Mercury toxicity in the Amazon: contrast sensitivity and color discrimination of subjects exposed to mercury

We measured visual performance in achromatic and chromatic spatial tasks of mercury-exposed subjects and compared the results with norms obtained from healthy individuals of similar age. Data were obtained for a group of 28 mercury-exposed subjects, comprising 20 Amazonian gold miners, 2 inhabitants of Amazonian riverside communities, and 6 laboratory technicians, who asked for medical care. Statistical norms were generated by testing healthy control subjects divided into three age groups. The performance of a substantial proportion of the mercury-exposed subjects was below the norms in all of these tasks. Eleven of 20 subjects (55 percent) performed below the norms in the achromatic contrast sensitivity task. The mercury-exposed subjects also had lower red-green contrast sensitivity deficits at all tested spatial frequencies (9/11 subjects; 81 percent). Three gold miners and 1 riverine (4/19 subjects, 21 percent) performed worse than normal subjects making more mistakes in the color arrangement test. Five of 10 subjects tested (50 percent), comprising 2 gold miners, 2 technicians, and 1 riverine, performed worse than normal in the color discrimination test, having areas of one or more MacAdam ellipse larger than normal subjects and high color discrimination thresholds at least in one color locus. These data indicate that psychophysical assessment can be used to quantify the degree of visual impairment of mercury-exposed subjects. They also suggest that some spatial tests such as the measurement of red-green chromatic contrast are sufficiently sensitive to detect visual dysfunction caused by mercury toxicity.

Long-term loss of color vision after exposure to mercury vapor

We evaluated the color vision of 24 subjects (41.6 ± 6.5 years; 6 females) who worked in fluorescent lamp industries. They had been occupationally exposed to mercury vapor (10.6 ± 5.2 years) and had been away from the source of exposure for 6.4 ± 4.04 years. Mean urinary concentration of mercury was 40.6 ± 36.4 æg/g creatinine during or up to 1 year after exposure and 2.71 ± 1.19 æg/g creatinine at the time of color vision testing or up to 1 year thereafter. All patients were diagnosed with chronic mercury intoxication, characterized by clinical symptoms and neuropsychological alterations. A control group (N = 36, 48.6 ± 11.9 years, 10 females, 1.5 ± 0.47 æg mercury/g creatinine) was subjected to the same tests. Inclusion criteria for both groups were Snellen VA 20/30 or better and absence of known ophthalmologic pathologies. Color discrimination was assessed with the Farnsworth D-15 test (D-15) and with the Lanthony D-15d test (D-15d). Significant differences were found between the two eyes of the patients (P < 0.001) in both tests. Results for the worst eye were also different from controls for both tests: P = 0.014 for D-15 and P < 0.001 for D-15d. As shown in previous studies, the D-15d proved to be more sensitive than the D-15 for the screening and diagnosis of the color discrimination losses. Since color discrimination losses were still present many years after the end of exposure, they may be considered to be irreversible, at least under the conditions of the present study.

O perfil oftalmológico dos candidatos à carterira de motorista na cidade de Pelotas - RS / Ophthalmological profile of the candidates for driving license in Pelotas city - RS

Objetivo: Estudar a acuidade visual dos candidatos a condutores de veículos da cidade de Pelotas e sua associação com as características sociodemográficas dos candidatos. Métodos; Foram examinados 1.010 candidatos a condutores em um serviço médico autorizado pelo Detran. Avaliou-se a acuidade visual, com e sem correção, bem como a sua relação com a visão de cores, sexo, idade e profissão dos entrevistados, por meio da análise de freqüências e de teste para associação. Resultados: Deste contingente 73,0 por cento eram do sexo masculino, 65,0 por cento tinham idade entre 18 e 45 anos, 51,4 por cento ocupavam o setor de serviços e 25,0 por cento utilizavam meio de correção visual: Sob o ponto de vista oftalmológico, 0,5 por cento dos entrevistados não poderiam dirigir veículos automotores e 4,7 por cento só poderiam obter habilitação para condução veicular; nas categorias A e B. Mostrou-se associada à acuídade visual baixa a maior longevidade. Conclusão: Baseado nos resultados, sugere-se menor intervalo de tempo para reavaliação visual dos motoristas das categorias C, D e E.