Study: older children more likely to develop strabismus, amblyopia

September 15, 2007

No difference exists regarding the prevalence of amblyopia and strabismus in a population of Hispanic and African-American preschool children, and the prevalence of the two pathologies increases with age, according to findings of the Multi-Ethnic Pediatric Eye Disease Study.

Key Points

The Multi-Ethnic Pediatric Eye Disease Study (MEPEDS)-a population-based study of eye disease conducted in the California cities of Monterey Park, Torrance, and Inglewood-included almost 5,000 children aged 6 to 72 months and assessed the ocular alignment, refractive error, and ocular structures.

Patients were recruited from 37 census tracts in the three cities and underwent clinical examinations that were age-specific, according to Dr. Varma. He is professor of ophthalmology and preventive medicine, and director of the glaucoma service and Ocular Epidemiology Center, Keck School of Medicine, University of Southern California, Los Angeles. Dr. Varma is also the principal investigator of MEPEDS.

The presence of amblyopia was determined using a predefined definition of a reduction in best-corrected visual acuity (BCVA) in the presence of a pre-determined amblyogenic factor. Strabismus was diagnosed based on the cover/uncover test at distance and near; Hirschberg testing was performed in cases in which cover testing was unsuccessful.

Strabismus was defined as constant or intermittent of any magnitude at distance and/or near fixation, and amblyopia was defined as a two-line difference in final BCVA between eyes, with 20/32 or worse in the weaker eye.

Dr. Varma reported that the overall prevalence of strabismus was 2.5%; esotropia was present in 1% of children in both ethnic groups, and exotropia was present in 1.5% in the Hispanic cohort and 1.6% in the African-American cohort. When stratified by gender, Dr. Varma and colleagues found no difference between boys and girls.

The overall prevalence of amblyopia was 2.6% in both ethnic groups. Unilateral anisometropia was seen in 2.6% and 1.9% of Hispanic and African-American children, respectively; unilateral strabismic amblyopia was seen in 1.6% and 1.1%, respectively. As with strabismus, no difference was seen when results were analyzed by gender.

The most important finding was that, when results were stratified by age, the investigators identified a trend toward increasing prevalence with increasing age for both strabismus and amblyopia, with older children more likely to develop the pathologies compared with younger patients, he said.

No significant difference was seen in the prevalence of both pathologies between the ethnic groups.

"The MEPEDS is the first evaluation of strabismus and amblyopia in those two ethnic groups," Dr. Varma said. "We found that the most common type of amblyopia is associated with anisometropic refractive error. Strabismus is likely to occur at an older age and less commonly associated with uncorrected visual acuity.

"The data offer insights into the approach and timing of screening," he concluded. "Amblyopia and strabismus can be detected at age 3, and screening at that age is likely to be beneficial if [the conditions are] treated."