This big data analysis using databases provided by the KDCA-NHIS, revealed a higher occurrence of DES in children under 18 years old during the COVID-19 season compared to the non-COVID-19 season. Moreover, older age, female sex, those living in metropolitan areas, and those with DM have been linked to DES. Other studies investigating the occurrence of DES in children in various countries during the COVID-19 pandemic have also reported an increased incidence of DES, corroborating our findings. For instance, a study by Tonkerdmongkol et al. [10] identified increased self-reported symptoms of DES in Thai school children, while a cross-sectional study by Lin et al. [11] reported a higher prevalence of DES among Chinese high school students using the Ocular Surface Disease Index and Perceived Stress Scale questionnaires.

However, it is important to note that most studies have assessed the prevalence of DES using Ocular Surface Disease Index questionnaires or other surveys. This variation in methodology makes direct comparisons challenging, particularly since our study utilized diagnostic codes to determine the prevalence. Additionally, previous research has predominantly focused on children aged 10 to 18 years, complicating comparisons with our broader age range that includes younger children. We aimed to capture the broader impact of COVID-19 on DES across all pediatric age groups rather than limiting our scope to a specific subset. Through the analysis of various risk factors influencing the occurrence of DES, it was found that individuals aged 13 to 18 years were at a higher risk of DES than those aged 0 to 12 years. Although our study focused on a sample cohort rather than the entire population, we believe it is meaningful to include the entire age range of children to provide a comprehensive analysis. However, further detailed analysis is needed to understand the differences between each age group.

Several studies have reported DES associated with increased screen time during the COVID-19 season. A study in Egypt suggested that increased screen time in children during the COVID-19 pandemic can contribute to symptoms of DES [12]. Similarly, Alnahdi et al. [13] showed that increased screen time has been associated with a higher incidence of DES in the pediatric population of the Western Region of Saudi Arabia during the COVID-19 pandemic. In the present study, we did not specifically measure screen time to elucidate the relationship between screen time and the prevalence of DES. However, considering the higher prevalence of DES among children aged 13 to 18 years compared to those aged 0 to 12 years, it is plausible that adolescents are more likely to engage in online educational activities, such as non-face-to-face classes. This increased screen time may consequently contribute to a higher incidence of DES [14-16]. Extended use of screens can induce DES by reducing the blink rate and causing increased evaporation from the ocular surface. These symptoms—such as dryness, irritation, pain, eye fatigue, and impaired vision—can adversely affect academic activities. During the COVID-19 pandemic, schools in Korea were closed and education was shifted to online platforms to maintain continuity. This transition to online learning has significantly increased the time children spend on digital devices, which may negatively impact the ocular surface and contribute to the development of DES. However, conclusive evidence regarding increased screen time leading to DES is lacking and there has been no known the number of people with DES actually decreased when restrictions were released [17,18]. Additional research is needed on the incidence of DES in relation to actual increases and decreases in screen time.

Girls exhibited a higher risk of DES compared to boys in our study, consistent with previous findings on the association between sex and DES incidence. This could be attributed to endocrine abnormalities contributing to DES, such as menopause and menstrual cycle variations [19,20]. However, there are few studies reporting the differences in prevalence between sex in the pediatric population [21,22]. For instance, Alnahdi et al. [13] found no statistically significant difference between genders. Conversely, another study reported a higher prevalence in boys [21]. In our study, girls continued to exhibit a higher risk of DES compared to boys, echoing previous research on hormonal influences and DES prevalence.

Individuals with a higher economic status and residing in metropolitan areas showed a slightly higher risk of DES compared to those in rural areas. Elhusseiny et al. [12] found that educational screen time was significantly less in rural residents compared to urban dwellers. Another report also demonstrated that rural residence correlated with reduced rates of DES symptoms [23]. These previous studies suggest that lower outdoor activities, increased screen time, and environmental factors such as climate and particulate matter are relevant risk factors for DES [24,25]. Although actual screen time and outdoor activity duration according to the two regions and economic status were not investigated, our study results also suggest that factors such as educational screen time, outdoor activity duration, climate, and other environmental factors, as demonstrated in previous research, may contribute to differences in DES incidence rates.

The presence of hypertension, DM, and hyperlipidemia showed a higher HR for DES compared to their absence. These findings are consistent with previous studies [26-30]. However, previous research has not specifically focused on children. Therefore, additional research is needed to investigate the relationship between underlying diseases such as hypertension, DM, and hyperlipidemia and the prevalence of DES in the pediatric population.

This study has some limitations. First, there is no objective scoring scale for DES, and diagnosing DES based solely on subjective symptoms may not accurately represent the true DES diagnosis [31]. Additionally, using diagnosis codes for patient selection may not always reflect the actual clinical situation, as some patients included in the cohort may not have been accurately diagnosed during the specified period. Moreover, the use of DES codes when prescribing artificial tear drops may inflate the number of reported DES cases due to the financial incentives in the healthcare system. We could have examined the co-prescribed eye drops to exclude patients who received a diagnostic code for DES without actually having symptoms, simply to obtain artificial tears. However, this approach is also not entirely accurate, and it is difficult to definitively determine that these patients do not have DES. Therefore, we chose to analyze based solely on the diagnostic codes. To mitigate some of the potential errors, we excluded cases where DES was diagnosed in conjunction with keratoconjunctivitis codes, as these are more likely to represent instances where the DES code was used primarily for prescribing artificial tears. This exclusion reduces the risk of overestimating DES prevalence due to such practices. Nevertheless, this remains a common limitation in studies relying on big data and diagnostic codes. Finally, it is important to note that this study did not directly measure or analyze specific factors such as screen time, masking, and outdoor exposure. Our findings a re based on diagnostic codes, and while these factors are hypothesized to contribute to the increased prevalence of DES, further research is needed to investigate their impact directly.

Despite these limitations, our study has several strengths. While there is ample research on DES in adults, there is limited data available on the pediatric population. To the best of our knowledge, this study is the first large-scale cohort analysis of DES occurrence and prevalence, as well as potential risk factors, in individuals under 18 years during the COVID-19 season compared to the non-COVID-19 season. Furthermore, unlike previous studies, our analysis utilized diagnosis codes from the KDCA-NHIS, providing a unique perspective on DES-related eye diseases during the pandemic. Several contributing factors were identified, including frequent masking, increased use of smart devices, reduced outdoor exposure, endocrine factors, and social infection control measures. Sharing this information with parents, school staff, and educators to formulate preventive measures would be beneficial. It is worth considering initiatives like establishing guidelines or launching campaigns for online education, which promote the importance of incorporating breaks during online learning sessions and encouraging physical activity at home. Given the recent resurgence of COVID-19 infections, we believe that our findings are timely and crucial for understanding the impact of pandemics on children’s eye health, serving as a valuable resource for future research and public health planning, especially in preparing for and preventing potential future pandemics.

In conclusion, this study demonstrates a rise in the diagnosis of DES among children during the COVID-19 pandemic compared to previous years. Children aged 13 to 18 years, female sex, those living in metropolitan areas, and those with DM had a higher risk of DES. We suggest potential contributing factors such as frequent masking, increased use of smart devices, low outdoor exposure, mental stress, and depression under quarantine and social infection control measures. Further research is needed to directly analyze these factors associated with crisis akin to COVID-19.