Visual evoked potentials in patients after methanol poisoning
Pavel Urban 1, 2  
Pavel Diblík 3
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National Institute of Public Health, Prague, Czech Republic (Centre for Industrial Hygiene and Occupational Medicine)
Charles University in Prague and General University Hospital in Prague, Prague, Czech Republic (Department of Occupational Medicine, 1st Faculty of Medicine)
Charles University in Prague and General University Hospital in Prague, Prague, Czech Republic (Department of Ophthalmology, 1st Faculty of Medicine)
Int J Occup Med Environ Health 2016;29(3):471–478
Objectives: We report the results of the visual evoked potentials (VEP) examination in patients after severe poisoning by methanol. Material and Methods: The group of 47 patients (38 males and 9 females) was assembled out of persons who survived an outbreak of poisoning by the methanol adulterated alcohol beverages, which happened in the Czech Republic in 2012–2013. The visual evoked potentials examination was performed using monocular checkerboard pattern-reversal stimulation. Two criteria of abnormality were chosen: missing evoked response, and wave P1 latency > 117 ms. Non-parametric statistical methods (median, range, and the median test) were used to analyze factors influencing the VEP abnormality. Results: The visual evoked potential was abnormal in 20 patients (43%), 5 of them had normal visual acuity on the Snellen chart. The VEP abnormality did not correlate significantly with initial serum concentrations of methanol, formic acid or lactate; however, it showed statistically significant inverse relation to the initial serum pH: the subgroup with the abnormal VEP had significantly lower median pH in comparison with the subgroup with the normal VEP (7.16 vs. 7.34, p = 0.04). The abnormality was not related to chronic alcohol abuse. Conclusions: The visual evoked potentials examination appeared sensitive enough to detected even subclinical impairment of the optic system. Metabolic acidosis is likely to be the key factor related to the development of visual damage induced by methanol. The examination performed with a delay of 1–9 months after the poisoning documented the situation relatively early after the event. It is considered as a baseline for the planned long-term follow-up of the patients, which will make it possible to assess the dynamics of the observed changes, their reversibility, and the occurrence of potential late sequelae.
Pavel Urban   
National Institute of Public Health, Šrobárova 48, 100 42 Praha 10, Czech Republic