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Anisometropia: Short-sighted in one eye and long-sighted in the other

disposable contact lens blister packs for anisometropia

It's unusual, but a person can indeed be nearsighted in one eye and farsighted in the other. There are two medical terms used to describe this condition: anisometropia and antimetropia.

Anisometropia is the condition where the two eyes have significantly different refractive (light-bending) powers. If your optician says you have anisometropia, the lens power for one eye on your eyeglass prescription usually will differ from the lens power for the other eye by two diopters or more.

In anisometropia, both eyes may be shortsighted, both may be longsighted, or one eye is shortsighted and the other is longsighted — a more specific condition called antimetropia.

Though antimetropia technically is the more accurate term when describing one eye being shortsighted and the other being longsighted, many opticians choose to use the term anisometropia for this condition.

Anisometropia symptoms

A person with anisometropia or antimetropia will see noticeably unequal blur in the two eyes at different distances. Also, it’s common for uncorrected anisometropia to cause poor depth perception, headaches, dizziness and even nausea.

In many cases, the brain will quickly learn to favour the eye with less refractive error to reduce these symptoms, which can result in the development of amblyopia in the other eye.

When unequal refractive errors are corrected with spectacles, a person with anisometropia will notice that objects seen by one eye will look larger or smaller than the same objects viewed by the other eye. This difference in image sizes is called aniseikonia. This, too, can cause problems with depth perception, headaches, dizziness and visual discomfort.

Treatment of anisometropia

Early diagnosis and treatment of anisometropia are critical so the brain doesn't ignore the weaker eye and cause irreversible amblyopia. Routine children's eye exams for kids in nursery and junior school are essential to rule out anisometropia and ensure normal visual development.

Since contact lenses are very thin and rest directly on the surface of the eye, they cause little or no aniseikonia and can sometimes provide more comfortable, natural-appearing vision than spectacles.

LASIK is another good option to correct significantly dissimilar refractive errors in the two eyes and avoid aniseikonia. However, this option should be considered only after the refractive errors (particularly the shortsightedness) are stable — generally after age 20.

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