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Abstract

Purpose
To review literature on anisometropia, concentrating on diagnostic criteria, contemporary prevalence and progression with regard to the changing distribution of refractive errors in many countries. Also, to consider anisometropia with respect to myopia and hyperopia control, regions/race/ethnicity, effects on visual function and associated conditions.

Methods
Scoping review based on searches of PubMed, Embase and Cochrane databases.

Results
Various diagnostic criteria have been used for anisometropia, most commonly a SER difference ≥1.00 D. Anisometropia is more common in people with higher refractive errors, and therefore, its prevalence changes with the frequency distribution of refractive errors. Anisometropia is traditionally mostly associated with hyperopia, and this is still the case in some populations. In East and South-East Asia, the rapid increase in myopia has resulted in increased anisometropia. This is associated with impaired stereopsis and binocularity, as well as increased rates of strabismus and amblyopia. When anisometropia is corrected with spectacles, there is an increased risk of spectacle non-tolerance arising from aniseikonia (different image sizes in each eye) and prismatic effects. Contact lenses alleviate most of the problems associated with anisometropia, but are under-prescribed for this condition. The increased association between anisometropia and myopia has led to trials of myopia control interventions, which show promise for reducing anisometropia in myopic cases. However, since myopia in one eye is often a precursor of bilateral myopia, the likelihood of pre-myopia in the non-myopic eye should be considered.

Conclusions
The association between anisometropia and the magnitude of refractive error means that in populations with a high prevalence of myopia, anisometropia has largely become a feature of that refractive error, in contrast to the traditional association with hyperopia. This has important implications for myopia control. Vision screening and/or routine professional eye care are recommended because anisometropia is under-diagnosed.

Publication Type:	Article
Additional Information:	This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Publisher Keywords:	Amblyopia, Aniseikonia, Anisometropia, Myopia control, Refractive error, Stereopsis
Subjects:	R Medicine > RE Ophthalmology
Departments:	School of Health & Medical Sciences School of Health & Medical Sciences > Department of Optometry & Visual Science
SWORD Depositor:	Symplectic Administrator

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