Ocular biometry distribution and one-year growth in eight-year-old Southern European schoolchildren under the CISViT project

Academic Editor: Hee-Young Choi Received: 14 January 2025 Revised: 5 February 2025 Accepted: 10 February 2025 Published: 12 February 2025 Citation: Gharbi, M.E.; Guisasola, L.; Galdón, A.; Vinuela-Navarro, V.; Pérez-Corral, J.; Tomás, N.; Vila-Vidal, N. Ocular Biometry Distribution and One-Year Growth in Eight-Year-Old Southern European Schoolchildren Under the CISViT Project. Children 2025,12, 221. https://doi.org/ 10.3390/children12020221 Copyright: © 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/ licenses/by/4.0/). Article Ocular Biometry Distribution and One-Year Growth in Eight-Year-Old Southern European Schoolchildren Under the CISViT Project Mariam El Gharbi 1,2,* , Laura Guisasola 1, Alba Galdón 1, Valldeflors Vinuela-Navarro 1,2 , Joan Pérez-Corral 1,2 , Núria Tomás 1and Núria Vila-Vidal 1,2 1Visió Optometria i Salut, Departament d’Òptica i Optometria, Universitat Politècnica de Catalunya, 08222 Terrassa, Spain; [email protected] (L.G.); [email protected] (A.G.); [email protected] (V.V.-N.); [email protected] (J.P.-C.); [email protected] (N.T.); [email protected] (N.V.-V.) 2Centre Universitari de la Visió, Universitat Politècnica de Catalunya, 08222 Terrassa, Spain *Correspondence: [email protected] Abstract: Objective: To analyse variations in axial length (AL), corneal radius (CR) and the AL/CR ratio over one year in eight-year-old schoolchildren, considering sex, ethnicity and refractive error. Methods: Vision screenings were conducted in 16 schools in Terrassa (Barcelona, Spain) with eight-year-old children as part of the CISViT project. Measurements included ocular biometrics (AL and CR) and non-cycloplegic autorefraction for refractive error. Parental questionnaires provided demographic data (birth date, ethnicity). The same procedures were repeated after one year. Results: Ocular biometric parameters differed by sex and ethnicity. Boys and children of Maghreb descent had longer AL and flatter CR than girls and Caucasian children (p< 0.001 for both visits). The AL/CR ratio was higher in boys than girls (p= 0.002 in the initial visit and p= 0.011 in the follow-up visit) but consistent across ethnicities (p= 0.291 and p= 0.390). AL and AL/CR ratio differed significantly by refractive error status (p< 0.001 in both visits), increasing in more myopic children, while CR showed no significant difference. In myopic children, the AL/CR ratio exceeded 3.0, and typical sex-based biometric differences diminished. Growth rates for AL and AL/CR ratio were similar across sex and ethnicity, indicating minimal demographic influence. Conclusions: AL and CR differ significantly by sex and ethnicity, with demographic differences evident in baseline measurements but not in growth rates over one year. The consistency of the AL/CR ratio across ethnicities, despite sex-based differences, supports its utility as a reliable metric for assessing refractive development in diverse populations. Keywords: axial length; corneal radius; ocular biometry; myopia; Southern Europe; schoolchildren 1. Introduction Myopia has emerged as a global public health concern in recent decades, significantly affecting a large portion of the population, particularly school-aged children [ 1 – 6 ]. Early onset of myopia is linked to the development of high myopia ( ≥− 6 D) in adulthood, which increases the risk of retinal and optic nerve pathologies, potentially leading to severe visual impairment or blindness [ 1 , 7 ]. Myopia and its associated complications are one of the leading causes of visual impairment and blindness worldwide [8,9]. Given the increasing prevalence and potential complications of myopia, it is crucial to have effective methods to identify children at risk of developing or increasing myopia. Children 2025,12, 221 https://doi.org/10.3390/children12020221 Children 2025,12, 221 2 of 16 Ocular biometry measurements, which provide detailed data on axial length (AL) and corneal curvature radius (CR), as well as the ratio between them (AL/CR), are important indicators for the prevention and management of childhood myopia [10–12]. Studies have shown that the CR undergoes significant variations during the first three or five years of life and stabilises thereafter [ 13 , 14 ]. In contrast, AL experiences significant growth until adolescence [10–12,14]. The myopic changes in refractive error are related to the excessive growth of AL, resulting in a mismatch with CR and other ocular biometric parameters. Therefore, although the myopic changes in refractive error are mainly related to the excessive growth of AL, analysing the AL value alone is not sufficient to identify children at risk of developing myopia; it is necessary to consider both its growth rate and its relationship with CR. The AL/CR ratio can serve as an important indicator of the onset and progression of myopia [12,14]. Longitudinal cohort studies of AL are more important than cross-sectional studies for identifying children at risk of myopia because they allow the monitoring of changes over time within the same individuals, providing a dynamic understanding of eye growth and myopia progression. These studies better predict future refractive changes, evaluate the effectiveness of myopia control treatments, enhance the understanding of the mechanisms behind myopia development and progression and examine correlations between AL and other ocular parameters, offering a comprehensive view that cross-sectional studies cannot capture. This long-term predictive capacity is crucial for pediatric refractive development and supports the creation of practical tools, such as online myopia progression or myopia risk calculators, which can help translate research findings into clinical practice. Such tools bridge the gap between empirical data and real-world applications, aiding clinicians in explaining potential myopia progression to parents and guiding personalized myopia management strategies. The AL development is influenced by various demographical factors, with age, sex, ethnicity and anthropometry being the most significant [ 10 , 14 – 18 ]. Geographical region of residence is also a critical variable, as there are notable differences in both the value and growth rates of AL between European and Asian populations, especially in schoolaged children [ 10 , 12 ]. While numerous cohort studies have been conducted on Asian and Northern European populations, research in Southern Europe remains sparse. So, considering the impact of environmental and cultural factors on myopia development, studies in diverse populations are crucial. The Terrassa Visual Health Children’s Cohort (CISViT) project is a pioneering schoolchildren cohort study in the Southern European population. With data collected from the CISViT project, this study aims to analyse variations in AL, CR and the ratio AL/CR over a one-year period in eight-year-old schoolchildren, taking into account sex, ethnicity and refractive error. By doing so, it seeks to provide valuable insights into regional differences in ocular biometric growth patterns and their implications for myopia prevention and management. 2. Materials and Methods 2.1. Study Design As part of the CISViT project, which involves 16 schools in the city of Terrassa (Barcelona, Spain), this prospective longitudinal epidemiological cohort study consists of two phases. The initial data collection phase involves a visual screening of eight-year-old schoolchildren at the Centre Universitari de la Visió (University Vision Center; the Universitat Politècnica de Catalunya optometry clinic) comprising monocular measurements of distance visual acuity in both eyes using Snellen charts, non-cycloplegic objective refraction measurements by WAM 5500 open-field autorefractor (Grand Seiko Co., Tokyo, Children 2025,12, 221 3 of 16 Japan) and ocular biometric measurements, including AL and CR, by MYAH biometer (Topcon Healthcare Co., Tokyo, Japan). Additionally, a distance and near cover test was conducted to detect binocular vision misalignments. In the follow-up phase, a visual screening was conducted one year later within the school premises consisting of monocular non-cycloplegic objective refraction measurements in both eyes (ARK-1e autorefractor, Nidek Co., Gamagori, Japan) and ocular biometric measurements, including AL and CR, by AL-SCAN M biometer (Nidek Co., Japan). For logistic reasons, participants were screened using different autorefractometers and biometers in the initial and follow-up phases. This should not result in significant differences in outcomes, as a previous study [ 19 ] has demonstrated minimal differences between open-field autorefractometers without fogging, such as the WAM 5500, and closed-field autorefractometers with fogging, like the Nidek ARK-1e. In cases of fluctuating measurements or discrepancies with visual acuity, retinoscopy was performed as an additional verification method. On the other hand, a comparative study between the two biometers used in the CISViT project [ 20 ] confirmed that they both provide reproducible and interchangeable data, showing a within-subject standard deviation of 0.01 mm and a repeatability limit of 0.04 mm, ensuring consistency and reliability across the study phases. In addition to these tests, before each visual screening, the participants’ parents were required to complete a detailed questionnaire, which collected, among other information, ethnic ancestry and birth data. 2.2. Ethics Statement This study was approved by the Drugs Medication Ethics Committee (CEIm) of Mútua Terrassa (P/22-090) and designed in accordance with the Declaration of Helsinki. Written informed consent was obtained from each parent or guardian prior to the schoolchildren’s involvement in the study, ensuring that they fully understood the nature and purpose of the research. Informed consent was required and re-confirmed at the follow-up visit. 2.3. Study Population Sample The study involved 476 eight-year-old schoolchildren enrolled in primary schools in Terrassa. A sample size calculation conducted with EpiData software (EpiData Association, Version 4.2) determined that a minimum of 435 participants was needed, assuming a 95% confidence level. Applying the inclusion criteria of astigmatisms equal to or less than 1.50 D and anisometropia not exceeding 1.50 D, the refractive error of the sample, measured in terms of spherical equivalent (SE), ranged from +3.00 to −4.25 D. To ensure the validity and reliability of the results, specific exclusion criteria were applied. Children undergoing any myopia control treatments were excluded to avoid confounding effects on ocular development. Additionally, children with amblyopia or strabismus were excluded, as these conditions could interfere with typical eye development. Participants were also excluded if they showed low cooperation during screening or if they did not participate in the follow-up phase of the study. 2.4. Measurements and Variable Definitions •Sociodemographic Variables The sociodemographic variables considered were sex and ethnicity. The sample was classified by ethnicity into Caucasian, Maghreb and Latin, as these were the most representative, and the category of Other, which included schoolchildren of sub-Saharan African, Asian and biracial descent. Children 2025,12, 221 4 of 16 •Ocular Biometric Variables The biometric variables considered were AL, CR and the AL/CR ratio. The CR was calculated as the average of the two principal corneal radii (Equation (1)). The ratio AL/CR was defined as the quotient of these two variables (Equation (2)). RC =R1 +R2 2(1) AL/CR ratio =AL CR (2) •Refractive Error To analyse refractive error, SE was used, defined as Equation (3). SE =Sphere +Cylindre(−) 2(3) The classification of SE was based on refractive status. Hyperopia was defined as SE greater than +0.50 D, emmetropia as SE between +0.50 D and − 0.50 D (inclusive) and myopia as SE less than − 0.50 D. Regarding SE progression, changes between the initial and follow-up visits were categorized as less than or equal to − 0.50 D or more negative than −0.50 D. 2.5. Statistical Analysis The Kolmogorov–Smirnov normality test was employed to assess the normal distribution of variables. The AL and CR parameters followed a normal distribution (p> 0.05), while SE and the AL/CR ratio did not follow a normal distribution (p< 0.001). Given the high correlation between measurements from both eyes for AL (Pearson’s r: 0.908, p< 0.001), CR (Pearson’s r: 0.948, p< 0.001), AL/CR ratio (Spearman’s rho: 0.925, p< 0.001) and SE (Spearman’s rho: 0.882, p< 0.001), only data from the right eye was included for the statistical analysis. To assess differences among the sample groups, an independent t-test or ANOVA was used for variables with a parametric distribution, while the Mann–Whitney U test or Kruskal–Wallis test were applied for non-parametric variables. Post hoc analysis was performed to identify specific group differences. All analyses were carried out using SPSS software (version 29.0.2.0), with statistical significance set at p< 0.05. 3. Results 3.1. Sample Population Characteristics This study included 478 schoolchildren who met the inclusion criteria. After excluding two participants due to the inability to measure refractive error during the follow-up visit, the final sample size was 476 schoolchildren. At the initial visit the mean age was 8.2 ± 0.5 years, which increased to 9.3 ± 0.5 years at the one-year follow-up visit. The study sample benefited from a wide ethnic diversity given that it comprised children of Southern European descent as well as a substantial proportion of children of Maghreb descent, a population that has not been previously studied. Table 1details the population sample demographic characteristics including sex, ethnicity and refractive error, and Figure 1 shows myopia prevalence found for the different demographic characteristics considered at the initial visit. Children 2025,12, 221 5 of 16 Table 1. Distribution of refractive error groups and ethnicity in the study sample at the initial visit, categorised by sex. p-values indicate differences by sex. All N = 476 Boys N = 231 (48.5%) Girls N = 245 (51.5%) p Refractive Error Hyperopic 90 (18.9%) 43 (18.6%) 47 (19.2%) 0.673 Emmetropic 340 (71.4%) 164 (71.0%) 176 (71.8%) 0.515 Myopic 46 (9.7%) 24 (10.4%) 22 (9.0%) 0.768 Ethnicity Caucasian 214 (45%) 106 (45.9%) 108 (44.1%) 0.891 Maghreb 141 (29.6%) 69 (29.9%) 72 (29.4%) 0.801 Latin 79 (16.6%) 38 (16.5%) 41 (16.7%) 0.736 Other 42 (8.8%) 18 (7.8) 24 (9.8%) 0.355 Children 2025, 12, x FOR PEER REVIEW 5 of 16 Table 1. Distribution of refractive error groups and ethnicity in the study sample at the initial visit, categorised by sex. p-values indicate differences by sex. All N = 476 Boys N = 231 (48.5%) Girls N = 245 (51.5%) P Refractive Error Hyperopic 90 (18.9%) 43 (18.6%) 47 (19.2%) 0.673 Emmetropic 340 (71.4%) 164 (71.0%) 176 (71.8%) 0.515 Myopic 46 (9.7%) 24 (10.4%) 22 (9.0%) 0.768 Ethnicity Caucasian 214 (45%) 106 (45.9%) 108 (44.1%) 0.891 Maghreb 141 (29.6%) 69 (29.9%) 72 (29.4%) 0.801 Latin 79 (16.6%) 38 (16.5%) 41 (16.7%) 0.736 Other 42 (8.8%) 18 (7.8) 24 (9.8%) 0.355 Figure 1. Myopia prevalence at the initial visit, categorised by sex and ethnicity. 3.2. General Ocular Biometric Parameter Distribution Table 2 shows the distribution of ocular biometric parameters found at the initial visit and the one-year follow-up. Significant differences were observed between boys and girls across all ocular biometric parameters in both the initial and follow-up visits. Boys exhibited a longer AL (p < 0.001 in both visits), a flatter CR (p < 0.001 in both visits) and a higher AL/CR ratio (p = 0.002 in the initial visit and p = 0.011 in the follow-up visit) compared to girls. Table 2. Ocular biometric parameter distribution categorised by sex at the initial and the one-year follow-up visits. p-values indicate differences between boys and girls. Initial Visit (8.2 Years Old) Follow-Up Visit (9.3 Years Old) All Boys Girls p All Boys Girls p AL (mm) 22.93 ± 0.78 23.22 ± 0.73 22.65 ± 0.72 <0.001 23.06 ± 0.81 23.35 ± 0.75 22.79 ± 0.77 <0.001 CR (mm) 7.79 ± 0.27 7.86 ± 0.27 7.72 ± 0.25 <0.001 7.78 ± 0.27 7.85 ± 0.28 7.71 ± 0.25 <0.001 AL/CR 2.95 ± 0.08 2.96 ± 0.09 2.93 ± 0.08 0.002 2.97 ± 0.09 2.98 ± 0.09 2.96 ± 0.08 0.011 Figure 1. Myopia prevalence at the initial visit, categorised by sex and ethnicity. 3.2. General Ocular Biometric Parameter Distribution Table 2shows the distribution of ocular biometric parameters found at the initial visit and the one-year follow-up. Significant differences were observed between boys and girls across all ocular biometric parameters in both the initial and follow-up visits. Boys exhibited a longer AL (p< 0.001 in both visits), a flatter CR (p< 0.001 in both visits) and a higher AL/CR ratio (p= 0.002 in the initial visit and p= 0.011 in the follow-up visit) compared to girls. Table 2. Ocular biometric parameter distribution categorised by sex at the initial and the one-year follow-up visits. p-values indicate differences between boys and girls. Initial Visit (8.2 Years Old) Follow-Up Visit (9.3 Years Old) All Boys Girls pAll Boys Girls p AL (mm) 22.93 ± 0.78 23.22 ± 0.73 22.65 ± 0.72 <0.001 23.06 ± 0.81 23.35 ± 0.75 22.79 ± 0.77 <0.001 CR (mm) 7.79 ± 0.27 7.86 ± 0.27 7.72 ± 0.25 <0.001 7.78 ± 0.27 7.85 ± 0.28 7.71 ± 0.25 <0.001 AL/CR 2.95 ± 0.08 2.96 ± 0.09 2.93 ± 0.08 0.002 2.97 ± 0.09 2.98 ± 0.09 2.96 ± 0.08 0.011 Children 2025,12, 221 6 of 16 3.3. Ocular Biometric Parameters by Refractive Error As shown in Table 3, AL values differed significantly among the refractive groups (p< 0.001 in both the initial and follow-up visits). As expected, a greater AL was associated with myopic refractive error. Post hoc analyses revealed significant differences in AL (p< 0.001 in both visits) across all three refractive groups. In contrast, no differences in CR were observed across refractive groups (p= 0.069 in the initial visit and 0.149 in the follow-up visit). Table 3. Ocular biometric parameter distribution categorised by sex and refractive error at both the initial and one-year follow-up visits. p(sex) indicates differences between boys and girls and p (refractive error) indicates differences among refractive error groups. Initial Visit (8.2 Years Old) Follow-Up Visit (9.3 Years Old) All Boys Girls p(Sex) p (Refractive Error) All Boys Girls p(Sex) p (Refractive Error) AL (mm) <0.001 <0.001 All 22.93 ± 0.78 23.22 ± 0.73 22.65 ± 0.72 <0.001 23.06 ± 0.81 23.35 ± 0.75 22.79 ± 0.77 <0.001 Hyperopic 22.47 ± 0.68 22.75 ± 0.65 22.21 ± 0.60 <0.001 22.59 ± 0.68 22.88 ± 0.65 22.32 ± 0.61 <0.001 Emmetropic 22.97 ± 0.74 23.29 ± 0.69 22.68 ± 0.67 <0.001 23.10 ± 0.76 23.40 ± 0.70 22.82 ±070 <0.001 Myopic 23.47 ± 0.68 23.62 ± 0.76 23.29 ± 0.83 0.169 23.64 ± 0.92 23.77 ± 0.85 23.50 ± 0.99 0.332 CR (mm) 0.069 0.149 All 7.79 ±0.27 7.86 ±0.27 7.72 ±0.25 <0.001 7.78 ±0.27 7.85 ±0.28 7.71 ±0.25 <0.001 Hyperopic 7.75 ±0.23 7.81 ±0.24 7.69 ±0.22 0.0017 7.74 ±0.23 7.80 ±0.24 7.69 ±0.22 0.022 Emmetropic 7.81 ±0.28 7.88 ±0.28 7.73 ±0.26 <0.001 7.79 ±0.29 7.88 ±0.29 7.71 ±0.26 <0.001 Myopic 7.73 ±0.23 7.76 ±0.19 7.71 ±0.27 0.512 7.73 ±0.23 7.74 ±0.20 7.71 ±0.27 0.670 AL/CR <0.001 <0.001 All 2.95 ±0.08 2.96 ±0.09 2.93 ±0.08 0.002 2.97 ±0.09 2.98 ±0.09 2.96 ±0.08 0.011 Hyperopic 2.90 ±0.07 2.92 ±0.07 2.89 ±0.06 0.044 2.92 ±0.07 2.93 ±0.07 2.90 ±0.06 0.016 Emmetropic 2.94 ±0.07 2.96 ±0.08 2.93 ±0.07 0.024 2.97 ±0.07 2.97 ±0.07 2.96 ±0.07 0.127 Myopic 3.04 ±0.10 3.05 ±0.11 3.02 ±0.10 0.612 3.06 ±0.12 3.07 ±0.12 3.05 ±0.11 0.660 The refractive groups also exhibited statistically significant differences in the AL/CR ratio (p< 0.001 in both visits), with higher ratios in groups with more myopic SE, primarily due to differences in AL. Notably, the myopic group displayed AL/CR ratio values exceeding 3.0 at both visits. When analysing the distribution of ocular biometry across refractive groups stratified by sex, significant differences were observed in the hyperopic and emmetropic groups only (Table 3). Boys exhibited a longer AL and a flatter CR compared to girls in both visits. At the initial visit, the AL/CR ratio was higher in hyperopic and emmetropic boys compared to girls. However, at the follow-up visit, while this difference persisted in the hyperopic group, no differences were found between emmetropic boys and girls. Conversely, no differences by sex were identified in the myopic group for any biometric parameter at any visit. 3.4. Correlation Between Ocular Biometric Parameters and Refractive Error A significant positive correlation was observed between AL and CR (Pearson coefficient 0.676, p< 0.001), indicating that subjects with a longer AL tend to have a flatter CR. As shown in Table 4, SE was inversely correlated with both AL and the AL/CR ratio, suggesting that these variables were higher in individuals with more negative SE. AL was not correlated with SE in hyperopes, and the significant correlation was stronger in myopes than in emmetropes. The correlation coefficient was higher for the AL/CR ratio than for AL alone. No correlation was observed between CR and SE in any of the refractive groups. Children 2025,12, 221 7 of 16 Table 4. Spearman’s rho correlation coefficient (p-value) for ocular biometric parameters and SE at the initial and follow-up visits. Initial Visit (8.2 Years Old) Follow-Up Visit (9.3 Years Old) AL CR AL/CR AL CR AL/CR All − 0.396 (p< 0.001) −0.018 (p= 0.694) − 0.410 (p< 0.001) − 0.312 (p< 0.001) 0.072 (p= 0.117) − 0.413 (p< 0.001) Hyperopic −0.204 (p= 0.054) 0.104 (p= 0.330) − 0.384 (p< 0.001) −0.014 (p= 0.893) 0.196 (p= 0.064) − 0.301 (p= 0.004) Emmetropic − 0.234 (p< 0.001) −0.011 (p= 0.840) − 0.233 (p< 0.001) − 0.229 (p< 0.001) 0.037 (p= 0.501) − 0.289 (p< 0.001) Myopic − 0.603 (p< 0.001) 0.081 (p= 0.593) − 0.682 (p< 0.001) − 0.661 (p< 0.001) 0.137 (p= 0.365) − 0.767 (p< 0.001) 3.5. Ocular Biometric Parameters by Ethnicity As shown in Table 5, significant differences were found in AL (p= 0.002 in the initial visit and p< 0.001 in the follow-up) and CR (p= 0.030 in the initial visit and p= 0.018 in the follow-up) among the ethnic groups. Post hoc analysis identified that these differences were primarily between Caucasians and Maghreb (p< 0.001), with Maghreb displaying a longer AL and flatter CR. In contrast, the AL/CR ratio distribution was similar across ethnic groups (p= 0.291 in the initial visit and 0.390 in the follow-up). Table 5. Ocular biometric parameter distribution categorised by sex and ethnicity at the initial and one-year follow-up visits. p(sex) values indicate differences between boys and girls and p(ethnicity) indicate the differences among ethnic groups. Initial Visit (8.2 Years Old) Follow-Up Visit (9.3 Years Old) All Boys Girls p(Sex) p (Ethnicity) All Boys Girls p(Sex) p (Ethnicity) AL (mm) 0.002 <0.001 Caucasian 22.78 ± 0.76 23.09 ± 0.69 22.48 ± 0.70 <0.001 22.91 ± 0.78 23.20 ± 0.70 22.61 ± 0.73 <0.001 Maghreb 23.10 ± 0.81 23.38 ± 0.79 22.84 ± 0.74 <0.001 23.25 ± 0.86 23.52 ± 0.82 23.00 ± 0.82 <0.001 Latin 23.00 ± 0.74 23.24 ± 0.73 22.77 ± 0.68 0.004 23.12 ± 0.76 23.36 ± 0.76 22.91 ± 0.67 0.008 Other 22.93 ± 0.78 23.37 ± 0.57 22.60 ± 0.70 <0.001 23.07 ± 0.75 23.53 ± 0.53 22.73 ± 0.72 <0.001 CR (mm) 0.030 0.018 Caucasian 7.75 ± 0.27 7.83 ± 0.28 7.68 ± 0.24 <0.001 7.74 ± 0.27 7.82 ± 0.28 7.66 ± 0.24 <0.001 Maghreb 7.84 ± 0.28 7.89 ± 0.28 7.80 ± 0.26 0.057 7.84 ± 0.28 7.88 ± 0.28 7.79 ± 0.26 0.060 Latin 7.78 ± 0.25 7.85 ± 0.25 7.72 ± 0.68 0.020 7.77 ± 0.26 7.84 ± 0.26 7.71 ± 0.25 0.028 Other 7.79 ± 0.27 7.93 ± 0.19 7.70 ± 0.25 0.002 7.78 ± 0.27 7.92 ± 0.21 7.67 ± 0.25 0.001 AL/CR 0.291 0.390 Caucasian 2.94 ± 0.07 2.95 ± 0.08 2.93 ± 0.06 0.062 2.96 ± 0.08 2.97 ± 0.08 2.95 ± 0.07 0.025 Maghreb 2.95 ± 0.09 2.97 ± 0.09 2.93 ± 0.09 0.029 2.97 ± 0.10 2.99 ± 0.10 2.95 ± 0.10 0.031 Latin 2.96 ± 0.09 2.96 ± 0.09 2.95 ± 0.09 0.575 2.98 ± 0.09 2.98 ± 0.10 2.97 ± 0.09 0.623 Other 2.94 ± 0.07 2.95 ± 0.06 2.94 ± 0.068 0.550 2.97 ± 0.08 2.97 ± 0.08 2.97 ± 0.07 0.848 Regarding sex, boys had a longer AL (p< 0.001 in both visits) than girls across all ethnic groups. Boys also had a significantly flatter CR in most of the ethnic groups, except in Maghreb where the differences in CR between boys and girls is minimal and without statistical significance. Caucasian and Maghreb boys showed higher values in AL/CR ratio than girls; no significant differences in the AL/CR ratio by sex were found in Latin and other ethnicities. 3.6. Ocular Biometric Parameters Compared Across Ethnicities When comparing our results with findings from other populations [ 6 , 10 ] (Table 6), it is observed that the AL in Southern Europe is lower than in Northern Europe (The Netherlands) [10], while the CR is very similar. On the other hand, the results obtained in the Maghreb population closely resembled those in East Asia (China) [ 6 ]. Non-differences were observed in the AL/CR ratio between all ethnicities. Children 2025,12, 221 8 of 16 Table 6. Comparison of ocular biometric parameters and refractive error among nine-year-old schoolchildren across different ethnic origins and studies: Southern European (CISViT study), Northern European (Generation R study) [ 10 ], Maghreb (CISViT study) and East Asian (Baoshan Eye study) [ 6 ]. The SE was obtained via cycloplegic autorefraction in the Generation R and Baoshan Eye studies. Population Group AL (mm) CR (mm) AL/CR Ratio SE (D) Study Southern Europe 22.91 ±0.78 7.74 ±0.27 2.96 ±0.08 +0.09 ±0.78 CISViT Northern Europe 23.10 ±0.84 7.78 ±0.26 2.97 ±0.09 +0.74 ±1.30 Generation R [ 10 ] Maghreb 23.25 ±0.86 7.84 ±0.28 2.97 ±0.10 −0.39 ±1.12 CISViT East Asia 23.29 ±0.87 7.84 ±0.25 2.97 ±0.10 0.02 ±1.29 Baoshan Eye [6] 3.7. Annual Growth in Ocular Biometric Parameters Table 7shows the one-year growth of the ocular biometric parameters. Significant growth in AL (p= 0.010) and AL/CR ratio (p< 0.001) was observed over the follow-up year, while CR remained constant (p= 0.574). This suggests that the significant AL/CR ratio variation was primarily due to AL growth. Table 7. One-year variation in AL and AL/CR ratio of the sample categorised by sex, refractive error and ethnicity. p(variation) indicates significance in the one-year variation and p(groups) indicates differences among sexes, refractive error and ethnicity. AL (mm) AL/CR Variation p(Variation) p(Group) Variation p(Variation) p(Group) All 0.13 0.010 0.021 <0.001 Sex 0.372 0.863 Boys 0.12 0.072 0.019 0.021 Girls 0.14 0.037 0.023 0.002 Refractive error 0.484 0.332 Hyperopic 0.12 0.223 0.016 0.116 Emmetropic 0.13 0.024 0.022 <0.001 Myopic 0.17 0.336 0.024 0.312 SE variation <0.001 <0.001 ∆SE ≥ −0.50 D 0.12 0.034 0.020 0.001 ∆SE < −0.50 D 0.17 0.144 0.024 0.038 Ethnicity 0.667 0.851 Caucasian 0.12 0.110 0.021 0.004 Maghreb 0.15 0.135 0.021 0.071 Latin 0.13 0.286 0.019 0.181 Other 0.14 0.390 0.024 0.127 Although no significant sex differences were found in AL growth (p= 0.372) ( Figure 2A ), girls exhibited a statistically significant variation in AL growth (p= 0.037), whereas boys did not (p= 0.072). No differences by sex were observed in CR (0.296) and AL/CR ratio (p= 0.863) variation. Considering ethnicity, there were no differences in the AL growth (p= 0.667) (Figure 2B), CR (p= 0.436) and the AL/CR ratio (p= 0.851) among the different ethnic groups. When analysing refractive error, significant variation was observed only in the emmetropic group, despite the absence of statistically significant differences in AL (Figure 2C) and AL/CR ratio variations across refractive error groups. Clinically, the myopic group exhibited greater variation but was not statistically significant. Children 2025,12, 221 9 of 16 Children 2025, 12, x FOR PEER REVIEW 9 of 16 Figure 2. One-year axial length growth (Δ mm) categorised as follows: (A) by sex, (B) by ethnicity, (C) by refractive error groups. When analysing refractive error, significant variation was observed only in the emmetropic group, despite the absence of statistically significant differences in AL (Figure 2C) and AL/CR ratio variations across refractive error groups. Clinically, the myopic group exhibited greater variation but was not statistically significant. On the other hand, we analysed the variation in SE to identify which groups within the stratified sample—classified by sex, ethnicity and refractive error—showed the greatest variability. As expected, the group showing a SE variation more negative than −0.50 D exhibited greater AL growth (Table 7). Figure 3 illustrates the percentage of schoolchildren exhibiting a SE variation more negative than −0.50 D during the one-year follow-up, with data stratified by sex, ethnicity and refractive error. No significant differences were observed in refractive error variations between sexes or ethnicities. However, it is important to emphasize that this negative SE shift was most pronounced among children initially classified as hyperopic, indicating a higher risk of myopia progression in this refractive group compared to emmetropic and myopic children. Figure 2. One-year axial length growth ( ∆ mm) categorised as follows: (A) by sex, (B) by ethnicity, (C) by refractive error groups. On the other hand, we analysed the variation in SE to identify which groups within the stratified sample—classified by sex, ethnicity and refractive error—showed the greatest variability. As expected, the group showing a SE variation more negative than − 0.50 D exhibited greater AL growth (Table 7). Figure 3illustrates the percentage of schoolchildren exhibiting a SE variation more negative than − 0.50 D during the one-year follow-up, with data stratified by sex, ethnicity and refractive error. No significant differences were observed in refractive error variations between sexes or ethnicities. However, it is important to emphasize that this negative SE shift was most pronounced among children initially classified as hyperopic, indicating a higher risk of myopia progression in this refractive group compared to emmetropic and myopic children. In the group with a SE variation more negative than − 0.50 D, the SE variation was − 0.80 D in hyperopes and − 1.01 D in myopes. This trend was reflected in axial length (AL) growth, with hyperopes showing a mean increase of 0.12 mm compared to 0.17 mm in myopes (Table 7and Figure 2C). Children 2025,12, 221 16 of 16 27. He, X.; Zou, H.; Lu, L. Axial length/corneal radius ratio: Association with refractive state and role on myopia detection combined with visual acuity in chinese schoolchildren. PLoS ONE 2015,10, e0111766. [CrossRef] 28. Ip, J.M.; Huynh, S.C.; Kifley, A. Variation of the contribution from axial length and other oculometric parameters to refraction by age and ethnicity. Investig. Ophthalmol. Vis. Sci. 2007,48, 4846–4853. [CrossRef] 29. Liu, S.; Chen, J.; Wang, J.; Zhu, Z.; Zhang, J.; Zhang, B.; Yang, J.; Du, L.; Zhu, J.; Zou, H.; et al. Cutoff values of axial length/corneal radius ratio for determining myopia vary with age among 3-18 years old children and adolescents. Graefes Arch. Clin. Exp. Ophthalmol. 2024,262, 651–661. [CrossRef] 30. O’Donoghue, L.; McClelland, J.F.; Logan, N.S.; Rudnicka, A.R.; Owen, C.G.; Saunders, K.J. Refractive error and visual impairment in school children in Northern Ireland. Br. J. Ophthalmol. 2010,94, 1155–1159. [CrossRef] 31. Li, L.; Zhong, H.; Li, J.; Li, C.R.; Pan, C.W. Incidence of myopia and biometric characteristics of premyopic eyes among Chinese children and adolescents. BMC Ophthalmol. 2018,18, 178. [CrossRef] [PubMed] 32. McCullough, S.; Adamson, G.; Breslin, K.M.M.; McClelland, J.F.; Doyle, L.; Saunders, K.J. Axial growth and refractive change in white European children and young adults: Predictive factors for myopia. Sci. Rep. 2020,10, 15189. [CrossRef] [PubMed] Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). 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