Contributing Factors for Economic Inequality in Refractive Errors: An Analysis Employing Concentration Index and Oaxaca-Blinder Decomposition Methods in the Tehran Geriatric Eye Study.

Abstract

Purpose: This study examined economic inequalityin various refractive errors and decomposed its contributing factors using the Oaxaca-Blinder decomposition.

Methods: Data were obtained from the Tehran Geriatric Eye Study, a population-based cross-sectional study conducted in 2019 involving 3200 individuals aged 60 years and older, selected through stratified random cluster sampling. All participants underwent comprehensive ophthalmic and optometric examinations. Economic inequality was assessed using the Concentration Index and further analyzed via Oaxaca-Blinder decomposition.

Results: Among the 3263 participants analyzed, the mean age was 69.36 (±7.63) years, and 41.92% (n = 1,368) were male. The concentration index revealed that astigmatism (C =  -0.059, p < 0.001) andmyopia (C =  -0.094, p < 0.001) were more concentrated among poorer individuals, whereas hyperopia (C = 0.056, p < 0.001) was more prevalent among wealthier individuals. Decomposition analysis showed significant economic disparities inrefractive errors: astigmatism (12.57%) and myopia (15.27%) were more common inlower-income groups, while hyperopia (12.21%) was more frequent in higher-income groups. The explained portion accounted for 98.17%, 85.33%, and 91.24% of the disparities in astigmatism, myopia, and hyperopia, respectively. Key contributors to inequality included age (19.96%) and sex (18.46%) forastigmatism, economic status (24.53%) and axial length (20.45%) for myopia, andcataract surgery (27.95%) along with economic status (21.77%) for hyperopia.

Conclusion: These findings demonstrate significant economic disparities in refractive errors, predominantly driven by identifiable factors. Age, education, cataract surgery history, and axial length were the most influential variables contributing to inequality.