Cumulative exposure to styrene and visual functions.

Background: Results from a 1990-1992 longitudinal study of several reinforced plastics plants showed that for those workers whose styrene exposure had decreased, color vision (CV) improved; while near visual contrast sensitivity (CS) was poorer.

Methods: In 1999, we retested these visual functions in 18 workers with good visual acuity. A cumulative exposure index (CEI), corrected for respirator use, was calculated for each worker.

Results: Intra-individual comparison of mandelic acid (MA) showed a significant decrease over time (Friedman; P = 0.015), but current values were not related to CEI. For CV, no significant difference was observed between 1992 and 1999; present results were not related to MA or CEI. The CS profile decreased over time, with significant differences at 3 cpd (Friedman; P < 0.05). CS did not vary with MA levels, but was significantly depressed at the intermediate frequencies among those in the upper CEIH category (Kruskal-Wallis; P < 0.05).

Conclusions: These findings suggest that CS loss increases with long-term cumulative exposure, reflecting chronic damage to the neuro-optic pathways.