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

Abstract

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.

Introduction

The prevalence of myopia is increasing and has become a major public health problem. According to epidemiological analysis of myopia, about 50% of the world's population is expected to have myopia in 2050, and one fifth will be highly myopic.¹ If myopia is not controlled, patients who develop high myopia will not only have poor distance vision but also be prone to glaucoma, macular degeneration, posterior scleral staphyloma, and retinal detachment, resulting in irreversible visual impairment.^2–5 

Orthokeratology has been shown to be effective in retarding axial elongation in myopic children.^6–11 By flattening the central cornea and steepening the mid-peripheral cornea, orthokeratology lenses create relative myopic defocus in the peripheral retina^12–14 and alter the higher-order aberrations (HOAs) of the human eye,¹⁵ which are considered the possible factors for myopia control. 

Decentration is a common and relatively unavoidable phenomenon in orthokeratology^16,17 and lens decentration is usually associated with a smaller axial length increase.^17–19 Li et al.¹⁹ found that larger treatment zone decentration was associated with slower axial growth when wearing orthokeratology lenses for 12 months. Wang et al.¹⁷ found that the off-centered eye underwent less axial elongation than the fellow eye in more than 12 months. 

The retardation of myopia progression by lens decentration may be associated with retinal peripheral defocus and ocular higher-order wavefront aberrations.^19,20 After lens wear, peripheral defocus drifted from hyperopic defocus to myopic defocus^14,21,22 and high-order aberrations increased, particularly spherical aberration (SA) and horizontal coma,^23,24 which may be the underlying mechanism of lens decentration for myopia control. However, previous studies measured only the refraction of horizontal or vertical meridians, without description of overall distribution characteristics. 

To overcome the limitations of previous research, we used the customized open-view fast scanning Hartmann-Shack peripheral wavefront sensor (VPR, VopticaSL, Murcia, Spain),²⁵ which can measure the peripheral refraction in the 60 degrees horizontal visual field in 1 degree steps and the 36 degrees vertical in 4 degree steps,²⁶ and the 2-dimensional graphs are generated after data processing. The main purposes of the study were to outline the optical features in the peripheral retina before and after orthokeratological lens fitting and to explore the associations between decentration severity, post-fitting refraction, and higher-order aberrations. 

Materials and Methods

Subjects

This prospective, longitudinal study was performed at the Aier Eye Hospital (Changsha, China). The inclusion and exclusion criteria were as follows: (1) aged between 10 and 16 years; (2) no previous use of rigid contact lenses or spectacles, other than single-vision spectacles, or any other myopia control modalities, including multifocal soft contact lenses and atropine; (3) good health without any systemic diseases that might affect the development of the visual system or refractive error medications; (4) spherical equivalent refraction between −0.75 diopters (D) and −6.00 D; (5) monocular corrected distance visual acuity no worse than 20/20; and (6) the subjects were instructed to wear the orthokeratology lenses for at least 8 hours per night. 

This study was approved by the Institutional Ethical Committee Review Board of Changsha Eye Hospital, and all work adhered to the tenets of the Declaration of Helsinki. Subjects and their parents all agreed to participate in the study, and written informed consent was given. 

Corneal Topography Measurement

Corneal topography was measured by the Pentacam Preocular Segment Analysis System (Pentacam, Oculus Inc., Germany) and performed in a dark room environment with natural pupils. 

Evaluation of Treatment Zone Decentration

Determination of the treatment zone center was based on the baseline and 1-month post-fitting front tangential corneal refraction maps. A senior practitioner was invited to compare the pre- and post-treatment maps to identify the power decreased zone, appearing as a circular or slightly elliptical area close to the vertex and surrounded by a power-reversed edge. The practitioner was required to manually select a point that best expressed the barycenter of the region, with the selected location representing the center of the treatment zone.^27–29 The magnitude of lens decentration was determined by measuring the distance between the center of the treatment zone and the corneal vertex. The process was performed using a customized MATLAB script and repeated three times. The average x- and y-coordinates were used to calculate the decentration. 

Peripheral Refraction and Higher-Order Aberration Measurement

Peripheral refraction (PR) and HOAs (SA, horizontal COMA, vertical COMA and root-mean square of higher order aberration [RMSHOA]) were obtained using an open-view Hartmann-Shack wavefront sensor (Voptica Peripheral Refractor [VPR]; Voptica SL, Murcia, Spain). The details of the VPR instrument and measurement process have been previously presented.²⁶ Higher-order wavefront aberrations were estimated for pupils measuring 4 mm in diameter. Relative peripheral refraction (RPR) was derived by subtracting the central refractive error from peripheral refraction. The VPR measurements were imported into MATLAB software to generate a 2D refractive map. In the abscissas, a positive value and a negative value, respectively, indicated the nasal retina and temporal retina. In the ordinates, a positive value and a negative value, respectively, indicated the superior retina and the inferior retina. To describe the regional characteristics, each 2D map was divided into 8 regions, segmenting the visual field using the standard nasal, temporal, and superior and inferior quadrants across 2 eccentricity ranges (approximately 20 degrees to 25 degrees and > 25 degrees) to assess the off-axis aberrations.²⁶ The mean value was calculated for each region. The data were processed according to our previously published study (Fig. 1).²⁶ 

Figure 1.

 

Schematic of two-dimensional refraction map segmentation. The map was divided into 8 regions based on twin circles of radius 20 degrees or 25 degrees and a central horizontal line (y = 0). The regions were labeled UZ1, UZ2, UZ3, and UZ4, and LZ1, LZ2, LZ3, and LZ4. Values beyond the superior 16 degrees were not included in the analysis to achieve a more uniformly distributed matrix.

Statistical Analysis

SPSS commercial software (version 25.00; IBM, Armonk, NY, USA) and MATLAB (MathWorks, Natick, MA, USA) were used for data analysis; only data from the right eyes were used. As asymmetrical peripheral refractive changes (peripheral refractions of the nasostemporal side) were observed in the refractive topography after orthokeratology, in order to objectively evaluate whether this asymmetric distribution was statistically different, this study compared the differences in RPR and HOAs in the horizontal direction (UZ1 versus UZ4, UZ2 versus UZ3, LZ1 versus LZ4, and LZ2 versus LZ3) and vertical direction (UZ1 versus LZ1, UZ2 versus LZ2, UZ3 versus LZ3, and UZ4 versus LZ4). A paired t-test was used to compare RPR and HOAs from the eight divisions of refraction maps. One-way analysis of variance (ANOVA) was used to compare differences between regions at baseline and after 1 month of orthokeratology lens wearing. Bonferroni corrections were applied for post hoc pairwise comparisons. The RPR and HOAs were analyzed concerning the magnitude of lens decentration using the Pearson correlation (r) test. A P < 0.05 value was defined as statistically significant. 

Results

Baseline Variables

One hundred thirty-four subjects (58 boys and 76 girls) were included in and finished the study. The mean age was 12.47 ± 1.70 years (range = 10–16 years). The mean refractive error was −2.44 ± 1.10 D (range = −4.88 to −0.75 D) and the initial astigmatism was −0.40 ± 0.41 D (range = −1.75 to 0 D). 

Lens Decentration

In the current study, the mean magnitude of lens decentration from the corneal vertex was 0.89 ± 0.40 mm (range = 0.02–1.86 mm), horizontal decentration was −0.59 ± 0.45 mm (range = −1.76 to –0.51 mm), and vertical decentration was −0.41 ± 0.49 mm (range = −1.55 to –1.39 mm). Using a quadrant from the center point of the cornea, lens decentration was as follows: 104 eyes (77.6%) were inferotemporal; 21 eyes (15.7%) were supertemporal; 7 eyes (5.2%) were inferonasal; and 2 eyes (1.5%) were supernasal. Lens decentration occurred most frequently in the inferotemporal quadrant. 

The Relationship Between Lens Decentration and RPR

After the lenses were worn, the average RPR changed from 1.09 ± 0.64 D to −0.49 ± 0.79 D (t = 27.098, P < 0.001) in areas outside circles of radius 20 degrees. In the baseline, the relative hyperopic defocus in the nasal retina is greater than the corresponding area in the temporal retina, which is limited to the upper retinal areas (UZ3 versus UZ2 and UZ1 versus UZ4 areas, all P < 0.001; Figs. 2a, 2b). After the lenses were worn, the relative hyperopic defocus of nasal retinal areas was greater than the corresponding temporal retinal areas, which extended to the whole retinal areas (UZ1 versus UZ4, UZ2 versus UZ3, LZ1 versus LZ4, and LZ2 versus LZ3, all P < 0.001; Figs. 2c, 2d). Peripheral refraction drifted from relative hyperopic defocus to relative myopic defocus in the whole region (all P < 0.001), but the change was more pronounced in the temporal retina (all P < 0.001; Figs. 2e, 2f). 

Figure 2.

 

(a) The refraction map in the baseline; (b) the RPR in the baseline; (c) the refraction map after lens wearing; (d) the RPR after lens wearing; (e) the differences refraction map before and after lens wearing; and (f) the RPR changes before and after lens wearing. For the panel of refraction map, the positive value and the negative value in the abscissas indicated the nasal retina and temporal retina, respectively, and the positive value and the negative value in the ordinates indicated the superior retina and the inferior retina, respectively. For the panel of RPR, the retinal area was divided into different regions by the dotted line. The horizontal solid line represents the statistical results in the corresponding horizontal areas, and the vertical solid line represents the statistical results in the corresponding vertical areas. The blue line indicates that the RPRs of the corresponding areas have no difference, and the red line indicates that the RPRs of the corresponding areas have a significant difference.

RPR changes in UZ2 (r = −0.27, P = 0.0014), UZ3 (r = 0.33, P < 0.001), UZ4 (r = 0.3, P < 0.001), LZ1 (r = −0.23, P = 0.0076), and LZ2 (r = −0.4, P < 0.001) regions were related to the total lens decentration. When dividing lens decentration into horizontal and vertical vectors, RPR changes in the UZ1 (r = 0.26, P = 0.0027), UZ2 (r = 0.37, P < 0.001), UZ3 (r = −0.48, P < 0.001), UZ4 (r = −0.5, P < 0.001), LZ2 (r = 0.24, P = 0.0058), LZ3 (r = −0.39, P < 0.001), and LZ4 (r = −0.41, P < 0.001) regions were associated with the horizontal vector of lens decentration, and RPR changes in the UZ3 (r = −0.29, P < 0.001), UZ4 (r = −0.23, P = 0.0067), LZ1 (r = 0.3, P < 0.001), LZ2 (r = 0.5, P < 0.001), LZ3 (r = 0.26, P = 0.0028), and LZ4 (r = 0.17, P = 0.0435) regions were associated with the vertical vector of lens decentration (Table 1). A relative myopic defocus drift occurred always on the side of decentration, whereas hyperopic defocus drift occurred on the opposite side. 

Table 1.

 

Correlations Between RPR Changes and Lens Decentration in Different Regions

 

The Relationship Between Lens Decentration and HOAs (SA, Horizontal COMA, Vertical COMA, and the Root-Mean Square of Higher Order Aberration)

In the baseline (Figs. 3a, 3b), there were significant differences in SA among UZ1 and UZ4 (P = 0.047), UZ2 and UZ3 (P = 0.003), and UZ2 and LZ2 (P = 0.038). For horizontal COMA (Figs. 4a, 4b), there were significant differences among UZ1 and UZ4 (P < 0.001), UZ2 and UZ3 (P < 0.001), LZ1 and LZ4 (P < 0.001), LZ2 and LZ3 (P < 0.001), UZ1 and LZ1 (P = 0.002), UZ4 and LZ4 (P = 0.012). For vertical coma (Figs. 5a, 5b), there were also significant differences in vertical coma among UZ1 and UZ4, UZ2 and UZ3, LZ1 and LZ4, LZ2 and LZ3, UZ1 and LZ1, UZ2 and LZ2, UZ3 and LZ3, and UZ4 and LZ4 (all P < 0.001). However, no significant differences were found in the RMSHOA (Figs. 6a, 6b) among UZ1 and UZ4, UZ2 and UZ3, LZ1 and LZ4, LZ2 and LZ3, UZ1 and LZ1, UZ2 and LZ2, UZ3 and LZ3, and UZ4 and LZ4 (all P > 0.05). 

Figure 3.

 

(a) The SA map in the baseline; (b) the SA in the baseline; (c) the SA map after lens wearing; (d) the SA after lens wearing; (e) the differences SA map before and after lens wearing; and (f) the SA changes before and after lenses wearing. For the panel of the SA map, the positive and values in the abscissas indicated the nasal retina and temporal retina, respectively, and the positive and negative values in the ordinates indicated the superior retina and the inferior retina, respectively. For the SA panel, the retinal area was divided into different regions by the dotted line. The horizontal solid line represents the statistical results in the corresponding horizontal areas, and the vertical solid line represents the statistical results in the corresponding vertical areas. The blue line indicates that the SAs of the corresponding areas have no difference, and the red line indicates that the SAs of the corresponding areas have a significant difference.

Figure 4.

 

(a) The horizontal COMA map in the baseline; (b) the horizontal COMA in the baseline; (c) the horizontal COMA map after lens wearing; (d) the horizontal COMA after lens wearing; (e) the differences in the horizontal COMA map before and after lens wearing; (f) the horizontal COMA changes before and after lens wearing. For the panel of the horizontal COMA map, the positive and negative values in the abscissas indicated the nasal retina and temporal retina, respectively, and the positive and negative values in the ordinates indicated the superior retina and the inferior retina, respectively. For the horizontal COMA panel, the retinal area was divided into different regions by the dotted line. The horizontal solid line represents the statistical results in the corresponding horizontal areas, and the vertical solid line represents the statistical results in the corresponding vertical areas. The blue line indicates that the horizontal COMAs of the corresponding areas have no difference, and the red line indicates that the horizontal COMAs of the corresponding areas have a significant difference.

Figure 5.

 

(a) The vertical COMA map in the baseline; (b) the vertical COMA in the baseline; (c) the vertical COMA map after lens wearing; (d) the vertical COMA after lens wearing; (e) the differences in the vertical COMA map before and after lens wearing; and (f) the vertical COMA changes before and after lens wearing. For the panel of the vertical COMA map, the positive and negative values in the abscissas indicated the nasal retina and temporal retina, respectively, and the positive and negative values in the ordinates indicated the superior retina and the inferior retina, respectively. For the vertical COMA panel, the retinal area was divided into different regions by the dotted line. The horizontal solid line represents the statistical results in the corresponding horizontal areas, and the vertical solid line represents the statistical results in the corresponding vertical areas. The blue line indicates that the vertical COMAs of the corresponding areas have no difference, and the red line indicates that the vertical COMAs of the corresponding areas have a significant difference.

Figure 6.

 

(a) The RMSHOA map in the baseline; (b) the RMSHOA map in the baseline; (c) the RMSHOA map after lens wearing; (d) the RMSHOA map after lens wearing; (e) the differences in the RMSHOA map before and after lens wearing; and (f) the RMSHOA map changes before and after lens wearing. For the panel of the RMSHOA map, the positive and negative values in the abscissas indicated the nasal retina and temporal retina, respectively, and the positive and negative values in the ordinates indicated the superior retina and the inferior retina, respectively. For the panel of the RMSHOA map, the retinal area was divided into different regions by the dotted line. The horizontal solid line represents the statistical results in the corresponding horizontal areas, and the vertical solid line represents the statistical results in the corresponding vertical areas. The blue line indicates that the RMSHOA map of the corresponding areas has no difference, and the red line indicates that the RMSHOA map of the corresponding areas has a significant difference.

After lenses were worn and in areas outside the circles of radius 20 degrees, the SA average changed from 0.03 ± 0.02 um to 0.06 ± 0.04 um (t = −10.014, P < 0.001), an increase of 0.03 ± 0.04 um; the horizontal COMA average changed from 0.01 ± 0.03 um to 0.03 ± 0.07 um (t = −3.214, P < 0.01), an increase of 0.02 ± 0.08 um; the vertical COMA average changed from 0.03 ± 0.05 um to 0.08 ± 0.11 um (t = −4.8, P < 0.001), an increase of 0.04 ± 0.11 um; and the RMSHOA average changed from 0.19 ± 0.05 um to 0.60 ± 0.24 um (t = −20.084, P < 0.001), an increase of 0.41 ± 0.24 um. A significant difference was found among SA changes in UZ1 and UZ4, UZ2 and UZ3, LZ1 and LZ4, and LZ2 and LZ3 (all P < 0.001), and the absolute values of SA changes on the nasal side were greater than those on the opposite temporal side (Figs. 3e, 3f). For horizontal COMA, a significant difference was found among UZ1 and UZ4 (P < 0.001), UZ2 and UZ3 (P < 0.001), LZ1 and LZ4 (P < 0.001), LZ2 and LZ3 (P < 0.001), and UZ4 and LZ4 (P = 0.002; Figs. 4e, 4f). For vertical COMA, a significant difference was found among LZ1 and LZ4, UZ1 and LZ1, UZ2 and LZ2, UZ3 and LZ3, and UZ4 and LZ4 (all P < 0.001; Figs. 5e, 5f). For RMSHOA, a significant difference was found among UZ1 and UZ4, UZ2 and UZ3, LZ1 and LZ4, LZ2 and LZ3, UZ1 and LZ1, UZ2 and LZ2, UZ3 and LZ3, and UZ4 and LZ4 (all P < 0.01), and the RMSHOA changes on the temporal side were greater than those on the opposite side (Figs. 6e, 6f). After lens wearing, the absolute total amount of HOAs increased. 

SA changes in the UZ1 (r = −0.38, P < 0.001), UZ2 (r = −0.35, P < 0.001), LZ1 (r = −0.44, P < 0.001), LZ2 (r = −0.48, P < 0.001), and LZ3 (r = −0.17, P < 0.05) regions were related to the total lens decentration. When dividing lens decentration into horizontal and vertical vectors, SA changes in the UZ1 (r = 0.47, P < 0.001), UZ2 (r = 0.38, P < 0.001), UZ4 (r = −0.23, P < 0.01), LZ1 (r = 0.33, P < 0.001), LZ2 (r = 0.19, P < 0.05), LZ3 (r = −0.19, P < 0.05), and LZ4 (r = −0.33, P < 0.001) regions were associated with the horizontal vector of lens decentration, and SA changes in the LZ1 (r = 0.37, P < 0.001), LZ2 (r = 0.56, P < 0.001), LZ3 (r = 0.34, P < 0.001), and LZ4 (r = 0.38, P < 0.001) regions were associated with the vertical vector of lens decentration (Table 2). 

Table 2.

 

Correlations Between Lens Decentration and SA Changes in Different Regions

 

Horizontal COMA changes in the UZ1 (r = −0.31, P < 0.001), LZ1 (r = −0.45, P < 0.001), LZ3 (r = 0.26, P < 0.01), and LZ4 (r = 0.25, P < 0.01) regions were related to the total lens decentration. When dividing lens decentration into horizontal and vertical vectors, horizontal COMA changes in the UZ1 (r = 0.35, P < 0.001), UZ3 (r = −0.38, P < 0.001), UZ4 (r = −0.17, P < 0.05), LZ1 (r = 0.25, P < 0.01), and LZ3 (r = −0.33, P < 0.001) regions were associated with the horizontal vector of lens decentration, and horizontal COMA changes in the LZ1 (r = 0.51 P < 0.001), LZ2 (r = 0.29, P < 0.01), LZ3 (r = −0.26, P < 0.01), and LZ4 (r = −0.46, P < 0.001) regions were associated with the vertical vector of lens decentration (Table 3). 

Table 3.

 

Correlations Between Lens Decentration and Horizontal COMA Changes in Different Regions

 

The vertical COMA changes in the UZ1 (r = 0.45, P < 0.001), UZ2 (r = 0.39, P < 0.001), UZ3 (r = 0.29, P < 0.01), UZ4 (r = 0.28, P < 0.01), and LZ1 (r = −0.2, P < 0.05) regions were related to the total lens decentration. When dividing lens decentration into horizontal and vertical vectors, the vertical COMA changes in the UZ1 (r = −0.24, P < 0.001) region were associated with the horizontal vector of lens decentration, and the vertical COMA changes in the UZ1 (r = −0.57, P < 0.001), UZ2 (r = −0.74, P < 0.001), UZ3 (r = −0.65, P < 0.001), UZ4 (r = −0.62, P < 0.001), LZ2 (r = −0.36, P < 0.001), LZ3 (r = −0.54, P < 0.001), and LZ4 (r = −0.31, P < 0.001) regions were associated with the vertical vector of lens decentration (Table 4). 

Table 4.

 

Correlations Between Lens Decentration and Vertical COMA Changes in Different Regions

 

RMSHOA changes in the UZ1 (r = 0.32, P < 0.001), UZ2 (r = 0.37, P < 0.001), LZ1 (r = 0.27, P < 0.01), and LZ2 (r = 0.36, P < 0.001) regions were related to the total lens decentration. When dividing lens decentration into horizontal and vertical vectors, RMSHOA changes in the UZ1 (r = −0.22, P < 0.05), UZ2 (r = −0.26, P < 0.01), UZ3 (r = 0.39, P < 0.001), UZ4 (r = 0.37, P < 0.001), LZ3 (r = 0.29, P < 0.01), and LZ4 (r = 0.26, P < 0.01) regions were associated with the horizontal vector of lens decentration, and RMSHOA changes in the LZ1 (r = −0.27, P < 0.01), LZ2 (r = −0.34, P < 0.001), LZ3 (r = −0.36, P < 0.001), and LZ4 (r = −0.3, P < 0.001) regions were associated with the vertical vector of lens decentration (Table 5). 

Table 5.

 

Correlations Between Lens Decentration and RMSHOA Changes in Different Regions

 

Discussion

There are numerous studies regarding lens decentration and myopic control effect^17–19 in orthokeratology treatment. An intriguing hypothesis suggests that the treatment effect of the lens is due to increased higher-order aberrations and relative myopic defocus resulting from the lens decentration.^19,20 However, only a few studies have investigated how peripheral refraction and aberrations are affected by lens decentration, which limited our understanding to the association between lens decentration and myopia control. To address this gap, we measured high-resolution wide-field peripheral refraction and higher-order aberrations with a custom Hartmann-Shack sensor. We found that the peripheral refraction changed from relative hyperopic defocus to relative myopic defocus after lens fitting, with the variation being more pronounced in the temporal retina. Additionally, the absolute total amount of HOAs (such as SA, horizontal COMA, vertical COMA, and RMSHOA) were found to be increased with the amount of lens decentration. This indicated that the myopia treatment effect of orthokeratology might be improved by increasing peripheral refraction and HOAs in the decentered lens. However, it is important to note that this interpretation is based on the assumption that a decentered orthokeratology lens yields a better myopia treatment effect. Nevertheless, our study lacks direct evidence to definitively support this point. 

Characteristics of Lens Decentration

In the current study, mean treatment decentration was 0.89 ± 0.40 mm, horizontal decentration was −0.59 ± 0.45 mm, vertical decentration was −0.41 ± 0.49 mm, and lens decentration occurred mostly in the inferotemporal quadrant (77.6%), results which are consistent with previous studies.^30,31 Hiraoka et al.³⁰ found an eccentricity toward the inferior temporal quadrant in 26 eyes of 23 participants (57%). The mean magnitude of decentration of the orthokeratology treatment zone from the pupillary center was 0.85 ± 0.51 mm. Lin³¹ found 36 inferotemporal eyes (72%) and that horizontal decentration (0.39 ± 0.20 mm) was greater than vertical (0.29 ± 0.21 mm). Several studies have explored the association of corneal asymmetry and lens decentration; the results have so far shown no convergence on any definite consensus. Chen³² found that corneal asymmetry could be used to predict lens decentration. Corneal asymmetry between the nasal and temporal sides may be the reason for lens decentration.^33,34 However, Wang studied subjects whose lenses were centric in one eye, whereas the fellow eye was off-centered, and no significant differences in corneal asymmetry or other ocular parameters were found between the two eyes.¹⁷ Lens decentration is influenced by lid morphology, lens fitting, lens diameter, initial refractive error, and gravitational corneas, as well as by corneal asymmetry, which could partially explain these contradictory research conclusions.^28,30,32,35 

Association Between Lens Decentration and Relative Peripheral Refraction

By flattening the central cornea and steepening the mid-peripheral cornea, orthokeratology could induce peripheral myopic retina defocus, which may be the reason for myopia retardation.^14,36 Lens decentration was associated with slower axial length growth, greater peripheral defocus, and aberration caused by lens decentration, which may account for the good control of myopia.^21–24 However, changes in peripheral defocus and aberration caused by lens decentration has not been fully studied before.^31,37 The current study proved that orthokeratology lenses push RPR toward myopic defocus in areas outside the circles of radius 20 degrees, that the amount of lens decentration was correlated with relative myopic defocus, and that greater myopic defocus in larger retinal regions may be the mechanism by which the off-centered eye undergoes lower axial length increases than the centric eye. Furthermore, we proved that the temporal retina had more myopic defocus than the nasal retina after lens fitting; greater asymmetry of peripheral optical defocus caused by lens decentration may be another mechanism for myopia control. However, the relationship between peripheral defocus and myopia remains unclear. Further research is needed. 

Association Between Lens Decentration and Higher-Order Wavefront Aberrations

In line with previous studies,^20,24 we found that the total amount of HOAs were increased in almost all of the fields after lens fitting. In theory, a decentered contact lens can more easily compress the cornea into an irregular shape, which would cause an increase in HOAs within the same side.³⁰ In the current study, we observed that SA increased in the central and peripheral fields after wearing the orthokeratology lenses. Similarly, Huang et al.²⁴ found that a positive shift in SA in the central field after orthokeratology. Batres et al.³⁸ also found that SA increased in the central field after wearing the orthokeratology lens. Prior to the lens fitting, the horizontal COMA distribution was negative and positive in the temporal and nasal retina, respectively. After treatment, the distribution pattern was completely reversed in the horizontal direction. A similar pattern was found for vertical COMA in the temporal retina, which returned positive values in the superior retina and negative values in the inferior retina of untreated eyes; the distribution was completely revised in the vertical direction after lens wearing. Overall, this indicates that in the natural eye, the tail of retinal image distortion points toward the center of the visual field, which then changes to an outward direction after orthokeratology. Hiraoka et al.³⁰ found that the combined COMA vector significantly increased with the magnitude of decentration.³⁰ However, other studies have provided concrete evidence for the influence of retinal COMA on myopia progression with orthokeratology treatment.^20,39 Our RMSHOA results show that HOAs increased across the whole field but were more noticeable in the temporal retina. This is generally aligned with our expectation that the flank of the lens closer to the nasal cornea has a more dominant impact on increasing relative peripheral myopic defocus than that on the other side of the cornea. We also found a significant correlation between the magnitude of decentration and number of HOAs. These findings indicate that a decentered orthokeratology treatment increases HOAs in the same direction as the direction of movement. More specifically, for the total amount of decentration, all HOAs were related to the LZ1 region; for horizontal decentration, all HOAs were related to UZ1; and for vertical decentration, all HOAs were related to LZ3. In this study, we cannot support or disprove the role of RPR and HOAs in myopia progression, but the correlation among lens decentration, RPR, and HOAs in peripheral regions could provide some insights for optimizing lens design. The amount of defocus and aberration in each area is also different; it is thus necessary to verify the feasibility of adding more defocus and aberration in a certain area for myopia retardation. However, superfluous lens decentration could cause an increased risk of corneal injury, eye infection, and poor visual quality, which may affect children's daytime performance and compliance.^18,30 Therefore, it is crucial to balance the pros and cons of lens decentration by optimizing the lens design. 

Advantages and Limitations of the Present Study

Few previous studies have explored the overall refraction of the retina for lack of appropriate instrumentation. Based on VPR, we measured the wide-field peripheral refraction of the retina and further analyzed its relationship with lens decentration to overcome the limitations of previous studies. However, the current study also has several limitations. First, the retardation of myopia progression by lens decentration was based on speculation, without direct analysis of its relationship with axial length growth. The possible speculation is that greater retinal peripheral defocus and larger HOAs were associated with slower axial length increase; an appropriately designed longitudinal study that shows the temporal relationship between retinal peripheral defocus, a high-order wavefront, and myopia progression in the developmental stages of children is needed. Second, we analyzed only the changes in RPR and high-order wavefronts after 1 month of lens wearing; longer follow-up time may be required to prove whether RPR and high-order wavefronts are stable. 

Conclusions

After lens fitting, peripheral refraction drifted from relative hyperopic defocus to relative myopic defocus, the total amount of HOAs increased, and the post-fitting RPR and aberrations changes were correlated with the amount of lens decentration, which might provide new insights for customized contact lens for myopia treatment solutions that are based on optics. 

Acknowledgments

The authors thank Chenglin Pan for determining the location of lens decentration. 

Supported by the Natural Science Foundation of Hunan Province (No. 2020JJ5004), the Natural Science Foundation of Hunan Province (2021JJ40004), and the Science Research Foundation of Aier Eye Hospital Group (AF2003D7). 

Disclosure: M. Xue, None; Z. Lin, None; H. Wu, None; Q. Xu, None; L. Wen, None; Z. Luo, None; Z. Hu, None; X. Li, None; Z. Yang, None