Visuocortical function in infants with a history of neonatal jaundice

Abstract

Purpose: High concentrations of unconjugated bilirubin are neurotoxic and cause brain damage in newborn infants. However, the exact level of bilirubin that may be neurotoxic in a given infant is unknown. The aim of this study was to use a quantitative measure of neural activity, the swept parameter visual evoked potential (sVEP) to determine the relationship between neonatal bilirubin levels and visual responsivity several months later.

Methods: We compared sVEP response functions over a wide range of contrast, spatial frequency, and Vernier offset sizes in 16 full-term infants with high bilirubin levels (>10 mg/dL) and 18 age-matched infants with no visible neonatal jaundice, all enrolled at 14 to 22 weeks of age. The group means of sVEP thresholds and suprathreshold response amplitudes were compared. The correlation between individual sVEP thresholds and bilirubin levels in jaundiced infants was studied.

Results: Infants who had a history of neonatal jaundice showed lower response amplitudes (P < 0.05) and worse or immeasurable sVEP thresholds compared with control infants for all three measures (P < 0.05). Swept parameter visual evoked potential thresholds for Vernier offset were correlated with bilirubin level (P < 0.05), but spatial acuity and contrast sensitivity measures in the infants with neonatal jaundice were not (P > 0.05).

Conclusions: These results indicate that elevated neonatal bilirubin levels affect measures of visual function in infancy up to at least 14 to 22 weeks of postnatal age.

Keywords: Vernier acuity; contrast sensitivity; hyperbilirubinemia; jaundice; spatial frequency; swept parameter visual evoked potentials.

Figure 1

Vector-averaged group response functions in infants with a history of neonatal jaundice (filled circles) and age-matched control infants (open squares). Error bars indicate SEM. The dashed line indicates EEG noise level. The solid lines indicate the regression lines calculated by a jackknife procedure. The black bars at the top of each panel indicate the epochs of the three most visible stimulus values. Infants with a history of neonatal jaundice show smaller suprathreshold response amplitudes at the three most visible stimulus values compared with control infants (see MANOVA results in Table 2). Group differences in thresholds are present over spatial frequency, contrast and Vernier-offset measurements (*P < 0.05; **P < 0.01; ***P < 0.001 with corrected P values; Table 3).

Figure 2

Correlation between sVEP thresholds for Vernier offset and bilirubin level among infants with a history of neonatal jaundice. The correlation was significant at the level P = 0.008. Without the outlier (Vernier threshold = 3.68 min arc), r² = 0.26004 and P = 0.0521.