The effect of the back optic zone diameter on the treatment zone area and axial elongation in orthokeratology.

PURPOSE: To investigate the influence of corneal parameters on the treatment zone area (TZA) after Corneal Refractive Therapy (CRT) with a 5.0-mm back optical zone diameter (BOZD) were worn and to compare changes in the axial length (AL) with traditional 6.0-mm BOZD lenses. METHODS: This retrospective study involved 146 subjects (7-12 years) who wore orthokeratology (ortho-K) lenses for one year: 86 subjects were treated with CRT 5.0-mm lenses, and 60 subjects were treated with CRT 6.0-mm lenses. The TZA was measured after one year of ortho-K treatment. Both TZA and AL elongation after wearing the two kinds of lenses was compared. The parameters were recorded in the CRT 5.0 group: flat K, steep K, corneal toricity, e value, and anterior corneal elevation values at the 3-, 4-, and 5-mm chords along the principal meridians of the superior, inferior, nasal, and temporal sides. The relationships between these data and the TZA were analyzed. RESULTS: The TZA was 12.90 ± 5.15 mm2 and 20.61 ± 4.54 mm2, and the AL elongation was 0.15 ± 0.18 mm and 0.26 ± 0.18 mm in the CRT 5.0 group and the CRT 6.0 group, respectively (all p < 0.001). The one-year AL elongation was significantly associated with initial age and the TZA (r =  - 0.394, 0.393; all p < 0.001) in the CRT 5.0 group. The following corneal parameters were found to have statistically significant correlations with the TZA: the e value, difference in corneal elevation (nasal-temporal at the 3-, 4-, and 5-mm chord), and the absolute value of elevation difference (nasal-temporal at the 3- and 4-mm chord and inferior-superior at the 3-, 4-, and 5-mm chord). The e value was the only relevant factor for the TZA by multiple regression analysis (unstandardized ß = 14.219, p = 0.008). In the CRT 6.0 group, the one-year AL elongation was statistically significantly associated only with initial age (r =  - 0.605, p = 0.005), but not with the TZA (p = 0.161). CONCLUSIONS: A smaller TZA induced by a smaller BOZD may be beneficial for retarding AL elongation in children undergoing ortho-K treatment. The morphology and eccentricity of the cornea may show effects on the TZA.

Different efficacy in myopia control: Comparison between orthokeratology and defocus-incorporated multiple segment lenses.

PURPOSE: To compare the efficiency of orthokeratology (OK) and defocus-incorporated multiple segment (DIMS) lenses in myopia control in children. METHODS: This prospective study involved 540 subjects (7-14 years) categorized into three groups: DIMS lenses (180 cases), OK lenses (180 cases), or single-vision spectacles (SVS) (180 cases). After a one-year follow-up, changes in axial length (AL) and differences among the groups were analyzed. The subjects were further divided into a low myopia degree subgroup (LM, -1.50 D ≤ SE ≤ -0.50 D), a moderate myopia degree subgroup (MM, -3.00 D ≤ SE ＜ -1.50 D), and a high myopia degree subgroup (HM, -5.00 D ≤ SE ＜ -3.00 D). A one-way ANOVA and multiple linear regression analysis were used to compare AL elongation and the factors influencing the different groups. RESULTS: A total of 496 (92 %) subjects completed the study. The mean AL change in the OK lenses, DIMS lenses, and SVS were 0.20±0.18 mm, 0.30±0.22 mm, and 0.38±0.19 mm, respectively (P < 0.001). In the LM subgroup, the OK and DIMS groups showed similar AL changes, but both exhibited slower changes than the SVS group (P = 0.001). In the MM and HM subgroups, the OK lens performed the shortest AL elongation compared with the DIMS lenses and SVS (P < 0.001). Multiple regression analysis showed that the AL change was associated with age (ß = -0.038 and P = 0.005), initial AL (ß = -0.010 and P = 0.011), initial SE (ß = 0.028 and P = 0.007), and interventions using OK lenses (ß = -0.172 and P = 0.020) and DIMS lenses (ß = -0.089 and P = 0.020). CONCLUSION: Over a one-year treatment period, OK and DIMS lenses can significantly retard AL elongation compared with SVS. In addition, the OK lenses were more effective than the DIMS lenses in controlling AL in patients with higher degrees of myopia.

The Influence of Accommodation on Retinal Peripheral Refraction Changes in Different Measurement Areas.

Background: The change in refraction caused by accommodation inevitably affects the peripheral defocus state and thus may influence the effect of retinal peripheral myopic defocus measures in myopia control. This study investigated accommodation changes in different peripheral retinas under cycloplegia to help improve myopia control. Methods: Fifty-six eyes of fifty-six myopic subjects were recruited for this prospective study. The center and peripheral retina refractions were measured using multispectral refractive topography. The subjects were divided into low-to-moderate myopia group (range: -1.25 D to -6.00 D) and high myopia group (range: -6.25 D to -9.75 D) according to spherical equivalent (SE). The compound tropicamide (0.5% tropicamide and 0.5% phenylephrine) was used to relax the accommodation. The difference between cycloplegia and non-cycloplegia peripheral retinal refraction was analyzed using the t-test. The correlation between eccentricity and changes in peripheral refraction was analyzed using Pearson's correlation analysis. Results: The manifest refraction of the retina significantly decreased with an increase in eccentricity after cycloplegia. The annular refraction difference value at 50°-53° (ARDV 50-53) showed the largest refraction decrease of 1.31 D compared with the central retinal refraction decrease of 0.84 D. The inferior quadrantal refraction difference value had the least change compared to the other quadrants. The relative peripheral refraction (RPR) changes in refraction difference value (RDV) at 15° (RDV-15), RDV-30, and RDV-45 were less than 0.15 D. When the range of annulus narrowed to 5°, the narrower annulus showed faster change with eccentricity increase in ARDV 30-35, ARDV 35-40, ARDV 40-45, ARDV 45-50, and ARDV 50-53. The RPR was highly correlated with eccentricity (R = 0.938 and P < 0.001). The high myopia group had a greater hyperopic shift in the periphery than the low-to-moderate group after cycloplegia. Conclusions: Peripheral refraction showed a significant hyperopic shift after cycloplegia with an increase in eccentricity. The RPR became more hyperopic than the central refraction. The high myopia group showed more hyperopic shifts in the peripheral region. Accommodation should be taken into consideration in peripheral defocus treatment.

Effects of Orthokeratology Lens Decentration Induced by Paracentral Corneal Asymmetry on Axial Length Elongation.

BACKGROUND: To determine the influence of the magnitude of treatment zone decentration on axial length (AL) elongation and to investigate the association between paracentral corneal asymmetry and orthokeratology (OK) lens decentration. METHODS: This retrospective study involved 268 subjects (7-14 years) who wore OK lenses for one year. The parameters that reflected the paracentral corneal asymmetry were recorded: corneal toricity; Q value; anterior corneal curvature; and elevation values at the 6-, 7-, and 8-mm chords along the horizontal meridian. The relationships between these data and the amount of treatment zone decentration were analyzed. The relationship of the decentration magnitude and AL elongation was also analyzed. RESULTS: AL elongation was significantly associated with initial age, baseline spherical equivalent, AL, and the decentration magnitude. The subjects with large decentration magnitude showed less AL elongation. The decentration was affected by corneal morphology at the 8-mm chord on the nasal side. In the low curvature group (≤41.0D), the decentration magnitude had a stronger correlation with AL elongation than in all subjects. In the high curvature group (>41.0D), the decentration magnitude was no longer correlated with the AL elongation. CONCLUSION: The decentration of the OK lens effectively slowed the elongation of the eyeball. When the nasal curvature was less than 41.0 D at the 8-mm chord, the magnitude of decentration was predetermined by the flatter curve.

Repeatability and correlation of corneal biomechanical measurements obtained by Corvis ST in orthokeratology patients.

PURPOSE: To evaluate the repeatability of the corneal biomechanical measurements obtained by Corvis ST in post-orthokeratology patients and analyze the correlation between the biomechanical and ocular parameters. METHODS: Fifty-one eyes of 51 myopic subjects were included in this study. The biomechanical parameters were assessed using Corvis ST. Repeatability was assessed using one-way ANOVA based on within-subject standard deviation (Sw), repeatability coefficient (RC), intraclass correlation coefficient (ICC) and correlation of variation (CoV). The correlation was evaluated using Pearson correlation analysis. RESULTS: All parameters measured by Corvis ST, except length of flattened cornea at the first and second applanations (A1L and A2L), showed a good intraobserver repeatability after a 3-month follow-up period. The ICC values for A1L and A2L were 0.444 and 0.654, whereas the other parameters were higher than 0.8. Similar trends were obtained for CoV, wherein the CoV values for A1L and A2L were greater than 13 %. The corneal biomechanical parameters were correlated with age, refraction, axial length (AL), steep and flat keratometry before and after orthokeratology, and central corneal thickness (CCT). Following orthokeratology treatment, post-keratometry demonstrated a higher correlation with stiffness parameter at first applanation (SP-A1), velocity of corneal apex at the first applanation (A1V), and radius than pre-keratometry, which showed a weak correlation with SP-A1. CONCLUSION: Corneal biomechanical parameters assessed using Corvis ST demonstrated a good repeatability, except A1L and A2L. The corneal biomechanical parameters were correlated with age, refraction, AL and pre- and post-keratometry. Thus, Corvis ST is a suitable device for investigating biomechanical parameter.

MiRNA-21-HIF-1α-VEGF Axis Is Associated with Myopic Choroidal Neovascularization in Guinea Pigs.

INTRODUCTION: Myopic choroidal neovascularization (CNV) often causes serious damage to central vision. The mechanisms behind it remain unclear. METHOD: In this study, monocular form deprivation was applied to induce high myopia, and 532-nm laser was employed to induce CNV in guinea pig. The development of neovascularization was measured comprehensively by fundus fluorescein angiography, optical coherence tomography and hematoxylin and eosin staining. Gene expression was detected by real-time polymerase chain reaction and immunohistochemistry. RESULTS: The proliferation of new blood vessels increased with time and peaked at 21 days. At each time point after laser photocoagulation, the incidence of CNV was higher in form-deprived myopia (FDM) group than in control group. Myopic CNV started earlier and decreased more slowly. The obvious continuous fluorescein leakage could last as long as 1 month. The expressions of hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) increased and peaked at 14 days in both groups after laser photocoagulation. Moreover, after laser photocoagulation, miR-21 expression was upregulated in both groups, reached a peak at 7 days, with a level much higher in FDM group. In addition, miR-21 expression was positively correlated with VEGF and HIF-1α expression in both groups. CONCLUSION: miR-21 correlated with HIF-1α-VEGF signaling pathway may promote CNV formation in high-myopia guinea.

Agreement and Repeatability of Central and Peripheral Refraction by One Novel Multispectral-Based Refractor.

Purpose: To evaluate the repeatability of a multispectral-based refractor in central and peripheral refraction measurement, and to assess the agreement of such measurements with objective refraction (OR) and subjective refraction (SR) in patients with myopia. Methods: A total of 60 subjects were recruited in this prospective research. Patients were divided into three groups according to the refractive error. Next, the central and peripheral refraction parameters were measured using multispectral refractive tomography (MRT) before and after cycloplegia. In addition, OR and SR measurements were also performed. The intraobserver repeatability was analyzed using within-subject standard deviation (Sw), test-retest repeatability (TRT), and intraclass correlation coefficient (ICC). Agreement was evaluated using Bland-Altman plot and 95% limits of agreement (LoA). Results: The ICC value of central and peripheral refraction were all higher than 0.97 with or without cycloplegia. The peripheral refraction in the nasal, temporal, superior, and inferior quadrants was slightly worse than other parameters, with the largest error interval being 1.43 D. The 95% LoA of the central refraction and OR or SR ranged from -0.89 to 0.88 D and -1.24 to 1.16 D without cycloplegia, respectively, and from -0.80 to 0.42 D and -1.39 to -0.84 D under cycloplegia, respectively. Conclusions: The novel multispectral refraction topography demonstrated good repeatability in central and peripheral refraction. However, the refraction in the nasal, temporal, superior, and inferior quadrants were not as good as that of central and circle peripheral refraction.

Corporate immunity to the COVID-19 pandemic.

We evaluate the connection between corporate characteristics and the reaction of stock returns to COVID-19 cases using data on more than 6,700 firms across 61 economies. The pandemic-induced drop in stock returns was milder among firms with stronger pre-2020 finances (more cash and undrawn credit, less total and short-term debt, and larger profits), less exposure to COVID-19 through global supply chains and customer locations, more corporate social responsibility activities, and less entrenched executives. Furthermore, the stock returns of firms controlled by families (especially through direct holdings and with non-family managers), large corporations, and governments performed better, and those with greater ownership by hedge funds and other asset management companies performed worse. Stock markets positively price small amounts of managerial ownership but negatively price high levels of managerial ownership during the pandemic.

Effect of Sunshine Duration on Myopia in Primary School Students from Northern and Southern China.

BACKGROUND: To assess the current myopia prevalence rate and evaluate the effect of sunshine duration on myopia among primary school students in the north and south of China. METHODS: This prospective cross-sectional study pooled data from 9171 primary school students (grades from 1 to 6) from four cities in the north and south of China. National Geomatics Center of China (NGCC) and China Meteorological Administration provided data about altitude, latitude, longitude, average annual temperature, and average annual sunshine duration. Non-cycloplegic refraction was recorded, and prevalence rates in primary school students and factors associated with myopia were analyzed. Univariate and multivariate logistic regression models were used to determine the independent association of risk factors of myopia. RESULTS: The overall myopia prevalence was 28.0%, from 7.5% to 50.6% for first and sixth grades, respectively. Low, moderate and high myopia significantly increased with school grades from 7.30% to 35.0%, 0.3% to 13.60% and 0.00% to 1.9%, respectively. Multiple regression analysis revealed that longer average cumulative daylight hours were connected to lower myopia prevalence in primary school students (OR, 0.721; 95% CI, [0.593-0.877]; P=0.001), whereas girls and higher grade was independently associated with higher myopia prevalence (girls: ß=0.189; OR, 1.208; 95% CI, [1.052-1.387]; P=0.007; higher grade: ß=0.502; OR, 1.652; 95% CI, [1.580-1.726]; P<0.001). CONCLUSION: This study demonstrated that myopia was highly prevalent in southern Chinese cities over northern ones, linked to shorter light exposure, higher education level, and female gender. Such findings reinforced the beneficial impact of daylight exposure with a protective role against myopia development.

Comparison of clinical results between trans-PRK and femtosecond LASIK for correction of high myopia.

BACKGROUND: To compare the clinical outcomes of transepithelial photorefractive keratectomy (TPRK) with femtosecond laser-assisted in situ keratomileusis (FS-LASIK) for correction of high myopia. METHODS: In this prospective, non-randomised, cohort study, 85 eyes of 46 patients treated with TPRK and 80 eyes of 42 patients treated with FS-LASIK were included. All eyes were highly myopic (spherical equivalent refraction <- 6.00 diopters). Both TPRK and FS-LASIK were performed by Schwind Amaris 750S excimer laser. Visual acuity, refraction, corneal high order aberration (HOA) and other variables were analyzed before and at 1, 3, 6, 12 months after surgery. RESULTS: At 12 months after surgery, uncorrected logMAR distance visual acuity (UDVA) in the TPRK and FS-LASIK groups was - 0.04 ± 0.04 and - 0.01 ± 0.08, respectively (P = 0.039). Corrected logMAR distance visual acuity (CDVA) was - 0.06 ± 0.05 and - 0.04 ± 0.05 in both groups (P = 0.621). For UDVA, 86% of eyes in the TPRK group and 80% in the FS-LASIK group remained unchanged or improved one or more logMAR lines (P = 0.314), compared to preoperative CDVA. For CDVA, 97% of eyes in the TPRK group and 90% in the FS-LASIK group remained unchanged or improved one or more lines (P = 0.096), compared to preoperative CDVA. Spherical equivalent refraction was - 0.05 ± 0.39 and - 0.26 ± 0.47 in both groups (P = 0.030). 87% of eyes in the TPRK group and 73% in the FS-LASIK group achieved ±0.50 D target refraction (P = 0.019). All 85 eyes (100%) in the TPRK group and 75 eyes (92%) in the FS-LASIK group were within ±1.00 D of target (P = 0.003). Root mean square (RMS) of corneal total HOA and vertical coma in the TPRK group were lower compared with the FS-LASIK group (P < 0.001 for both variables). CONCLUSIONS: TPRK and FS-LASIK showed good safety, efficacy and predictability for correction of high myopia. Clinical outcomes of TPRK were slightly better than FS-LASIK.