The Changing Natural History of Anisometropia: A Scoping Review
Bruce J W Evans1, Rakhee Shah2, Natalia Vlasak3
1Optometry and Visual Sciences at City St George's, University of London, London, UK. bruce.evans.1@city.ac.uk.
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.
