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S. H. Sharbini, K. A. Rose, G. Burlutsky, P. Mitchell, Sydney Childhood Eye Study; Natural History of Anisometropia and Its Association With Amblyopia. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4752.
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To examine the natural history of anisometropia and its association with amblyopia in a population-based random cluster sample of 6- and 12-year-old students.
The Sydney Myopia Study randomly selected 55 primary and secondary schools, stratified by socio-economic status (SES); 4069 children (70% response rate) were examined. Cycloplegic autorefraction, LogMAR visual acuity, cover tests (cover/uncover alternate, prism bar) at near and distance were performed. Anisometropia was defined by the spherical equivalent [SE = spherical refraction + (0.5 X cylindrical refraction)] and an astigmatic cylinder (AST) difference between the right and left eye of >1.0 dioptre. Amblyopia was defined as best corrected visual acuity in the worse eye less than 6/12 Snellen equivalent and/or a two line difference between the two eyes. Cases included those present at time of examination, as well as those reported by parents, and confirmed by a history of occlusion therapy.
Anisometropia was present in 3.8% (n = 155) of the population and of these 31.4% were amblyopic. There was a significant difference in the prevalence of anisometropia in the 6-year-old (2.5%) compared with the 12-year-old (4.7%) children (p = 0.0002). There were more amblyopic cases in the 6-year-olds (41.9%) than the 12-year-olds (27.9%).The number of amblyopic cases significantly increased with increasing degrees of anisometropia in 1.0D steps >1.0D (23.7%), >2.0D (46.7%), >3.0D (66.7%) and >4.0D (80.0%) (p < 0.0001).There was a marked increase in cases of amblyopia when astigmatic refraction increased from 2.0D to 3.0D (10.8% to 50.0%, respectively), a trend that continued with increasing refractive difference (p < 0.0001). The most frequent type of anismometropia was myopic anismoetropia (46.8%) and the least common was astigmatic anisometropia (21.2%).
Our study showed that the prevalence of anisometropia was higher in the older than the younger group. 1D difference of anisometropia significantly increased the risk of developing amblyopia. Astigmatic anisometropia degree of 3Ds seemed to show a marked increase in the number of amblyopic cases.
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