Chronal focus of acquired chromatic discrimination loss and solvent exposure among printshop workers

doi:10.1016/0300-483X(88)90017-0

Toxicology

Volume 49, Issues 2–3, May 1988, Pages 341-348

https://doi.org/10.1016/0300-483X(88)90017-0 Get rights and content

Abstract

Acquired dyschromatopsia has been associated with exposure to organic solvents. However, the chromal focus of the loss may be indicative of its gravity. According to Kollner's rule, blue-yellow loss reflects changes in external retinal layers, while red-green loss appears to be indicative of internal retinal or optic nerve damage. The objective of the present study was to examine chromatic discrimination capacity of 30 printshop workers exposed to organic solvent mixtures, and of a non-exposed reference group. Colour vision was assessed with a colour arrangement test designed to detect acquired dyschromatopsia, the Lanthony D-15 desaturated panel. Quantitative analysis, using Bowman's colour confusion index, revealed significantly higher scores indicative of colour vision loss among the exposed workers as compared to the non-exposed. Analysis of covariance, with age as co-variate, showed colour confusion index to be significantly associated with job category. Similarly, qualitative analysis showed that the exposed workers presented a significantly higher prevalence of acquired dyschromatopsia as compared to the non-exposed group. However, analysis of the type of chromatic discrimination loss showed that among the non-exposed persons, dyschromatopsia was localized only in the blue-yellow range, while for 35% of the dyschromatopic-exposed persons, red-green loss as well as blue-yellow loss were present. Three-dimensional gc²-analysis showed that the complex pattern of dyschromatopsia was not related to age, but on job category. These findings suggest that the type of dyschromatopsia, reflecting the gravity of neural alterations, may be a function of exposure level and/or the ophthalmotoxic properties of the particular solvents used.

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Among the 24 exposed workers, five made at least one blue–yellow error with the first or second eye, whereas none of the control subjects made an error (Muttray et al., 1997). An increase in blue–yellow deficiency was reported by most color vision-loss studies of solvent-exposed workers (Gobba et al., 1991; Mergler et al., 1988b). Similar to Mergler et al., our results support the KoÈllner's rule that changes in the blue–yellow range are frequent in solvent-exposed workers, where the early effects reflect changes in the external retinal layers (Mergler et al., 1987; KoÈllner, 1912).
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Despite an accumulating body of evidence demonstrating that the visual system is an important target for organic solvent toxicity in adults, little attention has been paid to the visual functioning of children with prenatal exposure to organic solvents. The present study aimed to: (1) determine prospectively whether prenatal solvent exposure increases the risk of visual deficits in infants and (2) assess the relationship between estimates of exposure level and integrity of visual responses. A sample of 21 infants born to women who were occupationally exposed to solvents during pregnancy was compared with 27 non-exposed age-matched control infants. All mothers were recruited from Motherisk, an antenatal counseling service in Toronto, Canada. Contrast sensitivity and grating acuity were assessed using a sweep visual evoked potential (VEP) technique whereas chromatic- and achromatic mechanisms were assessed using a transient VEP technique. Exposure level was estimated from questionnaire data obtained during pregnancy. Testers were masked to exposure status. Results showed a significant reduction in contrast sensitivity in the low and intermediate spatial frequency range in solvent-exposed infants compared to controls (p < 0.001). With respect to grating acuity, there was a significant effect of exposure level, with children in the high exposed having reduced grating acuity compared with children in the low exposed group (p < 0.025) and controls (p = 0.02). Regarding color vision, 26.3% of infants in the exposed group versus 0% of the controls produced abnormal VEP responses to the red–green onset stimulus (p < 0.01), but not to either blue–yellow or achromatic stimuli. No differences were found with respect to latency or amplitude of chromatic and achromatic response. These findings suggest that prenatal solvent exposure is associated with selective visual deficits, including reduced contrast sensitivity and abnormal red–green vision. Increasing levels of exposure may lead to further visual deficits affecting grating acuity. These findings support the need for a re-evaluation of current occupational exposure standards for pregnant women.
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The impairment of colour discrimination induced by occupational exposure to toluene, styrene and mixtures of organic solvents is reviewed and analysed using a meta-analytical approach. Thirty-nine studies were surveyed covering a wide range of exposure conditions. Those studies using the Lanthony Panel D-15 desaturated test (D-15d) were further considered. From these for 15 samples data on colour discrimination ability (Colour Confusion Index, CCI) and exposure levels were provided, required for the meta-analysis. In accordance with previously reported higher CCI values for the exposed groups, the computations yielded positive effect sizes for 13 of the 15 samples, indicating that in the great majority of the studies the exposed groups showed inferior colour discrimination. However, the meta-analysis showed great variation in effect sizes across the studies. Possible reasons for inconsistency among the reported findings are discussed. These pertain to exposure-related parameters, as well as to confounders such as conditions of test administration and characteristics of subject samples. Those factors vary considerably among the studies and might have greatly contributed to divergence in measured colour vision capacity, thereby obscuring consistent effects of organic solvents on colour discrimination.
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The effect of industrial chemicals on the sensory perception of exposed workers has received scant attention from the medical community to date, and the scientific literature is mainly limited to some case-reports or isolated studies. Possible explanations for this include the complexity of sensory perception, and the lack of agreement among researchers on methods for testing large groups of subjects. Nevertheless, some published studies showed that vision, hearing and olfactory function can be affected by various industrial metals and solvents, and some data exist also for touch and taste. This review discusses the main industrial chemicals involved. The pathogenesis of the toxicity of chemicals to sensory perception may be related to an action on receptors, nerve fibers, and/or the brain; probably, different pathogenetic mechanisms are involved. One of the main problems in this research field is that most of the studies to date evaluated the effect of a single industrial chemical on a single sense: as an example, we know that styrene exposure can impair smell and also hearing and vision but we have little idea whether different senses are impaired in the same worker, or whether each impairment is independent. In addition, workers are frequently exposed to different chemicals: co-exposure may have no effect, or result in both an increase or a decrease of the effect, as was observed for hearing loss, but studies on this aspect are largely insufficient. Research shows that both occupational and environmental exposure to industrial chemicals can affect sense organs, and suggests that the decline of perception with age may be, at least partly, related to this exposure. Nevertheless, available evidence is incomplete, and is largely inadequate for an estimation of a “safe” threshold of exposure. Good quality further research in this field is needed. This is certainly complex and demands adequate resources, but is justified by the ultimate result: the possibility to prevent an avoidable part of the decline in sensory function with age.
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Recent research shows that occupational exposure to several solvents, metals and other industrial chemicals can impair color vision in exposed workers. Occupation-related color vision impairment usually results in blue–yellow color discrimination loss or, less frequently, a combination of blue–yellow and red–green loss. The eyes may be unequally involved, and the course is variable depending on exposure and other factors. The pathogenesis of occupational color vision loss has not been elucidated; it may be due to, e.g. a direct action of neurotoxins on receptors, possibly on the cone’s membrane metabolism, and/or to an interference with neurotransmitters within the retina. Other possible pathogenetic mechanisms, such as a direct effect to the optic nerve, have also been suggested. Occupational color vision loss is usually sub-clinical, and workers are unaware of any deficit. It can be assessed using sensitive tests, such as the Farnsworth–Munsell 100 Hue (FM-100) or the Lanthony D-15 desaturated panel (D-15 d). The latter is the most widely used for studies in groups of exposed workers, and offers the possibility of a quantitative evaluation of the results by calculation of the Bowman’s Color Confusion Index (CCI), or of the Vingrys’ and King Smith’s Confusion Index (CI). Other advantages of D-15 d are the possibility to perform the test directly at the workplace, and the reproducibility when performed in standardized conditions. In most cases, occupation-related color vision impairment is correlated to exposure levels, and has often been observed in workers exposed to environmental concentrations below the current occupational limit proposed by the ACGIH. Progression with increasing cumulative exposure has been reported, while reversibility is still discussed. Acquired color vision impairment related to occupational exposure to styrene, perchloroethylene (PCE), toluene, carbon disulfide, n-hexane, solvent mixtures, mercury and some other chemicals are discussed. Results show that color vision testing should be included in the evaluation of early neurotoxicity of chemicals in exposed workers. The D-15 d would be useful in the surveillance of workers exposed to solvents and other chemicals toxic to the visual system.

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^∗: Affiliated to the Québec Institut de recherche en santé et en sécutrité du travail.

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Chronal focus of acquired chromatic discrimination loss and solvent exposure among printshop workers

Abstract

Vision Res.

La dyschromatopsie chez les personnes exposées professionnellement aux solvants organiques

J. Fr. Ophtalmol.

Neurologic dysfunction from exposure to 2-t-butylazo-2-hydroxy-5-methylhexane (BHMH): a new occupational neuropathy

Am. J. Publ. Health

Assessing colour vision loss among solvent exposed workers

Am. J. Ind. Med.

n-Hexane maculopathy in industrial workers

Alb. v Graef. Arch. Klin. Exp. Ophthalmol.

Impaired color discrimination among viscose rayon workers exposed to carbon disulfide

J. Occup. Med.

Congenital and Acquired Colour Defects

Neuropathies of the optic nerve and visual evoked potentials with special references to color vision and differential light threshold measured with the computer perimeter OCTOPUS

Doc. Ophthalmol.

Le Farnsworth D-15 désaturé

Bull. Soc. Ophtalmol. Fr.