Risk factors for esotropia and exotropia.

OBJECTIVE: To identify risk factors associated with the two major types of strabismus--esotropia and exotropia--in a cohort of children followed up from gestation to age 7 years.
DESIGN: Pregnant women were enrolled in the Collaborative Project of the National Institute of Neurological Disorders and Stroke, Bethesda, Md, from 1959 to 1965 at 12 university centers. This large multidisciplinary study was designed to evaluate the developmental consequences of complications during pregnancy and the perinatal period. Data on maternal, socioeconomic, perinatal, and neonatal characteristics were collected from 39,227 children and their mothers by medical examination and interview. Examinations of the children were performed at birth, 4 months, 8 months, 1 year, and 7 years. OUTCOME MEASURES: The evaluation of the presence of strabismus was performed during follow-up examinations and confirmed at the 7-year follow-up visit. Potential risk factors for strabismus were evaluated from the maternal, socioeconomic, perinatal, and neonatal characteristics.
RESULTS: Esotropia developed in 1187 children (3.0%), and exotropia developed in 490 children (1.2%). Esotropia was more common in whites (3.9% in whites vs 2.2% in blacks, P < .0001). The occurrence of exotropia was similar in the two races (1.2% in whites and 1.3% in blacks). Results of multivariable logistic regression models showed that the risk of strabismus increased with low birth weight (P < .0001). For infants weighing 1500 g at birth compared with those weighing 4000 g at birth, the odd ratios were 3.26 (95% confidence interval, 2.50 to 4.25) for esotropia and 4.01 (95% confidence interval, 2.77 to 5.80) for exotropia. Maternal cigarette smoking during pregnancy also increased the risk of each type of strabismus (P < .0001). For offspring of mothers who smoked more than two packs of cigarettes per day compared with those whose mothers did not smoke, the odds ratios were 1.83 (95% confidence interval, 1.51 to 2.22) for esotropia and 2.32 (95% confidence interval, 1.72 to 3.13) for exotropia. Maternal age was also a significant risk factor for esotropia (P = .0005). The risk of esotropia increased with increasing age until age 34 years. In particular, the odds ratio for mothers aged 30 to 34 years relative to that for mothers aged 20 to 24 years was 1.43 (95% confidence interval, 1.19 to 1.70).
CONCLUSIONS: Esotropia was more common in whites than in blacks. The occurrence of exotropia was similar in the two races. Maternal cigarette smoking during pregnancy and low birth weight were independent and important risk factors for both esotropia and exotropia. There was an increased risk of esotropia with increasing maternal age.