Objective: To quantify familial aggregation of esotropia and exotropia in children examined in a large multicenter study.
Methods: Pregnant women and their children were examined in the Collaborative Perinatal Project of the National Institute of Neurological Disorders and Stroke, Bethesda, Md. Strabismus was evaluated in the children during follow-up examinations up to the age of 7 years. The second-order generalized estimating equations approach to logistic regression was used to estimate familial aggregation of esotropia and exotropia.
Results: For any pair of siblings, the odds for one sibling having esotropia more than doubled when the other sibling had esotropia. For exotropia, there were differences in sibling associations based on birth relationships. In particular, there was no statistically significant association between siblings from separate single births. On the other hand, for the pairs of siblings from multiple births (ie, twins, triplets, and quadruplets), the odds for exotropia in one sibling were increased by at least a factor of 17 when the other sibling from that birth also had exotropia. For both esotropia and exotropia, adjustment for previously identified risk factors only somewhat reduced the magnitudes of the observed associations. Limited data on zygosity showed a stronger association between monozygotic twins than between dizygotic twins.
Conclusions: There is a significant familial component in the cause of strabismus. Furthermore, there are important contributions to this familial aggregation beyond those associated with known risk factors for strabismus.