Heredity versus abnormalities in pregnancy and delivery as risk factors for different types of comitant strabismus

Purpose: To elucidate risk factors for different types of comitant strabismus, the incidence of heredity and abnormalities in pregnancy and delivery was compared among different types of strabismus. Methods: Between May 1998 and January 1999, a prospective clinical study of 500 consecutive patients with comitant strabismus at a referral-based university hospital was performed using data collected from questionnaires and interviews. Inclusion criteria were infantile esotropia (168 patients), accommodative and partially accommodative esotropia (97 patients), microesotropia (15 patients), acquired esotropia (12 patients), intermittent or constant exotropia (205 patients), and congenital exotropia (3 patients). Exclusion criteria were strabismus associated with systemic and central nervous system abnormalities and organic eye diseases. Results: Family history was significantly more prevalent in intermittent or constant exotropia and accommodative or partially accommodative esotropia than in infantile esotropia (P<.0001 and P=.0267, respectively, Fisher's exact test). In contrast, abnormalities in pregnancy and delivery were noted at a significantly higher rate in infantile esotropia than in accommodative or partially accommodative and in intermittent or constant exotropia (P=.003 and P=.0215, respectively). Patients with infantile esotropia were significantly younger at the survey than those with the other two types of strabismus (P=.0004 and P<.0001). No significant difference was found in the number of siblings, birthweight, maternal age at delivery, or maternal cigarette smoking or alcohol drinking among these three types of strabismus. Conclusion: Heredity and abnormalities in pregnancy and delivery are two major risk factors for comitant strabismus and contribute at different levels to the development of infantile esotropia, accommodative or partially accommodative esotropia, and intermittent or constant exotropia.