Risk factors for amblyopia in the vision in preschoolers study

Abstract

Objective: To evaluate risk factors for unilateral amblyopia and for bilateral amblyopia in the Vision in Preschoolers (VIP) study.

Design: Multicenter, cross-sectional study.

Participants: Three- to 5-year-old Head Start preschoolers from 5 clinical centers, overrepresenting children with vision disorders.

Methods: All children underwent comprehensive eye examinations, including threshold visual acuity (VA), cover testing, and cycloplegic retinoscopy, performed by VIP-certified optometrists and ophthalmologists who were experienced in providing care to children. Monocular threshold VA was tested using a single-surround HOTV letter protocol without correction, and retested with full cycloplegic correction when retest criteria were met. Unilateral amblyopia was defined as an interocular difference in best-corrected VA of 2 lines or more. Bilateral amblyopia was defined as best-corrected VA in each eye worse than 20/50 for 3-year-olds and worse than 20/40 for 4- to 5-year-olds.

Main outcome measures: Risk of amblyopia was summarized by the odds ratios and their 95% confidence intervals estimated from logistic regression models.

Results: In this enriched sample of Head Start children (n = 3869), 296 children (7.7%) had unilateral amblyopia, and 144 children (3.7%) had bilateral amblyopia. Presence of strabismus (P<0.0001) and greater magnitude of significant refractive errors (myopia, hyperopia, astigmatism, and anisometropia; P<0.00001 for each) were associated independently with an increased risk of unilateral amblyopia. Presence of strabismus, hyperopia of 2.0 diopters (D) or more, astigmatism of 1.0 D or more, or anisometropia of 0.5 D or more were present in 91% of children with unilateral amblyopia. Greater magnitude of astigmatism (P<0.0001) and bilateral hyperopia (P<0.0001) were associated independently with increased risk of bilateral amblyopia. Bilateral hyperopia of 3.0 D or more or astigmatism of 1.0 D or more were present in 76% of children with bilateral amblyopia.

Conclusions: Strabismus and significant refractive errors were risk factors for unilateral amblyopia. Bilateral astigmatism and bilateral hyperopia were risk factors for bilateral amblyopia. Despite differences in selection of the study population, these results validated the findings from the Multi-Ethnic Pediatric Eye Disease Study and Baltimore Pediatric Eye Disease Study.

Figure 1

The percent of unilateral amblyopia by various levels of refractive error for myopia (A), hyperopia (B), Astigmatism (C) and Anisometropia (D) was presented. The refractive error in the most negative merdian of the most myopic eye was used for myopia; most positive meridian of the most hyperopic eye was used for hyperopia; the absolute cylinder in the more astigmatistic eye was used for astigmatism; and the inter-ocular difference of spherical equivalent (SE) was used for anisometropia. The percent of unilateral amblyopia by levels of refractive error was fitted by the locally weighted scatterplot smoothing (LOWESS) curve.

Figure 2

The percent of bilateral amblyopia by various levels of refractive error for astigmatism (A), hyperopia (B) was presented. The absolute cylinder in the less astigmatistic eye was used for astigmatism; and the spherical equivalent (SE) in the less hyperopic eye was used for hyperopia. The percent of bilateral amblyopia by levels of refractive error was fitted by the locally weighted scatterplot smoothing (LOWESS) curve.