Occupational Mercury Contamination Produces Loss of Color-and Contrast-Vision but no Effect in Full Field ERG

Abstract

Abstract: : Purpose: To assess the effect of mercury vapor exposure on visual function. Methods: Retired workers from a fluorescent lamp industry (n=24) were tested and compared to age-matched controls. Inclusion criteria were medical diagnosis of mercury contamination, with 20/20 Snellen VA and absence of known ophthalmological pathologies. Color vision was assessed with the following tests: FM-100 hue, Lanthony desaturated and Cambridge Colour Vision Test (Cambridge Research Systems Ltd). The sweep visual evoked potential system – sVEP (NuDiva2) using bipolar electrode placement was used to estimate contrast sensitivity. Full-field electroretinograms (ERG) were measured following the ISCEV protocol. All tests were performed monocularly in a darkened room. Results: Color vision loss was detected in 21/24 patients. Scores of patients ranged from 48 to 452 in the FM-100 test and from 152 to 302 in the Lanthony desaturated test and were statistically different from those of controls (p< 0.001). CCT ellipses of patients were significantly larger than those of controls in field 1 (p=0.02) and field 3 (p=0.01), but not in field 2 (p=0.07). Contrast sensitivity measured by the sVEP was reduced in all patients (n=14) relative to controls at the mid-frequency range - 0.8 (p<0.001), 2 (p=0.008) and 4 (p=0.01) cpd. No difference was found in contrast sensitivity at the lowest and highest spatial frequencies tested - 0.2, 15 and 30 cpd. Full-field ERG responses did not differ from controls in any of the ISCEV protocol test parameters. Conclusions: Visual function, assessed electrophysiologically by the VEP and also psychophysically, was clearly affected, in contrast to the ERG retinal function, suggesting central participation in the damage caused by mercury vapor exposure. More refined measurement of retinal function such as multifocal and pattern-ERG will be performed to investigate retinal damage.

Keywords: color vision • contrast sensitivity • electrophysiology: clinical