Visual system disorders in patients with occupational chronic solvent-encephalopathy

Abstract

The occupational chronic solvent encephalopathy (CSE) may develop after a long-term work exposure to organic solvents. There is a great need to develop effective screening tests for early detection of possible toxic effects. Because of repeated observations of visual system disorders, reduced color discrimination ability and contrast sensitivity, visual tests have been suggested for screening purposes. However, the pathogenesis of visual findings still remains unclear. Since 1995, we have performed visual function tests for CSE-patients (N=109). The lifetime solvent exposure has been assessed. Extensive differential diagnostic tests (neurological, neuropsychological, psychiatric, MRI, SPECT, CSF, laboratory examination) did not reveal other diseases and brain dysfunctions remained stable during 2 to 5 years of follow up. Patients' ocular health was assessed and visual functions were tested for visual field sensitivity (Octopus 101-automated perimetry), for color discrimination ability (F-M 100 hue), and for contrast sensitivity (Vistech). A group of patients with marked visual field defects were further studied with a multi-focal electroretinogram (Veris-mERG). Another group of patients were studied for visual search/attention tasks combined with simultaneous eye movement recordings (Eye-Link). In 31 % of the CSE-patients (N=70, with no ocular reasons) a wide range of color discrimination defects was found, while contrast sensitivity remained normal. Patients often showed tunnel-like, reduced peripheral visual field sensitivity, which was not always associated with reduced color vision. The mERG-recordings did not show any reduction in the amplitude or latency of retinal potentials and the preliminary studies did not reveal any oculomotor defects. Thus, the visual system disorders suggested possible cortical pathology. Possible screening methods and their relationship with solvent exposure is discussed.