Screen time and reduced outdoor activity during the pandemic may have lasting effects on children’s eye health, including changes in corneal curvature.

Study: Prevalence and Severity of Astigmatism in Children After COVID-19. Image Credit: Jelena Stanojkovic/Shutterstock.com

A recent study posted in JAMA Ophthalmology explores changes in astigmatism rates among children in the aftermath of the recent coronavirus disease 2019 (COVID-19) pandemic.

Introduction

Astigmatism is a common refractive error that causes blurred vision by distorting how light enters the eye. It affects about 15% of school-aged children and is often linked with myopia (nearsightedness).

Because astigmatism disrupts both near and distant vision, it can increase the risk of amblyopia—commonly known as “lazy eye”—in which the brain gradually stops processing input from the affected eye.

The condition arises from uneven curvature across the cornea’s meridians. Instead of focusing light on a single point on the retina, these irregular curvatures scatter the light, creating a blurred image.

Refractive astigmatism (RA) accounts for total astigmatism in the eye, combining corneal astigmatism (CA) and internal astigmatism (IA). IA results from irregularities behind the front surface of the cornea, including the posterior cornea and both sides of the crystalline lens.

Prevalence varies by region, with countries like China reporting higher rates. Children in urban environments are more affected than those in rural areas, pointing to a mix of genetic and environmental influences.

Importantly, the threshold for astigmatism to cause amblyopia lowers with age—from 3 diopters (D) or more in infancy to 1.5 D by ages 3 to 4—underscoring the need for early diagnosis and intervention.

The impact of COVID-19

During the COVID-19 pandemic, school closures and lockdowns kept children indoors at unprecedented levels. Learning, play, and communication shifted almost entirely to digital screens.

This change led to a sharp increase in “near work”—activities like reading or screen use that require prolonged close-up focus, often with a downward gaze. While links between near work and myopia are well-documented, its effects on the cornea—and specifically astigmatism—are less understood.

The Hong Kong Children Eye Study (HKCES) set out to explore these effects by tracking changes in astigmatism prevalence during and after the pandemic.

About the study

The HKCES analyzed eye data from 21,665 children (average age 7.3 years) enrolled in primary schools across Hong Kong. Participants were examined twice between 2015 and 2023.

Corneal astigmatism (CA) was defined as a 1 D or greater difference between the flattest and steepest meridians of the cornea.

Key findings

Before the pandemic, the prevalence of RA and CA at 1.0 D or more stood at 23.4% and 60%, respectively. By 2022–23, both had increased—RA rose by 13.3 percentage points to 34.7%, while CA climbed 5 points to 64.7%.

RA and CA rates in 2021 were already significantly higher than pre-pandemic levels, increasing by approximately 7% in boys and 8% in girls. Age also played a role: prevalence rose by 6%, 7%, and 9% in six-, seven-, and eight-year-olds, respectively.

Overall, children assessed during the pandemic had 20% higher odds of RA and a 26% increased risk of CA compared to those evaluated before the pandemic.

Interestingly, mean keratometry values—used to measure corneal curvature—remained relatively stable. However, the steepest corneal curvature increased while the flattest meridian decreased, suggesting changes in astigmatism were not driven by overall corneal size or shape, and occurred after the spike in myopia seen in 2019.

RA severity also increased: average values rose from 0.7 D pre-pandemic to 0.81 D in 2021 and 0.87 D in 2022–23. CA followed a similar pattern, rising from 1.24 D to 1.34 D after 2020.

Even after accounting for social and demographic variables, family history, and co-existing myopia, these increases remained statistically significant.

Researchers point to several likely factors: more time spent on digital devices, extended school closures, reduced outdoor activity, and associated increases in myopia. Outdoor time dropped by about 0.3 hours per day, while near work jumped from 3.3 to 4.9 hours—a 1.6-hour daily increase.

One theory suggests that prolonged reading or screen time places constant pressure from the eyelid on the upper cornea, gradually altering its curvature. This differs from earlier assumptions that such effects from near work were temporary and reversible.

As the researchers note, “We think that the change in corneal curvatures induced by near work takes time to develop.”

Conclusions

Both RA and CA increased in prevalence and severity following the COVID-19 pandemic, supporting findings from earlier research. Changes in corneal curvature—particularly in the steepest meridian—may be partly responsible, likely driven by extended near work.

Further studies are needed to understand better how lifestyle and environmental shifts influence eye development and contribute to astigmatism. These insights could help shape strategies to protect children’s vision as digital habits continue to evolve.