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V. Dobson, J. M. Miller, C. E. Clifford-Donaldson, E. M. Harvey; The Relation Between Magnitude of Anisometropia (Spherical Equivalent and Astigmatic) and Amblyopia in a Population of Children With a High Prevalence of Astigmatism. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1424. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the relation between magnitude of anisometropia (spherical equivalent [SE] and astigmatic), and best-corrected interocular acuity difference (IAD), and stereoacuity (SA), in children who are members of a Native American Tribe with a high prevalence of astigmatism.
Subjects were 972 children 4-13 years of age who attended school on the Tohono O’odham Reservation and who did not have non-refractive ocular abnormalities, based on an eye examination, with cycloplegic refraction. Monocular best-corrected visual acuity was measured with ETDRS letter charts at 4 m and best-corrected SA was measured with the Randot Preschool Stereoacuity test at 40 cm. Results were examined for 4 groups: Control (CON) group: <0.25 diopter (D) SE anisometropia and < 0.25 D cylinder (cyl) anisometropia, Spherical Hyperopic Anisometropia (SHA): hyperopic SE in both eyes, ≥ 0.25 D SE anisometropia, and <1.00 D cyl anisometropia; Spherical Myopic Anisometropia (SMA): myopic SE in both eyes, ≥ 0.25 D SE anisometropia, and <1.00 D cyl anisometropia; and Cyl Anisometropia (CA): ≥ 0.25 D cyl anisometropia and <1.00 D SE anisometropia.
Visual acuity data were obtained from 969 children and stereoacuity data were obtained from 964 children. Mean CON (n=115) IAD was <1 logMAR line on the ETDRS chart. In the SHA group, mean IAD was not significantly different from CON IAD in children with 0.25 to <1.00 D (n=290) of SHA, but was significantly greater (>2 logMAR lines) in children with ≥ 1.0 D of SHA (n=15, p<0.001). In the SMA group, mean IAD was not significantly different from CON IAD for children with 0.25 to <1.00 D (n=83), or for children with ≥ 1.0 D (n=11) of SMA. In the CA group, mean IAD was not significantly different from CON IAD in children with 0.25 to <3.00 D (n=627) of CA, but was significantly greater (>2 logMAR lines) in children with ≥ 3.0 D of CA (n=8, p<0.001). For SHA, SMA, and CA groups, ≥ 0.50 D of anisometropia produced a significant reduction in average best-corrected SA.
The amount of anisometropia that results in amblyopia (a significant difference between eyes in best-corrected visual acuity) is less in children with a difference in hyperopic spherical refractive error between eyes than in children with a difference in cylindrical refractive error between eyes. However, even a small (≥ 0.50 D) amount of spherical hyperopic, spherical myopic, or cylindrical anisometropia is sufficient to disrupt best-corrected stereoacuity.
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