Solvent related colour vision loss: an indicator of neural damage?

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Abstract
Previous studies have related colour vision loss to solvent exposure, raising the question as to its use as an indicator of solvent-related neurotoxic alterations. However, colour vision loss can likewise result from ocular damage. In the present study chromatic discrimination capacity and ocular integrity were examined among 23 workers of a paint manufacture plant exposed to solvent mixtures. Using industrial hygiene data, the workers were classified according to their exposure level: moderate (n = 13) and high (n = 10). Colour discrimination capacity was assessed using the Farnsworth-Munsell 100 Hue, a colour arrangement test, providing qualitative and quantitative data. Biomicroscopy, funduscopy and peripheral visual field tests were used to examine ocular integrity. The results showed a significantly higher prevalence (P < 0.02) of chromatic discrimination loss among the highly exposed workers (80%), as compared to the moderately exposed (23.1%). Ocular examination revealed no apparent major damage, although slight posterior sub-capsular opacification, indicative of incipient cataract, and, diminished foveal reflex were observed among 1/3 of the workers. Lens opacification was related to age and exposure duration, but not to exposure level. Diminished foveal reflex was not related to either age, exposure duration or level. Neither observation was related to chromatic discrimination loss. These findings support the hypothesis that chromatic discrimination impairment, associated with solvent exposure, reflects neural, rather than ocular, damage. The authors propose that tests of acquired colour vision loss be included in field batteries to evaluate neurotoxic effects of solvent exposure.