Amblyopia Risk in Kids: Are New Screening Thresholds Needed?

Jennifer Garcia

October 23, 2013

Using a larger sample size than previously reported, a new study validates the association between the presence of strabismus and significant refractive errors and the risk for unilateral amblyopia in preschoolers. The study, published online October 21 in Ophthalmology, also identifies thresholds of refractive error associated with the highest risk for amblyopia.

Among the 3869 children (aged 3 - 5 years) evaluated, researchers found unilateral and bilateral amblyopia in 7.7% (n = 296) and 3.7% (n = 144) of them, respectively. Strabismus (P < .0001) and greater magnitude of refractive errors such as myopia, hyperopia, astigmatism, and anisometropia were independently associated with an increased risk for unilateral amblyopia (P < .00001 for each). Researchers also found that astigmatism (P < .0001) and bilateral hyperopia (P < .0001) were independently associated with an increased risk for bilateral amblyopia.

Gui-shuang Ying, PhD, from the University of Pennsylvania, Philadelphia, and colleagues evaluated children from a variety of racial and ethnic groups enrolled from 5 clinical centers across the United States. The children underwent comprehensive eye examinations, including threshold visual acuity, cycloplegic retinoscopy, and cover testing, performed by study-certified ophthalmologists and optometrists.

"In our study, we found that most (87%) unilateral amblyopia cases had significant refractive error (hyperopia ≥2.0 D, astigmatism ≥1.0 D, anisometropia ≥0.5 D)," the authors write. Previous population-based pediatric eye disease studies such as the Multi-Ethnic Pediatric Eye Disease Study and Baltimore Pediatric Eye Disease Study have found similar results.

In addition, Dr. Ying and colleagues found an increased risk for the development of amblyopia at threshold levels below those recommended at present by expert opinions or professional organizations. "Among 296 children with unilateral amblyopia in this study, only 173 (58.5%) had refractive error meeting the American Association for Pediatric Ophthalmology and Strabismus criteria," note the study authors.

The authors acknowledge several study limitations such as the overrepresentation of children with visual disorders and subsequent overestimation of the absolute risk for amblyopia; however, these findings were similar to those estimated from population-based studies. In addition, the risk factors for amblyopia evaluated in this study were not comprehensive, and not all the visual acuity thresholds for defining amblyopia were measured with best correction.

Despite these limitations, the study authors note that these findings should prompt reevaluation of current guidelines for the screening of amblyopia to promptly identify preschool-aged children at high risk for this disorder.

Funding for this study was provided by grants from the National Eye Institute and the National Institutes of Health. The authors have disclosed no relevant financial relationships.

Ophthalmology. Published October 21, 2013. Abstract

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