Diet- and Mercury-induced Visual Loss
Inorganic mercury in our environment is absorbed into our bodies in the form of organic methylmercury. Diet is the main source of methylmercury in people not involved in mercury-related industries. Our knowledge of the toxic effects of mercury poisoning is based on two major industrial accidents, which resulted in widespread illness, ranging from neurological disease such as ataxia and paraplegia up to seizures and death. Visual symptoms reported from the aftermath of these accidents include sudden cortical blindness, constricted visual fields, optic atrophy, and poor night vision. As the average person is exposed to much lower doses of mercury through their diet, the toxic effects on methylmercury are less clearly defined. With many other confounding factors associated with diet and exposure, we describe the different investigations that are used to examine changes in visual function associated with exposure to methylmercury. MRI and electrophysiological testing are described and the abnormal findings associated with methylmercury toxicity are highlighted. Color vision testing can identify dyschromatopsia (color confusion) associated with mercury exposure and in some cases these changes persist for many years after exposure. We describe the recommended guidelines on fish consumption in place to limit exposure to mercury and other heavy metals. We discuss recent studies that look at fish consumption during pregnancy and the evidence on its effect on childhood neurodevelopment. Finally, we emphasize that on balance, the positive benefits of fish consumption outweigh the risks associated with mercury exposure.
KeywordsFish Consumption Visual Evoke Potential Inorganic Mercury Color Discrimination Mercury Exposure
The Environmental Protection Agency
The Seychelles Child Development Study
Visual evoked potential
- Cavalleri A, Gobba F. Color vision impairment in workers exposed to neurotoxic chemicals fabriziomaria Gobba1, Alessandro Cavalleri. Neurotoxicology. 1998;24(2003):693–702.Google Scholar
- Korogi Y, Takahashi M, Hirai T, Ikushima I, Kitajima M, Sugahara T, Shigematsu Y, Okajima T, Mukuno K. Representation of the visual field in the striate cortex: comparison of MR findings with visual field deficits in organic mercury poisoning (Minamata disease). Am J Neuroradiol. Jun-Jul 1997;18(6):1127–30.PubMedGoogle Scholar
- Raymond LJ, Ralston NV. Mercury: selenium interactions and health implications. Seychelles Med Dent J. 2004;7:72–7.Google Scholar
- Tsubaki T, Takahashi H. (editors) Recent advances in minimata disease studies: methylmercury poisoning in Minimata and Nigiita, Japan. Tokyo, Japan; 1986.Google Scholar
- US Environmental Protection Agency. Controlling power plant emissions: emissions progress. Washington: US Environmental Protection Agency; 2009a. http://www.epa.gov/mercury.
- US Environmental Protection Agency. Mercury Study report to Congress. Washington: US Environmental Protection Agency; 2009b. http://www.epa.gov/mercury/report.htm.
- US Environmental Protection Agency. What you need to know about mercury in fish and shellfish. Washington: US Environmental Protection Agency; 2009c. http://www.epa.gov/waterscience/fishadvice/advice.html.