Population Dynamic Projections of Near Vision Loss and Refractive Disorders in China and the G20 From 1990 to 2038

Introduction

Near vision loss (NVL) is mainly characterized by blurred or impaired vision at close distances [1]. Refractive disorders (RD), also known as refractive errors, refer to conditions in which – when the eyes are in a relaxed state of accommodation – parallel light rays from the external environment fail to accurately focus on the macula after passing through the ocular refractive system [2]. NVL and RD substantially affect quality of life, disrupt economic and educational opportunities, and impose a considerable economic burden [3,4]. According to a previous report, 36.0 million individuals were blind in 2015, 217 million experienced moderate to severe vision impairment, 188 million had mild vision impairment, and an additional 667 million individuals aged 50 years or older were affected by vision impairment due to uncorrected presbyopia [5]. Understanding long-term trends (1990–2021) and generating reliable projections (through 2038) are critical for public health planning; they enable policymakers to proactively allocate resources and prepare for future healthcare demands associated with an aging global population [6].

It is essential to clarify the distinction between NVL and RD within the Global Burden of Disease (GBD) framework used in the present study. Although NVL is classified as a form of uncorrected refractive error (specifically presbyopia) by the World Health Organization (WHO), the GBD Study categorizes “near vision loss” (GBD cause code: B.2.2) and “refractive disorders” (GBD cause code: B.2.3, including uncorrected myopia, hyperopia, and astigmatism) as non-overlapping entities for analysis and burden estimation. This classification enables more granular assessment of the distinct epidemiological profiles of presbyopia and non-presbyopic refractive conditions.

Multiple studies have examined the global burden of vision impairment [5,6], but important knowledge gaps remain. First, although cross-sectional burden estimates are available, comprehensive analyses that integrate long-term trend assessment (eg, using joinpoint regression to identify significant turning points) with forward-looking age-period-cohort projections are limited. Second, few studies have decomposed the drivers (eg, population growth, aging, and epidemiological changes) of burden trends for these conditions within major economies. Finally, evidence to inform targeted public health planning – such as the WHO’s SPECS 2030 initiative, which aims to increase refractive error coverage – requires granular, predictive data that incorporate demographic shifts [7]. The selection of 2038 as the projection horizon aligns with the long-term planning scope of such global initiatives and facilitates mid-term policy evaluation.

China and the G20 provide a strategically relevant comparison for several reasons. China is undergoing rapid demographic aging; the G20 collectively comprises both developed and emerging economies with diverse aging trajectories and eye care systems. Comparison of China with the G20 aggregate contextualizes China’s burden within a major economic bloc and enables the derivation of policy insights relevant to both national and international health planning.

This study aimed to (1) quantify the disease burden and long-term trends of NVL and RD among adults aged 40 years and older in China and the G20 from 1990 to 2021, (2) forecast the future burden through 2038, and (3) decompose the contributions of demographic and epidemiological factors to changes in burden.

Material and Methods

DATA EXTRACTION:

Data were extracted from the GBD 2021 Results Tool in January 2025. We analyzed “near vision loss” (B.2.2) and “refractive disorders” (B.2.3) using prevalence, years lived with disability (YLDs), and disability-adjusted life years (DALYs). To ensure methodological consistency and clarity, all reported metrics for disease burden trends, comparisons, and projections refer to age-standardized rates (age-standardized prevalence rate [ASPR] and age-standardized disability-adjusted life year rate [ASDR] per 100 000 population), unless otherwise specified in the decomposition analysis, which uses absolute counts. Accordingly, terms such as “prevalence,” “YLDs,” and “DALYs” in the Results section denote their respective age-standardized rates. G20 locations included all member countries (eg, Argentina, Australia, Brazil, Canada, China, etc). Age standardization followed the GBD standard population method. Analyses focused on individuals aged 40 years and older, stratified in 5-year intervals, to capture the onset of presbyopia and age-related refractive changes.

STATISTICAL ANALYSIS:

This descriptive analysis examined burdens of NVL and RD globally and across population subgroups from 1990 to 2021. Prevalence rates and DALY rates were age-standardized. The following formula was used:

Let i denote the i-th age group, ai represent the age-specific rate, and wi be the population size (or weight) of the corresponding age group in the selected reference standard population [8]. In the present study, age-standardized rates (ASRs) are expressed as cases per 100 000 population. Uncertainty intervals (UIs) were defined by the 2.5th and 97.5th percentiles derived from 1000 draws for each metric. This 1000-draw approach was consistently applied to adjust for and propagate statistical uncertainty in both joinpoint regression and Bayesian age-period-cohort (BAPC) modeling [9].

The estimated annual percentage change (EAPC) was used to describe overall temporal trends in disease burden, as follows:

Here, y denotes ln(ASR), x represents calendar year, β is the slope obtained from the regression analysis, and ɛ is the error term [10]. The 95% confidence interval (CI) was used to assess statistical significance. If both the EAPC estimate and the lower bound of the 95% CI are greater than 0, the age-standardized rate is considered to be increasing. If both the EAPC estimate and the upper bound of the 95% CI are less than 0, the rate is considered to be decreasing. If the 95% CI includes 0, the trend is considered stable [11].

The annual percentage change (APC) represents the rate of change within each segment when distinct trends or turning points occur across different time periods. Joinpoint regression divides the data into segments at these turning points, and the APC is calculated separately for each segment [12]. Joinpoint regression analysis was performed using the Joinpoint Regression Program (version 4.9.0.0; National Cancer Institute) based on historical ASPR and ASDR data from 1990 to 2021. A maximum of 3 joinpoints was allowed, and the optimal number of joinpoints was determined using permutation tests.

The predictive analysis mainly utilized the BAPC model to forecast disease burden from 2022 to 2038, using ASPR and ASDR data from 1990 to 2021 as inputs. The BAPC model was selected over simpler time-series models because it explicitly addresses the separate effects of age, period, and birth cohort, which is essential for long-term projections in populations undergoing substantial demographic transitions. The BAPC model is particularly suitable for predicting future trends in settings with broad population changes [13]. The model was implemented using the R package “BAPC” (version 3.1.2) in R (version 4.2.0). It applies a Bayesian framework with penalized splines to smooth age, period, and cohort effects, thereby generating robust long-term projections [14]. Specifically, penalized complexity priors were used for second-order random walk effects, and vague Gaussian priors () were specified for fixed effects. Model convergence was assessed using integrated nested Laplace approximation based on the effective number of parameters (pD). Model fit was evaluated using the deviance information criterion and the Watanabe-Akaike information criterion; robustness was confirmed via back-casting (training period: 1990–2010; validation period: 2011–2021), and more than 90% of observed values fell within the 95% credible intervals. Increasing uncertainty toward 2038 reflects stochastic variation in period extrapolation, demographic forecast uncertainty, and the propagation of historical errors; all population inputs were aligned with GBD 2021 reference scenarios.

Decomposition analysis was performed on the absolute number of cases to quantify the contributions of various factors to changes in disease burden over time. The method was based on the work of Das Gupta [15]. An additive decomposition approach was implemented to partition the change in total cases into contributions from 3 components: population growth (P), age structure change (A), and changes in age-specific rates (E; epidemiological factors). For interpretation, these components were categorized as population, aging, and epidemiological factors.

ETHICS STATEMENT:

This study used publicly available data from the GBD 2021 database. The data were de-identified and aggregated; therefore, they did not involve human participants. The requirement for ethical approval was waived.

Results

Descriptive Analysis of Disease Burden

DISEASE BURDENS IN THE G20 AND CHINA: Concerning NVL, the disease burden was higher in China than in the G20. Between 1990 and 2021, NVL ASPR in China increased by approximately 60%, rising from 25 176.52 to 40 341.49 per 100 000. Similarly, the G20 showed an increase from 23 675.04 to 35 934.92 per 100 000. In contrast, RD burden was lower in China than in the G20; a decreasing trend was detected in China. RD ASPR in China declined from 3452.55 in 1990 to 3044.90 in 2021 (Tables 1, 2).

SEX-STRATIFIED BURDEN: In both China and the G20, the burdens of NVL and RD were higher among women than among men. In 2021, NVL ASPR for women in China was 42 918.29, compared with 37 711.62 for men. A similar pattern was observed in the G20 (38 311.63 for women vs 33 394.29 for men). Regarding RD, the ASPR for women in the G20 (3846.06) also exceeded the rate for men (3535.74) (Tables 1, 2; Figures 1, 2).

AGE-STRATIFIED BURDEN: Concerning NVL, the highest burden occurred in the 60 to 64 age group in China; in the G20, it peaked in the 55 to 59 age group. RD burden was highest in the 80 to 84 age group in both China and the G20 (Tables 3, 4; Figures 3, 4).

EAPCS IN CHINA AND THE G20: From 1990 to 2021, age-standardized rates of NVL showed a consistent increasing trend in both China and the G20, with EAPCs ranging from 1.92 to 2.00 (Table 1; Figure 1). In contrast, RD burden declined over the same period, with EAPCs ranging from −0.50 to −0.36 (Table 2; Figure 2).

APCS IN CHINA AND THE G20: Joinpoint analysis indicated that NVL burden in both China and the G20 shifted from a declining to an increasing trend around 1995. The most rapid growth occurred during 2019 to 2021 in China (APC: ASPR 5.25, ASDR 5.31) and during 2011 to 2014 in the G20 (APC: ASPR 5.21, ASDR 5.20) (Table 5; Figure 5).

Concerning RD burden, China experienced the steepest increase during 1995 to 2000, peaking in 2000 (APC: ASPR 2.03, ASDR 3.36). In the G20, the trend shifted from decline to increase around 2015, with the most rapid growth observed during 2015 to 2019 (APC: ASPR 1.37, ASDR 0.65) (Table 6; Figure 5).

The apparent discrepancy between the overall declining trend (negative EAPC) and segments of increase (positive APC) warrants clarification. The EAPC reflects the average trend over the entire study period (1990–2021); joinpoint regression identifies specific inflection points where trend slopes change. Regarding RD burden in the G20, although the long-term trajectory is downward due to substantial declines in earlier decades, the positive APC observed after 2015 reflects a recent, localized reversal or plateau that does not offset the overall historical decline when calculating the EAPC.

PREDICTIVE ANALYSIS (2022 TO 2038):

According to the BAPC model, NVL burden is projected to continue increasing through 2038 in both China and the G20. The ASPR is expected to rise from 40 341 to approximately 51 500 (95% UI: 25 000–84 000) in China and from 35 935 to approximately 46 000 (95% UI: 23 000–71 000) in the G20 (Figure 6). In contrast, RD burden is projected to decline, with the ASPR decreasing from 3045 to approximately 2500 (95% UI: 1900–3200) in China and from 3695 to approximately 3100 (95% UI: 2400–3900) in the G20 (Figure 7).

DECOMPOSITION ANALYSIS:

Decomposition analysis was performed on the absolute counts of prevalence, YLDs, and DALYs for NVL and RD among individuals aged 40 years and older, comparing 1990 and 2021. The additive decomposition method proposed by Das Gupta was utilized to quantify the proportional contributions of 3 driving factors: population growth, population aging, and epidemiological changes (ie, changes in age-specific rates). Concerning both NVL and RD in China and the G20, population growth was the primary driver of increases in absolute case numbers. The proportional contributions of each factor to prevalence, YLDs, and DALYs are presented in Table 7. Regarding NVL, epidemiological factors also positively contributed to the increase in disease burden in both China and the G20 (China: 36.4%; G20: 39.2%); aging showed a smaller positive contribution with the lowest proportional impact. With respect to RD, epidemiological factors negatively contributed to the overall burden (China: −31.7%; G20: −28.0%), partially offsetting the increases driven by population growth and aging. Notably, the contributions of population growth to DALYs for RD exceeded 100% in China (105.0%) and the G20 (117.5%). Decomposition results for NVL were highly consistent across the 3 metrics (prevalence, YLDs, and DALYs), with identical proportional contributions of population growth (59.1%), epidemiological changes (36.4%), and aging (4.5%) in China, and 58.8%, 39.2%, and 2.0% in the G20, respectively (Table 7; Figure 8).

Discussion

This study used data from the GBD 2021 database to evaluate disease burdens of NVL and RD. NVL burden was higher in China than in the G20, whereas RD burden was lower in China. Both conditions have a substantial impact on affected populations [5,16].

In both China and the G20, NVL and RD burdens were higher among women than among men. Notably, this sex disparity persisted after age standardization, indicating that differences in population age structure do not fully explain the observed gap. Age-stratified analyses (Tables 3, 4) showed that higher rates in women were evident across most age groups within the population aged 40 years and older, rather than being driven by a single demographic cohort. Although the underlying mechanisms remain unclear, several hypotheses have been proposed. Longer life expectancy in women has historically been considered a contributing factor for increased exposure to age-related eye conditions [6,17]; however, the persistence of disparities after age standardization suggests additional mechanisms. Potential contributors include sex-specific hormonal changes (eg, postmenopausal shifts) and differences in social or behavioral risk profiles [18]. Given the ecological nature of the present study, these factors cannot be definitively established as causal and should be interpreted as plausible explanations. Further individual-level studies are needed to clarify the relative contributions of biological susceptibility and sex-related exposures.

Concerning NVL, the burden was highest among middle-aged individuals. Specifically, the highest burdens were observed in the 60 to 64 age group in China and the 55 to 59 age group in the G20. In contrast, RD burden was greatest among older adults, peaking in the 80 to 84 age group in both China and the G20. Similar age-specific patterns have been reported in the literature [6]. Effective management of aging populations is essential to control age-related eye diseases [5,19].

Overall, NVL burden in China and the G20 has slightly increased over the past few decades, whereas RD burden has modestly declined. Regarding temporal inflection points, NVL burden in both China and the G20 reached its lowest level around 1995 and has since increased. RD burden in China peaked in 2000 and subsequently declined, whereas the G20 exhibited a generally continuous downward trend in RD burden. These patterns may be consistent with lifestyle changes identified in previous studies, including increased near work and digital device use [20,21].

Projected trends for NVL and RD in China and the G20 are broadly similar. Forecasts through 2038 indicate continued divergence, where NVL burden is expected to increase and RD burden will decrease. However, these BAPC projections are scenario-based estimates. Wide uncertainty intervals suggest that future trajectories may be substantially influenced by advances in assistive technologies, changes in healthcare policy, or demographic shifts. Overall, greater attention should be directed toward the rising NVL burden, and appropriate policies should be developed to mitigate its impact.

In both China and the G20, population growth was the main factor contributing to the increased burdens of NVL and RD from 1990 to 2021; proportional contributions to NVL DALYs reached 59.1% in China and 58.8% in the G20, whereas contributions to RD DALYs peaked at 105.0% in China and 117.5% in the G20 (Table 7). These findings highlight the importance of addressing challenges associated with population growth. Epidemiological factors also substantially contributed to the increased contributed burden (China: 36.4%; G20: 39.2%), suggesting increased exposure to risk factors or changes in social behaviors [22]. Aging had the smallest impact on NVL burden, with proportional contributions of 4.5% in China and 2.0% in the G20. Epidemiological changes negatively contributed to RD DALYs (China: −31.7%; G20: −28.0%), representing the main driver of the decline in age-standardized RD burden and partially offsetting increases associated with population growth and aging. Considering the effects of population growth and aging, investments in reducing visual impairment over recent decades have yielded substantial benefits [5,23,24]. Moreover, evidence indicates that most visual impairment conditions in underdeveloped regions are preventable and treatable [25]. These findings underscore the need for continued and increased investment in eye health.

Given that the highest NVL burden occurs among middle-aged individuals (55–64 years), who represent a key working population, policy interventions should prioritize occupational eye health screening and subsidized access to reading glasses for this group. To address the increasing NVL burden, resource allocation should emphasize accessible, low-cost primary eye care models, consistent with the WHO Global Eye Health Strategy (2022–2030), which promotes integrated, people-centered eye care [26]. Countries with rapidly aging populations, such as Japan and Italy (both G20 members), have implemented community-based screening programs to improve early detection of age-related eye diseases, providing valuable models for China and other G20 countries [27,28]. In an international context, cohort studies in East Asia have shown that factors such as intensive educational demands and increased near work contribute to the high prevalence of non-presbyopic RD [29]. The higher burden observed among women highlights the need for sex-specific interventions that address potential eye care access barriers related to socioeconomic or biological factors.

Compared with recent studies concerning NVL and RD burden, which have mainly provided cross-sectional estimates or short-term trend analyses, the present study offers an integrated approach by combining long-term trend assessment, age-period-cohort projections through 2038, and decomposition of contributing factors within a China-G20 comparative framework. This comprehensive approach captures historical dynamics and provides scenario-based projections, offering more robust evidence for policy planning.

This study has some limitations. First, the most recent available data extend only through 2021, which may affect the accuracy of predictive analyses. Second, internal heterogeneity within regions was not examined, which may obscure disparities in development across countries. Further in-depth research is warranted. Finally, in economically underdeveloped regions, limited diagnostic capacity and healthcare infrastructure may result in incomplete data collection, potentially leading to underestimation of disease burden.

Conclusions

Using GBD 2021 data, this study provides an integrated assessment of long-term trends and future projections of NVL and RD among adults aged 40 years and older in China and the G20, incorporating joinpoint analysis, BAPC modeling, and decomposition of demographic drivers. The findings indicate that, although age-standardized rates of RD have modestly declined, NVL burden has increased since the mid-1990s and is projected to continue rising through 2038; population growth was the primary driver of increases in absolute case numbers. Burdens remain higher among women – particularly in middle-aged groups for NVL and older groups for RD – highlighting persistent sex- and age-related disparities. However, the projections are scenario-based and subject to wide uncertainty intervals; analyses relying on aggregated GBD estimates may obscure within-country heterogeneity and data limitations in under-resourced settings. Within these constraints, the findings underscore the need for sustained, demographically responsive eye health planning in China and across the G20.

Data Availability

Datasets generated and/or analyzed during this study are available from the Global Burden of Disease (GBD) 2021 repository, which is publicly accessible online at: https://vizhub.healthdata.org/gbd-results/.