Influence of Corneal Topographic Parameters in the Decentration Of

ARTICLE

Inﬂuence of Corneal Topographic Parameters in the Decentration of Orthokeratology

Tianpu Gu, M.S., Boteng Gong, M.M., Daqian Lu, M.M., Weiping Lin, M.S., Na Li, M.S., Qing He, M.M., and Ruihua Wei, M.D., Ph.D.

index, CCCV, 5 mm-K , and 3 mm-K may be more preferable parameters Objective: nt si To investigate the lens decentration (LD) of orthokeratology in terms of the assessment of LD of ortho-k. (ortho-k) and the association between pretreatment corneal topographic parameters and LD of the ortho-k. Key Words: Orthokeratology—Decentration—Corneal topographic parameters. Methods: Fifty right eyes of 50 myopes wearing ortho-k lenses were – included in the prospective study. Corneal topography was conducted (Eye & Contact Lens 2019;45: 372 376) pretreatment to get topographic corneal parameters, including flat-K (K1); steep-K (K2); corneal astigmatism (CA), CA at 0 to 3 mm (3 mm-CA), 3 to 5 mm (5 mm-CA), 5 to 7 mm (7 mm-CA); surface asymmetry index (SAI); odern orthokeratology (ortho-k) is a process that uses surface regularity index; the curvature of best-fit sphere; the diameter of reverse-geometry–designed rigid contact lenses. Ortho-k cornea (DC); the distance from the corneal center to the corneal vertex M is a clinical, nonsurgical method that reduces temporarily the (CCCV); flat eccentricity (E1), steep eccentricity (E2), and E1/E2 (E ratio); and the corneal curvature differences between the nasal and temporal quad- refractive error of the central cornea for the desired myopia cor- 1–3 rants at 0 to 3 mm (3 mm-Knt), and the corneal curvature differences rection and even controls myopic progression in adolescents. between the superior and inferior quadrants at 0 to 3 mm (3 mm-Ksi), 5 Because of hydraulic forces within the tear-lens pressure on the 4 mm-Knt (at 3–5 mm), 5 mm-Ksi (at 3–5 mm), 7 mm-Knt (at 5–7 mm), and 7 eye during sleep, the refractive error is corrected with the central – mm-Ksi (at 5 7 mm). The relationship between these cornea topographic flattened corneal region. parameters and LD of the ortho-k was tested using stepwise multiple linear As one of the most common fitting challenges of ortho-k, the regression models. lens decentration (LD) has attracted the attention of many Results: 6 – The mean magnitude of LD was 0.51 0.23 mm (0.06 1.03 mm). researchers around the world in recent decades. Modern ortho-k, According to the stepwise analysis, 4 factors were associated with the over- which involves four curves, has improved significantly the efficacy all LD (P,0.01): SAI (b¼0.252), CCCV (b¼0.539), 5 mm-CA of the refractive correction and lens centration.5,6 Nevertheless, in (b¼20.268), and 3 mm-Ksi (b¼20.374); 5 factors were associated with the horizontal LD (P,0.01): DC (b¼0.205), CCCV (b¼0.881), 3 mm-CA clinical practice, mild to moderate LD is common and unavoidable, fi (b¼20.217), 5 mm-Knt (b¼0.15), and 3 mm-Ksi (b¼20.18); and 3 factors even under ideal tting conditions. Lens decentration remains an were associated with the vertical LD (P,0.01): SAI (b¼0.542), 5 mm-CA important potential source of post-treatment deficits in visual qual-

(b¼20.188), and 3 mm-Ksi (b¼20.213). ity, including halos, glare, decreased visual acuity, and increased Conclusion: Lens decentration is most common, but in most cases, the aberrations.7,8 amount of LD is moderate and acceptable. The magnitude of LD can be Corneal topographic techniques offer possible ways to evaluate predetermined by topographic corneal parameters. Surface asymmetry not only the initial corneal shape, but also the induced change in the cornea. The information provided by the topographical maps is From the Center of Optometry (T.G., B.G., D.L., W.L., N.L., Q.H., and used to design a more suitable lens for the patient and plan a better R.W.), Tianjin Medical University Eye Hospital, Tianjin, China; Tianjin management protocol.9 Some parameters in the corneal topograph- Medical University Eye Institute (T.G., B.G., D.L., Q.H., and R.W.), Tianjin, ical maps are considered predictors of LD, such as corneal China; The School of Optometry & Ophthalmology (T.G., B.G., D.L., W.L., toricity,10–12 paracentral corneal asymmetry,12 corneal elevation,10 N.L., Q.H., and R.W.), Tianjin Medical University, Tianjin, China. 10,12 13 The authors have no funding or conflicts of interest to disclose. the diameter of the cornea (DC), and the Q value. Supported by (1) National Nature Science Foundation of China (No: Identification of corneal astigmatism (CA) on a topographical 81770901); (2) National Nature Science Foundation of China (No: map has been used extensively to represent the CA of the entire 81570834); (3) Science Committee Nature Science Foundation of Tianjin cornea. However, it is controversial as to whether the CA identified (No: 17ZXHLSY00070). on a topographical map has an impact on LD,10–12 indicating that R. Wei conceived and supervised this study. T. Gu, B. Gong, D. Lu, W. fl Lin, Q. He, and N. Li performed the study. B. Gong collected the data, and a single value cannot re ect the CA precisely. In this study, we T. Gu analyzed the data. T. Gu and B. Gong wrote the manuscript. T. Gu investigated CA at 0 to 3 mm (3 mm-CA), 3 to 5 mm (5 mm-CA), and B. Gong contributed equally to this work and both were considered first and 5 to 7 mm (7 mm-CA) to explore the relationship between CA authors. and LD. Address correspondence to Ruihua Wei, M.D., Ph.D., Tianjin Medical University Eye Hospital, Tianjin Medical University Eye Institute, School Considering the effect of corneal surface irregularities on LD, of Optometry and Ophthalmology, Tianjin Medical University, Tianjin we chose three parameters, including the surface asymmetry index 300384, China; e-mail: [email protected] (SAI), surface regularity index (SRI), and the distance from the Accepted December 24, 2018. corneal center to the corneal vertex (CCCV), with which to study DOI: 10.1097/ICL.0000000000000580 this relationship. The SAI provides a quantitative measure of the

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Copyright © 2019 Contact Lens Association of Ophthalmologists, Inc. Unauthorized reproduction of this article is prohibited. Eye & Contact Lens Volume 45, Number 6, November 2019 Corneal Topographic Parameters and Decentration radial symmetry of the four central photokeratoscopic mires TABLE 1. The Results of Pretreatment Corneal Topographic surrounding the vertex of the cornea. Furthermore, the SRI is Parameters a quantitative measure of the central and paracentral corneal Means6SD Range regularity derived from the summation of ﬂuctuations in corneal K1/D 43.0861.34 40.05–46.6 power that occur along the semimeridians of the 10 central 6 K2/D 44.28 1.33 41.53–47.78 photokeratoscopic mires. Furthermore, to obtain a better under- CA/D 1.1860.45 0.29–1.96 standing of the effect of corneal asymmetry on LD, we included the 3 mm-CA/D 1.3860.38 0.63–2.34 – 5 mm-CA/D 1.2460.35 0.53–2.04 corneal curvature differences between the superior inferior and 7 mm-CA/D 1.3260.36 0.84–3.03 nasal-temporal quadrants at 0 to 3 mm, 3 to 5 mm, and 5 to 7 mm SAI 0.6360.19 0.38–1.18 to investigate the association between the pretreatment of these SRI 0.5360.17 0.29–0.97 cBFS/mm 7.960.23 7.45–8.48 parameters and LD in the ortho-k. E1 0.6460.09 0.45–0.84 6 A previous study has shown that the corneal topography usually E2 0.49 0.15 0.17–0.85 6 stabilizes within 1 month after ortho-k begins14; thus, the 1-month E ratio 1.42 0.48 0.72–3.53 3 mm-Knt/D 0.3660.43 0.02–2.33 6 topographic outputs were assumed to be representative of the post- 3 mm-Ksi/D 0.34 0.29 0–1.15 6 –ortho-k topography. In this study, we conducted a prospective 5 mm-Knt/D 0.57 0.33 0.11–1.7 6 5 mm-Ksi/D 0.47 0.39 0–2.06 study to determine LD after 1 month of ortho-k and analyzed the 6 7 mm-Knt/D 1.04 0.55 0.26–3.88 relationship between the cornea topographic parameters and LD. 7 mm-Ksi/D 0.5860.48 0.01–1.73 DC/mm 11.0260.29 10.2–11.6 CCCV/mm 0.2660.09 0.06–0.45

METHODS 3 mm-CA: CA at 0 to 3 mm; 3 mm-Knt: the corneal curvature differences between the nasal and temporal quadrants at 0 to 3 mm; Subjects and Ortho-K Lenses 3 mm-Ksi: the corneal curvature differences between the superior This prospective study was conducted at the Tianjin University and inferior quadrants at 0 to 3 mm; 5 mm-CA: CA at 3 to 5 mm; Eye Hospital (Tianjin, China) between August 2017 and December 5 mm-Knt:Knt at 3 to 5 mm; 5 mm-Ksi:Ksi at 3 to 5 mm; 7 mm-CA: 2017. This study adhered to the tenets of the Declaration of CA at 5 to 7 mm; 7 mm-Knt:Knt at 5 to 7 mm; 7 mm-Ksi:Ksi at 5 to Helsinki and was approved by the Institutional Ethical Committee 7 mm; CA: corneal astigmatism; cBFS: the curvature of best-fit sphere; CCCV: the distance from the corneal center to the corneal Review Board of Tianjin University Eye Hospital. Written vertex; DC: the diameter of cornea; E ratio: E1/E2;E1: flat eccentricity; informed consent was obtained from all patients or their guardians E2: steep eccentricity; K1: flat-K; K2: steep-K; SAI: surface asymmetry before their participation in our study. index; SRI: surface regularity index. A total of 50 subjects were enrolled in the optometry clinic (Table 1). The same experienced doctor treated all 50 patients. Only data pertaining to the right eye were obtained. The inclusion formed. A good fitting was indicated by an optical zone centered criteria were as follows: patients needed to be between 8 and 14 over the pupil, no apparent decentration of the lens, lens movement years of age, have a myopic spherical refractive error between of less than 1 mm during a blink, and a bulls-eye pattern with 21.00 D and 25.00 D, have a refractive astigmatism up to sodium fluorescein. Microadjustments, the changes by as small 21.50 D, have a visual acuity correctable to 0.0 (logarithm of mi- an amount as 0.05 mm in reverse curve or alignment curve, were nimal angle of resolution [logMAR]) or better, and have no contact possible based on the fitting evaluation. The ortho-k lenses with the lens–related contraindications. None of the subjects had received optimal fit were prescribed after several try-ons. ortho-k treatment previously. In the current study, all ortho-k lenses (Euclid Systems Corp) were made from Boston Equalens II material (Boston, MA) (DK: Examinations of Corneal 211 2 90$10 [cm /s] [mL O2/mL$mm Hg]) and had spherical, 4-zone, Topographic Parameters reverse-geometry shape. The optical center thickness was 0.24 mm. A series of examinations were conducted before the ortho-k The back optical zone radius was determined by subtraction of the lenses were fitted, including examinations for uncorrected visual spherical refractive error and a Jessen factor of 0.75 from the acuity (logMAR) and subjective refraction (Phoroptor, Topcon flattest meridian of the original corneal curvature (flat-K). CV-3000; Tokyo, Japan), a slit-lamp evaluation (SL-D2; Topcon), as well as fluorescein staining. Corneal profiles were measured The Fitting Approach using corneal topography (Medmont E300 topographer; Nunawad- Each ortho-k lens had a back optical zone diameter of 6.0 mm, ing), and each of the profiles used was the best-focused image a reverse curve of 0.6 mm in width, an alignment curve of 1.25 mm (with an accuracy of .95%) of the frames that were captured in width, and a peripheral curve of 0.4 mm in width. The total automatically. The corneal topographic parameters were recorded diameter of a typical trial lens was 10.6 mm. The total diameter of and further analyzed in terms of flat-K (K1); steep-K (K2); CA; 3 the final lens was tailored to be smaller than the horizontal visible mm-CA, 5 mm-CA, and 7 mm-CA; SAI; SRI; the curvature of the iris diameter (HVID) by 0.1 mm, with modifications made best-fit sphere (cBFS); flat eccentricity (E1), steep eccentricity (E2), exclusively to the width of the alignment curve. and E ratio (E1/E2); the corneal curvature differences between the The alignment curve radius of the first trial lens was chosen nasal and temporal quadrants at 0 to 3 mm (3 mm-Knt), 5 mm-Knt according to the corneal flat-K and the corneal eccentricity over (at 3–5 mm), and 7 mm-Knt (at 5–7 mm); and the corneal curvature a 5-mm chord on the corneal topography15 (E300; Medmont, Nu- differences between the superior and inferior quadrants at 0 to nawading, Victoria, Australia). As described in previous 3 mm (3 mm-Ksi), 5 mm-Ksi (at 3–5 mm), and 7 mm-Ksi (at research,6,12 lens-fitting evaluations using fluorescein were per- 5–7 mm).

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The SAI is a centrally weighted summation of the differences in mm-Ksi, 7 mm-Knt, 7 mm-Ksi, DC, and CCCV are summarized in corneal power between corresponding points 180° apart on 128 Table 1. equally spaced meridians that cross the 4 central photokeratoscopic – mires.16 18 The SRI is determined through the summation of local Lens Decentration Locations fluctuations in power along 256 equally spaced hemimeridians on The mean magnitude of the LD was 0.5160.23 mm – the 10 central mires.16 18 Clinically, the SAI reflects the asymmetry (0.06–1.03 mm). In terms of the horizontal displacement, the mean and local abnormal increases in corneal power; hence, it is used as magnitude of the LD was 0.3960.20 mm, and for the vertical a quantitative indicator for monitoring changes in corneal topog- displacement, the mean magnitude of the LD was raphy, whereas the SRI reflects the optical quality of the central 0.2960.21 mm. In terms of the horizontal displacement, temporal – cornea and correlates with visual acuity.16 21 LD was observed in 45 eyes (90%). In terms of the vertical displacement, inferior LD was observed in 41 eyes (84%). Finally, in Diameter of Cornea and Corneal Center to the terms of the overall displacement, inferotemporal LD was most Corneal Vertex commonly observed, making an appearance in 36 eyes (72%). Using the iris tool in the Medmont topography software, the cornea An overview of the LD for all subject eyes is presented in Figure zone was defined when the software’s circle was tangent to the bound- 1. ary of the visible iris on a high-resolution photograph of the eye. The diameter of the circle was defined as the DC, and its center was fi Association Analysis de ned as the center of the cornea. The corneal vertex, i.e., the point According to the stepwise analysis, 4 factors were associated fi (0, 0) on the corneal topography, was de ned as the line joining the with the overall LD (P,0.01): SAI (b¼0.252), CCCV (b¼0.539), fixation point and the fovea as it passed through the nodal points.22 5 mm-CA (b¼20.268), and 3 mm-Ksi (b¼20.374); 5 factors Thus, the distance from its the center to corneal vertex was regarded as were associated with the horizontal LD (P,0.01): DC the distance between the corneal center and corneal vertex. (b¼0.205), CCCV (b¼0.881), 3 mm-CA (b¼20.217), 5 mm- Knt (b¼0.15), and 3 mm-Ksi (b¼20.18); and furthermore, 3 fac- The Lens Decentration of Ortho-k tors were associated with the vertical LD (P,0.01): SAI The corneal topography was redone at 1-month follow-up within (b¼0.542), 5 mm-CA (b¼20.188), and 3 mm-K (b¼20.213). 2 hours after ortho-k lens removal. A difference map was then si obtained by subtracting the post–ortho-k tangential curvature map from the pre–ortho-k tangential curvature map. As described in the previous research,7,12 eight points were plotted surrounding the DISCUSSION central flattened area on which the power is all zero on the dif- Our result showed that most of the lens were decentered by less ference map. Using a circle fit function in a MATLAB program, than 0.5 mm (50%). When the cornea was divided into four these points were then used to calculate the best-fitting circle. The quadrants, the inferotemporal quadrant most commonly housed at center of the circle was defined as the center of the treatment zone, least a portion of the displacement (72%), and the LD in the and its distance from the corneal vertex normal was defined as the horizon direction (0.3960.20 mm) was greater than that in the magnitude of LD. vertical direction (0.2960.21 mm). When considering displacement in the horizon direction, LD to the temporal side (90%) Statistical Analysis was more frequent than that to the nasal side, which is consistent Statistical analyses were performed with the SPSS 22.0 statis- with previous studies.8,10–13,23 The reason for this tendency may be tical package and Matlab R2017b (MathWorks). The relationship that the temporal corneal shape is commonly steeper than the nasal between the corneal topographic parameters (K1,K2, CA, 3 mm- corneal shape.10 It suggests that the lenses tended to drift to the CA, 5 mm-CA, 7 mm-CA, SAI, SRI, cBFS, E1,E2, E ratio, 3 mm- steeper side. Referring to Tsai and Lin’s24 proposal for corneal Knt, 3 mm-Ksi, 5 mm-Knt, 5 mm-Ksi, 7 mm-Knt, 7 mm-Ksi, DC, refractive surgery, ablation decentration less than 0.5 mm was and CCCV) and LD were tested using stepwise multiple linear graded mild and optimal; between 0.5 and 1.0 mm (moderate de- regression models. The F test with P values set at 0.05 and 0.1 centration) was acceptable; and greater than 1.0 mm (severe decen- ’ was used to determine each variable s enter and exit criteria in the tration) was to be avoided. Our study showed that 98% of LD is model, respectively (in collinearity diagnostic tests, all variance mild or moderate, which is tolerable and accepted. fl , in ation factors were 10, indicating no multicollinearity). The An interesting finding in our study is that the magnitude of ¼b multiple linear regression model equation is as follows: y 0+ overall LD has shown no relationship with the overall CA, which is b b ⋯ b e b fi 1X1+ 2X2+ + pXp+ , where is the coef cient of the regres- opposite to the findings in previous literature10,11 but agrees with e sion model, and is called the error term. P values below 0.05 were Chen et al.12 Maseedupally et al.11 adopted the conventional and fi considered statistically signi cant. adjusted method for participants with 1.50 to 3.50 D corneal toricity and found that increased corneal toricity gave rise to increased amounts of treatment zone decentration. With the previous adjusted RESULTS method,11 which may be helpful in terms of improving lens cen- Corneal Topographic Parameters, Diameter of tration, a slightly steeper base curve or deeper sag was applied in Cornea, and Corneal Center to the the case of high corneal toricity in this study. Another reason Corneal Vertex accounting for this phenomenon may be that we adopted the step- The results for K1,K2, CA, 3 mm-CA, 5 mm-CA, 7 mm-CA, wise multiple linear regression analysis, thus minimizing CA’s 12 SAI, SRI, cBFS, E1,E2, E ratio, 3 mm-Knt, 3 mm-Ksi, 5 mm-Knt,5 influence, agreeing with Chen et al.

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center would be the corneal vertex. The corneal vertex is a highly useful reference for describing the geometric properties of the cornea, and its position is not always coordinated with the center of the cornea. In this study, the average of the CCCV was 0.2660.09 mm. The vertex is regarded as the center of the topographic map, which is based on the Placido principle. Thus, the length of the CCCV indicates the severity of the corneal surface asymmetry. Our results show that SAI has a notable effect on overall LD and the vertical LD, which agrees with Chen et al.,12 who reported that the magnitude of the LD is predetermined by the paracentral corneal asymmetry. The SAI provides a quantitative measure of the corneal surface asymmetry. Corneal shape asymmetry increases the difficulty in terms of the alignment curve being able to support the weight of the lens. Thus, more attention should be paid to clinical patients with significant corneal asymmetry. During sleep, the ortho-k lenses are relatively restricted and easily fixed to the more curved region of the cornea. Previous studies have found that most lenses decentered to the temporal and inferior quadrants of the cornea.8,10–13,23 Juan et al.13 confirmed that the Q- value difference between the nasal–temporal and superior–inferior FIG. 1. Scatterplot showing the distribution of the treatment center quadrants is a convenient and reliable predictor for LD in ortho-k of ortho-k with respect to the corneal vertex (T, temple; N, nasal; S, lens. However, little attention has been paid to the influence of the K superior; I, inferior; unit of length, mm). differences between the nasal–temporal and superior–inferior quadrants on LD. According to our results, there is a positive correlation Furthermore, we found that eyes with low amounts of corneal between 5 mm-Knt and the horizontal LD, which means that corneal toricity at 5 mm gave rise to increased amounts of vertical LD in shape asymmetry in the horizontal quadrant contributes to the hor- ortho-k as well as overall LD, and eyes with low corneal toricity at izontal LD. There is also a negative correlation between 3 mm-Ksi 3 mm give rise to increased vertical LD of ortho-K. These findings and the horizontal LD, the vertical LD, as well as the overall LD. It is suggest that central CA affects LD, but not dominantly. The typical important to note that central corneal curvature differences between chord of the first alignment curve of an ortho-k lens most likely the superior and inferior quadrants may prevent severe LD. As eyes falls between the chords of 7 and 9 mm.25 Thus, the corneal shape blink frequently overnight when wearing ortho-k lenses, the lenses within this region is critical for lens centration and warrants scru- tend to slide in the superior or inferior direction because of greater tiny. However, according to our study, the 7 mm-CA does not central corneal curvature differences between the superior and infe- affect LD. The reason may be that the corneal toricity at 0 to rior quadrants. The vertical DC is usually smaller than the horizontal 5 mm plays a decisive role in the sagittal height difference between DC. A lens can be supported by the vertical limbus of the cornea the 2 principal meridians of this region, which, in turn, affects the without severe LD. lens centration. There have controversies regarding whether the final refractive This study adopted methods based on individual HVID10,12 and outcome has an impact on LD. Our result was that the amount of confirmed that there is no correlation between the magnitude of LD the refractive error reduction has no relationship with LD, which and lens total diameter, agreeing with previous findings.10,12 How- agrees with two previous studies11,12 but disagrees with Hiraoka ever, this finding suggested that the smaller the lens, the larger the et al.8 and Li et al.13 Hiraoka et al.8 used lens diameters, which LD in other studies.8,11 Hiraoka et al.8 used mostly 10.0-mm-diam- were mostly 10.0 mm, and Maseedupally et al.11 used 11.0-mm eter lenses on their subjects and found the magnitude of LD to be diameters based on higher corrections perhaps causing a greater 0.8560.51 mm. Maseedupally et al.11 found the magnitude of LD compressive effect on the central cornea and thus requiring a larger to be 0.4860.20 using 11.0-mm-diameter lenses. But, given the lens diameter (with a wider alignment curve, not a wider base difference between individual HVID and post-treatment efficacy, curve) to support the weight of lens.26 uniform lens diameters should be avoided. Once the diameters of Although the manufacturers provide guidance and trial lenses or the ortho-k lens were adjusted, the two previous studies obtained software to guarantee success, ortho-k lens fitting is always an results similar to ours (0.7260.26 mm and 0.7360.15 mm, respec- empirical fitting method, requiring good centration and more tively); however, our finding of LD (0.5160.23 mm) was slightly detailed guidelines to avoid undesired outcomes. Corneal reshap- less severe than their results. This difference could be attributed to ing is a dynamic process; hence, any long-term investigation needs the steeper corneas and tightly fitting treatment in our study.11 to monitor the effect of LD on the parameters of corneal reshaping. However, our results showed the contrary correlation between Whether LD affects the impact of the myopia control is still the lens diameter and the horizon LD, indicating that the lens unknown, meaning that a long-term investigation is needed diameter has a mild and inconspicuous effect on the LD. urgently. Another limitation of this study is that we have not Our results show that the larger the CCCV, the larger the LD. In investigated ocular higher-order aberrations related to LD. More- clinical practice, the visual axis would be the ideal reference for the over, we will recruit ortho-k wearers with higher astigmatism for treatment center of ortho-K, and thus, the attempted treatment further study to investigate LD in ortho-k.

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In conclusion, LD is most common, but in most cases, the 11. Maseedupally VK, Gifford P, Lum E, et al. Treatment zone decentration amount of LD is moderate and acceptable. The magnitude of during orthokeratology on eyes with corneal toricity. Optom Vis Sci 2016; – overall LD can be predetermined by topographic corneal param- 93:1101 1111. 12. Chen Z, Xue F, Zhou J, et al. Prediction of orthokeratology lens decentra- eters. Surface asymmetry index, CCCV, 5 mm-Knt, and 3 mm-Ksi tion with corneal elevation. Optom Vis Sci 2017;94:903–907. may be more preferable parameters in terms of the assessment of 13. Li J, Yang C, Xie W, et al. Predictive role of corneal Q-value differences LD of ortho-k. It is important to note that DC affects horizontal LD between nasal-temporal and superior-inferior quadrants in orthokeratology moderately but does not affect overall LD in ortho-k. lens decentration. Medicine (Baltimore) 2017;96:e5837. 14. Alharbi A, Swarbrick HA. The effects of overnight orthokeratology lens wear on corneal thickness. Invest Ophthalmol Vis Sci 2003;44:2518–2523. ACKNOWLEDGMENTS 15. Mountford J, Ruston D, Dave T. Orthokeratology: Principles and practice. The authors thank Bei Du for her kind assistance during the In: Design Variables and Fitting Philosophies of Reverse Geometry Lenses. study. 1st ed. Philadelphia, PA, Elsevier, Butterworth-Heinemann, 2004, pp. 89–91. 16. Dingeldein SA, Klyce SD, Wilson SE. Quantitative descriptors of corneal REFERENCES shape derived from computer-assisted analysis of photokeratographs. 1. Lipson MJ, Brooks MM, Koffler BH. The role of orthokeratology in myopia Refract Corneal Surg 1989;5:372–378. control: A review. Eye Contact Lens 2018;44:224–230. 17. Wilson SE, Klyce SD. Advances in the analysis of corneal topography. Surv 2. Liu YM, Xie P. The safety of orthokeratology—A systematic review. Eye Ophthalmol 1991;35:269–277. Contact Lens 2016;42:35–42. 18. Wilson SE, Klyce SD. Quantitative descriptors of corneal topography. A 3. Li SM, Kang MT, Wu SS, et al. Efficacy, safety and acceptability of clinical study. Arch Ophthalmol 1991;109:349–353. orthokeratology on slowing axial elongation in myopic children by 19. Dave T. Current developments in measurement of corneal topography. Cont meta-analysis. Curr Eye Res 2016;41:600–608. Lens Anterior Eye 1998;21(Suppl 1):S13–S30. 4. Wang J, Fonn D, Simpson TL, et al. Topographical thickness of the epithe- 20. Kobayashi Y, Yanai R, Chikamoto N, et al. Reversibility of effects of lium and total cornea after overnight wear of reverse-geometry rigid contact orthokeratology on visual acuity, refractive error, corneal topography, and lenses for myopia reduction. Invest Ophthalmol Vis Sci 2003;44:4742–4746. contrast sensitivity. Eye Contact Lens 2008;34:224–228. 5. Lui WO, Edwards MH, Cho P. Contact lenses in myopia reduction—from ortho- 21. Sun Y, Wang L, Gao J, et al. Influence of overnight orthokeratology on focus to accelerated orthokeratology. Cont Lens Anterior Eye 2000;23:68–76. corneal surface shape and optical quality. J Ophthalmol 2017;2017: 6. Lu D, Gu T, Lin W, et al. Efficacy of trial fitting and software fitting for 3279821. orthokeratology lens: One-year follow-up study. Eye Contact Lens 2018;44: 22. Reinstein DZ, Archer TJ, Gobbe M. Is topography-guided ablation profile 339–343. centered on the corneal vertex better than wavefront-guided ablation profile 7. Liu G, Chen Z, Xue F, et al. Effects of myopic orthokeratology on visual centered on the entrance pupil? J refractive Surg 2012;28:139–143. performance and optical quality. Eye Contact Lens 2017;44:316–321. 23. Chen J, Huang W, Zhu R, et al. Influence of overnight orthokeratology lens 8. Hiraoka T, Mihashi T, Okamoto C, et al. Influence of induced decentered fitting decentration on corneal topography reshaping. Eye Vis (Lond) 2018; orthokeratology lens on ocular higher-order wavefront aberrations and con- 5:5. trast sensitivity function. J Cataract Refract Surg 2009;35:1918–1926. 24. Tsai YY, Lin JM. Ablation centration after active eye-tracker-assisted pho- 9. Cho P, Lam AK, Mountford J, et al. The performance of four different torefractive keratectomy and laser in situ keratomileusis. J Cataract Refract corneal topographers on normal human corneas and its impact on orthoker- Surg 2000;26:28–34. atology lens fitting. Optom Vis Sci 2002;79:175–183. 25. Tahhan N, Du Toit R, Papas E, et al. Comparison of reverse-geometry lens 10. Li Z, Cui D, Long W, et al. Predictive role of paracentral corneal toricity designs for overnight orthokeratology. Optom Vis Sci 2003;80:796–804. using elevation data for treatment zone decentration during orthokeratology. 26. Charm J, Cho P. High myopia-partial reduction ortho-k: A 2-year random- Curr Eye Res 2018;43:1083–1089. ized study. Optom Vis Sci 2013;90:530–539.

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