Anisometropia means that the two eyes have different degrees of refractive error. This can mean that one eye is more nearsighted than the other, that one eye is farsighted while the other is nearsighted, or that one eye also has a stronger corneal curvature irregularity (astigmatism).
Small differences are normal and usually do not cause problems. Larger differences, however, can disrupt how the eyes work together. The brain then has difficulty forming a clear overall image from two very different pictures. This can result in headaches, rapid eye fatigue, uncertainty when reading, or impaired spatial perception.
In children, pronounced anisometropia is particularly important to detect. If it is not corrected in time, the brain may “suppress” the weaker eye—leading to reduced vision (amblyopia).
Anisometropia is usually treated with appropriately prescribed glasses or contact lenses, sometimes supplemented with vision therapy (occlusion therapy). This helps ensure that both eyes participate in seeing as evenly as possible.