同: ジオブター

WordNet

a unit of measurement of the refractive power of a lens which is equal to the reciprocal of the focal length measured in meters; used by oculists (同)dioptre

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ジオプトリー(レンズの屈折力の大きさを示す単位)

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/11/19 23:19:01」(JST)

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A dioptre (uk), or diopter (us), is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres (that is, 1/metres). It is thus a unit of reciprocal length. For example, a 3-dioptre lens brings parallel rays of light to focus at ¹⁄₃ metre. A flat window has an optical power of zero dioptres, and does not converge or diverge light.

Dioptres are also sometimes used for other reciprocals of distance, particularly radii of curvature and the vergence of optical beams. The usage was proposed by French ophthalmologist Ferdinand Monoyer in 1872, based on earlier use of the term dioptrice by Johannes Kepler.^[1]^[2]^[3]

The main benefit of using optical power rather than focal length is that the lensmaker's equation has the object distance, image distance, and focal length all as reciprocals. A further benefit is that when relatively thin lenses are placed close together their powers approximately add. Thus, a thin 2-dioptre lens placed close to a thin 0.5-dioptre lens yields almost the same focal length as a 2.5-dioptre lens would have.

Though the dioptre is based on the SI-metric system it has not been included in the standard so that there is no international name or abbreviation for this unit of measurement—within the international system of units, this unit for optical power would need to be specified explicitly as the inverse metre (m⁻¹). However most languages have borrowed the original name and some national standardization bodies like DIN specify a unit name (dioptrie, dioptria, etc.) and derived unit symbol "dpt".

In vision correction

The fact that optical powers are approximately additive enables an eye care professional to prescribe corrective lenses as a simple correction to the eye's optical power, rather than doing a detailed analysis of the entire optical system (the eye and the lens). Optical power can also be used to adjust a basic prescription for reading. Thus an eye care professional, having determined that a myopic (nearsighted) person requires a basic correction of, say, −2 dioptres to restore normal distance vision, might then make a further prescription of 'add 1' for reading, to make up for lack of accommodation (ability to alter focus). This is the same as saying that −1 dioptre lenses are prescribed for reading.

In humans, the total optical power of the relaxed eye is approximately 60 dioptres.^[4] The cornea accounts for approximately two-thirds of this refractive power (about 40 dioptres) and the crystalline lens contributes the remaining one-third (about 20 dioptres).^[4]) In focusing, the ciliary muscle contracts to reduce the tension or stress transferred to the lens by the suspensory ligaments. This results in increased convexity of the lens which in turn increases the optical power of the eye. As humans age, the amplitude of accommodation reduces from approximately 15 to 20 dioptres in the very young, to about 10 dioptres at age 25, to around 1 dioptre at 50 and over.

Convex lenses have positive dioptric value and are generally used to correct hyperopia (farsightedness) or to allow people with presbyopia (the limited accommodation of advancing age) to read at close range. Concave lenses have negative dioptric value and generally correct myopia (nearsightedness). Typical glasses for mild myopia will have a power of −1.00 to −3.00 dioptres, while over the counter reading glasses will be rated at +1.00 to +3.00 dioptres. Optometrists usually measure refractive error using lenses graded in steps of 0.25 dioptres.

Curvature

The dioptre can also be used as a measurement of curvature equal to the reciprocal of the radius measured in metres. For example, a circle with a radius of 1/2 metre has a curvature of 2 dioptres. If the curvature of a surface of a lens is C and the index of refraction is n, the optical power is φ = (n − 1)C. If both surfaces of the lens are curved, consider their curvatures as positive toward the lens and add them. This will give approximately the right result, as long as the thickness of the lens is much less than the radius of curvature of one of the surfaces. For a mirror the optical power is φ = 2C.

Relation to magnifying power

The magnifying power V of a simple magnifying glass is related to its optical power φ by

.

This is approximately the magnification observed when a person with normal vision holds the magnifying glass close to his or her eye.

References

^ Monoyer, F. (1872). "Sur l'introduction du système métrique dans le numérotage des verres de lunettes et sur le choix d'une unité de réfraction". Annales d'Oculistiques (in French). Paris. 68: 101.
^ Thomas, C. "Monoyer, Ferdinand". La médecine à Nancy depuis 1872 (in French). Retrieved 2011-04-26.
^ Colenbrander, August. "Measuring Vision and Vision Loss" (PDF). Smith-Kettlewell Institute. Retrieved 2009-07-10.
^ ^a ^b Najjar, Dany. "Clinical optics and refraction". Eyeweb. Retrieved 2008-03-25.

Greivenkamp, John E (2004). Field Guide to Geometrical Optics. SPIE Field Guides vol. FG01. Bellingham, Wash: SPIE. ISBN 978-0-8194-5294-8. OCLC 53896720.
Hecht, Eugene; Alfred, Zając (1987). Optics (2nd ed.). Reading, Mass: Addison–Wesley. ISBN 978-0-201-11609-0. OCLC 13761389.

UpToDate Contents

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English Journal

Influence of Patient Age at Surgery on Long-Term Corneal Astigmatic Change Subsequent to Cataract Surgery.

Hayashi K1, Ogawa S2, Manabe S2, Hirata A2.
American journal of ophthalmology.Am J Ophthalmol.2015 Jul;160(1):171-178.e1. doi: 10.1016/j.ajo.2015.04.015. Epub 2015 Apr 16.
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CHOROIDAL THICKNESS AND VOLUME IN A HEALTHY PEDIATRIC POPULATION AND ITS RELATIONSHIP WITH AGE, AXIAL LENGTH, AMETROPIA, AND SEX.

Herrera L1, Perez-Navarro I, Sanchez-Cano A, Perez-Garcia D, Remon L, Almenara C, Caramello C, Cristóbal JA, Pinilla I.
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Symmetrical Versus Asymmetrical PresbyLASIK: Results After 18 Months and Patient Satisfaction.

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Cornea.Cornea.2015 Jun;34(6):651-7. doi: 10.1097/ICO.0000000000000339.
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Excessive Corneal Flattening and Thinning After Corneal Cross-linking: Single-Case Report With 5-Year Follow-up.

Kymionis GD1, Tsoulnaras KI, Liakopoulos DA, Paraskevopoulos TA, Kouroupaki AI, Tsilimbaris MK.
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Japanese Journal

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Postural Stability Changes during Large Vertical Diplopia Induced by Prism Wear in Normal Subjects

Matsuo Toshihiko,Yamasaki Hanako,Yasuhara Hirotaka,Hasebe Kayoko
Acta Medica Okayama 67(3), 177-183, 2013-06
… To test the effect of double vision on postural stability, we measured postural stability by electric stabilometry before prism-wearing and immediately, 15, 30, and 60min after continuous prism-wearing with 6 prism diopters in total (a 3-prism-diopter prism placed with the base up in front of one eye and with the base down in front of the other eye) in 20 normal adult individuals with their eyes open or closed. …
NAID 120005295916

めがねのレンズ固定がレンズひずみに及ぼす影響

格内敏,徳田直子,金子弘,西村淳
実験力学 13(1), 93-99, 2013
… Three kinds of plastic lenses which are different in the lens diopter with aspect ratio of 1.4 are retained to the same frame and these lens strain are evaluated by experiments and finite element analysis. …
NAID 130004934782

めがねのレンズ度数に及ぼすレンズ固定力の影響 (2012年度年次講演会)

坂本康平,格内敏,阿保政義 [他]
日本実験力学会講演論文集 (12), 52-54, 2012
NAID 40019492040

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