Prevalence and Severity of Astigmatism in Children After COVID-19

Ka Wai Kam; Erica Shing; Yuzhou Zhang; Xiu Juan Zhang; Arnold S H Chee; Mandy P H Ng; Patrick Ip; Wei Zhang; Alvin L Young; Amanda French; Ian Morgan; Kathyrn Rose; Clement C Tham; Chi Pui Pang; Li Jia Chen; Jason C Yam

doi:10.1001/jamaophthalmol.2025.0205

. 2025 Mar 20;143(5):383–391. doi: 10.1001/jamaophthalmol.2025.0205

Prevalence and Severity of Astigmatism in Children After COVID-19

Ka Wai Kam ^1,², Erica Shing ¹, Yuzhou Zhang ¹, Xiu Juan Zhang ^1,¹⁰, Arnold S H Chee ^1,², Mandy P H Ng ¹, Patrick Ip ⁴, Wei Zhang ⁷, Alvin L Young ^1,², Amanda French ⁸, Ian Morgan ⁹, Kathyrn Rose ⁸, Clement C Tham ^1,^2,^3,^5,⁶, Chi Pui Pang ^1,³, Li Jia Chen ^1,^2,^3,^✉, Jason C Yam ^1,^2,^3,^5,^6,^✉

¹Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong SAR, China

²Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, Hong Kong SAR, China

³Hong Kong Hub of Paediatric Excellence, The Chinese University of Hong Kong, Hong Kong SAR, China

⁴Department of Paediatrics and Adolescent Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China

⁵Hong Kong Eye Hospital, Kowloon, Hong Kong SAR, China

⁶Department of Ophthalmology, Hong Kong Children’s Hospital, Hong Kong SAR, China

⁷Tianjin Eye Hospital, Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Institute, Tianjin, China

⁸University of Technology Sydney, Graduate School of Health, Sydney, Australia

⁹Division of Biochemistry and Molecular Biology, Research School of Biology, Australian National University, Canberra, ACT, Australia

¹⁰Department of Ophthalmology, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China

Accepted for Publication: December 23, 2024.

Published Online: March 20, 2025. doi:10.1001/jamaophthalmol.2025.0205

^✉

Corresponding Author: Jason C. Yam, MD (yamcheuksing@cuhk.edu.hk), and Li Jia Chen, PhD (lijia_chen@cuhk.edu.hk), Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong Eye Hospital, 147K Argyle Street, Kowloon, Hong Kong SAR, China.

Author Contributions: Drs Kam and Yam had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Dr Kam and Ms Shing contributed equally as co–first authors.

Concept and design: Kam, Y. Zhang, X. Zhang, Chee, W. Zhang, French, Rose, Pang, Chen, Yam.

Acquisition, analysis, or interpretation of data: Kam, Shing, Y. Zhang, Ng, Ip, Young, French, Morgan, Tham, Chen, Yam.

Drafting of the manuscript: Kam, Shing, Ng, Young.

Critical review of the manuscript for important intellectual content: Kam, Shing, Y. Zhang, X. Zhang, Chee, Ip, W. Zhang, French, Morgan, Rose, Tham, Pang, Chen, Yam.

Statistical analysis: Shing, Y. Zhang, Young, Rose.

Obtained funding: X. Zhang, Yam.

Administrative, technical, or material support: Kam, Y. Zhang, Chee, Ng, W. Zhang, Pang, Chen, Yam.

Supervision: Kam, X. Zhang, Ip, Tham, Chen, Yam.

Conflict of Interest Disclosures: Dr Morgan reported other support from Eyerising International outside the submitted work. Dr Yam reported a patent pending for 0.05% low-concentration atropine for delaying myopia onset and serving as a nonexecutive director and shareholder of OCUS Innovation (Hong Kong) outside the submitted work. No other disclosures were reported.

Funding/Support: This study was supported in part by the General Research Fund, Research Grants Council, Hong Kong (14111515 and 14103419 [Dr Yam]); Collaborative Research Fund (C7149-20G [Dr Yam]); Health and Medical Research Fund, Hong Kong (5160836 [Dr Chen] and 07180826 [Dr X. Zhang]); Direct Grants of the Chinese University of Hong Kong (4054193 [Dr Chen], 4054121 and 4054199 [Dr Yam], and 4054634 [Dr X. Zhang]); Innovation and Technology Fund (7010590 [Dr Yam]), UBS Optimus Foundation Grant 8984 (Dr Yam); Centaline Myopia Fund (Dr Yam); Lim Por-yen Eye Genetics Research Centre; CUHK Jockey Club Children’s Eye Care Programme; and CUHK Jockey Club Myopia Prevention Programme.

Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication.

Data Sharing Statement: See Supplement 2.

Additional Contributions: We thank the children and their parents participating in the Hong Kong Children Eye Study and our volunteer helpers for their dedicated work.

^✉

Corresponding author.

PMCID: PMC11926732 PMID: 40111372

This cross-sectional study analyzed 9 years of data from Hong Kong schoolchildren to report the prevalence of refractive astigmatism and corneal astigmatism and explore the associations between the COVID-19 pandemic and child astigmatism.

Key Points

Question

What is the association between the COVID-19 pandemic and child astigmatism?

Findings

This cross-sectional study involving 21 655 children from 2015 to 2023 revealed substantial increases in the prevalence and severity of refractive and corneal astigmatism, independent of myopia. The pandemic was associated with increased risks and magnitudes of child astigmatism, regardless of sociodemographic background, parental astigmatism, or presence of myopia.

Meaning

Lifestyle changes after the pandemic were associated with an increase in the prevalence and severity of child astigmatisms, likely associated with changes in the developing cornea.

Abstract

Importance

Astigmatism can cause blurred vision at near and distance. It is common among schoolchildren and associated with ametropia. Although the COVID-19 pandemic generated a surge in myopia prevalence in children, the association with child astigmatism remains unknown.

Objective

To report the prevalence of refractive astigmatism and corneal astigmatism in schoolchildren from 2015 to 2023 and explore the associations between the pandemic and astigmatism.

Design, Setting, and Participants

This population-based cross-sectional study stratified all the primary schools registered with Education Bureau in Hong Kong into 7 clustered regions used by Hospital Authority Services in Hong Kong. Participants were schoolchildren aged 6 to 8 years who underwent comprehensive ocular examinations at 2 academic medical centers in Hong Kong from 2015 to 2023. Astigmatism was measured with optical biometry and auto-refractor after cycloplegia.

Exposure

COVID-19 pandemic.

Main Outcomes and Measures

The annual prevalence rates of refractive astigmatism and corneal astigmatism were the primary outcome measures. Logistic regression was used to evaluate the association of the pandemic with the risks of refractive astigmatism and corneal astigmatism. Linear regression was used to explore the association of the pandemic with the magnitudes of refractive astigmatism and corneal astigmatism.

Results

The cohort consisted of 21 655 children: 11 464 boys (52.9%) and 10 191 girls (47.1%); their mean (SD) age was 7.31 (0.90) years. The prevalence rate of refractive astigmatism of at least 1.0 diopter (D) was 21.4% and corneal astigmatism of at least 1.0 D 59.8% in 2015 and increased to 34.7% (difference, 13.3%; 95% CI, 9.3%-17.3%) and 64.7% (difference, 4.9%; 95% CI, 0.5%-9.2%), respectively, in 2022-2023. The pandemic was associated with a 20% increase in the risk of refractive astigmatism (odd ratio [OR], 1.20; 95% CI, 1.09-1.33; P < .001), 26% increase in the risk of corneal astigmatism (OR, 1.26; 95% CI, 1.15-1.38; P < .001), 0.04 D in the magnitude of refractive astigmatism (95% CI, 0.02-0.07; P < .001), and 0.05 D in the magnitude of corneal astigmatism (95% CI, 0.02-0.08; P < .001), compared with the prepandemic period of 2015-2019 and after adjusting for sociodemographic factors, parental astigmatism, and child myopia.

Conclusions and Relevance

This study found an increase in both the prevalence and severity of refractive astigmatism and corneal astigmatism after the COVID-19 pandemic. Corneal changes especially along the steepest meridian may explain some of the progression of corneal astigmatism. The potential impact of higher degrees of astigmatism may warrant dedicated efforts to elucidate the relationship between environmental and/or lifestyle factors, as well as the pathophysiology of astigmatism.

Introduction

Astigmatism is the most common refractive error and a universal cause of visual impairment. It is caused by 1 or more spherocylindrical surfaces in our ocular system that converge distant lights differentially into more than 1 focal point on the retina, resulting in a blurred image. Refractive astigmatism (RA) refers to the total amount of astigmatism in the eye. It is a summation of 2 components, corneal astigmatism (CA) and internal astigmatism (IA).

In a global review on the prevalence of refractive errors from 1990 to 2016, 14.9% of children worldwide had astigmatism of more than 0.5 diopter (D).¹ While the prevalence varied among individuals of different ethnicities, as evidenced by a higher prevalence of astigmatism in China compared with the western Pacific region (16.5% vs 12.1%), the condition was also more common in the urbanized parts than the rural areas of the same country, suggesting an environmental factor in addition to inherent factors, such as genetics.² In Hong Kong, a metropolitan city in southeast China, we found that 63.6% of children had at least 0.5 D astigmatism and 21.9% had at least 1.0 D.³ In the latest American Academy of Ophthalmology Preferred Practice Pattern on pediatric eye evaluation and amblyopia, an age-dependent amblyogenic threshold for children with astigmatism was defined. As children matured from younger than 1 year to age 3 to 4 years, the amblyogenic threshold of astigmatism reduced from 3.0 D or more to 1.5 D or more.⁴ Unlike myopia or hyperopia, children affected by astigmatism could not see clearly at neither near nor distance, putting them at a greater risk of amblyopia if the condition is left untreated.^5,6

The COVID-19 pandemic changed the ways people lived, including children. Schooling became virtual, which was associated with more frequent or prolonged use of electronic gadgets or reduced outdoor time as a result of social restrictions for many children. These changes were associated with a surge in myopia prevalence in children of Hong Kong as well as other parts of the world across the COVID-19 pandemic.^7,8 Given the known association between myopia and astigmatism, 2 local studies evaluated the prevalence of RA in Hong Kong during the enforcement of restrictions in 2020 and compared with historical data from earlier years.^9,10 The high co-occurrence of astigmatism with myopia suggested that the change in the prevalence of RA could be a byproduct of axial elongation. Nonetheless, there were no data on the changes of corneal component of astigmatism, which might also be related to an increase in RA. Furthermore, no study reported the prevalence of astigmatism after the lift of social and school restrictions.

Established in 2015, the Hong Kong Children Eye Study (HKCES) is a population-based cross-sectional study on childhood ocular conditions. In this study, we evaluated 9 years of consecutive data from 2015 to 2023 from the HKCES, which covered the prepandemic, pandemic, and postpandemic periods, on the prevalence changes in RA and CA, as well as related corneal parameters. We also explored the associations of astigmatism with myopia and other ocular factors.

Methods

Study Population

Schoolchildren aged 6 to 8 years were recruited from the HKCES. Our selection was based on a stratified and clustered randomized sampling frame, where we stratified all the primary schools registered with Education Bureau in Hong Kong into 7 clustered regions used by Hospital Authority Services in Hong Kong. All children underwent comprehensive ocular examinations, and their parents completed standardized questionnaires on lifestyle and environmental risk factors at the Chinese University of Hong Kong Eye Centre and the Chinese University Medical Centre from 2015 to 2023. None of these children was analyzed more than once during this multiyear recruitment. The study protocol was previously published.¹¹ Participants with congenital ocular diseases, ocular trauma, or prior ocular surgery and those with no data on either autorefraction or keratometry were excluded from the study. Ethics approval was obtained from the Chinese University of Hong Kong, and the study conformed to the tenets of the Declaration of Helsinki. Written informed consent was obtained from both the child and their parents ahead of their participation. None of study participants received any stipend or other incentive to participate in this study. We use the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guidelines for this cross-sectional study.¹²

Ocular Examinations

Cycloplegic autorefraction was performed on all children with an autorefractor (ARK-510A; NIDEK Co) after a cycloplegic regimen. At least 2 cycles of eye drops were administered. Two drops of cyclopentolate, 1% (Cyclogyl; Alcon-Convreur), and tropicamide, 1% (Santen), were administered to both eyes at 5 minutes apart in the first cycle. For the second cycle, the same cycloplegic drops were applied 10 minutes after the first cycle. An additional third cycle was given at 30 minutes after the second cycle if the pupil size was less than 6.0 mm or the pupillary light reflex was still present. Corneal parameters, including flattest keratometry (K1) and steepest keratometry (K2), were measured with a noncontact partial-coherence laser interferometry (IOL Master; Carl Zeiss Meditec).

Definition and Outcomes

Data of the right eye from each study participant were used because of the high correlation between the 2 eyes of the participants (Pearson r = 0.82, P < .001). Refractive astigmatism (RA) was defined as at least 1.0 cylindrical diopters, expressed in a positive notation. Corneal astigmatism (CA) was defined as an absolute difference of at least 1.0 D between the flattest and the steepest keratometry of the cornea, expressed in a positive notation. The primary outcome was the annual prevalence of RA and CA. Secondary outcomes included the mean cylindrical powers of RA and CA, K1 and K2, and the mean keratometry values (mean K). The period 2015-2019 was defined as the pre–COVID-19 period and the reference, whereas 2020 was considered the COVID-19 period when social and school restrictions were in place, and 2021-2023 the post–COVID-19 period when restrictions were gradually lifted. Since February 2022, Hong Kong experienced the fifth wave of COVID-19, primarily driven by the Omicron BA2 variant, resulting in an increase in infection rates and mortality. This situation adversely impacted our recruitment efforts, prompting us to combine study participants from 2022 and 2023 to achieve a subtotal comparable with that of the other years.¹³

Statistical Analysis

Descriptive statistics were used to investigate the demographic characteristics of study participants. Binary or categorical variables were reported using counts and percentages while their group differences were examined using the Pearson χ² test. Continuous variables were reported as mean (SD). The associations between COVID-19 pandemic, age, sex, family income, and self-reported parental astigmatism with child RA and CA were analyzed using logistic regression while those with cylindrical powers of RA and CA were estimated using linear regression. All statistical analyses were performed using R version 4.2.1 (R Core Team, 2022). All P values were 2-sided but not adjusted for multiple analyses. Sensitivity analysis was performed using data from the left eyes (eTable 1 in the Supplement).

Results

Study Population

Data for a total of 21 655 children, consisting of 11 464 boys (52.9%) and 10 191 girls (47.1%) with a mean (SD) age of 7.31 (0.90) years, were analyzed. The demographic characteristics are summarized in eTable 2 in the Supplement.

Increase in Prevalence and Severity of RA and CA After COVID-19

Before the pandemic, the prevalence of RA was 23.4% from 2015-2019 (Table 1 and eTable 3 in the Supplement). During COVID-19, it increased slightly to 24.6% in 2020 (difference, 1.1%; 95% CI, –1.4% to 3.7%). After the lift of restrictions, the prevalence of RA continued to increase to 30.0% (difference, 6.5%; 95% CI, 4.7% to 8.3%) in 2021 and 34.7% (difference, 11.2%; 95% CI, 8.2% to 14.3%) in 2022-2023. Subgroup analyses revealed an increase in prevalence of RA in both sexes and across all ages from 2021 onwards when compared with the pre–COVID-19 period (eTable 3 in the Supplement).

Table 1. Annual Prevalence and Mean (SD) of Refractive and Corneal Astigmatisms by Age and Sex, 2015-2023.

Characteristic	No.	2015	2016	2017	2018	2019	P value	Period in relation to COVID-19 pandemic and restrictions				P value^a
Characteristic	No.	2015	2016	2017	2018	2019	P value	(1) Before, 2015-2019	(2) During, 2020	(3) After restriction 1, 2021	(4) After restriction 2, 2022 + 2023	(2) vs (1)	(3) vs (1)	(4) vs (1)
Total No. by year		1021	1525	1368	5479	7100		16 493	1201	2831	1007
Refractive astigmatism prevalence, No. (%)^b
Total	21 532	218 (21.35)	343 (22.49)	287 (20.98)	1317 (24.04)	1698 (23.92)	.04	3863 (23.42)	295 (24.56)	848 (29.95)	349 (34.66)	.55	<.001	<.001
Age, y
6	8418	62 (20.46)	131 (23.52)	92 (21.15)	609 (24.69)	776 (25.25)	.16	1670 (24.43)	94 (23.86)	255 (32.61)	144 (35.38)	.69	<.001	<.001
7	7406	98 (21.97)	123 (22.32)	103 (20.32)	367 (22.31)	525 (22.46)	.89	1216 (22.16)	136 (23.94)	292 (28.57)	113 (34.35)	.43	<.001	<.001
8	5708	58 (21.32)	89 (21.34)	92 (21.60)	341 (24.95)	397 (23.51)	.37	977 (23.42)	65 (27.02)	301 (29.31)	92 (33.95)	.24	.002	.01
Sex
Male	11 403	107 (21.10)	194 (24.74)	168 (22.55)	731 (24.86)	944 (25.25)	.20	2144 (24.60)	164 (26.75)	460 (30.56)	209 (36.37)	.24	<.001	<.001
Female	10 129	111 (21.60)	149 (20.11)	119 (19.10)	586 (23.09)	754 (22.43)	.15	1719 (22.10)	131 (22.28)	388 (29.26)	140 (31.96)	.76	<.001	<.001
Total No. by year		1027	1514	1342	5258	6858		15 999	1187	2803	962
Corneal astigmatism prevalence, No. (%)^c
Total	20 951	614 (59.79)	885 (58.45)	751 (55.96)	3129 (59.51)	4172 (60.83)	.01	9551 (59.70)	696 (58.64)	1874 (66.86)	622 (64.66)	.61	<.001	<.001
Age, y
6	8092	175 (57.76)	333 (59.89)	248 (58.35)	1430 (61.64)	1845 (62.69)	.20	4031 (61.57)	219 (56.44)	524 (67.88)	263 (68.31)	.09	<.001	.002
7	7238	273 (60.94)	322 (59.30)	273 (55.49)	902 (56.45)	1353 (59.76)	.12	3123 (58.43)	336 (59.79)	668 (65.68)	195 (62.10)	.49	<.001	.08
8	5621	166 (60.14)	230 (55.42)	230 (54.12)	797 (59.48)	974 (58.99)	.20	2397 (58.36)	141 (59.49)	682 (67.26)	164 (62.36)	.68	<.001	.18
Sex
Male	11 030	276 (54.33)	424 (54.71)	401 (54.86)	1620 (57.84)	2099 (58.60)	.08	4820 (57.40)	349 (57.59)	955 (64.05)	334 (62.31)	.91	<.001	.02
Female	9921	338 (65.13)	461 (62.38)	350 (57.28)	1509 (61.42)	2073 (63.28)	.03	4731 (62.23)	347 (59.72)	919 (70.05)	288 (67.61)	.40	<.001	.01
Total No. by year		1021	1525	1368	5479	7100		16 493	1201	2831	1007
Cylinder, mean (SD), D
Total	21 532	0.70 (0.65)	0.68 (0.67)	0.66 (0.66)	0.72 (0.68)	0.70 (0.67)	.09	0.70 (0.67)	0.71 (0.66)	0.81 (0.72)	0.87 (0.79)	.76	<.001	<.001
Age, y
6	8418	0.70 (0.7)	0.69 (0.66)	0.66 (0.63)	0.72 (0.66)	0.71 (0.66)	.41	0.71 (0.66)	0.70 (0.68)	0.84 (0.74)	0.85 (0.74)	.60	<.001	<.001
7	7406	0.70 (0.65)	0.68 (0.65)	0.66 (0.67)	0.71 (0.70)	0.70 (0.68)	.78	0.69 (0.68)	0.71 (0.66)	0.78 (0.67)	0.88 (0.80)	.98	<.001	<.001
8	5708	0.69 (0.60)	0.68 (0.69)	0.67 (0.68)	0.72 (0.68)	0.70 (0.67)	.61	0.70 (0.67)	0.72 (0.60)	0.81 (0.73)	0.90 (0.84)	.90	<.001	<.001
Sex
Male	11 403	0.68 (0.63)	0.70 (0.68)	0.69 (0.70)	0.73 (0.68)	0.73 (0.70)	.29	0.72 (0.69)	0.74 (0.67)	0.81 (0.72)	0.90 (0.81)	.47	<.001	<.001
Female	10 129	0.71 (0.67)	0.67 (0.65)	0.64 (0.61)	0.70 (0.67)	0.68 (0.64)	.13	0.69 (0.65)	0.67 (0.64)	0.80 (0.71)	0.84 (0.75)	.23	<.001	<.001
Total No. by year		1027	1514	1342	5258	6858		15 999	1187	2803	962
K1-K2, mean (SD), D
Total	20 951	1.25 (0.75)	1.25 (0.70)	1.20 (0.68)	1.24 (0.69)	1.24 (0.66)	.29	1.24 (0.68)	1.24 (0.66)	1.34 (0.70)	1.35 (0.75)	.87	<.001	<.001
Age, y
6	8092	1.30 (0.95)	1.28 (0.67)	1.22 (0.69)	1.26 (0.69)	1.26 (0.67)	.59	1.26 (0.70)	1.21 (0.68)	1.36 (0.71)	1.36 (0.69)	.42	<.001	.001
7	7238	1.25 (0.68)	1.24 (0.65)	1.20 (0.70)	1.23 (0.70)	1.23 (0.65)	.75	1.23 (0.67)	1.25 (0.68)	1.32 (0.68)	1.37 (0.79)	.31	<.001	<.001
8	5621	1.19 (0.57)	1.21 (0.80)	1.19 (0.66)	1.23 (0.67)	1.24 (0.66)	.57	1.23 (0.68)	1.23 (0.61)	1.33 (0.70)	1.32 (0.80)	.76	<.001	.02
Sex
Male	11 030	1.17 (0.63)	1.22 (0.65)	1.21 (0.71)	1.22 (0.68)	1.23 (0.69)	.50	1.22 (0.68)	1.22 (0.67)	1.30 (0.69)	1.33 (0.78)	.75	<.001	<.001
Female	9921	1.33 (0.84)	1.28 (0.75)	1.20 (0.65)	1.27 (0.70)	1.26 (0.64)	.03	1.27 (0.69)	1.25 (0.65)	1.37 (0.70)	1.38 (0.72)	.97	<.001	<.001

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Abbreviations: D, diopter; K1, flattest keratometry; K2, steepest keratometry.

^{^a}

P values are adjusted for age, sex, and sphere.

^{^b}

Refractive astigmatism was defined as cylinder refraction ≥1 D in the right eye.

^{^c}

Corneal astigmatism was defined as the absolute difference between K1 and K2 more than or equal to ≥1 D in the right eye.

The prevalence of CA in children was 59.7% between 2015 and 2019 (Table 1 and eTable 3 in the Supplement). It increased to 66.9% (difference, 7.2%; 95% CI, 5.3%-9.1%) in 2021 and maintained at 64.7% (difference, 5.0%; 95% CI, 1.8%-8.1%) in 2022-2023. Likewise, boys and girls across all ages had higher prevalence of CA in 2021 compared with the pre–COVID-19 period (from prevalence in pre–COVID-19 period to prevalence in 2021: boys, 57.4% to 64.1%; difference; 6.7% [95% CI, 4.0%-9.3%]; girls, 62.2% to 70.1%; difference; 7.8% [95% CI, 5.1%-10.5%]; aged 6 years, 61.6% to 67.9%; difference; 6.3% [95% CI, 2.8%-9.8%]; aged 7 years, 58.4% to 65.7%; difference; 7.3% [95% CI, 4.1%-10.5%]; aged 8 years, 58.4% to 67.3%; difference; 8.9% [95% CI, 5.6%-12.2%]). In 2022-2023, a similar significance was observed for both boys (57.4% in pre–COVID-19 period to 62.3% in 2022-2023; difference, 4.9%; 95% CI, 0.7%-9.2%) and girls (62.2% in pre–COVID-19 period to 67.6% in 2022-2023; difference, 5.4%; 95% CI, 0.8%-10.0%), and among the 6-year-olds (61.6% in pre–COVID-19 period to 68.3% in 2022-23; difference, 6.7%; 95% CI, 2.0%-11.5%) (eTable 3 in the Supplement).

The magnitude of mean cylindrical power of RA gradually increased from 0.70 D from 2015-2019 (Table 1 and eTable 3 in the Supplement) to 0.71 D in 2020 (difference, 0.01 D; 95% CI, –0.03-0.05 D), 0.81 D in 2021 (difference, 0.11 D; 95% CI, 0.08-0.14 D; P < .001), and 0.87 D in 2022-2023 (difference, 0.17; 95% CI, 0.12-0.22 D; P < .001). A similar trend was observed for CA, where the mean cylindrical power of CA increased from 1.24 D during 2015-2020 (difference, 0 D; 95% CI, –0.04-0.4 D) to 1.34 D in 2021 (difference, 0.1 D; 95% CI, 0.07-0.13 D; P < .001) and 1.35 D in 2022-2023 (difference, 0.11 D; 95% CI, 0.06-0.16 D; P < .001). The same phenomenon was observed in all subgroups by sex and age when comparing the data of 2021-2023 to the pre–COVID-19 period (eTable 3 in the Supplement). The prevalence and mean (SD) of RA in negative notation are summarized and reported in eTable 5 in the Supplement. The majority of children continued to have with-the-rule astigmatism during these 9 years (eTable 6 in the Supplement).

Changes in Corneal Curvatures After COVID-19

The K1 value decreased from 42.91 D in 2015-2019 to 42.85 D in 2022-2023 (difference, –0.06 D; 95% CI, –0.15-0.03 D), while the K2 value increased from 44.15 D in 2015-2019 to 44.20 D in 2021-2023. However, the only potential difference was observed when comparing the K2 value (44.2 D) in 2021 to the baseline K2 value of 44.15 D during 2015-2019 (difference, 0.05 D; 95% CI, –0.01-0.11 D; P after adjusting for age, sex, and spherical values from the child = .03). The widening difference between K2 and K1 was supported by no differences identified in the mean keratometry, which was the average of K1 and K2 values. The mean keratometry value was not shown to be different across all ages and both sexes from 2015 to 2023 (Table 2 and eTable 4 in the Supplement).

Table 2. Annual Mean (SD) of K1, K2, and Mean K by Age and Sex, 2015-2023.

Characteristic	No.	2015	2016	2017	2018	2019	P value	Period in relation to COVID-19 pandemic and restrictions				P value^a
Characteristic	No.	2015	2016	2017	2018	2019	P value	(1) Before, 2015-2019	(2) During, 2020	(3) After restriction 1, 2021	(4) After restriction 2, 2022 + 2023	(2) vs (1)	(3) vs (1)	(4) vs (1)
Total No. by year		1027	1514	1342	5258	6858		15 999	1187	2803	962
K1, mean (SD), D
Total	20 951	42.93 (1.80)	42.93 (1.38)	42.95 (1.36)	42.87 (1.41)	42.93 (1.41)	.12	42.91 (1.43)	42.94 (1.37)	42.87 (1.43)	42.85 (1.44)	.75	.10	.22
Age, y
6	8092	42.89 (1.36)	42.83 (1.44)	42.94 (1.36)	42.94 (1.43)	43.00 (1.41)	.32	42.94 (1.41)	43.05 (1.41)	42.95 (1.46)	42.88 (1.37)	.31	.78	.22
7	7238	42.96 (2.21)	42.98 (1.33)	43.03 (1.41)	42.81 (1.39)	42.92 (1.41)	.012	42.91 (1.48)	42.90 (1.37)	42.87 (1.40)	42.82 (1.48)	.80	.26	.63
8	5621	42.90 (1.44)	43.01 (1.37)	42.88 (1.31)	42.84 (1.39)	42.90 (1.41)	.29	42.89 (1.39)	42.88 (1.30)	42.82 (1.42)	42.84 (1.48)	.79	.14	.75
Sex
Male	11 030	42.56 (2.08)	42.59 (1.30)	42.66 (1.34)	42.53 (1.35)	42.57 (1.34)	.27	42.57 (1.39)	42.54 (1.27)	42.54 (1.36)	42.57 (1.34)	.65	.25	.73
Female	9921	43.28 (1.37)	43.30 (1.38)	43.30 (1.30)	43.26 (1.37)	43.33 (1.38)	.42	43.30 (1.37)	43.36 (1.41)	43.25 (1.41)	43.21 (1.47)	.35	.23	.14
Total No. by year		1027	1514	1342	5258	6858		15 999	1187	2803	962
K2, mean (SD), D
Total	20 951	44.17 (1.98)	44.17 (1.57)	44.14 (1.53)	44.11 (1.55)	44.18 (1.57)	.26	44.15 (1.59)	44.17 (1.52)	44.20 (1.58)	44.20 (1.55)	.70	.03	.13
Age, y
6	8092	44.19 (1.64)	44.10 (1.60)	44.15 (1.53)	44.19 (1.54)	44.22 (1.57)	.49	44.19 (1.56)	44.26 (1.59)	44.30 (1.61)	44.24 (1.48)	.53	.05	.65
7	7238	44.22 (2.36)	44.21 (1.53)	44.21 (1.58)	44.03 (1.57)	44.14 (1.56)	.052	44.13 (1.64)	44.15 (1.50)	44.19 (1.57)	44.19 (1.61)	.79	.27	.17
8	5621	44.09 (1.61)	44.20 (1.56)	44.06 (1.48)	44.07 (1.55)	44.14 (1.58)	.49	44.11 (1.56)	44.10 (1.45)	44.15 (1.56)	44.17 (1.59)	.82	.42	.38
Sex
Male	11 030	43.73 (2.20)	43.80 (1.44)	43.85 (1.53)	43.75 (1.52)	43.80 (1.50)	.48	43.78(1.6)	43.76 (1.42)	43.84 (1.51)	43.90 (1.43)	.73	.16	.12
Female	9921	44.61 (1.62)	44.56 (1.60)	44.49 (1.47)	44.52 (1.49)	44.59 (1.54)	.31	44.56 (1.53)	44.61 (1.50)	44.62 (1.55)	44.59 (1.61)	.34	.09	.59
Total No. by year		1027	1514	1342	5258	6858		15 999	1187	2803	962
Mean K, mean (SD), D
Total	20 951	43.55 (1.85)	43.55 (1.43)	43.54 (1.41)	43.49 (1.44)	43.55 (1.45)	.19	43.53 (1.47)	43.56 (1.41)	43.54 (1.46)	43.53 (1.45)	.70	.69	.81
Age, y
6	8092	43.54 (1.43)	43.47 (1.48)	43.54 (1.41)	43.56 (1.44)	43.59 (1.45)	0.4	43.57 (1.45)	43.65 (1.46)	43.62 (1.50)	43.56 (1.38)	.40	.35	.73
7	7238	43.59 (2.26)	43.60 (1.40)	43.61 (1.45)	43.42 (1.44)	43.53 (1.45)	0.024	43.52 (1.53)	43.52 (1.40)	43.53 (1.45)	43.51 (1.49)	.96	.95	.60
8	5621	43.49 (1.50)	43.60 (1.41)	43.47 (1.36)	43.45 (1.43)	43.52 (1.46)	0.4	43.50 (1.44)	43.49 (1.33)	43.48 (1.45)	43.51 (1.48)	.80	.77	.73
Sex
Male	11 030	43.14 (2.12)	43.19 (1.33)	43.26 (1.39)	43.14 (1.40)	43.18 (1.38)	0.48	43.18 (1.44)	43.15 (1.30)	43.19 (1.40)	43.23 (1.33)	.70	.84	.49
Female	9921	43.95 (1.44)	43.93 (1.44)	43.89 (1.35)	43.89 (1.38)	43.96 (1.43)	0.31	43.93 (1.41)	43.98 (1.39)	43.93 (1.44)	43.90 (1.50)	.33	.74	.68

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Abbreviations: D, diopter; K, keratometry; K1, flattest keratometry; K2, steepest keratometry.

^{^a}

P values are adjusted for age, sex, and sphere.

Associations of COVID-19 Pandemic With RA and CA

The COVID-19 pandemic was associated with a higher prevalence of RA (odds ratio [OR], 1.20; 95% CI, 1.09-1.33; P < .001; prevalence in 2015-2019, 23.4%; prevalence in 2020-2023, 29.6%; prevalence difference, 6.2% [95% CI, 4.8%-7.6%]) and CA (OR, 1.26; 95% CI, 1.15-1.38, P < .001; prevalence in 2015-2019, 59.7%; prevalence in 2020-2023, 64.5%; prevalence difference, 4.8% [95% CI, 3.3%-6.3%]) in both univariate and multiple logistic regressions (Table 3). Likewise, the magnitudes of RA and CA were both associated with the COVID-19 pandemic (RA: β, 0.04 D; 95% CI, 0.02-0.07; P < .001; mean [SD] in 2015-2019, 0.70 [0.67] D; mean [SD] in 2020-2023, 0.80 [0.72] D; mean difference, 0.1 D [95% CI, 0.08-0.12 D]; and CA: β, 0.05 D; 95% CI, 0.02-0.08; P < .001; mean [SD] in 2015-2019, 1.24 [0.68] D; mean [SD] in 2020-2023, 1.32 [0.70] D; mean difference, 0.08 D [95% CI, 0.06-0.1 D]), adjusted for the age, sex of child, spherical value, familial income, and presence of parental astigmatism (Table 4). Logistic and linear regressions done with RA in negative notation are summarized in eTables 7 and 8 in the Supplement. When compared with the prepandemic period 2015-2019, we observed a decrease in the amount of outdoor time (from 1.43 to 1.16 hours per day; difference, –0.27 hours; 95% CI, –0.29 to –0.25 hours; P < .001) and an increase in the amount of near work (from 3.33 to 4.91 hours per day; difference, 1.58 hours; 95% CI, 1.52-1.64 hours; P < .001) during 2020-2023 (eTable 11 in the Supplement).

Table 3. Logistic Regression on the Associations Between COVID-19 Pandemic and Astigmatism.

Characteristic	Model 1^a		Model 2^b
Characteristic	OR (95% CI)	P value	OR (95% CI)	P value
Refractive astigmatism (≥1.0 D)
COVID-19 pandemic (2015-2019 as reference)^c	1.26 (1.15-1.39)	<.001	1.20 (1.09-1.33)	<.001
Age, y	NA	NA	0.81 (0.77-0.85)	<.001
Sex (male as reference)	NA	NA	0.90 (0.83-0.98)	.02
Parental astigmatism (no as reference)	NA	NA	1.20 (1.06-1.35)	<.001
Sphere, diopters	NA	NA	0.69 (0.67-0.70)	<.001
Family income (>HK$25 000 as reference^d)	NA	NA	0.92 (0.85-1.00)	.03
Corneal astigmatism (≥1.0 D)
COVID-19 pandemic (2015-2019 as reference)^c	1.26 (1.15-1.37)	<.001	1.26 (1.15-1.38)	<.001
Age, y	NA	NA	0.91 (0.88-0.95)	<.001
Sex (male as reference)	NA	NA	1.28 (1.19-1.37)	<.001
Parental astigmatism (no as reference)	NA	NA	1.21 (1.08-1.36)	<.001
Sphere, D	NA	NA	0.88 (0.86-0.91)	<.001
Family income (>HK$25 000 as reference^d)	NA	NA	0.97 (0.90-1.05)	.44

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Abbreviations: D, diopter; OR, odds ratio; NA, not applicable.

^{^a}

Model 1: not adjusted for covariates.

^{^b}

Model 2: adjusted for age, sex, parental astigmatism, sphere, and family income.

^{^c}

COVID-19 pandemic refers to the period 2020-2023.

^{^d}

US $3215.79.

Table 4. Linear Regression of Effects of COVID-19 Pandemic on RA and CA.

Characteristic	Model 1^a		Model 2^b
Characteristic	β (95% CI)	P value	β (95% CI)	P value
Refractive astigmatism (cylinder)
COVID-19 pandemic (2015-2019 as reference)^c	0.07 (0.04 to 0.10)	<.001	0.04 (0.02 to 0.07)	.001
Age, y	NA	NA	−0.07 (−0.08 to −0.06)	<.001
Sex (male as reference)	NA	NA	−0.02 (0.04 to 0)	.09
Parental astigmatism (no as reference)	NA	NA	0.05 (0.02 to 0.08)	.004
Sphere, D	NA	NA	−0.15 (−0.16 to −0.15)	<.001
Family income (>HKD$25 000 as reference^d)	NA	NA	−0.02 (−0.04 to 0)	.08
Corneal astigmatism (K1-K2)
COVID-19 pandemic (2015-2019 as reference)^c	0.07 (0.04 to 0.09)	<.001	0.05 (0.02 to 0.08)	<.001
Age, y	NA	NA	−0.05 (−0.07 to −0.04)	<.001
Sex (male as reference)	NA	NA	0.06 (0.04 to 0.08)	<.001
Parental astigmatism (no as reference)	NA	NA	0.07 (0.03 to 0.10)	<.001
Sphere, D	NA	NA	−0.09 (−0.10 to −0.08)	<.001
Family income (>HK$25 000 as reference^d)	NA	NA	−0.005 (−0.03 to 0.02)	.70

Open in a new tab

Abbreviations: D, diopter; K1, flattest keratometry; K2, steepest keratometry; NA, not applicable.

^{^a}

Model 1: not adjusted for covariates.

^{^b}

Model 2: adjusted for age, sex, parental astigmatism, sphere, and family income.

^{^c}

COVID-19 pandemic refers to the period 2020-2023.

^{^d}

US $3215.79.

Increase in Astigmatism Independent of Myopia

Our data demonstrated a delayed in increased prevalence of both RA and CA from 2020 to 2023, following the increase in myopia in 2019 during the pandemic (Figure). The absolute magnitude of RA and CA also increased from 2021 to 2023 (eFigure 1 in the Supplement).

Discussion

In this 9-year population-based study (from 2015 to 2023) conducted in Hong Kong and using standard measurements among children from the same region, we observed a sustained increase in the prevalence and severity of both refractive and corneal astigmatism in Chinese schoolchildren of Hong Kong. While myopia increased during the onset of the pandemic and related restrictions, astigmatism started to increase only in 2021 after the restrictions were gradually lifted. The increase in prevalence continued into 2023. By considering the spherical values for the children, we showed that the increase in astigmatism prevalence was independent from the surge in myopia. The pandemic itself imposed additional odds of RA and CA by 20%, or by a magnitude of 0.04 D.

Astigmatism remained highly prevalent after pandemic-related restrictions were lifted. The COVID-19 pandemic brought about lifestyle changes, particularly in the mode of learning and the school curriculum of schoolchildren. Switching from in-person classes to virtual, children were required to spend longer hours viewing electronic devices, which was intensive near work, compared with the prepandemic period.^7,14 In our current study, the prevalence of RA before 2019 was 23.4%, which was already higher than the 20.2% reported previously in Hong Kong during 2015-2016⁹ and the 18.1% by our own institution during 1998-2000.¹⁵ Compared with earlier reports, we observed an increase in the prevalence of RA and CA only in 2021. Wong et al⁹ reported a prevalence of 28.9% in 418 schoolchildren during October to December 2020 using a 1 D or more threshold and an open-field autorefractor without cycloplegia and cited up to a 1.49-fold increase in the prevalence of RA when compared with historical data from another local study using a similar study design in 2015-2016, as well as a Singaporean Chinese study in 1999. Liang et al¹⁰ also reported a similar 1.5-fold increase of astigmatism prevalence from 33.9% in 2018 to 49.1% in 2020 using a 0.75 D or more threshold among 285 students in Hong Kong. Both studies suggested school closure, increased use of digital device, and reduced outdoor time as well as axial myopia as possible associated factors. Like these published studies, our data suggested a similar extent in the increase of astigmatism prevalence; however, the timing of increase was later than that of myopia (Figure).

Our study showed an increase in the steepest corneal curvature and the prevalence and magnitude of CA in children after the COVID-19 pandemic, which might contribute to the increase in RA. We speculate that the increase in CA was due to an increasing trend of K2, which showed increases in 2021 at a value of 44.2 D. An increase was not demonstrated in 2022-2023 as the K2 value appeared to remain the same to that in 2021, which might be attributed to a lower number of children recruited in 2022-2023.

As most children had with-the-rule astigmatism (eTable 6 in the Supplement),³ the steeper corneal curvature was almost exclusively located in the vertical meridian. We hypothesize that the habit of using digital devices during COVID-19 had an impact on the corneal curvatures. This had previously been reported at the superior region of the cornea in relation to the position of the upper eyelid during reading or using electronic devices.¹⁶ Although these changes were thought to be transient and reversible after shifting from downward to primary gaze,¹⁷ we speculate a cumulative effect on CA after habitual and prolonged periods of such gaze, leading to an increase in K2 value with time.

Compared with the change in myopia prevalence in Hong Kong over the pandemic, the increase in RA and CA exhibited a delayed onset. While the increase in myopia prevalence started from 2019-2020 during the COVID-19 restrictions, astigmatism only began to increase in 2021 and started to ease off in 2023.⁷ Based on the previous reports that astigmatism and myopia are highly correlated and that astigmatism may be a byproduct of myopia,^3,15,18,19 the findings in our present study provided additional data on the corneal component, which is a major contributor to RA. We think that the change in corneal curvatures induced by near work takes time to develop. Moreover, the independent increase in astigmatism prevalence from myopia was supported by the regression models, which were adjusted for the spherical values from the children.

While parental astigmatism has been found to be an important risk factor for child astigmatism,^20,21,22 such information was often omitted in the published studies. Our regression models took into consideration the effects from parents, as well as the socioeconomic status of the family, which play a role in determining the mode of learning of the child.^23,24 After adjusting for the above factors, the association between the COVID-19 pandemic and the prevalence and severity of astigmatism remained.

Limitations

Our study has several limitations. The majority of the children were Han Chinese, and our results may not be generalizable to other ethnicities or geographical locations. In addition, in defining time periods in relation to COVID-19, each country or region may have their unique governmental policies on social restrictions. Local practices, including both the extent of the restrictions and population adherence, were variable, so our results may not be reproducible in countries with alternative quarantine measures during the pandemic. Apart from that, our sample size for the year 2022 and 2023 was smaller than those of the previous years. This may have affected the precision of data. Lastly, parental astigmatism, self-reported via questionnaire, was subject to recall bias. Although our previous trio study pinpointed parental astigmatism as a risk factor for child astigmatism, excluding this variable did not reveal any confounding effect on the associations between the COVID-19 pandemic and child astigmatism in our regression analyses.

Conclusions

This study identified an increase in both the prevalence and severity of refractive and corneal astigmatisms after the COVID-19 pandemic among schoolchildren in Hong Kong. Given the high prevalence of astigmatism, the potential impact of higher degrees of astigmatism may warrant dedicated efforts to elucidate the relationship between environmental and/or lifestyle factors, as well as the pathophysiology of astigmatism, in order to preserve children’s eyesight and quality of life.

Supplement 1.

eTable 1. Annual prevalence and mean (standard deviation) of refractive and corneal astigmatisms from left eye data by age and sex, 2015-2023

eTable 2. Participant demographics

eTable 3. Difference in prevalence and mean of RA and CA during and after COVID-19 period compared with pre-COVID-19 period

eTable 4. Difference in means of K1, K2 and mean K during and after COVID-19 period compared with pre-COVID period

eTable 5. Annual Prevalence and Mean (Standard Deviation) of Refractive Astigmatism in Negative Notation by Age and Sex, 2015-2023

eTable 6. Prevalence of different types of RA, 2015-2023

eTable 7. Logistic regression on the association of COVID-19 pandemic with refractive astigmatism (≤ -1.0D) and corneal astigmatism (≥ 1.0D).

eTable 8. Linear regression on the association between COVID-19 pandemic and refractive astigmatism (cylindrical power in negative notation) and corneal astigmatism.

eTable 9. Leave-one-out sensitivity analysis for the effect of parental astigmatism on the logistic regression on the association of COVID-19 pandemic with refractive astigmatism (≤ -1.0D) and corneal astigmatism (≥ 1.0D).

eTable 10. Leave-one-out sensitivity analysis for the effect of parental astigmatism on the linear regression on the association between COVID-19 pandemic and refractive astigmatism (cylindrical power in negative notation) and corneal astigmatism.

eTable 11. Mean (SD) of near-work and outdoor time in 2015-2019 VS 2020-2023

eFigure 1. Annual Mean Diopter of Refractive and Corneal Astigmatism from 2015-2023

eFigure 2. Annual Mean Value of Flattest (K1) and Steepest (K2) Corneal Curvatures from 2015-2023

eAppendix. Information from validated questionnaires

jamaophthalmol-e250205-s001.pdf^{(598.3KB, pdf)}

Supplement 2.

Data sharing statement

jamaophthalmol-e250205-s002.pdf^{(13.4KB, pdf)}

References

1.Hashemi H, Fotouhi A, Yekta A, Pakzad R, Ostadimoghaddam H, Khabazkhoob M. Global and regional estimates of prevalence of refractive errors: systematic review and meta-analysis. J Curr Ophthalmol. 2017;30(1):3-22. doi: 10.1016/j.joco.2017.08.009 [DOI] [PMC free article] [PubMed] [Google Scholar]
2.Tang Y, Chen A, Zou M, et al. Prevalence and time trends of refractive error in Chinese children: a systematic review and meta-analysis. J Glob Health. 2021;11:08006. doi: 10.7189/jogh.11.08006 [DOI] [PMC free article] [PubMed] [Google Scholar]
3.Kam KW, Chee ASH, Tang RCY, et al. Differential compensatory role of internal astigmatism in school children and adults: the Hong Kong Children Eye Study. Eye (Lond). 2023;37(6):1107-1113. doi: 10.1038/s41433-022-02072-9 [DOI] [PMC free article] [PubMed] [Google Scholar]
4.Jacobs DS, Afshari NA, Bishop RJ, et al. ; American Academy of Ophthalmology Preferred Practice Pattern Refractive Management/Intervention Panel . Refractive Errors Preferred Practice Pattern®. Ophthalmology. 2023;130(3):1-P60. doi: 10.1016/j.ophtha.2022.10.031 [DOI] [PubMed] [Google Scholar]
5.Read SA, Vincent SJ, Collins MJ. The visual and functional impacts of astigmatism and its clinical management. Ophthalmic Physiol Opt. 2014;34(3):267-294. doi: 10.1111/opo.12128 [DOI] [PubMed] [Google Scholar]
6.Zhang XJ, Wong PP, Wong ES, et al. Delayed diagnosis of amblyopia in children of lower socioeconomic families: the Hong Kong Children Eye Study. Ophthalmic Epidemiol. 2022;29(6):621-628. doi: 10.1080/09286586.2021.1986551 [DOI] [PubMed] [Google Scholar]
7.Zhang XJ, Zhang Y, Kam KW, et al. Prevalence of myopia in children before, during, and after COVID-19 restrictions in Hong Kong. JAMA Netw Open. 2023;6(3):e234080. doi: 10.1001/jamanetworkopen.2023.4080 [DOI] [PMC free article] [PubMed] [Google Scholar]
8.Li M, Xu L, Tan CS, et al. Systematic review and meta-analysis on the impact of COVID-19 pandemic-related lifestyle on myopia. Asia Pac J Ophthalmol (Phila). 2022;11(5):470-480. doi: 10.1097/APO.0000000000000559 [DOI] [PubMed] [Google Scholar]
9.Wong SC, Kee CS, Leung TW. High prevalence of astigmatism in children after school suspension during the COVID-19 pandemic is associated with axial elongation. Children (Basel). 2022;9(6):919. doi: 10.3390/children9060919 [DOI] [PMC free article] [PubMed] [Google Scholar]
10.Liang Y, Leung TW, Lian JT, Kee CS. Significant increase in astigmatism in children after study at home during the COVID-19 lockdown. Clin Exp Optom. 2023;106(3):322-330. doi: 10.1080/08164622.2021.2024071 [DOI] [PubMed] [Google Scholar]
11.Yam JC, Tang SM, Kam KW, et al. High prevalence of myopia in children and their parents in Hong Kong Chinese Population: the Hong Kong Children Eye Study. Acta Ophthalmol. 2020;98(5):e639-e648. doi: 10.1111/aos.14350 [DOI] [PubMed] [Google Scholar]
12.von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP; STROBE Initiative . The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. J Clin Epidemiol. 2008;61(4):344-349. doi: 10.1016/j.jclinepi.2007.11.008 [DOI] [PubMed] [Google Scholar]
13.Cheung PH, Chan CP, Jin DY. Lessons learned from the fifth wave of COVID-19 in Hong Kong in early 2022. Emerg Microbes Infect. 2022;11(1):1072-1078. doi: 10.1080/22221751.2022.2060137 [DOI] [PMC free article] [PubMed] [Google Scholar]
14.Zhang X, Cheung SSL, Chan HN, et al. Myopia incidence and lifestyle changes among school children during the COVID-19 pandemic: a population-based prospective study. Br J Ophthalmol. 2022;106(12):1772-1778. doi: 10.1136/bjophthalmol-2021-319307 [DOI] [PubMed] [Google Scholar]
15.Fan DS, Lam DS, Lam RF, et al. Prevalence, incidence, and progression of myopia of school children in Hong Kong. Invest Ophthalmol Vis Sci. 2004;45(4):1071-1075. doi: 10.1167/iovs.03-1151 [DOI] [PubMed] [Google Scholar]
16.Buehren T, Collins MJ, Carney L. Corneal aberrations and reading. Optom Vis Sci. 2003;80(2):159-166. doi: 10.1097/00006324-200302000-00012 [DOI] [PubMed] [Google Scholar]
17.Ghosh A, Collins MJ, Read SA, Davis BA, Iskander DR. The influence of downward gaze and accommodation on ocular aberrations over time. J Vis. 2011;11(10):17. doi: 10.1167/11.10.17 [DOI] [PubMed] [Google Scholar]
18.Heidary G, Ying GS, Maguire MG, Young TL. The association of astigmatism and spherical refractive error in a high myopia cohort. Optom Vis Sci. 2005;82(4):244-247. doi: 10.1097/01.OPX.0000159361.17876.96 [DOI] [PubMed] [Google Scholar]
19.Gwiazda J, Grice K, Held R, McLellan J, Thorn F. Astigmatism and the development of myopia in children. Vision Res. 2000;40(8):1019-1026. doi: 10.1016/S0042-6989(99)00237-0 [DOI] [PubMed] [Google Scholar]
20.Kam KW, Chee ASH, Zhang Y, et al. Association of maternal and paternal astigmatism with child astigmatism in the Hong Kong Children Eye Study. JAMA Netw Open. 2022;5(12):e2247795. doi: 10.1001/jamanetworkopen.2022.47795 [DOI] [PMC free article] [PubMed] [Google Scholar]
21.Yang Z, Lu Z, Shen Y, et al. Prevalence of and factors associated with astigmatism in preschool children in Wuxi City, China. BMC Ophthalmol. 2022;22(1):146. doi: 10.1186/s12886-022-02358-2 [DOI] [PMC free article] [PubMed] [Google Scholar]
22.Wang Z, Tong H, Hao Q, et al. Risk factors for astigmatic components and internal compensation: the Nanjing Eye Study. Eye (Lond). 2021;35(2):499-507. doi: 10.1038/s41433-020-0881-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
23.Kong C, Yasmin F. Impact of parenting style on early childhood learning: mediating role of parental self-efficacy. Front Psychol. 2022;13:928629. doi: 10.3389/fpsyg.2022.928629 [DOI] [PMC free article] [PubMed] [Google Scholar]
24.Qiu Y, Ye P. The influence of family socio-economic status on learning engagement of college students majoring in preschool education: the mediating role of parental autonomy support and the moderating effect of psychological capital. Front Psychol. 2023;13:1081608. doi: 10.3389/fpsyg.2022.1081608 [DOI] [PMC free article] [PubMed] [Google Scholar]

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Supplementary Materials