Occupational styrene exposure and acquired dyschromatopsia: A systematic review and meta‐analysis

Abstract

Background Styrene is a chemical used in the manufacture of plastic-based products worldwide. We systematically reviewed eligible studies of occupational styrene-induced dyschromatopsia, qualitatively synthesizing their findings and estimating the exposure effect through meta-analysis. Methods PubMed, EMBASE, and Web of Science databases were queried for eligible studies. Using a random effects model, we compared measures of dyschromatopsia between exposed and non-exposed workers to calculate the standardized mean difference (Hedges’ g). We also assessed between-study heterogeneity and publication bias. Results Styrene-exposed subjects demonstrated poorer color vision than did the non-exposed (Hedges’ g = 0.56; 95% CI: 0.37, 0.76; p < 0.0001). A non-significant Cochran’s Q test result (Q = 23.2; p = 0.171) and an I2 of 32.2% (0.0%, 69.9%) indicated low-to-moderate between-study heterogeneity. Funnel plot and trim-and-fill analyses suggested publication bias. Conclusions This review confirms the hypothesis of occupational styrene-induced dyschromatopsia, suggesting a modest effect size with mild heterogeneity between studies.

Evaluation of potential health effects associated with occupational and environmental exposure to styrene – an update

“…However, the analysis was not designed to yield a threshold concentration or NOAEC, and the authors reported no consensus regarding a threshold exposure concentration that causes acquired dyschromatopsia. Of the 15 studies evaluated qualitatively by Choi et al (2017), only that reported by Seeber, Bruckner, and Triebig (2009b) did not support the hypothesis. Of possible relevance in this regard is the fact that Seeber, Bruckner, and Triebig (2009b) excluded participants on the basis of demonstrated red-green deficiency (as well as "congenital color-blindness") in order to avoid potential impacts of this predominantly inherited deficiency on the color discrimination test that could have "inflated" styrene impacts in other studies.…”

“…A "mild" publication bias against smaller studies with negative results was suggested, but implications were not discussed. Choi et al (2017) concluded that available evidence supports the hypothesis that chronic occupational exposure to styrene at "levels below most regulatory agency-prescribed exposure limits" can induce subclinical deficits in color vision. However, the analysis was not designed to yield a threshold concentration or a No-Observed-Adverse-Effect-Concentration (NOAEC), and the authors reported no consensus regarding a threshold exposure concentration that causes acquired dyschromatopsia.…”

“…Epidemiological studies. Studies reporting effects on color vision (usually of the tritan type affecting blue-yellow color discrimination) and/or CS in workers exposed to high styrene concentrations have been re-reviewed in the past 20 years (Benignus et al 2005;Betancur-Sánchez, Vásquez-Trespalacios, and Sardi-Correa 2017;Choi et al 2017;Gobba 2000;Gobba andCavalleri 2000, 2003;Good and Nichols 2006;Kishi, Tozaki, and Gong 2000;Lomax, Ridgway, and Meldrum 2004;Paramei, Meyer-Baron, and Seeber 2004;Sheedy 1997). Some of the relevant epidemiological studies are discussed below and summarized in Table S1.…”

“…Summary of dyschromatopsia. The preponderance of evidence indicates an effect on color vision at high styrene concentrations, but the magnitude of these effects is small, dose-response and reversibility are unclear, and the implications for IADL are uncertain (Benignus et al 2005;Choi et al 2017;Good and Nichols 2006). The systematic review and meta-analysis recently performed by Choi et al (2017) concluded that chronic occupational exposure to styrene at "levels below most regulatory agency-prescribed exposure limits" can induce subclinical deficits in color vision.…”

Toxic and Nutritional Optic Neuropathies—An Updated Mini-Review

“…Occupational exposure to solvents or some other chemicals, such as organophosphate pesticides, may lead to color vision loss that is usually subclinical, and thereby vision testing may be favorable in the evaluation of early neurotoxicity of chemicals in exposed workers [ 129 ]. The impairment of color discrimination was notified in cases of exposure to environmental levels lower than the occupational limits proposed [ 130 ].…”