a negative correlation between age and axial elongation.23,24,42 However, the “net” influence of ortho-k on axial growth at any given age is not clear without a control group, because an increase in AL is expected in spectacle and ortho-k children of the same ages of those enrolled in this study. A control group would have aided in understanding how much reduction in axial elongation was solely attributed to the effect of ortho-k lens wear and how initial age affected axial elongation in modalities other than ortho-k. The corneal power change, however, is unique to ortho-k lens wear. Further studies with different ortho-k lens designs are warranted. 
In conclusion, axial elongation in children undergoing ortho-k therapy is negatively correlated with the age of the wearer and summed corneal power change from the central to the mid-peripheral cornea. We speculate that axial elongation is influenced by the extent to which the retinal defocus profile is altered with ortho-k lens wear. 
Acknowledgments
The authors thank Chris OFlaherty, Lin Wang, Lingling Niu, and Jiaqi Zhou for technical support, and Mariana Garcia, Pauline Kang, Craig Norman, and Stephanie Ramdass for editorial advice. 
Supported by the Key Project of Science and Technology of Shanghai, Grant No. 11JC1402000. 
Disclosure: Y. Zhong, None; Z. Chen, None; F. Xue, None; H. Miao, None; X. Zhou, None 
References
Fan DS, Lam DS, Lam RF, et al. Prevalence, incidence, and progression of myopia of school children in Hong Kong. Invest Ophthalmol Vis Sci. 2004; 45: 1071–1075.
He M, Zeng J, Liu Y, et al. Refractive error and visual impairment in urban children in southern china. Invest Ophthalmol Vis Sci. 2004; 45: 793–799.
Jung SK, Lee JH, Kakizaki H, et al. Prevalence of myopia and its association with body stature and educational level in 19-year-old male conscripts in Seoul, South Korea. Invest Ophthalmol Vis Sci. 2012; 53: 5579–5583.
Lin LL, Shih YF, Hsiao CK, et al. Prevalence of myopia in Taiwanese schoolchildren: 1983 to 2000. Ann Acad Med Singapore. 2004; 33: 27–33.
Mitchell P, Hourihan F, Sandbach J, et al. The relationship between glaucoma and myopia: the Blue Mountains Eye Study. Ophthalmology. 1999; 106: 2010–2015.
Brown NA, Hill AR. Cataract: the relation between myopia and cataract morphology. Br J Ophthalmol. 1987; 71: 405–414.
Burton TC. The influence of refractive error and lattice degeneration on the incidence of retinal detachment. Trans Am Ophthalmol Soc. 1989; 87: 143–155 discussion 155–157.
Schaeffel F, Glasser A, Howland HC. Accommodation, refractive error and eye growth in chickens. Vision Res. 1988; 28: 639–657.
Smith EL,III Hung LF, Huang J. Relative peripheral hyperopic defocus alters central refractive development in infant monkeys. Vision Res. 2009; 49: 2386–2392.
Smith EL,III Kee CS, Ramamirtham R, et al. Peripheral vision can influence eye growth and refractive development in infant monkeys. Invest Ophthalmol Vis Sci. 2005; 46: 3965–3972.
Mutti DO, Hayes JR, Mitchell GL, et al. Refractive error, axial length, and relative peripheral refractive error before and after the onset of myopia. Invest Ophthalmol Vis Sci. 2007; 48: 2510–2519.
Mutti DO, Sinnott LT, Mitchell GL, et al. Relative peripheral refractive error and the risk of onset and progression of myopia in children. Invest Ophthalmol Vis Sci. 2011; 52: 199–205.
Cheng D, Woo GC, Drobe B, et al. Effect of bifocal and prismatic bifocal spectacles on myopia progression in children: three-year results of a randomized clinical trial. JAMA Ophthalmol. 2014; 132: 258–264.
Gwiazda J, Hyman L, Hussein M, et al. A randomized clinical trial of progressive addition lenses versus single vision lenses on the progression of myopia in children. Invest Ophthalmol Vis Sci. 2003; 44: 1492–1500.
Anstice NS, Phillips JR. Effect of dual-focus soft contact lens wear on axial myopia progression in children. Ophthalmology. 2011; 118: 1152–1161.
Walline JJ, Greiner KL, McVey ME, et al. Multifocal contact lens myopia control. Optom Vis Sci. 2013; 90: 1207–1214.
Queiros A, Gonzalez-Meijome JM, Jorge J, et al. Peripheral refraction in myopic patients after orthokeratology. Optom Vis Sci. 2010; 87: 323–329.
Kang P, Swarbrick H. Peripheral refraction in myopic children wearing orthokeratology and gas-permeable lenses. Optom Vis Sci. 2011; 88: 476–482.
Lian Y, Shen M, Jiang J, et al. Vertical and horizontal thickness profiles of the corneal epithelium and Bowman's layer after orthokeratology. Invest Ophthalmol Vis Sci. 2013; 54: 691–696.
Nieto-Bona A, Gonzalez-Mesa A, Nieto-Bona MP, et al. Long-term changes in corneal morphology induced by overnight orthokeratology. Curr Eye Res. 2011; 36: 895–904.
Queiros A, Gonzalez-Meijome JM, Villa-Collar C, et al. Local steepening in peripheral corneal curvature after corneal refractive therapy and LASIK. Optom Vis Sci. 2010; 87: 432–439.
Maseedupally V, Gifford P, Lum E, et al. Central and paracentral corneal curvature changes during orthokeratology. Optom Vis Sci. 2013; 90: 1249–1258.
Cho P, Cheung SW. Retardation of myopia in Orthokeratology (ROMIO) study: a 2-year randomized clinical trial. Invest Ophthalmol Vis Sci. 2012; 53: 7077–7085.
Hiraoka T, Kakita T, Okamoto F, et al. Long-term effect of overnight orthokeratology on axial length elongation in childhood myopia: a 5-year follow-up study. Invest Ophthalmol Vis Sci. 2012; 53: 3913–3919.
Walline JJ, Jones LA, Sinnott LT. Corneal reshaping and myopia progression. Br J Ophthalmol. 2009; 93: 1181–1185.
Kakita T, Hiraoka T, Oshika T. Influence of overnight orthokeratology on axial elongation in childhood myopia. Invest Ophthalmol Vis Sci. 2011; 52: 2170–2174.
Cho P, Cheung SW, Edwards M. The longitudinal orthokeratology research in children (LORIC) in Hong Kong: a pilot study on refractive changes and myopic control. Curr Eye Res. 2005; 30: 71–80.
Santodomingo-Rubido J, Villa-Collar C, Gilmartin B, et al. Myopia control with orthokeratology contact lenses in Spain: refractive and biometric changes. Invest Ophthalmol Vis Sci. 2012; 53: 5060–5065.
Zhong Y, Chen Z, Xue F, et al. Corneal power change is predictive of myopia progression in orthokeratology. Optom Vis Sci. 2014; 91: 404–411.
Alharbi A, Swarbrick HA:, The effects of overnight orthokeratology lens wear on corneal thickness. Invest Ophthalmol Vis Sci. 2003; 44: 2518–2523.
Chen D, Lam AK, Cho P:, Posterior corneal curvature change and recovery after 6 months of overnight orthokeratology treatment. Ophthalmic Physiol Opt. 2010; 30: 274–280.
Queiros A, Villa-Collar C, Gutierrez AR, et al. Anterior and posterior corneal elevation after orthokeratology and standard and customized LASIK surgery. Eye Contact Lens. 2011; 37: 354–358.
Tsukiyama J, Miyamoto Y, Higaki S, et al. Changes in the anterior and posterior radii of the corneal curvature and anterior chamber depth by orthokeratology. Eye Contact Lens. 200834: 17–20.
Gonzalez-Mesa A, Villa-Collar C, Lorente-Velazquez A, et al. Anterior segment changes produced in response to long-term overnight orthokeratology. Curr Eye Res. 2013; 38: 862–870.
Schmid GF:, Association between retinal steepness and central myopic shift in children. Optom Vis Sci. 2011; 88: 684–690.
Liu Y, Wildsoet C:, The effect of two-zone concentric bifocal spectacle lenses on refractive error development and eye growth in young chicks. Invest Ophthalmol Vis Sci. 2011; 52: 1078–1086.
Liu Y, Wildsoet C:, The effective add inherent in 2-zone negative lenses inhibits eye growth in myopic young chicks. Invest Ophthalmol Vis Sci. 2012; 53: 5085–5093.
Tse DY, Lam CS, Guggenheim JA, et al. Simultaneous defocus integration during refractive development. Invest Ophthalmol Vis Sci. 2007; 48: 5352–5359.
Smith EL. 3rd: Optical treatment strategies to slow myopia progression: effects of the visual extent of the optical treatment zone. Exp Eye Res. 2013; 114: 77–88.
Chen Z, Niu L, Xue F, et al. Impact of pupil diameter on axial growth in orthokeratology. Optom Vis Sci. 2012; 89: 1636–1640.
Lu F, Simpson T, Sorbara L, et al. The relationship between the treatment zone diameter and visual, optical and subjective performance in Corneal Refractive Therapy lens wearers. Ophthalmic Physiol Opt. 2007; 27: 568–578.
Santodomingo-Rubido J, Villa-Collar C, Gilmartin B, et al. Factors preventing myopia progression with orthokeratology correction. Optom Vis Sci. 2013; 90: 1225–1236.
Figure 1
 
Follow-up flow chart and details of dropouts.
Figure 1
 
Follow-up flow chart and details of dropouts.
Figure 2
 
(A) Means and standard errors of corneal refractive power at 0.1-mm steps between the chord of 0.5 and 7.2 mm diameter centered on corneal apex before and after orthokeratology (ortho-k) lens wear. *Significant decrease in corneal power after ortho-k. **Significant increase in corneal power after ortho-k. °No significant change in corneal power after ortho-k. (B) Curves showing relative peripheral corneal power before and after ortho-k lens wear. The areal difference between the two curves, highlighted in gray, is defined as SCPC.
Figure 2
 
(A) Means and standard errors of corneal refractive power at 0.1-mm steps between the chord of 0.5 and 7.2 mm diameter centered on corneal apex before and after orthokeratology (ortho-k) lens wear. *Significant decrease in corneal power after ortho-k. **Significant increase in corneal power after ortho-k. °No significant change in corneal power after ortho-k. (B) Curves showing relative peripheral corneal power before and after ortho-k lens wear. The areal difference between the two curves, highlighted in gray, is defined as SCPC.
Table 1
 
Inclusion and Exclusion Criteria
Table 1
 
Inclusion and Exclusion Criteria
Table 2
 
Baseline Variables (Mean ± SD) of the Completed Cases and the Dropouts
Table 2
 
Baseline Variables (Mean ± SD) of the Completed Cases and the Dropouts
Table 3
 
Baseline and Follow-up Data (Mean ± SD) of the Right Eyes of 64 Subjects Who Completed the Study
Table 3
 
Baseline and Follow-up Data (Mean ± SD) of the Right Eyes of 64 Subjects Who Completed the Study
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