Effects of lifetime lead exposure on spatial and temporal visual function in monkeys

Detailed characterization of several aspects of visual function was performed in two groups of monkeys (Macaca fascicularis) exposed to lead continuously from birth. One group of four monkeys was dosed from birth onward with 500 microg/kg/day of lead as lead acetate, while another group of six monkeys was dosed with 2000 microg/kg/day. Blood lead levels peaked in the former group at 50 microg/dl early in life; the latter group had peak blood lead concentrations averaging 115 microg/dl during infancy. Blood lead concentrations decreased before one year of age to stable levels of 25 or 35 microg/dl in the low and high dose groups respectively. Spatial and temporal visual function was assessed using a psychophysical procedure at 7-9 years of age. Six age-matched controls were tested concurrently. Two treated monkeys had severe hyperopia: one was assessed on temporal vision only and the other was not assessed. Spatial data from a third monkey were considered suspect and excluded. Six of the nine treated monkeys in which temporal vision was assessed had thresholds below control values at low and/or middle frequencies under high luminance conditions. Low-luminance temporal vision was not affected. There was no evidence of impairment of spatial visual function in lead-exposed monkeys with normal refractive status at either high or low luminance. This study suggests that temporal visual function may be preferentially impaired as a result of lifetime exposure to a moderate body burden of lead, although these results require replication before definitive conclusions may be drawn.