Aims/background: In a previous study longitudinal changes of anisometropia were investigated. It was shown that anisometropia arises and vanishes during the emmetropization process and that the associated risk for amblyopia is low. The aim of this study was to follow acuity and refraction longitudinally in children with marked anisometropia at 1 year of age.

Methods: Refractive errors and visual acuity were estimated every sixth month for a selected group of 20 children with marked anisometropia > or = 3.0 D (spherical equivalent) at 1 year of age from approximately 3 to 10 years of age.

Results: The children could be classified into three groups. In six subjects the anisometropia increased (mean 1.4 D) and they all developed amblyopia. The remaining children could be classified into two groups of equal size. One group developed no amblyopia and the anisometropia decreased with a mean of 3.0 D. The seven remaining children developed amblyopia and/or strabismus; the mean anisometropia decrease was 1.2 D.

Conclusion: Anisometropia at 1 year of age that is larger or equal to 3.0 D will in 90% of the cases still be there at 10 years of age. There is a substantial risk of this group developing amblyopia (60%).