Anisometropia is a condition in which each eye has a different refractive error, i.e. a different degree of short-sightedness, long-sightedness or astigmatism. Minor differences in optical power between the eyes are physiological and do not usually cause any problems. However, with larger differences (over 2 dioptres), this can lead to disturbances in binocular vision, difficulties with depth perception, headaches, and the development of reduced vision in one eye (amblyopia), particularly in children. Anisometropia may be congenital or develop with age, for example following surgery cataracts, when a lens of a different power is implanted in each eye. Correcting anisometropia can be difficult - glasses can produce different sized images (aniseikonia). In such cases, it is preferable to contact lenses or refractive surgery procedures. Early detection of anisometropia, especially in children, is crucial in preventing permanent visual impairment in the weaker eye.
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