Refraction anomaly
In ophthalmology and optometry , the term refraction describes the refractive power of an optical arrangement (e.g. a lens) with which the eye can sharply image a point at an infinite distance on the retina without having to accommodate . If this refractive index is 0.00 D (unit: dioptre ), one speaks of the state of emmetropia , if not, of that of ametropia . As a result, the term refraction anomaly is a kind of pleonasm , since the state “Refraction ≠ 0” already describes the anomaly.
Nonetheless, in common usage the term refraction anomaly is equated with an optical ametropia and thus represents a different term for ametropia . This includes hyperopia (also: hypermetropia or clarity), myopia (nearsightedness) and astigmatism ( astigmatism or astigmatism ). The presbyopia (age-related farsightedness) does not belong to this group.
Refraction anomalies can be measured very precisely with various objective methods ( refractometry ), the results of which usually form the basis for determining the subjective refraction and finally the prescription of optical corrections ( glasses , contact lenses, etc.).
Further meaning
In astronomy and geodesy , refraction anomalies are not directly detectable deviations from the normal refraction of rays in the atmosphere. The causes are mostly horizontal temperature gradients in air layers close to the ground, but also on structures - for example a side refraction in the tunnel or the hall refraction at the gap in an observatory dome.
See also
literature
- Herbert Kaufmann: Strabismus. 3rd completely revised and expanded edition, Thieme, Stuttgart December 10, 2003, ISBN 978-3131297235 .
- Theodor Axenfeld (founder), Hans Pau (ed.): Textbook and atlas of ophthalmology. 12th, completely revised edition. Gustav Fischer, Stuttgart et al. 1980, ISBN 3-437-00255-4 .
- Wolfgang Torge : Geodesy (2nd edition), Chapter 5.1 Atmospheric refraction . DeGruyter, Berlin 2003.
