en Epidemiology Epidemiology Original Research Original Research <strong>Background: </strong>Since there was no evidence about economic inequity in utilization of cataract surgery in developing countries, such as Iran, this study was designed to measure horizontal inequity in the utilization of cataract surgery and its changes in an Iranian middle-aged population in 2009 and 2014.<br> &nbsp;&nbsp; <strong>Methods:</strong> Using data from the first and second phases of Shahroud Eye Cohort Study (2009-2014), the economic inequity in the utilization of cataract surgery in an Iranian middle-aged population aged 40-64 years in 2009 and 2014 was evaluated. The horizontal inequity index (HI) was determined using the indirect standardization method based on a nonlinear (probit) model and the concentration index (C) was decomposed into the contribution of each factor. The analyses were performed using STATA software version 12/SE, and significance level was set at less than 0.05.<br> &nbsp;&nbsp; <strong>Results:</strong> The HI in the utilization of cataract surgery increased from 0.080 (95% CI: 0.011-0.098) in 2009 to 0.166 (95% CI: 0.0821-0.228) in 2014. Decomposition of changes in the concentration index showed that among need and non-need variables, older age and economic status (being among the wealthiest 20%) were the greatest contributors, with shares of 67.5% and 57.5%%, respectively, which led to pro-rich inequity during the study periods.<br> &nbsp;&nbsp; <strong>Conclusion:</strong> The present study demonstrated that utilization of cataract surgery did not have an equal distribution among economic quintiles, despite considering equal needs based on cataract severity. Results demonstrated that older age and economic status were the greatest contributors to HI increase in 2009 and 2014.<br> &nbsp; Horizontal inequity index, Concentration index, Cataract surgery utilization, Middle-aged population, Iran 693 701 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-4818-1&slc_lang=en&sid=1 Maedeh Raznahan maraznahan@gmail.com 200319475328460062360 200319475328460062360 No Noor Ophthalmology Research Center, Noor Eye Hospital & Deputy of Research, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Hassan Emamian emamian@shmu.ac.ir 200319475328460062361 200319475328460062361 No Center for Health Related Social and Behavioral Sciences Research, Shahroud University of Medical Sciences, Shahroud, Iran Fateme Alipour shiva_mehrdad@yahoo.com 200319475328460062362 200319475328460062362 No Eye Research Center, Farabi Eye Hospital, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Hassan Hashemi hashemi@noorvision.com 200319475328460062363 200319475328460062363 No Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran Hojjat Zeraati zeraatih@tums.ac.ir 200319475328460062364 200319475328460062364 No Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Akbar Fotouhi afotouhi@tums.ac.ir 200319475328460062365 200319475328460062365 Yes Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran