Epidemiology

The prevalence of amblyopia in children is 2% to 5% in the UK.[8][9][10]​​​​ Boys and girls are affected equally. A 2019 population-based observational study of amblyopia and refractive error in schoolchildren in Ireland and Northern Ireland found that amblyopia prevalence was significantly lower in Northern Ireland (1%) than in Ireland (4.5%). The prevalence of two key amblyogenic factors, strabismus and anisometropia, did not differ significantly between the two cohorts. However, children living in Ireland, where school-entry vision screening coverage is less comprehensive, free eye care is less accessible, and long waiting times exist, had a higher prevalence of amblyopia, which was associated with socioeconomic disadvantage.[11] The multi-ethnic paediatric eye disease study from Los Angeles County showed that the prevalence of amblyopia varies with ethnicity, with a prevalence of 1.5% among African-American children and 2.6% among Hispanic or Latino children.[5] A population study of inner-city Baltimore youth found a prevalence of 3.9%.[12]

In a population-based study from the UK, 3.6% of 7-year-old children had past/present amblyopia, and the number of cases tended to increase as the social class decreased.[13] Higher rates have been recorded from children in Canada (4.7%) and Taiwan (5%).[14][15] Lower rates have been recorded from children in Northern Ireland (1.13%), Iran (1.7%), Australia (0.7%), and Japan (0.20%).[16][17][18][19]

Most cases of amblyopia in the multi-ethnic paediatric eye disease study from the US were attributable to refractive error (about 75%).[5] Anisometropic amblyopia is the most common subtype of refractive amblyopia.[6] The next most common cause of amblyopia is strabismus.[6] However, other studies have found strabismus to be a more common subtype of amblyopia than is anisometropia.[7] Such differences may be explained by the populations studied (eye clinic patients versus population-based surveys) and the way in which studies define amblyopia. In addition, strabismus and anisometropia frequently co-exist (combined-mechanism amblyopia); thus, classification into one category or another is arbitrary. Form-deprivation amblyopia is least common but tends to be the most visually devastating, in part because it often presents in infancy.[6] Amblyopia prevalence does not vary with age.[5] However, detection of amblyopia is more challenging in young pre-verbal children than in older children. Anisometropic amblyopia tends to be diagnosed later than strabismic amblyopia, because anisometropic children exhibit signs of a vision problem only when monocular visual acuity is tested.[6][7]

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