Visual evoked potentials in workers with chronic solvent encephalopathy

Objectives. Two promising variations of visual evoked potentials (VEPs) were studied in solvent-exposed workers: the effect of a low-contrast stimulus in comparison with the usually applied high contrast, and the ability of pattern-onset VEP to reveal damage to specific visual cortical areas. In addition, we studied disturbances of a visual event-related potential (P300). Methods. Thirty male patients (48+/-9 years of age) with solvent-induced chronic encephalopathy, and 41 controls (46+/-8 years) without solvent exposure, participated. Pattern-reversal checkerboards with low (11%) contrast and with high (93%) contrast between the checks were used. For onset VEPs two dedicated stimulus patterns were used. P300 was elicited with an "oddball" paradigm. Results. At low contrast the N75-P100 peak-to-peak amplitude in the controls was 9.6+/-4.9 muV, i.e. 57% of the amplitude at high contrast (16.3+/-7.2 muV). In the patients the response at low contrast was only 48% of that at high contrast; the corresponding amplitudes were 7.5+/-3.5 muV and 15.8+/-4.9 muV. For the pattern-onset VEPs no effect of exposure was found. With regard to the P300, the patients missed more targets (average 3.6%) than did the controls (average 0.5%). Patients had a smaller P300 amplitude (8.8+/-4.5 muV) than the controls (11.5+/-5.3 muV), and a longer latency (390+/-34 ms compared to 376+/-24 ms). Conclusion. The results point to a physiological basis for the solvent-induced decrease of visual contrast sensitivity as found by others by means of psychophysical methods. The results also suggest that the neurophysiological examination of the visual system in persons who have undergone exposure to toxins might be benefited by the addition of low-contrast stimul