Purpose: To determine the dose-response relationship between blood lead concentration ([PbB]) and scotopic ERG amplitude in 7- to 10-year-old children with lifetime lead exposure.
Methods: Full-field flash scotopic ERGs were recorded over a 4-log-unit range in 45 dark-adapted children with normal visual acuity. [PbB] was measured throughout pregnancy and postnatal development, and the subjects' [PbB] levels were grouped at each age by tertiles.
Results: The median [PbB] during pregnancy was, from lowest to highest tertile, 2.5 to 5.0, 7.5 to 9.0, and 14.0 to 16.5 microg/dL, and after birth was 4.0 to 8.0, 6.0 to 14.5, and 7.5 to 21.0 microg/dL. Only maternal [PbB] at 12 weeks of pregnancy showed a significant dose-response relationship with the ERG measures, so that with increasing [PbB] there were significant increases in leading-edge a-wave amplitude, peak a-wave amplitude, and b-wave amplitude and sensitivity, with no changes in implicit times. Data analyses showed that children whose mothers had [PbB] of 10.5 microg/dL or more at 12 weeks of pregnancy had relatively increased a- and b-waves.
Conclusions: Lead exposure during the first trimester of pregnancy produces dose-dependent increases in scotopic a- and b-wave amplitudes in 7- to 10-year-old children. The results suggest that the increases in a- and b-wave amplitudes originate from rods; however, the increased b-wave amplitude and sensitivity may also originate in the inner retina. These alterations occurred at maternal [PbB] at or below currently accepted safe levels. These novel findings reveal that the developing retina is a sensitive target for lead and suggest that lead-exposed children be examined for possible future visual system deficits.