Prevalence and estimation of the evolution of myopia in Spanish children

doi:10.21203/rs.3.rs-2844750/v1

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Prevalence and estimation of the evolution of myopia in Spanish children

https://doi.org/10.21203/rs.3.rs-2844750/v1

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Purpose: This study aims to analyze the myopia prevalence in Spanish children from five to seven years old over the last five years and to predict the rate of myopia in Spain by 2030.

Methods: The sample consisted of children aged between 5 and 7, who underwent an optometric examination consisting of the measurement of visual acuity (VA) and determination of objective and subjective refraction. In addition, they completed a lifestyle questionnaire. The cut-off points to define the refractive error are established according to the spherical equivalent (SE) value as hyperopia, for SE over +0.50D, myopia, for SE under -0.50D, or emmetropia, when the SE is between -0.50D and +0.50D.

Results: The myopia rate in Spanish children aged between five and seven was 19%. Myopia prevalence progressively increased as children grew up (p≤0.001). It is estimated that, in the year 2030, the rate of myopia will be 30.2% [CI: 25.3–35.0]. Of which 81.9% [CI: 78.3–85.3] will have low myopia, 10.0% [CI: 7.2–12.8] moderate myopia, and 7.3% [CI: 4.9–9.7] high myopia.

Conclusion: Nineteen percent of Spanish children between five and seven are myopes. In 2030 is expected that 30.2% of Spanish children between 5 and 7 years of age will be myopes. These estimations will support eye care professionals in recommending children spend more time outdoors to prevent the onset of myopia and the use of methods to control myopia to avoid reaching these figures of high myopia.

myopia

childhood

Spain

estimation

As a result of the impact of environmental factors, myopia is reaching epidemic proportions quickly [1]. Nowadays, myopia is already affecting one-third of the worldwide population, although its frequency depends on the geographical region. Myopia prevalence is higher in developed countries, particularly in East Asia, and most evidence suggests that this prevalence is increasing. These differences in terms of the rate of myopia reflect the tendency among children from many countries to spend long periods reading, studying, or more recently, using computers or smartphones. The fast development of the modern economy, digitalization, and many changes in children's lifestyles have had an impact on myopia onset and development [2].

In 2016, Holden et al. [1] performed a worldwide systematic review and a meta-analysis of the rates of myopia and high myopia to make an estimation of the trends over time between 2000 and 2050. They included 145 studies with 2.1 million participants, and the results estimated that in the year 2000 there were 1.406 billion myopes globally, of which 163 million had high myopia. They calculated that by 2050, there will be more than 4.758 billion, that is, half the global population, of which 938 million will have high myopia. However, myopia prevalence differs in the different countries, so estimations will vary geographically. Children with myopia at a young age have the highest risk, given that the duration of the condition is longer, of developing high myopia and thus also myopic macular degeneration. For this reason, the starting age and its progression are the main indicators of the risk that the child could develop high myopia [3].

The first study to analyze the pediatric prevalence of myopia in Spain was the one conducted by Montés-Micó et al. [4] in 2000. This study found the myopia prevalence among children of 3-8 years to be 2.5%, increasing to 25.7% for the 9–19-year age group. This research group has analyzed myopia prevalence in school age (five to seven years old) since 2016. Thus, it has been found that the percentage of myopia has gone from 19.1% to 20% between 2016 and 2020 [5,6]. In recent years, children have gone through several lockdown periods due to the SARS-CoV-2 pandemic, which has required them to spend longer at home and shorter outdoors. Recent studies have found a significant association between myopic progression and policies during the pandemic by governments [7]. Therefore, this study aims to evaluate the rate of myopia in Spanish children aged from five to seven over the last five years, and to predict the evolution of myopia in Spain by 2030.

Definition of variables

The spherical equivalent, defined as SE=sphere+(cylinder/2), was used to establish the refractive error. The classification was: emmetropia: SE between -0.50D and +0.50D; hyperopia: SE over +0.50D and myopia SE less than -0.50D. Being myopia subclassified as low: between -0.50D and -3.00D; medium: between -3.00D and -6.00D; or high: more negative than -6.00D, following the classification of the American Academy of Optometry [8] and International Myopia Institute [9].

First, a cross-sectional study was carried out on the prevalence of myopia in Spain between the years 2016 and 2021. Children from 5 to 7 years were recruited by convenience sampling in opticians from different autonomous communities in Spain.

The Research Ethics Committee of the European University of Madrid (CEI-UE) approved this research under the code CIPI/19/102. The research adheres to the principles of the Declaration of Helsinki. Parental consent was required, and they signed the informed consent form.

Inclusion criteria were ages between 5 and 7 years old.

In terms of the exclusion criteria, participants that failed to collaborate properly, and cases in which the forms and survey were not filled in correctly or were incomplete, were excluded.

Before starting the optometric exam, all the boys and girls had to complete a questionnaire made up of six sections. Questions included information about the reason for the consultation, ophthalmic and medical records of the subjects and their families, and extracurricular activities (asking specifically how long, in hours per day excluding school hours, they spent outdoors, doing activities at near distances, and using digital devices).

Following, the visual exam was performed, consisting of visual acuity, objective refraction through Mohindra retinoscopy, subjective refraction, and evaluation of the anterior segment with the slit lamp.

The software used for carrying out the statistical analysis was SPSS 27.0 software (SPSS Inc., Chicago, Illinois). To know the normality of the variables, the Kolmogorov-Smirnov test was used. Kruskal Wallis test was used to analyze the statistical significance of the variables, considering a cut-off point of p≥0.05.

To verify the variables were independently associated with variable myopia and the spherical equivalent, a binary and linear logistic regression analysis were performed, respectively. The criteria used to select the variables that were included in the model were those that were statistically significant in a previously performed univariate analysis or those that were clinically relevant.

Secondly, an analysis of the estimated prevalence of myopia between the years 2016 and 2030 has been carried out. Estimations were calculated through a predictive model, considering the Spanish population and the myopia prevalence in children from 5 to 7. To carry out the predictions in the adjustment measures, the Ljung-Box statistic, the number of outliers, stationary R square, root mean square of the errors, maximum absolute percentage error, and goodness of fit have been calculated. In turn, the confidence interval of the predictions and the fitted values have been obtained.

For the forecast function in SPSS, the time series modeler approximates exponential smoothing; In addition, it estimates univariate autoregressive integrated moving average (ARIMA) and multivariate ARIMA models for time series and produces forecasts for vehicle population data.

The SPSS Forecast Modeler automatically identifies and estimates the ARIMA or exponential smoothing model that best fits the vehicle population data (series of dependent variables).

Assumptions for the forecast in SPSS:

• The data for vehicle population (dependent variable) and years (independent variable) are time series, which means that each case represents a point in time separated by a constant time interval.

• The data used are assumed to be stationary.

• The independent variables do not have missing values in the period used for the estimation.

Demographic data

A total of 15672 Spanish children participated in this study, but 1994 were excluded for not fulfilling the inclusion criteria. Therefore, the studied sample was comprised of 13728 participants. The median age of the subjects was 6.14±0.79 (Median [IQR]: 6[1]). With regards to gender, 52.3% of the participants (n=7647) were male and 47.7% (n=6982) were female.

Prevalence results

The myopia rates in children between five and seven years old have been 19%, hyperopia 44.2%, and emmetropia 36.8%. Figure 1 shows the refractive error prevalence according to age. With regards to the SE, there was a decrease in these values as age increased (p<0.001). So, at five years the mean value of SE was 0.84±2.10 D (Median [IQR]: 0.00[1,75]), at six years it was 0.74±1.99 D (Median [IQR]: 0.12 [1.50]) and at seven years it was 0.60±1.97 D (Median [IQR]: 0.99[1.75]). There weren´t differences between gender and refractive error (p>0.05).

Among myopes, 88.7% (n=2484) had low myopia, 8.8% (n=243) had medium myopia and 2.4% (n=69) had high myopia. There were significant differences between age and myopia degree (p<0.001). Thus, from five to six years old, the rate of low myopia increased by 3.8% (CI 95%: 1.2-6.5; p<0.001), medium myopia prevalence decreased by 2.4% (CI 95%: 0.01-4.7; p<0.001), and high myopia rates did not vary (CI 95%: 0.00-2.9; p>0.05). Children aged six or seven did not show significant differences in the myopia degree (p<0.05). Figure 2 shows the prevalence of the different degrees of myopia by age.

Estimations of myopia prevalence

In the trend analysis, estimations showed that by 2025 the rate of myopia would grow to 25.4% [IC: 20.6–30.3] and by 2030 to 30.2% [IC: 25.3–35.0]. Thus, between 5 and 7 years of age, in the year 2025, the number of children with myopia in Spain would be 264,173 [CI: 203,119-325,226], and in the year 2030 it would be 264,173 [CI: 203,053-325,293]. As for the rate of low myopia, we can predict it would decrease, so it would be 84.8% of the myopes by 2025 [IC: 81.3–88.3] and 81.8% by 2030 [IC: 78.3–85.3]. The rate of moderate myopia also would be constant, so by 2025 it would be 10.0% of the myopes [IC: 7.2–12.8] and by 2030 it would be 10.8% [IC: 8.0 – 13.6]. On the other hand, it is foreseen that the rate of high myopia would increase, so by 2025 it would be 5.1% of all the myopes [IC: 2.7–7.5] and by 2030 it would be 7.3% [IC: 4.8–9.7]. Figure 3 shows the estimations of myopia prevalence in Spain by 2030. In figure 4 the estimations are shown by the myopia degree.

This study is the first in collecting data of Spanish children for six years, analyzing the myopia prevalence and some of the risk factors related to myopia. The study shows as, like in other countries, there has been an increase of the myopia rates in Spain. Thus, from 2016 to 2021, the percentage of myopic children increased from 16.8% to 19.7%. It estimates that, if the number of hours in near vision continue increasing and children spend less time outdoors, by 2030 30.2% of children aged between 5 and 7 may be myopes. Compared to Holden et al.'s study[1], our results are lower than for the global population. This is due to the current high prevalence of myopia in Asia [10-12] and the early age of our study population. There are hardly any studies covering this topic in Europe in recent years, however, a study comprised of participants from London found that the myopia prescriptions rates increased from 24 to 32% between 2008 and 2017 [13]. According to the estimations made by Holden et al. [1], the myopia prevalence within our group of age should have been 36.7% in 2020, however, the rate recorded in our results was much lower. Likewise, it is worth noting that no changes have been observed over the last year. This may be surprising given that during the last two years children were required to stay at home for extended periods due to lockdowns because of the COVID-19 pandemic, which meant that they spent more time performing near-vision activities and less outdoors time. As shown in previous studies, SE decreased during this time in Spain, indicating that children from five to seven years had greater levels of myopia and pre-myopia [14]. This is in line with the results obtained in other studies [15,16]. Thus, in a study conducted by Wang et al. [15] myopia prevalence increased between 1.2 and 3 times after the COVID-19 pandemic, experiencing the greatest increase within the 6 to 8 years children. In the study carried out in Hong Kong, the incidence of myopia has gone from 11.63% before COVID-19 to 29.68% after COVID-19[16]. This increase in myopia rates may be because of both, the duration of the lockdown and therefore less outdoor activities. Likewise, the hard lockdown that Spanish children suffered last 2020 has had a rebound effect, making parents concerned about the importance of spending time outside, which may explain why we have not found a significant increase in myopia incidence in the last two years in Spain. More and more companies and organizations are making parents aware of how important it is for their children to spend time outdoors, and reduce the time doing near-vision tasks[17]. Spain and Poland are the two European countries that better understood the importance of spending outdoors-time after the pandemic given the benefits this offers in terms of wellness. Thus, in Poland 80% of the population and in Spain 78% of the population agreed or strongly agreed on the importance of outdoor activities[18]. In Asia, some studies were carried out to improve life quality. Therefore, a study carried out in China in 1903 children from 12 schools shown that children with a compulsory outdoor activity had lower myopia prevalence and a lower variation in the refractive error than a control group after a 3-year follow-up. However, a rebound effect seems to happen 3 years after the interruption of the program that included 30 minutes outdoors every day [19].

Concerning the growth of myopia that has been forecast in our results, it matches Holden et al.'s study[1]. This is one of the biggest challenges for eye care professionals since they need to know the children that may become myopes or whose myopia is growing rapidly. Chua et al. [3] proved that age is the best predictor of developing myopia and of high myopia. Nevertheless, Williams et al.[20] found that age only accounts for 15% of growth in myopia.

As previously demonstrated, the progression of high myopia is higher than the one of moderate myopia. Thus, in the study by Kumar Verkicharla et al. [21], they have already shown that in moderate myopes under 15 years of age the rate of myopia progresses by 8%. The reason for this decrease in the rate of moderate myopia may be that there are more and more methods to control the evolution of myopia, and therefore people have greater access to use these methods.

As previously mentioned, the greatest strength of this study was the inclusion of a large number of subjects and the resulting data which made it possible to make annual estimations for myopia prevalence. So far, this is the biggest sample of data that has been used to determine myopia prevalence in a Spanish population. However, this study has certain limitations: To select the sample, randomization was not used, and it was carried out through convenience sampling. In addition, glasses were given to those children who needed them. However, this limitation is compensated given the extent of the sample size to estimate the myopia prevalence. On the other hand, the refraction was not performed under cycloplegia. However, Yeotikar[22] found that in children aged 7 to 16 years, the difference in SE using non-cycloplegic refraction with contralateral nebulization compared with cycloplegic refraction was shorter (median 0.29 D) and not clinically significant. The choice of the spherical equivalent as the main measure is widely accepted. However, according to what is reported by the International Myopia Institute [9] , care should be taken that both eyes are used in a study, the use of "either eye" to define myopia means that some hyperopic o emmetropic eyes can be included in a study population of myopes. For this reason and to avoid classifying hyperopic patients within the myopic group, we have used only the right eye. Regarding the estimation of the prevalence of myopia, we would like to highlight that it is based only on the data obtained from the past five years. However, during these years, children went through a time of confinement due to COVID-19. That year, the spherical equivalent became more negative, which led us to think that the prevalence of myopia would grow significantly[14]. Despite this, as proven in 2021, the growth continued in the same proportion in times with no confinement. This enables us to predict the prevalence of myopia until 2030, assuming that similar situations to COVID-19 may arise.

In conclusion, the myopia rate in Spanish children aged between five and seven stood at 19% between 2016 and 2021. If environmental factors do not change, by 2030 30.2% of Spanish children aged between 5 and 7 years would be myopes. With these estimations, programs for the prevention and control of myopia in children are needed to help to decrease it.

Ethical approval: The Research Ethics Committee of the European University of Madrid (CEI-UE) approved this research under the code CIPI/19/102. The research adheres to the principles of the Declaration of Helsinki.

Consent to participate: Informed consent was obtained from all individual participants included in the study.

Competing Interests: The authors have no relevant financial or non-financial interests to disclose.

Funding: The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Acknowledgments:The “Grupo de Investigación Alain Afflelou” is composed by the following members: Adorna-Duran, T.; Alonso-Corona, S.; Amurrio-Manzanos, E.; Ariza-, M.; Bañuls-, V.; Burillo-Casao, L.; Cantalejo-Bocanegro, I.; Carchi-Vicente, D.; Casanova-, C.; Cobas-Gómez, L.; Coronado-Hernández, I.; Cruz-Lozano, A.; de Diego-López, P.; Díaz-Llorente, A.; Embid-, M.; Encalada-Arévalo, V.; Escámez-de Vera, S.; Fernández de la Pradilla-Miguel, B.; Fernández-Pardo, A.; Gaona-Bosque, S.; García-Burgos, A.; García-de Arriba, C.; García-Gómez, O.; García-Heras, D.; García-Ruiz, M.; García-Salas, A.; García-Saldaña, A.; Gargallo-Insa, L.; Gil-, R.; Gómez-, M.; González-, N.; González-Lafuente, T.; González-Lahuerta, S.; González-Ordúñez, A.; Gordo-, L.; Grima-Cañizares, R.; Guasque-, S.; Homs-, M.; Huelves-, J.; Juárez-López, V.; Khlus-, T.; Lapuente-Ortínez, S.; López-Neo, A.; López-Nieto, M.; Manero-García, S.; Martínez-, E.; Melero-Sánchez, C.; Miralles-Zahonero, S.; Moral-Sayago, M.; Nadal-Gil, N.; Ortega-García, R.; Ortuño-Moya, J.; Padilla-Escámez, A.; Padilla-Pedreño, F.; Paños-Berlanga, M.; Peiró-Navarrete, E.; Picañol-, E.; Plá-Ribes, F.; Rodriguez-Maceiras, I.; Rodríguez-Muixi, M.; Romera-Caballero, S.; Rubio-Rincón, M.; Ruiz-Ortiz, J.; Santander-, M.; Sanz-Mendoza, I.; Serrano-Jiménez, G.; Simón-Martinez, B.; Torresano-Aguilar, E.; Vázquez-Rodríguez, E.; Velasco-Hurado, E.; Vicente-López, R.

Author Contributions

Conceptualization, C.A.-P., M.A.S.-T., C.M.-P. and C.V.-C.; methodology, C.A.-P., M.A.S.-T., C.M.-P. and C.V.-C.; software, C.A.-P., M.A.S.-T., C.M.-P., A.G.-A, A.A. and C.V.-C.; validation, C.A.-P., M.A.S.-T., C.M.-P. and C.V.-C.; formal analysis, C.A.-P., M.A.S.-T., C.M.-P. and C.V.-C.; investigation, C.A.-P., M.A.S.-T., C.M.-P., A.G.-A and C.V.-C. ;resources, A.A.; A.G.-A and M.G.-P.; data curation, C.A.-P., M.A.S.-T., C.M.-P. and C.V.-C.; writing—original draft preparation, C.A.-P., M.A.S.-T., C.M.-P. and C.V.-C.; writing—review and editing, C.A.-P., M.A.S.-T., C.M.-P., M.G.-P and C.V.-C.; visualization, C.A.-P., M.A.S.-T., C.M.-P. and C.V.-C.; supervision, C.A.-P., M.A.S.-T., C.M.-P. and C.V.-C.; project administration, C.A.-P., M.A.S.-T., C.M.-P. and C.V.-C.; All authors have read and agreed to the published version of the manuscript.

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No competing interests reported.

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Prevalence and estimation of the evolution of myopia in Spanish children

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