In the<3-year-old cohort,( Birch and Holmes, 2010) 82% of amblyopia was associated with strabismus, 5% with anisometropia, and 13% with combined mechanisms. Overall, mean refractive error in the amblyopic eye was +4.52 D and in the fellow eye was +2.83D, but fellow eye refractive error was higher in the strabismic children (+3.54 D) and lower in the anisometropic children (+1.95 D). In the Pediatric Eye Disease Investigator Group (PEDIG) study, we assessed the clinical characteristics of 409 children age 3вЂ“6.9 years with moderate amblyopia who were enrolled in a multicenter randomized study of amblyopia treatment.( Pediatric Eye Disease Investigator Group, 2002a) Strabismus or anisometropia each accounted for about 40% of amblyopia, with just over 20% of amblyopia in children with both strabismus and anisometropia ( Figure 1). Two large studies have defined the clinical profile of amblyopic children.( Birch and Holmes, 2010 Pediatric Eye Disease Investigator Group, 2002a) Both studies included children with strabismic, anisometropic, or combined-mechanism amblyopia referred by multiple community- and university-based pediatric ophthalmologists. Our research studies on amblyopia have revealed that binocular dysfunction plays an important role in amblyopia and has laid the groundwork for a new approach for the development of more effective treatment. However, there are significant shortcomings to this approach to understanding and treating amblyopia. Thus, the mainstay of treatment for amblyopia has been patching of the normal fellow eye to improve the monocular function of the amblyopic eye. The predominant theory is that amblyopia results when there is a mismatch between the images to each eye one eye is favored while the information from the other eye is suppressed.( Harrad et al., 1996) Because amblyopia typically affects visual acuity in one eye, amblyopia is often considered to be a monocular disease.

The consequences of not identifying and treating strabismus and amblyopia early include permanent visual impairment, adverse effects on school performance, poor fine motor skills, social interactions, and self-image.( Choong et al., 2004 Chua and Mitchell, 2004 Horwood et al., 2005 OвЂ™Connor et al., 2010b OвЂ™Connor et al., 2009 Packwood et al., 1999 Rahi et al., 2006 Webber et al., 2008a, b) Importantly, permanent monocular visual impairment due to amblyopia is a risk factor for total blindness if the better eye is injured or if the fellow eye is affected by disease later in life.( Harrad and Williams, 2003) ( Wu and Hunter, 2006) Many affected children will suffer irreversible vision loss that could have been prevented. With 625 million children under the age of 5 years worldwide, more than 15 million may have amblyopia, and more than half of them will not be identified before they reach school age. Overall, results of the studies are consistent, with a mean prevalence of 2.8% for strabismus, 3.5% for anisometropia, and 2.4% for amblyopia. US = United States, UK = United Kingdom, N=Netherlands, S=Sweden, A=Australia

Binocular vision