Strabismus Risk in the Opiate Exposed Infant

Purpose. Methadone maintenance is the gold standard of treatment for opiate addiction during pregnancy. In humans, little is known about the teratogenicity of opiate exposure; however, an increased incidence of ocular misalignments was noticed anecdotally in children of women in local treatment. Ocular abnormalities, specifically strabismus, have been previously reported in methadone exposed children. Strabismus is one type of deficiency in ocular alignment. Etiological factors thought to contribute to strabismus include prematurity, low birthweight, and hypoxia at birth. Genetic factors play a role in specific forms of strabismus that vary in type and temporal onset. It is well established that prenatal exposure to substances, including some prescription drugs, tobacco, and alcohol have also been associated with visual system abnormalities. While the mechanism underlying strabismus is not well understood, a central question is whether early-onset strabismus is a defect of extra-ocular muscle innervation or a result of neural circuitry formation during the development of the visual system early in gestation. Methods. As part of a larger longitudinal study, rural, disadvantaged mothers who were maintained on methadone during pregnancy and their infants (n=19 dyads) were recruited in the 3rd trimester from local narcotics treatment programs in Bangor, ME. A comparison sample (n=12), who were matched for sociodemographic factors, alcohol, and tobacco use was recruited from the hospital family medicine clinic. Third trimester interviews were conducted to determine quantity-variability-frequency patterns of drug and alcohol use during both the pre-pregnancy and pregnancy periods and for psychiatric status. Daily maternal methadone dose, number of missed doses, and magnitude of dose increase during pregnancy were extracted from medical records. At follow-up, infants (M= 388, 5m) were examined for signs of ocular deviations using standardized eye-following tasks. Photographic images were digitally coded for alignment using a modified version of the Hirschberg Corneal reflection test. A measurement protocol to identify vertical deviations in ocular alignment was followed. Results. Findings showed that 57% (11/19) of methadone-exposed group were positive for signs of strabismus, whereas, only 8% (1/12) of the nonexposed comparison group did (LR 1 = 8.63, p<.003). A logistic regression model found that risk of strabismus was associated with group (methadone) (p < .001); age of assessment (p< .005); and prepregnancy alcohol binge drinking (p = .014). The model accounted for 59% of variance (Nagelkerke R Square = Conclusion. Preliminary findings suggest that prenatal methadone exposure and conditions associated with it, including likely alcohol abuse, may increase the risk for strabismus. Although identifying the type, dose and pattern of exposure in human teratogenic studies has proved especially difficult, this prospective study suggests that methadone exposure, tobacco and alcohol binge drinking may act synergistically. These findings argue for further investigation of the prenatal factors, including a possible role for methadone in infantile strabismus.