If the difference between the eyes is up to 3 diopters, iseikonic lenses can compensate. At a difference of 3 diopters the lenses would however be very visibly different — one lens would need to be at least 3 mm thicker and have a base curve increased by 7.5 spheres. Example
Consider a pair of spectacles to correct for myopia with a prescription of −1.00 m−1 in one eye and −4.00 m−1 in the other.
Secondly, different criteria have been employed to define anisometropia, and the boundary between anisometropia and isometropia depend on their definition.Several studies have found that anisometropia occurs more frequently and tends to be more severe for persons with high ametropia, and that this is particularly true for myopes. Anisometropia follows a U-shape distribution according to age: it is frequent in infants aged only a few weeks, is more rare in young children, comparatively more frequent in teenagers and young adults, and more prevalent after presbyopia sets in, progressively increasing into old age.One study estimated that 6% of those between the ages of 6 and 18 have anisometropia.Notwithstanding research performed on the biomechanical, structural and optical characteristics of anisometropic eyes, the underlying reasons for anisometropia are still poorly understood.Anisometropic persons who have strabismus are mostly far-sighted, and almost all of these have (or have had) esotropia. However, there are indications that anisometropia influences the long-term outcome of a surgical correction of an inward squint, and vice versa. More specifically, for patients with esotropia who undergo strabismus surgery, anisometropia may be one of the risk factors for developing consecutive exotropia and poor binocular function may be a risk factor for anisometropia to develop or increase. References


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