Introduction: The aim of this study was to explore the association between parental myopia and high myopia with children’s refraction and ocular biometry in large-scale Chinese preschool children from the Beijing Hyperopia Reserve Study. Subjects/Methods: This cross-sectional kindergarten-based study enrolled children aged 3–6 years. Cycloplegic refraction, axial length (AL), and corneal radius (CR) were measured for all children. Parents were asked to complete a questionnaire about refractive status (no myopia, mild myopia <−3 D, moderate myopia ≥−3 D and ≤−6, and high myopia >−6 D). Results: The study enrolled 2,053 children (1,069 boys and 984 girls), with a mean age of 4.26 ± 0.96 years and mean spherical equivalent refraction (SER) of 1.11 ± 0.97 diopter. Of the children, 90.7% had at least one myopic parent, and 511 children (24.9%) had at least one highly myopic parent. SER decreased significantly with increasing severity of parental myopia (p < 0.001). Preschool children’s myopia was independently associated with parental myopia (OR, 10.4 and 11.5 for one and two highly myopic parent[s]). Age (OR = 1.1), gender (OR = 1.7; girls as references), near work time (OR = 1.2), and both maternal (OR, 1.4 and 2.0 for moderate and high myopia) and paternal myopia (OR, 1.6 and 1.9 for moderate and high myopia) were independent risk factors for lacking hyperopia reserve. Conclusion: Severe parental myopia was associated with a lower SER, longer AL, and higher AL/CR ratio in preschool children. Parental myopia and near work may predispose children to faster elimination of hyperopia reserves before exposure to higher educational stress.

Myopia has become a major public health threat in China, and many intervention projects have been launched with government support. Myopia is projected to affect 4.758 million people of all ages by 2050 [1]. It is also estimated that there will be approximately 324 million myopic children before adulthood in 2025, within nearly 80% in Asia [2]. In recent years, an earlier onset of myopia has also been reported [3‒10]. It is widely accepted that early onset is strongly associated with higher risks of high myopia in adulthood [11], followed by increased risks of glaucoma, retinal detachment, and myopic macular degeneration.

The number of interventions for controlling myopia onset has proven to be effective; however, when to start the preventive treatments remains in question [12]. Before answering that, it is important to understand the normal refractive development and process of myopia. Prior to the onset of myopia, age-specific rates of myopic shift in refraction are generally lower than in myopes, but it is clear that for a year or two prior to the formal diagnosis of myopia, rates of progression are elevated and being the highest during the year of myopia onset [13, 14]. There is increasing evidence that the natural endpoint for refraction is around 1–1.5 D [15, 16]. Hyperopia reserve is considered a physiological hyperopic refractive status (mild hyperopia) that precedes emmetropia and myopia, which has raised special awareness of myopia around the country in those few years. In recent years, hyperopia reserves have become a matter of interest to both parents and practitioners in China. The clinicians and parents should start to take action to prevent myopia when refraction drops below the natural hyperopia reserves.

Several reports have shown that parental myopia is associated with a high risk of early-onset myopia [17‒22]. A 12-year annual observation of 1,831 participants from age 7 to 20 from the Guangzhou Twin Eye study illustrated a faster rate of spherical equivalent progression and axial length (AL) elongation in children with parental myopia [21]. However, the association between refractive status in preschool children and parental myopia was rarely studied [19, 22]. In addition, there was a lack of further classification/categorization of the parental refractive status due to the limited number of myopic parents in most previous studies. The influence of parental myopia on refractive changes in children might be affected by a combination of genetic and environmental factors created by myopic parents. In a part of data extracted from the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort study, Mojarrad et al. [23] found that the number of myopic parents and genetic risk score independently predicted incident myopia and refractive error. The predictive performance was further enhanced when both predictors were combined, attributable to the number of myopic parents serving not only as an indicator of genetic risk but also the risk of myopia from environmental factors. This becomes particularly pronounced in regions like East Asia, known for its greater environmental pressures.

The Beijing Hyperopia Reserve Research (BHRR) is a prospective observational study that investigated the 3-year trajectory of hyperopia reserve elimination in a kindergarten-based sample of Chinese children aged 3–6 years in an urban city in Beijing. This study was conducted in the Haidian District, which is well known for its advancement in science, technology, and education in Beijing. The concentration of highly educated parents resulted in a high prevalence of parental myopia in this population, making it ideal to explore how the severity of parental myopia influences refractive status and ocular biometry in preschool children. This study also emphasized the impact of highly myopic (HM) parents on ocular development in children before exposure to educational stress.

Study Population

The population recruited in the present study was the baseline collection from the BHRR. Children with potential complications of cycloplegia and non-compliance with ophthalmic examinations, such as glaucoma, heart disease, epilepsy, traumatic brain injury, and Down’s syndrome, were excluded from this study. The study was approved by the Ethics Committee of Beijing Tongren Eye Center, Beijing Tongren Hospital, Beijing, China. All the study procedures adhered to the tenets of the Declaration of Helsinki. The purpose and procedures of the study and the complications of cyclopentolate eye drops, including temporal photophobia and blurred close vision, as well as the importance of myopia prevention, were explained to the parents or guardians during a school seminar before written informed consent was obtained.

Ocular Examination

All children underwent comprehensive ocular examinations, including visual acuity, cycloplegic refraction, AL, anterior chamber depth, and corneal radius (CR). Uncorrected visual acuity was obtained using a retro-illuminated logMAR chart with Tumbling E optotypes (XingKang Medical Tech. Co., Ltd, Wenzhou, China) at a distance of 4 m. Biometric parameters, such as anterior chamber depth, AL, keratometry values, corneal dioptric power, and white-to-white distance, were examined using an optical biometry device (AL-Scan, Nidek Co., Ltd, Japan). The AL to CR (AL/CR ratio) was also calculated.

Each child received one drop of 0.4% oxybuprocaine in each eye, followed by three drops of 1.0% cyclopentolate, 5–10 min apart. Cycloplegia and pupil dilation were evaluated after an additional 1 h. If the pupil size was ≥6 mm and light reflex was absent, cycloplegia was deemed adequate. Children with complete cycloplegia underwent refraction examinations at least three times using an autorefractor (KR-8900; Topcon, Japan). The average value of 3 good measurements was then analyzed. The spherical equivalent refractive error (SER) was calculated as the spherical diopters plus half of the cylindrical diopter. SER categories were defined as myopia: ≤−0.50 D; emmetropia: >−0.50 D but ≤+0.50 D; mild hyperopia: >+0.50 D but ≤+2.00 D; and significant hyperopia: >+2.00 D. In children younger than 5 years, high myopia was defined by an SER of less than −4.0 D, and in children 5-6 years of age, high myopia was defined by a myopic refractive error of less than −6.0 D. There is increasing evidence that the natural endpoint for refraction is around 1–1.5 D [15, 16]; thus, presence of hyperopia reserve was defined as SER >+1 D. “Pre-myopia” was defined as −0.50 D < SE ≤+0.75 D [24].

Questionnaire

Parents were asked to complete a questionnaire using a smartphone by scanning the QR code, which included questions about past history, family history, near activities, outdoor activity time, and reading habits. More specific information was provided: the refractive status of both parents with five given choices (normal, mild myopia <−3 D, moderate myopia ≥−3 D and ≤−6, high myopia >−6 D, and other ocular diseases), parents’ age at the child’s birth, parental education level, and annual family income. The number of hours per day for indoor activity (involving near work) included three parts: the time used to watch television, time to play with electronic devices, and time to read, write, and draw pictures (near work time). Educational level was categorized as doctorate, master’s degree, bachelor’s degree, associate degree, or lower. Parental refractive status was first classified into ten categories using refraction data as follows: neither parent was myopic (non-non), one parent was nonmyopic and the other was mild myopic (non-mild), one parent was nonmyopic and the other was moderate myopia (non-mod), one parent was nonmyopic and the other was HM (non-high), both parents were mild myopic (mild-mild), one parent was mild myopic and the other was moderate myopic (mild-mod), one parent was mild myopic and the other was high myopic (mild-high), both parents were moderately myopic (mod-mod), one parent was moderate myopic and the other was HM (mod-high), and both parents were HM (high-high).

Statistical Analysis

A statistical software package (SPSS version 24.0 IBM-SPSS, Chicago, IL, USA) was used for the statistical analyses. Data from the right eye of each child were analyzed. The distribution of the main parameters was described by calculating the medians, means, and standard deviations. One-way analysis of variance with the least significant difference method was performed to compare the age, AL, SER, activity time, and other ocular parameters among the various groups. An independent-sample T test was used to compare all ocular parameters between the boys and girls. The prevalence of myopia was compared using the χ2 test. Stepwise linear regression was performed with SER as the dependent variable. Other parameters that showed a significant association with the main parameters in univariate analysis were counted as independent variables. We also carried out a binary regression analysis with the presence of myopia in children and a lack of hyperopia reserve as the dependent variable in the two models, with age, gender, parental refractive status, and environmental factors (outdoor activity and all three types of indoor activity time) as independent variables. We calculated the odds ratios and 95% confidence intervals. Statistical significance was set at p < 0.05.

Among the 2,091 children enrolled in the Beijing Hyperopia Reserve study, 2,074 (98.3%) children’s parents completed the questionnaire. After excluding those whose parents had ocular diseases such as congenital cataract, suspected glaucoma, and amblyopia, a total of 2,053 children (98.2%) aged 3–6 years were finally enrolled, with 1,069 boys and 984 girls. Among them, 477, 828, 482, and 266 children were aged 3, 4, 5, and 6 years, respectively. The mean age was 4.26 ± 0.96 years old. The mean spherical power of all children was 1.38 ± 0.98 D (median: 1.25 D), and the mean cylindrical power was −0.54 ± 0.53 D (median: −0.50 D), making the mean SER 1.11 ± 0.97 D (median: 1.13 D). The mean AL was 22.3 ± 0.7 mm, and the mean calculated AL/CR ratio was 2.86 ± 0.07. The prevalence of myopia was 3.8% (78 children), of which 4 children (0.02%) had high myopia. The majority of children (1,639, 79.8%) had mild hyperopia and hyperopia, as expected. There were 1,881 children (91.6%) having hyperopia reserve.

Table 1 shows the educational level and refractive information of the 2,053 pairs of parents. The distribution of parental refractive status in the different categories is shown in Figure 1. No age difference was found between the groups (F = 0.512, p = 0.867). Among the children, 90.7% had at least one myopic parent. The parental educational level was weak positively correlated with the severity of parental refractive error (father: r: 0.241, p < 0.001; mother: r: 0.248, p < 0.001).

Table 1.

Age, educational level, and refractive status of 2,053 pairs of parents

Parental informationMaternalPaternal
Age at birth, mean±SD, years 32.5±4.1 34.5±4.1 
Education level, n (%) 
 Doctoral degree 212 (10.3) 204 (9.9) 
 Master’s degree 745 (36.3) 684 (33.3) 
 Bachelor’s degree 839 (40.9) 708 (34.5) 
 Associate degree or below 256 (12.5) 456 (22.2) 
Refractive status, n (%) 
 No myopia 434 (21.1) 602 (29.3) 
 Mild myopia 567 (27.6) 545 (26.5) 
 Moderate myopia 724 (35.3) 664 (32.3) 
 High myopia 328 (16) 242 (11.8) 
Parental informationMaternalPaternal
Age at birth, mean±SD, years 32.5±4.1 34.5±4.1 
Education level, n (%) 
 Doctoral degree 212 (10.3) 204 (9.9) 
 Master’s degree 745 (36.3) 684 (33.3) 
 Bachelor’s degree 839 (40.9) 708 (34.5) 
 Associate degree or below 256 (12.5) 456 (22.2) 
Refractive status, n (%) 
 No myopia 434 (21.1) 602 (29.3) 
 Mild myopia 567 (27.6) 545 (26.5) 
 Moderate myopia 724 (35.3) 664 (32.3) 
 High myopia 328 (16) 242 (11.8) 
Fig. 1.

Distribution of parental refractive status. Parental refractive status was classified into ten categories using refraction data as follows: neither parent was myopic (non-non), one parent was nonmyopic and the other was mild myopic (non-mild), one parent was nonmyopic and the other was moderate myopic (non-mod), one parent was nonmyopic and the other was HM (non-high), both parents were mild myopic (mild-mild), one parent was mild myopic and the other was moderate myopic (mild-mod), one parent was mild myopic and the other was high myopic (mild-high), both parents were moderate myopic (mod-mod), one parent was moderate myopic and the other was HM (mod-high), and both parents were HM (high-high).

Fig. 1.

Distribution of parental refractive status. Parental refractive status was classified into ten categories using refraction data as follows: neither parent was myopic (non-non), one parent was nonmyopic and the other was mild myopic (non-mild), one parent was nonmyopic and the other was moderate myopic (non-mod), one parent was nonmyopic and the other was HM (non-high), both parents were mild myopic (mild-mild), one parent was mild myopic and the other was moderate myopic (mild-mod), one parent was mild myopic and the other was high myopic (mild-high), both parents were moderate myopic (mod-mod), one parent was moderate myopic and the other was HM (mod-high), and both parents were HM (high-high).

Close modal

Impact of Parental Refractive Status on SER, AL, AL/CR Ratio, the Presence of Hyperopia Reserve, Pre-Myopia and Myopia Prevalence

Figure 2 shows the changes in SER, AL, and AL/CR ratio in children from the different categories of parental refractive status. Parental refractive status was further divided into four groups: no myopia (non-non), mild to moderate myopia (non-mild, non-mod, mild-mild, mild-mod, mod-mod), one parent having high myopia (non-high, mild-high, mod-high), and both having high myopia (high-high). With increasing severity of parental refractive status, SER was significantly decreased (F = 20.437, p < 0.001), and AL and AL/CR increased accordingly (F = 4.329, p = 0.005, F = 14.899, p < 0.001). The prevalence of children with hyperopia reserve was the lowest, and those with myopia were the highest among both HM parents (Table 2; online suppl. Table S1; for all online suppl. material, see https://doi.org/10.1159/000535193).

Fig. 2.

Graphs showing the trends of SER (a), AL (b), and AL-to-CR ratio (c) with increasing severity of parental refractive status. SER, spherical equivalent refractive error; AL, axial length, AL-to-CR ratio, AL to corneal radius of curvature ratio.

Fig. 2.

Graphs showing the trends of SER (a), AL (b), and AL-to-CR ratio (c) with increasing severity of parental refractive status. SER, spherical equivalent refractive error; AL, axial length, AL-to-CR ratio, AL to corneal radius of curvature ratio.

Close modal
Table 2.

Comparisons of children’s age, family history, ocular biometry, and activity time among different parental refractive status

No myopiaMild to moderate myopiaOne high myopiaBoth high myopiap value
No. of children 191 1,351 452 59  
Children age, years 4.2±1.0 4.3±1.0 4.2±1.0 4.4±1.0 0.692 
Maternal age, years 32.3±5.1 32.5±4.0 32.4±3.7 32.7±3.8 0.835 
Paternal age, years 34.5±5.7 34.3±4.9 34.4±4.5 34.3±4.5 0.948 
SER, diopter 1.41±0.94 1.15±0.95 0.91±0.96 0.56±1.20 <0.001 
AL, mm 22.14±0.75 22.24±0.71 22.34±0.72 22.37±0.80 0.005 
AL/CR ratio 2.84±0.08 2.86±0.07 2.88±0.07 2.91±0.08 <0.001 
Outdoor activity time, h 1.92±0.92 1.68±0.79 1.61±0.81 1.63±0.68 <0.001 
Indoor activity time, h 2.96±1.79 2.33±1.29 2.24±1.37 2.15±1.20 <0.001 
 Watch TV 1.01±0.95 0.56±0.67 0.46±0.60 0.43±0.46 <0.001 
 Play with electronic devices 0.98±0.75 0.80±0.65 0.74±0.64 0.70±0.49 <0.001 
 Read, write, and draw picture 1.05±0.77 1.08±0.78 1.17±0.93 1.21±0.80 0.158 
Presence of hyperopia reserve 118 (61.8%) 760 (56.3%) 208 (46.0%) 19 (32.2%) <0.001 
Prevalence of pre-myopia 44 (23.0%) 328 (24.3%) 155 (34.3%) 26 (44.1%) <0.001 
Prevalence of myopia 1 (0.5%) 48 (3.6%) 24 (5.3%) 5 (8.5%) 0.009 
No myopiaMild to moderate myopiaOne high myopiaBoth high myopiap value
No. of children 191 1,351 452 59  
Children age, years 4.2±1.0 4.3±1.0 4.2±1.0 4.4±1.0 0.692 
Maternal age, years 32.3±5.1 32.5±4.0 32.4±3.7 32.7±3.8 0.835 
Paternal age, years 34.5±5.7 34.3±4.9 34.4±4.5 34.3±4.5 0.948 
SER, diopter 1.41±0.94 1.15±0.95 0.91±0.96 0.56±1.20 <0.001 
AL, mm 22.14±0.75 22.24±0.71 22.34±0.72 22.37±0.80 0.005 
AL/CR ratio 2.84±0.08 2.86±0.07 2.88±0.07 2.91±0.08 <0.001 
Outdoor activity time, h 1.92±0.92 1.68±0.79 1.61±0.81 1.63±0.68 <0.001 
Indoor activity time, h 2.96±1.79 2.33±1.29 2.24±1.37 2.15±1.20 <0.001 
 Watch TV 1.01±0.95 0.56±0.67 0.46±0.60 0.43±0.46 <0.001 
 Play with electronic devices 0.98±0.75 0.80±0.65 0.74±0.64 0.70±0.49 <0.001 
 Read, write, and draw picture 1.05±0.77 1.08±0.78 1.17±0.93 1.21±0.80 0.158 
Presence of hyperopia reserve 118 (61.8%) 760 (56.3%) 208 (46.0%) 19 (32.2%) <0.001 
Prevalence of pre-myopia 44 (23.0%) 328 (24.3%) 155 (34.3%) 26 (44.1%) <0.001 
Prevalence of myopia 1 (0.5%) 48 (3.6%) 24 (5.3%) 5 (8.5%) 0.009 

Parental refractive status was divided into no myopia (non-non), mild to moderate myopia (non-mild, non-mod, mild-mild, mild-mod, mod-mod), one parent having high myopia (non-high, mild-high, mod-high), and both having high myopia (high-high).

Impact of HM Parent(s) on Age-Specific SER, AL, and AL/CR Ratio

To analyze the impact of HM parents, the children were then divided into two groups based on whether the parents had high myopia: 511 children (24.9%) with one or two HM parent(s) and 1,542 children (75.1%) without HM parent(s). The impact of parental high myopia on age-specific SER, AL, and the AL/CR ratio is shown in Table 3 and Figure 3. There is influence of HM parent(s) on children’s SER and AL in all ages even though statistical significance was not found in AL in ages 3 and 4 years. A significant difference in age-related trend was found in AL (p = 0.015) but not in SER (p = 0.525) or AL/CR ratio (p = 0.716) between children with and without HM parents. To understand the independent role of parental and maternal high myopia, the comparison of SER, AL, and AL/CR ratio between children with maternal and paternal high myopia is shown in online supplementary Table S2.

Table 3.

Comparison of age-specific SER, AL, and AL/CR ratio between children with and without HM parents

SERALAL/CR ratio
3 years4 years5 years6 years3 years4 years5 years6 years3 years4 years5 years6 years
0 HM parent 1.30±1.0 1.14±0.91 1.18±0.87 1.12±1.11 21.90±0.65 22.21±0.69 22.38±0.67 22.59±0.72 2.82±0.07 2.85±0.07 2.88±0.07 2.90±0.07 
1 or 2 HM parent(s) 1.00±0.84 0.90±0.91 0.75±1.06 0.74±1.32 22.02±0.65 22.20±0.68 22.65±0.73 22.80±0.74 2.84±0.77 2.87±0.06 2.91±0.07 2.92±0.09 
p value 0.003 0.001 <0.001 0.019 0.071 0.895 <0.001 <0.001 0.017 0.003 0.001 0.001 
SERALAL/CR ratio
3 years4 years5 years6 years3 years4 years5 years6 years3 years4 years5 years6 years
0 HM parent 1.30±1.0 1.14±0.91 1.18±0.87 1.12±1.11 21.90±0.65 22.21±0.69 22.38±0.67 22.59±0.72 2.82±0.07 2.85±0.07 2.88±0.07 2.90±0.07 
1 or 2 HM parent(s) 1.00±0.84 0.90±0.91 0.75±1.06 0.74±1.32 22.02±0.65 22.20±0.68 22.65±0.73 22.80±0.74 2.84±0.77 2.87±0.06 2.91±0.07 2.92±0.09 
p value 0.003 0.001 <0.001 0.019 0.071 0.895 <0.001 <0.001 0.017 0.003 0.001 0.001 

HM, highly myopic; SER, spherical equivalent refractive error; AL, axial length; AL/CR ratio, axial length to corneal radius of curvature ratio.

Fig. 3.

The age-specific SER (a), AL (b), and AL/CR ratio (c) on preschool children with and without HM parents. SER, spherical equivalent refractive error; AL, axial length; AL/CR ratio, AL to corneal radius of curvature ratio; ns, not significant. *p < 0.05.

Fig. 3.

The age-specific SER (a), AL (b), and AL/CR ratio (c) on preschool children with and without HM parents. SER, spherical equivalent refractive error; AL, axial length; AL/CR ratio, AL to corneal radius of curvature ratio; ns, not significant. *p < 0.05.

Close modal

Multiple Regression Analyses for SER, Preschool Children Myopia, and Lack of Hyperopia Reserve

Multiple linear regression models showed that SER was associated with age (β = 0.281, p < 0.001), sex (β = −0.256, p < 0.001), AL (β = −0.508, p < 0.001), AL/CR ratio (β = −8.042, p < 0.001), and severity of parental myopia (β = −0.069, p = 0.004) after adjusting for indoor (p = 0.131) and outdoor activity time (p = 0.390). Another linear regression model, including maternal and paternal refractive status as independent variables confirmed that a lower SER was associated with more severe maternal myopia (β = −0.073, p < 0.001) after adjusting for paternal myopia (p = 0.278).

Two models confirmed that the severity of parental myopia and sex were associated with preschool children’s myopia (Table 4) and a lack of hyperopia reserve (Table 5). Compared with children without myopic parents, the risk of myopia in children with one or two HM parents was 10- to 11-fold higher. The risk of myopia was 29-fold higher in those with HM mothers. Both maternal and paternal myopia are related to the presence of hyperopia reserve in preschool children.

Table 4.

Risk factors for children myopia in the two models with age, gender, parental refractive status, and environmental factors

FactorsOR95% CIp value
Model 1 (parental myopia) 
 Gender (girl as reference) 1.832 1.095–3.066 0.021 
 Parental refractive status 
  Mild to moderate myopia 6.519 0.891–47.703 0.065 
  One HM parent 10.440 1.391–78.331 0.023 
  Two HM parents 11.520 1.168–113.658 0.036 
Model 2 (maternal and paternal myopia, separately) 
 Gender (girl as reference) 1.864 1.112–3.124 0.018 
 Maternal refractive status 
  Mild myopia 14.047 1.860–106.062 0.010 
  Moderate myopia 21.229 2.885–156.227 0.003 
  High myopia 28.693 3.804–216.427 0.001 
FactorsOR95% CIp value
Model 1 (parental myopia) 
 Gender (girl as reference) 1.832 1.095–3.066 0.021 
 Parental refractive status 
  Mild to moderate myopia 6.519 0.891–47.703 0.065 
  One HM parent 10.440 1.391–78.331 0.023 
  Two HM parents 11.520 1.168–113.658 0.036 
Model 2 (maternal and paternal myopia, separately) 
 Gender (girl as reference) 1.864 1.112–3.124 0.018 
 Maternal refractive status 
  Mild myopia 14.047 1.860–106.062 0.010 
  Moderate myopia 21.229 2.885–156.227 0.003 
  High myopia 28.693 3.804–216.427 0.001 

CI, confidence interval; OR, odds ratio.

Table 5.

Risk factors for lacking hyperopia reserve in the two models with age, gender, parental refractive status, and environmental factors

FactorsOR95% CIp value
Model 1 (parental myopia) 
 Age 1.127 1.020–1.245 0.019 
 Gender (girl as reference) 1.639 1.352–1.987 <0.001 
 Parental refractive status   <0.001 
  Mild to Moderate myopia 1.301 0.932–1.818 0.122 
  One HM parent 1.787 1.229–2.600 0.002 
  Two HM parents 4.186 2.046–8.561 <0.001 
 Near work time (reading, writing, and drawing) 1.218 1.081–1.373 0.001 
Model 2 (maternal and paternal myopia, separately) 
 Age 1.125 1.018–1.244 0.021 
 Gender (girl as reference) 1.682 1.385–2.043 <0.001 
 Maternal refractive status   <0.001 
  Mild myopia 1.349 1.021–1.781 0.035 
  Moderate myopia 1.436 1.099–1.876 0.008 
  High myopia 2.021 1.458–2.800 <0.001 
 Paternal refractive status   <0.001 
  Mild myopia 1.178 0.906–1.532 0.222 
  Moderate myopia 1.584 1.238–2.026 <0.001 
  High myopia 1.852 1.322–2.595 <0.001 
 Near work time (reading, writing, and drawing) 1.206 1.069–1.362 0.002 
FactorsOR95% CIp value
Model 1 (parental myopia) 
 Age 1.127 1.020–1.245 0.019 
 Gender (girl as reference) 1.639 1.352–1.987 <0.001 
 Parental refractive status   <0.001 
  Mild to Moderate myopia 1.301 0.932–1.818 0.122 
  One HM parent 1.787 1.229–2.600 0.002 
  Two HM parents 4.186 2.046–8.561 <0.001 
 Near work time (reading, writing, and drawing) 1.218 1.081–1.373 0.001 
Model 2 (maternal and paternal myopia, separately) 
 Age 1.125 1.018–1.244 0.021 
 Gender (girl as reference) 1.682 1.385–2.043 <0.001 
 Maternal refractive status   <0.001 
  Mild myopia 1.349 1.021–1.781 0.035 
  Moderate myopia 1.436 1.099–1.876 0.008 
  High myopia 2.021 1.458–2.800 <0.001 
 Paternal refractive status   <0.001 
  Mild myopia 1.178 0.906–1.532 0.222 
  Moderate myopia 1.584 1.238–2.026 <0.001 
  High myopia 1.852 1.322–2.595 <0.001 
 Near work time (reading, writing, and drawing) 1.206 1.069–1.362 0.002 

CI, confidence interval; OR, odds ratio.

The present study was conducted in a prospective large-scale kindergarten-based cohort including 2,109 preschool children living in Haidian District, Beijing, northern China. Our study confirmed that parental myopia leads to less hyperopic refraction in preschool children, which is comparable to observations from previous studies [19, 22]. The region where the study was conducted is not only a very urban city but also occupied by many universities and scientific research institutions, resulting in high parental educational backgrounds and an extremely high prevalence of parental myopia (90.7%). Compared to previous studies [19, 22, 25], the proportion of myopic parents in our cohort was the highest, making it possible to divide the whole population into ten specific categories depending on the severity of parental myopia, and the number of each group was relatively even.

Our results showed a progressive decrease in SER in preschool children with increasing severity of parental myopia. In addition, parental myopia was also an independent risk factor for myopia in children, and a lack of hyperopia reserve and maternal myopia might play a more powerful role. Our findings are comparable with those of Guo et al. [26] who reported that the prevalence of myopia using noncycloplegic refractions in primary school was significantly associated with maternal myopia but not with paternal myopia in both rural and urban regions of Beijing. However, a difference between paternal and maternal effects could be due to the generally greater role taken by mothers in child care, particularly for young children. Whether this is genetically based needs to be clarified in further studies.

Only the presence of myopia in one or two parents was analyzed in most earlier studies. More myopic SER was detected in children with two myopic parents than in those without myopic parents in a large population-based data of 9,793 multi-ethnic preschool children [22]. From Figure 2, the children in the non-high group had less SER than those without myopic parents but were identical to those with both myopic parents (mild-mild and mild-mod). Children in the mild-high group had lower SER than those in the mod-mod groups. This emphasizes that the influence of parental myopia on refractive development in early life is complicated, not just related to the number of myopic parents, but may also highly depend on the severity of parental myopia. In addition, it is notable that no significant difference in the mean SER was found among the non-non, non-mild, and non-mod groups but was discovered among the mild-mod, mod-mod, and mod-high groups. In contrast, Xiang et al. [25] found that there was a progressive increase in the prevalence of myopia and mean myopic SER in children with increasing severity of parental myopia after categorizing the participants into the non-non, non-mild, non-mod, and non-high groups. The discrepancy may be because the enrolled children in their study were from 12 to 15 years old who had already been exposed to environmental risk factors, potentially suggesting that intensive education stress may have a strong power to eliminate the protective effect and may gradually dominate the risk of myopia after school age.

Further analysis of children with and without HM parent(s) showed significant differences between the groups in both SER and AL. This finding strengthens the idea that familial patterns of inheritance might differ between children with myopic and HM parents. A graph showing AL and SER changes in Chinese children aged 3–9 years from the Shenzhen kindergarten study and Guangzhou outdoor study implied that AL starts to increase earlier (aged 5 years) when little myopic shift occurs until 6 years of age [27], which can be considered as a relatively normal refractive development in Chinese children.

Our results showed no association between indoor and outdoor activities and refractive error or myopia onset in preschool children, in agreement with the STARS study [19] and GUSTO study [18]. It is worth noting that our study population consisted of preschool children, whereas previous researches [28‒30] demonstrating a positive association between near work and myopia development primarily involved school students. Our results suggest that parents with a higher degree of myopia or higher education levels encouraged their children to engage more in academic activities and less in leisure activities involving television and electronic devices thanks to the advocation of myopia prevention. Indoor activities such as studying and using electronic devices are considered forms of near work. This lack of association between the time spent watching television and refractive errors or myopia can be attributed to the absence of accommodation (eye focusing) while watching television, unlike activities involving close-up tasks such as reading or using electronic devices. Additionally, our study identified that the duration of time spent on reading, writing, and drawing was an independent risk factor associated with the absence of hyperopia reserves. This suggests that even at a young age, higher educational demands may not directly lead to myopia development but could be linked to the depletion of hyperopia reserves, which could potentially contribute to myopia progression in later years. There is a strong clinical significance that for children with myopic parents, especially for more severe ones, early intervention, such as more attention paid to reading habits or increased time outdoors, should be started earlier. Due to the global increase in myopia in the current generation, it is predicted that the number of myopic parents will also increase in the future. It is known that 2-h outdoor activity per day for elementary students has been proven to reduce the onset of myopia [31]. It is strongly recommended that the time spent on outdoor activities should be increased, and any protective intervention on myopia should be started at the preschool stage. In addition, even when parents are myopic, myopia prevalence is still low in preschool children, suggesting that the onset of myopia is primarily during the primary school years, and myopia prevention policies are crucial for both preschools and primary schools.

The limitations of this study must also be acknowledged. First, the severity of parental myopia was based solely on a self-report questionnaire. Second, the proportion of children aged 6 years is much less than that of children in other age-groups, making a possible bias in our results since age is one of the impact factors on SER. Third, only the Haidian District in Beijing was included in this study. Considering the high frequency of education institutions in the Haidian District, our results may not represent the whole situation of Beijing, but it is a very useful cohort to understand the association between parental myopia and SER in preschool children.

Our study showed a clear relationship between SER, AL, and AL/CR ratio and the severity of parental myopia in large-scale Chinese preschool children, in which 91% had at least one myopic parent. The negative genetic contribution to SER may be enhanced in children with more severe parental myopia. Compared to the children without HM parent(s), the children with HM parent(s) had longer AL and different patterns of age-related trend of AL elongation. Parental myopia and near work may predispose to faster elimination of the hyperopia reserve and play a crucial role in children’s myopia before exposure to education stress. Protective intervention for myopia should be started at the preschool stage for children, especially those with severely myopic parents.

The authors thank Professor Yaxing Wang for critical discussions and revision of the final manuscript.

This study protocol was reviewed and approved by Ethics Committee of Beijing Tongren Hospital, approval number TRECKY2019-152. Signed informed consent documentation was obtained from the participants’ parents to participate in the study.

The authors have no conflicts of interest to declare.

The Beijing Hyperopia Reserve Research was supported by the “Capital Clinical Diagnosis and Treatment Technology Research and Translational Medicine Application” (2020–2024, project number Z201100005520034).

Jianing Pu: data collecting and data analysis. Yuxin Fang: manuscript writing, data analysis, and modification and discussion. Zhen Zhou: data analysis. Wei Chen: conception and modification and discussion. Jianping Hu, Xinli Liu, Lihua Wang, Jingjing Feng, Huan Tong, and Shanshan Xing: data collecting. Shanshan Jin: data preparing. Yonghong Jiao: conception and manuscript discussion.

Additional Information

J.P. and Y.F. contributed equally to the work presented here and should therefore be regarded as equivalent authors.

Data are not publicly available due to ethical reasons. Further inquiries can be directed to the corresponding author.

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