A review on the epidemiology of myopia in school children worldwide

Methodological quality of the review: Low confidence

Author: Andrzej Grzybowski, Piotr Kanclerz, Kazuo Tsubota, Carla Lanca and Seang-Mei Saw

Region: Worldwide

Sector: Myopia

Subsector: Epidemiology of myopia

Equity focus: School children

Study population: School children (aged between 6 and 19 years old)

Type of programme: School based

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: The modern rise in myopia mirrors a trend with children in many countries spending considerable amounts of time engaged in reading, studying or, more recently, using computers and smartphones. The evidence suggests that not only genetic, but also environmental factors, such as time spent outdoors, play a major role in this rise, and probably explain the epidemic of myopia. Myopia has gained particular importance in epidemiological studies. It is estimated that 1.4 billion people were myopic in 2000, and it is predicted that by 2050 the number will reach 4.8 billion. Children with early onset are at particular risk of complications associated with myopia, as progression over time might result in high myopia and myopic macular degeneration. Both genetic and environmental factors play a role in the increasing prevalence of myopia.

Objectives: The aim of this study is to present a review on the current epidemiology and risk factors for myopia in school children aged 6 to 19 years.

Main findings: Twenty-eight articles fulfilled the criteria for being included in the main analysis (myopia prevalence). One study was excluded, as it presented data from primary care optometry clinics. Additionally, 55 articles were included in the analysis of risk factors.

The prevalence ranged from 0.7% in Saudi Arabia (children aged 3 to 10 years), 1.4% in South America (children aged 5 to 15 years) to 65.5% in a cohort of 3^rd year junior high school students (age 14 to 15 years; mean 15.25 ± 0.46 years) in the Haidian district of Beijing. The highest prevalence of myopia in schoolchildren was reported in East Asia and Singapore, urban areas of China, Taiwan and South Korea. In Europe, the prevalence rates reached 42.7% in a 10 to 19-year-old French cohort. Compared with cycloplegic measurements, the majority of the studies reporting on myopia prevalence with noncycloplegic measurements reported much higher prevalence rates. There are some countries where the prevalence rates remain low, such as Brazil (3.14 and 9.6%) and Ghana (3.4%).

A critical parameter for epidemiological analysis of myopia is age, as prevalence rates of myopia are known to increase significantly with age. Moreover, myopia beginning at school continues to progress up to adulthood in almost half of the patients.

In several countries, the prevalence of myopia has increased in the last years. In a study from the Haidian District in Beijing, China, the prevalence of myopia in a cohort of 15-year-old schoolchildren increased from 55.95% in 2005 to 65.48% in 2015. There are some risks factors that can contribute for the prevalence increase, such as parental myopia, ethnic differences, less time outdoors, increased near work, population density and socioeconomic status. Although genetic factors have some impact on eye growth, the development of myopia appears to be mainly influenced by environmental factors, such as education. Myopia progression was not strongly associated either with near work or outdoor/sports activity in siblings with common environmental exposures.

The Childhood Health, Activity, and Motor Performance Eye Study determined the association between physical activity and myopia; in a group of 307 Danish children, accelerometer measurements were conducted at mean ages of 9.7, 11.0, 12.9 and 15.4 years. The prevalence of myopia at the final time-point was 17.9% and was not associated with physical activity. The SAVES study revealed that near work was a risk factor for myopia, but only for the 6-year-old children, and not in the 12-year-old cohort. This result might indicate that near work can be a factor for inducing the earlier onset of myopia in smaller children. In a study by Pan et al., conducted on 2,346 Chinese children aged 13 to 14-years-old, using LED lamps for homework after school had a higher prevalence of myopia (SER less than − 0.75 D) and longer axial length than those using incandescent (P=0.04 and P=0.007, respectively) or fluorescent lamps (P=0.02 and P=0.003, respectively). Higher population density seems to be associated with myopia risk, independent of time spent outdoors and other environmental factors.

In the North India Myopia Study, the prevalence of myopia was 13.1%. Myopia was more common among children with higher SES and among private school students, compared to governmental school pupils. Presumably, children in private schools spend more hours at school compared to children in public schools; they spend more time reading and writing at home, with significantly more pressure and a greater likelihood of extra classes.

Overall, authors conclude that low levels of outdoor activity and near work are well-established risk factors for myopia; this review provides evidence on additional environmental risk factors. Authors stated that new epidemiological studies should be carried out on implementation of public health strategies to tackle and avoid myopia. As the myopia prevalence rates in noncycloplegic studies are overestimated, they recommend considering only cycloplegic measurements.

Methodology:

Full-text articles on prevalence analysis were required to meet the following criteria: 1) a cross-sectional or cohort design; 2) refractive error measurements taken with a refractometer; 3) clear definition of myopia and information on cycloplegic or non-cycloplegic measurements; 4) prevalence assessed in children aged 6 to 19 years; 5) studies with a minimum sample of 100 children. If more than one definition of myopia was used in a study, the prevalence for the more commonly used one was selected in order to enable comparison. Results for up to two age-groups were presented, and if data for more than two cohorts was reported, the average for the study or the most common age-group was selected.

PubMed and Medline were searched to identify the prevalence of myopia among children, as reported in articles between January 2013 and March 2019. The following keywords were used in various combinations: prevalence, incidence, myopia, refractive error, and visual impairment ((prevalence[All Fields] OR incidence[All Fields]) AND (refractive error[All Fields] OR myopia[All Fields] OR visual impairment[All Fields])). All publications in English and abstracts from non-English publications were reviewed. The reference lists of relevant publications were also considered as a potential source of information. If other studies (for example, older than five years) were essential to draw conclusions, they were included in the discussion section. Studies were critically reviewed for study methodology and robustness of data, particularly the myopia definition and measurements under cycloplegia. No attempts to discover unpublished data were made.

Applicability/external validity: Though the authors did not use any method to assess applicability/external validity, the results show that they can be applied in other settings. The meta-analysis was conducted worldwide.

Geographic focus: This meta-analysis was conducted worldwide, including in low and middle income countries, or all countries.

Summary of quality assessment:

Low confidence was attributed to the conclusions about the effects of this review. Articles included in this review were published between January 2013 and March 2019. This review has some methodological concern: there was only one person reviewing the paper and extracting data. The authors just critically reviewed the methodology and robustness of the studies. They have not reported how the quality of those studies was measured and what method was used.