Occupational lead exposure. Effects on saccadic eye movements.

Abstract

Quantitative measures of saccadic eye movements were examined in 52 lead exposed autobody shop workers and 52 age matched controls with no history of occupational lead exposure. Three characteristics of saccadic eye movements were studied: 1) saccade accuracy; 2) number of overshoots; and 3) maximum velocity. The results indicated that workers exposed to inorganic lead showed a decrease in saccade accuracy and an increase in overshoots compared with controls. Saccade maximum velocity was lower in lead exposed workers than in controls but the difference was just short of statistical significance. Correlations between measures of saccadic eye movements and indicators of lead absorption--blood lead (Pb-B) and zinc protoporphyrin (ZPP) levels--were analyzed in the lead exposed workers. Saccade accuracy was negatively correlated with both Pb-B and ZPP levels. The number of overshoots was not correlated with either Pb-B or ZPP levels. Saccade maximum velocity was not correlated with Pb-B, however, there was a significant negative correlation with ZPP. Age effects observed in the control group were disrupted in lead exposed workers. In addition, saccadic eye movements in younger workers (below 30 years old) were more affected by exposure to inorganic lead than were saccadic eye movements in older workers (50 years and older). It is proposed that these findings are consistent with a relatively rapid buildup of metabolically active lead burden observed in the study group. The data suggest that quantitative assessment of eye movements may be an important tool for studying subclinical central nervous system (CNS) dysfunction due to inorganic lead exposure.