Refractive error

Ametropia ( from Ancient Greek ἀμετρία ametría "imbalance " and ὤψ ops " eye") - misleading called " refractive error " - referred to in the medical optics the state of an eyeball that is not sharply defined an optically lying at infinity subject in a relaxed accommodation on the retina. It is the antonym of emmetropia.

In contradiction to that of the term " refractive error " suggested inaccuracy is the fact that the vast majority of human eyes is ametrop. It is therefore in the ametropia usually not an abnormal condition, but rather a normal variant.

Forms of ametropia

Hyperopia, farsightedness, hyperopia

As hyperopic ametropia is referred to, in the image of lying in the optically infinite object and parallel incident light rays come to lie in a relaxed accommodation behind the retina. The majority of the human eye is hyperopic. The average refraction of the human eye is about 0.5 dpt.

Myopia, myopia

As myopia ametropia is referred to, in the image of lying at infinity object comes to rest in a relaxed accommodation in front of the retina.

Hyperopia and myopia are called " axis ametropias " summarized. Among these, myopia is predominant.

Astigmatism, astigmatism

When astigmatism is defined as the state of an eyeball from its plane of incidence are refracted to different degrees depending on the parallel incident light rays. The levels usually perpendicular to each other with the maximum and minimum power. As strength of the astigmatism, the refractive power difference between these two levels is specified. An astigmatism up to 0.5 D is normal. Astigmatism, in which the planes are not associated with the maximum and minimum power perpendicular referred to as " irregular " astigmatism.

More ametropias

Theoretically possible and rarely encountered are ametropia in which incident light rays are parallel to their distance from the optical axis not only broken depending on their plane of incidence but also on different. Such ametropia may arise as a result of diseases of the cornea (such as keratoconus ), personal injury or eye surgery (eg, penetrating keratoplasty ).

Correction of ametropia

Ametropia may have the consequence that the eye does not reach its full vision without correction. For correction are eyeglasses, contact lenses and refractive surgery. With a pair of glasses can be corrected axis ametropia and regular astigmatism. Contact lenses complement this range to the irregular astigmatism and in appropriate cases the further ametropia. Refractive surgery can correct high ametropia axis and irregular corneal situations under suitable conditions depending on the used method. Here, however, there are numerous limitations.