Strabismus Risk Much Higher in Very Low Birth Weight Infants

Jenni Laidman

July 24, 2014

The risk for strabismus was 14 times higher in very premature infants who weighed less than 2000 g at birth, independent of gestational age (GA), according to a study published online July 21 in JAMA Pediatrics.

Shilpa Gulati, MS, fourth-year medical student, W.K. Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, and colleagues calculated strabismus risk among 38,055 otherwise healthy premature infants who were enrolled from birth to at least age 6 months in a managed care plan.

The researchers excluded chronically ill children from the study. Infants with a GA of 32 weeks or less were defined as very premature, and those with a GA of between 33 and 36 weeks were identified as mildly premature. Very low birth weight (BW) was defined as a weight of less than 2000 g. Of 25,601 premature infants for whom BW and gestational age were known, 6571 (25.7%) of the infants were considered very low BW and 19,030 (74.3%) were mildly low BW.

Of the premature infants, 21,956 (85.8%) were mildly premature and 3645 (14.2%) were very premature. Among very premature infants, 2980 (81.8%) were also very low BW. Among 19,030 infants with mildly low BW, 96.5% were mildly premature. By age 5 years, 3.0% (583) of the infants were diagnosed with strabismus.

The researchers adjusted for GA, sex, race, urban/rural residence, household net worth, delivery method, retinopathy of prematurity (ROP), and other ocular conditions. Infants with very low BW were at a 61% increased hazard of developing strabismus (adjusted hazard ratio [AHR], 1.61; 95% confidence interval [CI], 1.22 - 2.13). The risk for strabismus increased by 13% for every 250 g below a BW of 2500 g (AHR, 1.13; 95% CI, 1.04 - 1.23).

After adjusting for BW and other covariates, the researchers found no significant association between strabismus and GA (HR, 0.98; 95% CI, 0.69 - 1.38). In very low BW infants, a GA of 32 weeks or fewer conveyed no significant risk for strabismus compared with the risk of infants born later than 32 weeks (HR, 1.27; 95% CI, 0.86 - 1.88) Conversely, among infants with a GA of 32 weeks or fewer, very low BW was associated with a 14-fold increase in risk compared with infants who weighed more than 2000 g (HR, 14.39; 95%, 1.99 - 104.14).

The results suggest a potential need for increased routine pediatric eye examinations for strabismus and amblyopia in very low BW infants.

"The 2012 American Academy of Ophthalmology Preferred Practice Pattern for Pediatric Eye Evaluations offers guidelines on how frequently children should undergo ocular examinations to check for strabismus and other ocular diseases," the authors write. "Neither these guidelines nor guidelines put forth by the American Academy of Pediatrics recommend that clinicians carefully monitor premature infants of low BW for strabismus and amblyopia beyond the standard monitoring in the first 10 weeks of life to check for ROP. Based on the findings of our analysis and the analyses of others, future guidelines may consider recommending that premature infants with low BW undergo periodic assessment in the first few years of life to check for strabismus."

Strabismus affects 2% to 4% of children aged 6 months to 5 years. When untreated, strabismus increases the risk for amblyopia. Further, it can affect a child's self-image and social interactions. Early intervention achieved the best visual acuity in earlier studies, reducing the need for additional surgical intervention, the authors write.

The cause of increased strabismus in premature infants has been a subject of debate, with studies finding both BW and GA to be independent risk factors. Two studies pointed to GA only, and another study suggested that both BW and GA increased risk. Other studies looking at strabismus in premature infants found no association between strabismus and either GA or BW; however, the studies looked at only infants who were severely premature.

Other strabismus risk factors include anisometropia and refractive error, genetics, older parental age, maternal smoking during pregnancy, neurodevelopmental impairment, low Apgar scores, craniofacial abnormalities and chromosomal abnormalities, in utero toxin exposure, ROP, and cesarean delivery.

This study was supported by the W.K. Kellogg Foundation and a National Eye Institute K23 Mentored Clinician Scientist Award and a Research to Prevent Blindness Physician Scientist Award to one coauthor, and a Lew R. Wasserman Merit Award to another coauthor. The authors disclosed no other relevant financial relationships.

JAMA Pediatrics. Published online July 21, 2014. Abstract

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