Nationwide trends in the prevalence of cataract, glaucoma, and macular degeneration among Korean adults amid the COVID-19 pandemic, 2015-2021: A representative study in South Korea

This study utilized data from KNHANES, conducted by the Korea Disease Control and Prevention Agency. KNHANES has been a critical source of data since 1998, aimed at understanding the health and nutritional status of the South Korean population. Conducted under the National Health Promotion Act, it provides a nationally representative cross-sectional survey of roughly 10,000 individuals annually[6]; our study utilized data from this dataset, spanning from 2015 to 2021. The final dataset of our study included 51,682 individuals aged between 20 to over 60 years across the study timeframe. The distribution of these participants throughout the study period was as follows: 14,781 from 2015 to 2016, 15,358 from 2017 to 2018, 7,716 in 2019, 7,096 in 2020, and 6,731 in 2021 (Table 1). The research protocol, approved by the Institutional Review Board of Kyung Hee University and the Korea Disease Control and Prevention Agency, ensured informed written consent was obtained from all participants involved in the survey. Throughout the study, the Declaration of Helsinki was strictly abided by.

The primary aim of our study was to ascertain the occurrence of cataracts, glaucoma, and macular degeneration over seven years, from 2015 to 2021. Participants were asked a targeted question regarding their history of diagnosed cataracts, glaucoma, and macular degeneration, explicitly inquiring, “Have you ever received a clinical diagnosis of cataracts?” “Have you ever received a clinical diagnosis of glaucoma?” and “Have you ever received a clinical diagnosis of macular degeneration?”.[7,8]

According to previous studies, covariates known to influence ocular fundus diseases were selected. Covariates included age (20–39, 40–59, and ≥60 years), sex, region of residence (urban and rural), BMI group[9], education background (high school or lower), smoking status (non-smoker, ex-smoker, and smoker)[10], alcohol consumption (1–5 days/month, 6–30 days/month, and non-drinker), and household income (low and high). Utilizing the self-reported height and body weight, BMI was calculated; the calculated BMI was separated into two categories: normal (<23.0 kg/m²) and overweight to obese (≥23.0 kg/m²).

This study’s outcomes were presented after examining survey-reported data, which were expressed as proportions or percentages. Weighted multivariate regression models were employed to analyze and compare the prevalence of cataracts, glaucoma, and macular degeneration before and during the pandemic. The estimates were reported using weighted odds ratios (wORs) and 95% confidence intervals (CIs).[11] The prevalence of cataract, glaucoma, and macular degeneration was calculated by analyzing data from the KNHANES, covering the period from 2015 to 2021, and stratifying the data into different year groups. The weighted complex sampling analysis was conducted to ensure accurate estimation. The study employed a binomial logistic model to compute the wORs with 95% CIs and linear logistic regression models for calculating β-coefficients with 95% CIs; these statistical methods facilitated the analysis of the prevalence of cataract, glaucoma, and macular degeneration. Furthermore, the β difference (β_diff) was calculated to evaluate the change in prevalence of cataract, glaucoma, and macular degeneration before and during the pandemic. ORs were calculated for each year group to assess the prevalence of cataracts, glaucoma, and macular degeneration. The SAS software (version 9.4; SAS Institute, Cary, NC, USA) was used for statistical analyses, employing a two-sided test, with a p-value ≤ 0.05 considered statistically significant.[12]

The study revealed a general decline in cataract prevalence (3.27% [95% CI, 2.94-3.60] in 2015-2016; 3.22 [2.73-3.72] in 2021), contrasted by an increase in glaucoma (0.70% [95% CI,0.57-0.84] in 2015-2016; 1.15 [0.85-1.45] in 2021) and macular degeneration (0.21% [95% CI, 0.14-0.29] in 2015-2016; 0.45 [0.30-0.61] in 2021). Specific demographic groups, particularly those with higher economic status and urban residents, showed an increased prevalence of cataracts. The ROR analysis indicated varied impacts of the pandemic on different socioeconomic and behavioral factors. This correlation underscores a potential linkage between high economic status within South Korean society and an increased vulnerability to key ocular diseases. These findings suggest that lifestyle or environmental factors, inherently associated with socioeconomic standing, may contribute to heightened risk.

Leveraging a comprehensive national population dataset, our study tracked changes in the prevalence and incidence of key ocular diseases, which are cataracts, glaucoma, and macular degeneration. Our analysis identified a constellation of cultural, environmental, and social factors that correlate with key ocular diseases, necessitating ongoing evaluation.[13] During the study period, the prevalence of cataracts exhibited a statistically insignificant, but slight decrease in the pre-pandemic period, followed by a slight increase in the pandemic period. Glaucoma showed a slight increase in both pre- and during-pandemic periods. Conversely, macular degeneration increased slightly pre-pandemic but slightly decreased during the pandemic period, potentially influenced by lockdown and social distancing measures. The advent of COVID-19 in South Korea prompted the government to implement stringent lockdown policies,[14] mirroring global trends, necessitating the temporary closure of most establishments, except essential institutions such as schools and hospitals. This reduction in social engagement may have possibly led to the heightened prevalence of key ocular disease, discernible both overall and specifically during the pandemic period.

Out of various factors that might have contributed to such a trend of key ocular diseases, one potential driver of this trend could be increased screen time followed by decreased physical activity during the COVID-19 pandemic period. Similar to its established association with other eye-related diseases,[15-20] reduced physical activity and augmented screen time might have directly influenced the incidence of cataracts, glaucoma, and macular degeneration.

Moreover, our risk factor analysis, encompassing diverse socioeconomic and behavioral factors, indicated that individuals with high economic status are more likely to experience key ocular diseases. Notably, cataracts, glaucoma, and macular degeneration often remain undiagnosed in early stages due to their asymptomatic nature until significant vision impairment occurs.[21,22] Consequently, the general population may struggle to receive timely diagnoses and treatment. However, individuals with high economic status often have access to superior medical resources, including regular, high-quality health check-ups,[23,24] potentially leading to increased detection of these conditions during the clinically silent stages, which may explain the higher prevalence rate compared to those with a low economic status.

Our study has elucidated that there has been either a general increase or a specific increase in the prevalence of key ocular diseases among the South Korean population during the COVID-19 pandemic. Additionally, our risk factor analysis highlights those individuals of high economic status as well as those aged 40-59 years, have demonstrated a heightened likelihood of experiencing all key ocular diseases. Moreover, individuals who have quit smoking or are current smokers are shown to have an elevated occurrence for more than half of these key diseases.

Given these findings, it becomes imperative for the government to prioritize these identified groups in its healthcare strategies.[11] The South Korean government can possibly set a required regular health check-up through people’s jobs under these sociodemographic features, using the insurance system of South Korea.[25] However, it is also crucial for the government and companies that can provide extra healthcare support to acknowledge that this trend may be partly attributable to more frequent health check-ups in these groups, leading to a higher diagnosis rate of key ocular diseases.[26] Consequently, the government should be cognizant of the potential risks among other demographic groups.[27] To address this, similar to the policy recommendation suggested above, the government could implement a national screening program for key ocular diseases at local public health centers,[28] with targeted outreach efforts toward groups that do not engage in health services. The outreach should be careful not to overlook groups that appear to have a low prevalence of these diseases, since the prevalence may be a matter of inadequate access to services, which can result in under-detection.

When considering the outcomes of this study, it is crucial to recognize several inherent limitations. First, the data utilized in the study was derived from the KNHANES, which restricts the extrapolation of our findings exclusively to South Korean populations. Furthermore, within this dataset, certain data points, such as the WOR of cataracts in the 20-29 age group, were classified as non-applicable; this resulted in informational gaps, consequently impacting the uniformity of analysis across the entire study duration. Second, the absence of data pertaining to the child and adolescents constrains the generalizability of our results to this particular demographic segment. This limitation is significant as it potentially omits crucial insights into the prevalence and evolving patterns of the key ocular diseases under study within this younger population. Third, the reliance of our study on self-reported data introduces potential biases. Specifically, the risks of recall bias, where participants may not accurately remember past events or conditions, and social desirability bias, where responses might be influenced by the desire to present oneself in a favorable light, cannot be discounted.6 These factors may skew the authenticity of the reported data, thus affecting the accuracy and reliability of our study findings.

Despite the acknowledged limitations, the significance of this study remains robust. It represents a comprehensive, nationwide, population-based exploration, delineating the longitudinal trends of critical ocular diseases—cataracts, glaucoma, and macular degeneration. Furthermore, it delves into an in-depth investigation of risk factors, with a particular focus on sociodemographic characteristics, through the analysis of seven consecutive years of data from the KNHANES; this method enables our study to provide a detailed portrayal of the prevalence of these key ocular diseases spanning both pre- and during-COVID-19 pandemic periods. Additionally, it provides a thorough analysis of the OR corresponding to various risk factors. Thus, our research contributes a significant perspective on the evolving landscape of ocular health issues in the context of ongoing global health challenges, serving as a valuable resource for future studies and public health policy formulation.