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L. R. Pasquale, J. Kang, N. Talwar, B. Nan, D. M. Reed, S. E. Hankinson, W. Willett, J. L. Wiggs, J. E. Richards, J. D. Stein; An Inverse Association Between Latitude and Risk of Exfoliation Syndrome in the US Is Confirmed in Two Separate Study Populations. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6435.
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Prior cross-sectional studies suggest there is a positive relation between geographic latitude and prevalence of exfoliation syndrome (ES). However there have been no studies in a geographically defined region with adequate control for important confounders such as age and race. We aimed to create a multivariate model of the relation between latitude and risk of ES in one US population based sample and confirm the association in a second US sample.
We used data from two US populations: a cohort of male and female health professionals (the Nurses Health Study and the Health Professionals Follow-up Study) followed from 1980 to 2004 and the i3 InVision Data Mart database that contains detailed fully de-identified records of US beneficiaries in a managed care network followed from 2001 to 2007. In both study samples, we defined populations under ophthalmic surveillance and identified incident ES cases. In each study sample, the continental US was divided into tiers and we compared the risk of ES in specified geographic regions to reference regions using Cox multivariate models.
For the health professional cohort, we identified 214 ES cases during 1.2 million person-years of follow-up. After adjusting for age and Scandinavian ancestry, living in southern tier states below 37° latitude from birth to age 15 was associated with a reduced risk of ES (RR=0.22 [95% CI: 0.10-0.46] compared to living in states north of 41° - 42° latitude. In the managed care database 628,342 individuals were under ophthalmic care and 3,465 had at least one ICD9 code for ES. Multivariate models confirmed that currently living in states below 37° south was associated with a reduced risk of ES (HR=0.73, [95% CI: 0.65-0.82]) and living in states north of 41° - 42° latitude was associated with an increased risk of ES (HR=1.87, [95% CI: 1.69-2.08]) compared to living in middle tier states such as MD, IA or KS. In the managed care dataset, results were similar when only non-Caucasians were considered (n=244 ES cases; HR=2.88 [95% CI: 1.80-4.61] for living in northern vs. middle tier states).
In this study of a geographic region spanning 15° of latitude, living in northern regions was associated with increased risk of ES. These results have implications for understanding the pathogenesis of ES.
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