Longitudinal changes in global cataract surgery rate inequality and associations with socioeconomic indices

Author: Yan W, Wang W, van Wijngaarden P, Mueller A, He M.

Geographical coverage: Not reported

Sector: Cataract surgery

Sub-sector: Risk, inequalities, socioeconomic development

Equity focus: Not reported

Study population: Patients with cataract

Review type: Effectiveness review

Quantitative synthesis method: Narrative synthesis, statistical analysis, General Estimation Equation modelling

Qualitative synthesis method: Not applicable

Background: Cataract remains the leading cause of global blindness and a major cause of vision impairment, particularly in low-income individuals. Despite the cost-effectiveness of cataract surgery, unoperated cataracts continue to burden low- and middle-income nations. Cataract surgery rate (CSR) serves as a proxy for both disease burden and access to eye care. Socioeconomic indicators like gross domestic product (GDP) and human development index (HDI) are closely linked to CSR disparities across and within countries. The tools like the Gini coefficient and Concentration Index are used to assess health-related inequalities. Understanding of longitudinal CSR changes can help identify gaps in service equity and inform policy adjustments.

Objectives: To evaluate the longitudinal changes of Cataract surgery rate (CSR) inequality globally and by income groups.

Main findings: The study analysed global CSR data from 2000 to 2015 across multiple countries and found significant associations between CSR and socioeconomic indicators. Specifically, CSR was strongly correlated with both Human Development Index (HDI) and GDP per capita, with R² values of 49.2% and 38.9%, respectively (P < 0.001 for both). Longitudinal analysis using Generalised Estimating Equations (GEE) showed that higher CSR was significantly associated with HDI (P < 0.001), GDP per capita (P < 0.001), and the proportion of the population aged 50 and above (P = 0.001). Over time, most countries experienced increased CSRs, with the largest gains observed in Argentina and Iran.

Despite overall increases in CSR, global inequality in CSR distribution remained relatively stable during the study period (2006 to 2014). The Gini coefficient showed minimal change (from 0.484 to 0.487), while inequality slightly increased within both high-income (0.369 to 0.413) and low- and middle-income (0.395 to 0.429) countries. The Concentration Index (CI), when measured against HDI, decreased globally (0.431 to 0.390) but increased within both income groups (high-income: 0.222 to 0.266, and low and middle-income: 0.265 to 0.286, respectively). Similar patterns were observed with the Thiel and Atkinson indices—inequality declined globally but rose within income groupings. A comparative analysis of CSRs relative to Australia highlighted disparities in performance, with countries like Sri Lanka, Argentina, and Suriname improving over time, while Kenya, Togo, and Sierra Leone experienced declines.

Overall, while socioeconomic development was associated with CSR growth, inequality in service delivery persisted, particularly when countries were grouped by income.

Methodology: The searches were conducted in PubMed, Medline, Embase, Web of Science, and grey literature to identify reports of age-related cataract among adults using any cataract surgery method. Furthermore, reference lists of the included studies and relevant review articles were scanned to identify additional relevant publications. The studies were included if they were published from January 2000 to December 2015, clearly described sampling methodology, had a response rate of greater than 50%, and were cross-sectional, cohort, or surveys in study design. No language limits were applied.

Relevant GDP data per capita were obtained from the World Bank and standardised using 2011 International Dollars. The Human Development Index (HDI) data were collected from the United Nations Development Program (UNDP) Human Development Reports. Data extraction was performed using a standardised data extraction form. Countries were assigned to high, and low- to middle income groups based on GNI/P data (a high-income country: GNI/P > $12,736 USD, while low and moderate-income countries: GNI/P ≤ $12,736 USD).

Statistical analysis was performed between October 2017 and January 2018. Scatterplots representing the associations between socioeconomic indicators and the GDP were generated. A mixed-effects linear model was used to examine the longitudinal changes in CSR and GDP over the study period. Several socioeconomic indices were used to assess the degree of inequality in the provision of cataract surgery. Regression curve estimation procedures were used to assess the association between CSR and GDP/P with R² statistic used to determine the statistical fit of the model, and the effect of HDI on CSR rates was investigated by linear regression analysis.

Applicability/external validity: The authors acknowledged that several factors may limit the applicability/external validity of the review’s findings. The use of non-standardised data sources and incomplete CSR data, particularly from high-income countries, may have introduced variability and reduced comparability across settings. National-level socioeconomic indicators like HDI and GDP may mask important regional disparities, limiting the applicability of results to subnational contexts. Additionally, the study did not account for other relevant factors such as gender, education, or healthcare financing. As a result, while the findings provide valuable insights into global trends, they are best interpreted as high-level associations rather than directly generalisable to individual countries or healthcare systems.

Geographic focus: The review did not apply any geographical limits, and the authors did not provide geographical distribution of the included studies. However, it should be noted that study data was collected from multiple sources. Details are provided in the methods section above.

Summary of quality assessment: Confidence in the study’s conclusions is low. The review did not specify the number of reviewers for article screening or data extraction, nor did it assess bias risk or list included and excluded studies.