Association between exposure to organophosphates and carbamates and refractive error (myopia and astigmatism): NHANES 1999-2004

The study investigated association between exposure to cholinesterase-inhibiting pesticides and vision (nearsightedness and astigmatism) in general population of age 12 and older. Data from National Health and Nutrition Examination Survey 1999-2004 (n = 5171) were analyzed using Stata survey suite. Exposure to cholinesterase inhibitors was measured as urine concentrations of organophosphate and carbamate metabolites. Odds of having nearsightedness or farsightedness (vs. neither) were modeled using multinomial regression. Potential confounders considered include: age-sex strata; race; urine creatinine; fasting time; poverty-income ratio; difficulty in walking (a measure of mobility). Preliminary analyses with or without adjustment revealed that nearsightedness was: positively associated with dimethylthiophosphate, dimethyldithiophosphate, and malathion metabolite; and negatively associated with chlorpyrifos and parathion metabolites. Various combination of these urine metabolites were examined in models adjusted for confounders. Among such models, a parsimonious model with malathion metabolite and chlorpyrifos metabolite showed a positive association with the former (odds ratio [OR] = 1.53 for 10 fold-increase in metabolite concentration, p = 0.001) and negative associated with the latter (OR = 0.57, p = 0.001). Other metabolite variables, when individually added to this model, did not achieve statistical significance nor was a confounder. Similar patterns of association were observed for astigmatism. The negative association with a chlorpyrifos metabolite is consistent with the experimental evidence for anti-nearsightedness effects of chlorpyrifos. While cross-sectional nature of the observation limits causal interpretation, the reverse causality (i.e., increased “near-work” due to vision impairment or other life-style factors leading to higher exposure to indoor use pesticides) seems unlikely given the negative association observed for chlorpyrifos.