Qualitative color vision impairment in toluene-exposed workers

Abstract

Objective : The aim of this study was to evaluate whether toluene, like many other organic solvents and solvent mixtures, could impair color vision. Subjects and methods : We investigated color vision impairment in three groups of workers, two groups occupationally exposed to toluene and a nonexposed group. The first exposed group, group E₁, comprised 41 workers (median value of toluene in air 35.00 ppm, range 11.3–49.3 ppm) and the second exposed group, group E₂, comprised 32 subjects (median value of toluene in air 156.00 ppm, range 66.0–250.0 ppm). The nonexposed group, group NE, comprised 83 subjects. Color vision was evaluated by the Lanthony D-15 desaturated test according to Verriest's classification: type I, loss in the red-green range; type II, loss in the blue-yellow and red-green ranges, and type III, loss in the blue-yellow range. Subjects were classified as dyschromates if specific acquired loss was determined in at least one eye. In both exposed groups, exposure was evaluated by measurement of the concentration of toluene in the ambient air and in the blood. In group E₂, level of hippuric acid and orthocresol in urine after the work shift were also determined. The Mann-Whitney U-test, t-test, χ²-test, and Spearman's rank correlation and multiple regression analysis were used for statistical analysis. Results : Type III dyschromatopsia was detected in all groups examined: 26.6% of the workers in group NE, 31.7% of those in group E₁, and 50% of those in group E₂. As many as 15.6% of the workers in group E₂, 4.8% of those in group E₁, and only 1.2% of those in group NE had type II dyschromatopsia. A statistically significant difference in the prevalence of total dyschromatopsia (type III + type II) was established among the three examined groups together (χ²=14.13; df=2;P<0.01), between group E₂ and group E₁ (χ²=4.96;P<0.05), and between group E₂ and group NE (χ²=12.50;P< 0.005), whereas no significant difference was found between groups E₁ and NE. Type III dyschromatopsia was significantly correlated with age in group NE (P<0.01) and in group E₁ (P<0.005). In group E₂, both type II (P<0.05) and type III dyschromatopsia correlated with toluene in ambient air and with the duration of exposure to toluene (both P<0.005). In group E₂, total dyschromatopsia correlated significantly with toluene in ambient air and in blood (both P<0.05) as well as with hippuric acid in urine after the work shift (P<0.001). Conclusion: This study suggests that toluene can impair color vision.