Background: Little is known about the aetiological factors underlying strabismus. We undertook a large cohort study to investigate perinatal risk factors for strabismus, overall and by subtype.
Methods: Orthoptists reviewed ophthalmological records for Danish National Birth Cohort (DNBC) children examined for strabismus in hospital ophthalmology departments or by ophthalmologists in private practice. Information on perinatal characteristics was obtained from national registers. We used log-linear binomial regression and polytomous logistic regression to estimate risk ratios for strabismus overall and by strabismus subtype, respectively.
Results: Among 96,842 DNBC children born in Denmark between 1996 and 2003, we identified 8783 children who had been evaluated for strabismus. Ophthalmological records were available for 5655 of these children, of whom 1321 were diagnosed with strabismus. In multivariable analysis, low birth weight, prematurity, large head circumference and presence of congenital abnormalities were all associated with increased risk of strabismus. Presence of congenital abnormalities was more strongly associated with exotropia than with esotropia. Of 183 exotropia cases, 40 (22%) had congenital abnormality. Although not associated with esotropia, delivery by Caesarean section was associated with exotropia (relative risk = 1.65; 95% confidence interval 1.16-2.34). After adjustment for birth weight, Apgar score at 5 min, multiple gestation and parental ages were not associated with strabismus overall.
Conclusions: Congenital abnormalities, low birth weight, prematurity and large head circumference were independent risk factors for strabismus. Differences in risk factors for esotropia and exotropia suggest that strabismus subtypes may have different underlying aetiologies. The proportion of exotropic children with congenital abnormalities suggests that a large angle constant exotropia in an infant should alert physicians to the possibility of a congenital abnormality.