Anisometropia is a condition in which each of a person’s two eyes has a different refractive power. The specifics of this difference in refractive power could vary. In some cases, this could mean that one eye has a refractive power that is higher than normal, while the other eye has a refractive power that is lower than normal. In other words, one eye is near sighted or myopic, while the other eye is far sighted or hyperopic. In other cases, either both eyes may be near sighted or both eyes may be far sighted, but to different degrees. To a lay person this might seem like a minor problem, but the truth is that it can have some rather serious consequences.
In infants suffering from anisometropia, if the difference in refractive power is too great, the brain is unable to properly combine the two images as it normally would. Normally, the brain combines the two images that have been produced by two eyes of the same refractive power but from different angles, to give what we call a three dimensional image, in short, a sense of depth. With severe anisometropia, instead of doing this, the brain starts to use the images coming from only a single eye, while the signals coming from the other eye are ignored. Eventually, the child could turn effectively blind in one eye; mainly the eye whose images are being ignored.
In other cases, the difference in refractive power could also cause the sufferer to “see double”. This is a condition known as diplopia, and is essentially the result of the brain failing to properly combine the two different images. Anisometropia could also result in simple eyestrain, which in ophthalmological terms is known as asthenopia. This could lead to a variety of symptoms, ranging from headaches to red eyes. Blurred vision and double vision are also symptoms of eyestrain.
Anisometropia is sometimes not detected in infancy, because there are no obvious, clear signs at that stage in the condition. Once it is detected, spectacles or lenses are usually prescribed in order to correct the refractive power of the eyes. However, in some cases, simply bringing the two eyes to the same refractive power may not be enough. If the brain has already developed a preference for one eye, the child may need to use an eye patch on this eye. This will force the brain to use and develop the vision in the other eye.