Correlation Between Increase of Axial Length and Height Growth in Chinese School-Age Children

Causal relationships between height, screen time, physical activity, sleep and myopia: univariable and multivariable Mendelian randomization

Background

This study aims to investigate the independent causal relation between height, screen time, physical activity, sleep and myopia.

Methods

Instrumental variables (IVs) for exposures and outcome were obtained from the largest publicly available genome-wide association studies (GWAS) databases. First, we performed a bidirectional univariate MR analysis using primarily the inverse variance weighted method (IVW) with height, screen time, physical activity and sleep as the exposure and myopia as the outcome to investigate the causal relationship between exposures and myopia. Sensitivity analysis was used to demonstrate its robustness. Then the multivariable MR (MVMR) and MR-based mediation approach was further used to estimate the mediating effect of potential confounders (education and time outdoors) on causality.

Results

The results of univariate MR analysis showed that taller height (OR = 1.009, 95% CI = 1.005-1.012, p = 3.71 × 10-7), longer time on computer (OR = 1.048, 95% CI = 1.029-1.047, p = 3.87 × 10-7) and less moderate physical activity (OR = 0.976, 95% CI = 0.96-0.991 p = 2.37 × 10-3) had a total effect on the increased risk of developing myopia. Meanwhile our results did not have sufficient evidence to support the causal relationship between chronotype (p = 0.637), sleep duration (p = 0.952) and myopia. After adjusting for education, only taller height remains an independent risk factor for myopia. After adjusting for education, the causal relationship between height, screen and myopia still had statistical significance. A reverse causal relationship was not found in our study. Most of the sensitivity analyses showed consistent results with those of the IVW method.

Conclusion

Our MR study revealed that genetically predicted taller height, longer time on computer, less moderate physical activity increased the risk of myopia. After full adjustment for confounders, only height remained independently associated with myopia. As a complement to observational studies, the results of our analysis provide strong evidence for the improvement of myopia risk factors and provide a theoretical basis for future measures to prevent and control myopia in adolescents.

Axial length elongation profiles from 3 to 6 years in an Asian paediatric population: the Growing Up in Singapore Towards Healthy Outcomes birth cohort study (GUSTO)

AIMS

To determine axial length (AL) elongation profiles in children aged 3-6 years in an Asian population.

METHODS

Eligible subjects were recruited from the Growing Up in Singapore Towards Healthy Outcomes birth cohort. AL measurement was performed using IOLMaster (Carl Zeiss Meditec, Jena, Germany) at 3 and 6 years. Anthropometric measurements at birth, cycloplegic refraction at 3 and 6 years, questionnaires on the children's behavioural habits at 2 years and parental spherical equivalent refraction were performed. Multivariable linear regression model with generalised estimating equation was performed to determine factors associated with AL elongation.

RESULTS

273 eyes of 194 children were included. The mean AL increased from 21.72±0.59 mm at 3 years to 22.52±0.66 mm at 6 years (p<0.001). Myopic eyes at 6 years had greater AL elongation (1.02±0.34 mm) compared with emmetropic eyes (0.85±0.25 mm, p=0.008) and hyperopic eyes (0.74±0.16 mm, p<0.001). The 95th percentile limit of AL elongation was 1.59 mm in myopes, 1.34 mm in emmetropes and 1.00 mm in hyperopes. Greater birth weight (per 100 g, β=0.010, p=0.02) was significantly associated with greater AL elongation from 3 to 6 years, while parental and other behavioural factors assessed at 2 years were not (all p≥0.08).

CONCLUSION

In this preschool cohort, AL elongates at an average length of 0.80 mm from 3 to 6 years, with myopes demonstrating the greatest elongation. The differences in 95th percentile limits for AL elongation between myopes, emmetropes and hyperopes can be valuable information in identifying myopia development in preschool children.

Repeatability and reproducibility of a new fully automatic measurement optical low coherence reflectometry biometer and agreement with swept-source optical coherence tomography-based biometer

AIMS

To assess the repeatability and reproducibility of the ocular measurements obtained with the Suoer SW-9000 μm Plus, a new fully automatic biometer based on optical low coherence reflectometry (OLCR) biometer, and to compare them to those obtained by a swept-source optical coherence tomography (SS-OCT)-based biometer.

METHODS

This prospective study consisted of 115 eyes of 115 healthy subjects. The measurements were taken by the two optical biometers in random order. The measured parameters were axial length (AL), central corneal thickness (CCT), aqueous depth (AQD), anterior chamber depth (ACD), mean keratometry (Km), lens thickness (LT) and corneal diameter (CD). To evaluate the intraobserver repeatability and interobserver reproducibility, the within-subject SD, test-retest variability, coefficient of variation (CoV) and intraclass correlation coefficient (ICC) were adopted. The Bland-Altman plot was drawn to assess the agreement.

RESULTS

The repeatability and reproducibility of all parameters for the new device were excellent (ICC>0.960 and CoV<0.71%). The Bland-Altman plots showed high agreement between the OLCR-based and SS-OCT-based devices for AL, CCT, AQD, ACD, Km and LT, with narrow 95% limit of agreements (LoAs) (-0.08 mm to 0.06 mm, -15.91 µm to -1.01 µm, -0.09 mm to 0.09 mm, -0.09 mm to 0.08 mm, -0.47 D to 0.35 D, -0.05 mm to 0.16 mm, respectively) and moderate agreement for CD (95% LoA: -0.67 mm to -0.01 mm).

CONCLUSIONS

The new Suoer SW-9000 μm Plus biometer showed excellent repeatability and reproducibility. All the parameters obtained by this biometer were similar to those measured by SS-OCT-based biometer.

Association between body stature and prevalence of reduced visual acuity in high school graduates in Hangzhou, China

CLINICAL RELEVANCE

The association between myopia and body stature is of great significance for understanding prevention and control of myopia. It has been extensively studied in previous studies but without consistent conclusions.

BACKGROUND

The aim of this study is to investigate the association between body stature and prevalence of reduced visual acuity in high school graduates in Hangzhou, China.

METHODS

50,620 high school graduates who finished the physical examination of the national college entrance examination in 2020 were included. Data were derived from the database of physical examination of the national college entrance examination. Height and weight were measured, and body mass index (BMI) was calculated according to the general formula. Visual acuity was measured by the standard logarithmic visual acuity chart.

RESULTS

The prevalence of reduced visual acuity was 90.38% in high school graduates. Girls had a higher prevalence of reduced visual acuity than boys (93.07% vs 87.60%, P < 0.001). Boys with normal visual acuity were significantly taller (P < 0.001) and heavier (P < 0.001) than those with reduced visual acuity. Girls with normal visual acuity were significantly taller than those with reduced visual acuity (P < 0.001). The prevalence of reduced visual acuity was significantly inversely associated with height in both boys (P < 0.001) and girls (P < 0.001). The risk of reduced visual acuity was the lowest in the fourth quartile of height. The prevalence of reduced visual acuity was significantly associated with BMI only in boys (P < 0.001). The risk of reduced visual acuity was the lowest in the third quartile of BMI.

CONCLUSIONS

The prevalence of reduced visual acuity was inversely associated with height in both boys and girls, and there was a U-shaped association with BMI only in boys.

Distribution of Axial Length in Australians of Different Age Groups, Ethnicities, and Refractive Errors

Purpose

Treatments are available to slow myopic axial elongation. Understanding normal axial length (AL) distributions will assist clinicians in choosing appropriate treatment for myopia. We report the distribution of AL in Australians of different age groups and refractive errors.

Methods

Retrospectively collected spherical equivalent refraction (SER) and AL data of 5938 individuals aged 5 to 89 years from 8 Australian studies were included. Based on the SER, participants were classified as emmetropes, myopes, and hyperopes. Two regression model parameterizations (piece-wise and restricted cubic splines [RCS]) were applied to the cross-sectional data to analyze the association between age and AL. These results were compared with longitudinal data from the Raine Study where the AL was measured at age 20 (baseline) and 28 years.

Results

A piece-wise regression model (with 1 knot) showed that myopes had a greater increase in AL before 18 years by 0.119 mm/year (P < 0.001) and after 18 years by 0.011 mm/year (P < 0.001) compared to emmetropes and hyperopes, with the RCS model (with 3 knots) showing similar results. The longitudinal data from the Raine Study revealed that, when compared to emmetropes, only myopes showed a significant change in the AL in young adulthood (by 0.016 mm/year, P < 0.001).

Conclusions

The AL of myopic eyes increases more rapidly in childhood and slightly in early adulthood. Further studies of longitudinal changes in AL, particularly in childhood, are required to guide myopia interventions.

Translational Relevance

The axial length of myopic eyes increases rapidly in childhood, and there is a minimal increase in the axial length in non-myopic eyes after 18 years of age.

Baseline metrics that may predict future myopia in young children

PURPOSE

We used baseline data from the PICNIC longitudinal study to investigate structural, functional, behavioural and heritable metrics that may predict future myopia in young children.

METHODS

Cycloplegic refractive error (M) and optical biometry were obtained in 97 young children with functional emmetropia. Children were classified as high risk (HR) or low risk (LR) for myopia based on parental myopia and M. Other metrics included axial length (AXL), axial length/corneal radius (AXL/CR) and refractive centile curves.

RESULTS

Based on the PICNIC criteria, 46 children (26 female) were classified as HR (M = +0.62 ± 0.44 D, AXL = 22.80 ± 0.64 mm) and 51 (27 female) as LR (M = +1.26 ± 0.44 D, AXL = 22.77 ± 0.77 mm). Based on centiles, 49 children were HR, with moderate agreement compared with the PICNIC classification (k = 0.65, p < 0.01). ANCOVA with age as a covariate showed a significant effect for AXL (p < 0.01), with longer AXL and deeper anterior chamber depth (ACD) (p = 0.01) in those at HR (differences AXL = 0.16 mm, ACD = 0.13 mm). Linear regression models showed that central corneal thickness (CCT), ACD, posterior vitreous depth (PVD) (=AXL - CCT - ACD-lens thickness (LT)), corneal radius (CR) and age significantly predicted M (R = 0.64, p < 0.01). Each 1.00 D decrease in hyperopia was associated with a 0.97 mm elongation in PVD and 0.43 mm increase in CR. The ratio AXL/CR significantly predicted M (R = -0.45, p < 0.01), as did AXL (R = -0.25, p = 0.01), although to a lesser extent.

CONCLUSIONS

Although M and AXL were highly correlated, the classification of pre-myopic children into HR or LR was significantly different when using each parameter, with AXL/CR being the most predictive metric. At the end of the longitudinal study, we will be able to assess the predictability of each metric.

Associations between anthropometric indicators and refraction in school-age children during the post-COVID-19 era

Purpose

To explore the associations between anthropometric indicators and refraction in school-aged children in the post-COVID-19 era.

Methods

Data were collected from 25,644 children aged 7 to 12 years in 48 elementary schools in Tianjin. The comprehensive examination included height, weight, systolic blood pressure (SBP), diastolic blood pressure (DBP), refraction, and calculation of BMI, with a follow-up visit after 6 months. Myopia was defined as spherical equivalent refraction (SER) ≤-0.50 diopter (D). Bivariate correlation coefficients and multiple linear regression models were used to explore the cross-sectional and longitudinal associations between anthropometric indicators (height, weight, BMI, SBP, and DBP) and refraction.

Results

The mean changes in height, weight, BMI, SBP, DBP, and SER of the participants were 4.03 ± 2.18 cm, 3.10 ± 2.39 kg, 0.45 ± 1.16 kg/m², 2.26 ± 14.74 mmHg, 2.18 ± 11.79 mmHg and -0.17 ± 0.51 D, respectively. Overall, height, weight, BMI, SBP, and DBP were all correlated with SER (r = -0.324, r = -0.234, r = -0.121, r = -0.112, r = -0.066, both p < 0.001), and changes in height and weight were correlated with changes in SER (r = -0.034, -0.031, both p < 0.001). Furthermore, multiple linear regression analysis revealed that the association of BMI, SBP, and DBP with SER was significant in myopic children but not in non-myopic children. The association between changes in weight and changes in SER was only present in non-myopic children but not in myopic children.

Conclusion

Height and weight were negatively correlated with SER in both cross-sectional analysis and longitudinal changes, indicating that children's height, weight and growth rate may be used as a reference indicator for myopia risk prediction and myopia progression monitoring.

Prevalence of Myopia and Its Associated Factors Among Japanese Preschool Children

Purpose

To investigate the prevalence of myopia and factors associated with spherical equivalent (SE), axial length (AL), and axial length to corneal radius of curvature (AL/CR) ratio among Japanese preschool children.

Study Design

Prospective observational study.

Methods

This cross-sectional study evaluated subjects aged 4–6 years from a preschool. Non-cycloplegic autorefraction was measured using the Spot Vision Screener, while AL and corneal radius (CR) were measured using the Myopia Master. Parental myopia and environmental factors were investigated using the myopia-related factor questionnaire. The worse eye with higher myopic SE was chosen for analysis, and multiple linear regression models was performed using AL, SE, and AL/CR ratio as dependent variables.

Results

A total of 457 out of 514 participants (239 males, 52.3%) aged 4–6 years (mean 4.77 ± 0.65 years) were included. The mean SE was 0.13 ± 0.63 D, AL was 22.35 ± 0.67 mm, CR was 7.76 ± 0.25 mm, and AL/CR ratio was 2.88 ± 0.72. The overall prevalence of myopia and high myopia were 2.9 and 0.2%, respectively. Multiple regression analysis showed that myopic SE was significantly associated with male sex (β = −0.14, p = 0.02) and parental myopia (β = −0.15, p = 0.04). Meanwhile, longer AL was significantly associated with older age (β = 0.13, p = 0.02), male sex (β = 0.44, p < 0.001), parental myopia (β = 0.24, p = 0.01), and screen time (including smartphones, tablets, and computers) (>1 h, β = 0.14, p = 0.04). A higher AL/CR was significantly associated with older age (β = 0.02, p < 0.001), male sex (β = 0.03, p < 0.001), ratio and parental myopia (β = 0.03, p = 0.02).

Conclusion

The prevalence of myopia and high myopia were 2.9 and 0.2%, respectively, among Japanese preschool children in 2021. Longer AL was associated with older age, male sex, parental myopia, and screen time in children aged 4–6 years. Children with a high risk of myopia can be identified early based on parental myopia information for early prevention.