|Physical quantity (s)||Refractive power|
|In SI units|
Diopter ( ancient Greek διά dia , German , pass ' and ὄψις opsis , German , seeing' , plural: diopter), the unit of measure for the refractive power (rarely also: refractive index ) of optical systems and represents the reciprocal of the length unit meters represents . Your unit symbol in Germany is dpt .
Relation to the focal length
The refractive power is the reciprocal of the focal length :
Convex lenses have positive power and concave lenses have negative power.
The unit diopter is used as a legal unit in the EU and Switzerland to indicate the refractive power of optical systems, especially in ophthalmic optics . The optical system can be an optical lens , a curved mirror or an eye .
At the suggestion of the French ophthalmologist Ferdinand Monoyer , diopter was introduced into ophthalmic optics in 1872 . The refractive power of the normally sighted, healthy human eye in the accommodationless state is about 59 to 60 D (corresponding to a focal length of about 16.6 mm) and can be enlarged to adapt to smaller viewing distances; this ability to adapt is age-dependent and already declines in youth.
Converging lenses are used to correct farsightedness , diverging lenses correcting myopia and toric lenses to correct a astigmatism . The refractive power is also the parameter of a spectacle lens or an eyepiece with diopter compensation . The larger it is, the stronger the correction of the ametropia .
- Reciprocal value of the distance (in m) at which you want to read your newspaper
- Reciprocal value of the distance (in m) at which one can still see clearly
- gives the refractive power of the reading glasses .
Example: reading distance ⅓ m ≙ 3.0 dpt; minimum visual range: ½ m ≙ 2.0 dpt; so reading glasses of 3.0 dpt - 2.0 dpt = 1.0 dpt (i.e. a converging lens) are required.
- Units implementing ordinance to the law on units in metrology and time determination
- Ferdinand Monoyer: Sur l'introduction du système métrique dans le numérotage des verres de lunettes et sur le choix d'une unité de refraction . In: Annales d'Oculistiques . tape 68 . Paris 1872, p. 101 (French).
- Herbert Kaufmann (Ed.): Strabismus . 3. Edition. Georg Thieme, Stuttgart et al. 2004, ISBN 3-13-129723-9 .
- accommodation. In: Lexicon of Biology. Spectrum, accessed November 6, 2016 .