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, over-representing children with vision disorders.
Methods
All children underwent comprehensive eye exams 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 single-surround HOTV letter protocol without correction, and retested with full cycloplegic correction when retest criteria were met. Unilateral amblyopia was defined as an inter-ocular difference in best-corrected VA ≥2 lines. 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 (ORs) and their 95% confidence intervals (95% CIs) estimated from logistic regression models.
Results
In this enriched sample of Head Start children (N=3869), 296 (7.7%) children had unilateral amblyopia, and 144 (3.7%) children had bilateral amblyopia. Presence of strabismus (p<0.0001), greater magnitude of significant refractive errors (myopia, hyperopia, astigmatism, and anisometropia, each p<0.00001) were independently associated with increased risk of unilateral amblyopia. Presence of strabismus, hyperopia ≥2.0 D, astigmatism ≥1.0 D, or anisometropia ≥0.5 D were present in 91% of children with unilateral amblyopia. Greater magnitude of astigmatism (p<0.0001) and of bilateral hyperopia (p<0.0001) were independently associated with increased risk of bilateral amblyopia. Bilateral hyperopia ≥3.0 diopters (D) or astigmatism ≥1.0 D were present in 76% of children with bilateral amblyopia.
Conclusion
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 study population, these results validated the findings from the Multi-ethnic Pediatric Eye Disease Study and Baltimore Pediatric Eye Disease Study.
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