n.

非点収差、乱視

WordNet

(ophthalmology) impaired eyesight resulting usually from irregular conformation of the cornea; common in nearsighted people (同)astigmia
(optics) defect in an optical system in which light rays from a single point fail to converge in a single focal point (同)astigmia

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乱視

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/12/28 19:22:17」(JST)

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An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different focus. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- (a-) meaning "without" and στίγμα (stigma), "a mark, spot, puncture".^[1]

Forms of astigmatism

Astigmatism

There are two distinct forms of astigmatism. The first is a third-order aberration, which occurs for objects (or parts of objects) away from the optical axis. This form of aberration occurs even when the optical system is perfectly symmetrical. This is often referred to as a "monochromatic aberration", because it occurs even for light of a single wavelength. This terminology may be misleading, however, as the amount of aberration can vary strongly with wavelength in an optical system.

The second form of astigmatism occurs when the optical system is not symmetric about the optical axis. This may be by design (as in the case of a cylindrical lens), or due to manufacturing error in the surfaces of the components or misalignment of the components. In this case, astigmatism is observed even for rays from on-axis object points. This form of astigmatism is extremely important in vision science and eye care, since the human eye often exhibits this aberration due to imperfections in the shape of the cornea or the lens.

Third-order astigmatism

Page explaining and illustrating astigmatism^[2]

In the analysis of this form of astigmatism, it is most common to consider rays from a given point on the object, which propagate in two special planes. The first plane is the tangential plane. This is the plane which includes both the object point being considered and the axis of symmetry. Rays that propagate in this plane are called tangential rays. Planes that include the optical axis are meridional planes. It is common to simplify problems in radially-symmetric optical systems by choosing object points in the vertical ("y") plane only. This plane is then sometimes referred to as the meridional plane.

The second special plane is the sagittal plane. This is defined as the plane, orthogonal to the tangential plane, which contains the object point being considered and intersects the optical axis at the entrance pupil of the optical system. This plane contains the chief ray, but does not contain the optic axis. It is therefore a skew plane, in other words not a meridional plane. Rays propagating in this plane are called sagittal rays.

In third-order astigmatism, the sagittal and transverse rays form foci at different distances along the optic axis. These foci are called the sagittal focus and the transverse focus, respectively. In the presence of astigmatism, an off-axis point on the object is not sharply imaged by the optical system. Instead, sharp lines are formed at the sagittal and transverse foci. The image at the transverse focus is a short line, oriented in the direction of the sagittal plane; images of circles centered on the optic axis, or lines tangential to such circles, will be sharp in this plane. The image at the sagittal focus is a short line, oriented in the tangential direction; images of spokes radiating from the center are sharp at this focus. In between these two foci, a round but "blurry" image is formed. This is called the medial focus or circle of least confusion. This plane often represents the best compromise image location in a system with astigmatism.

The amount of aberration due to astigmatism is proportional to the square of the angle between the rays from the object and the optical axis of the system. With care, an optical system can be designed to reduce or eliminate astigmatism. Such systems are called anastigmats.

Astigmatism in systems that are not rotationally symmetric

Blur from astigmatic lens at different distances.

If an optical system is not axisymmetric, either due to an error in the shape of the optical surfaces or due to misalignment of the components, astigmatism can occur even for on-axis object points. This effect is often used deliberately in complex optical systems, especially certain types of telescope.

In the analysis of these systems, it is common to consider tangential rays (as defined above), and rays in a meridional plane (a plane containing the optic axis) perpendicular to the tangential plane. This plane is called either the sagittal meridional plane or, confusingly, just the sagittal plane.

Ophthalmic astigmatism

In optometry and ophthalmology, the vertical and horizontal planes are identified as tangential and sagittal meridians, respectively. Ophthalmic astigmatism is a refraction error of the eye in which there is a difference in degree of refraction in different meridians. It is typically characterized by an aspherical, non-figure of revolution cornea in which the corneal profile slope and refractive power in one meridian is less than that of the perpendicular axis.

Astigmatism causes difficulties in seeing fine detail. Astigmatism can be often corrected by glasses with a lens that has different radii of curvature in different planes (a cylindrical lens), contact lenses, or refractive surgery.^[3]

Astigmatism is quite common. Studies have shown that about one in three people suffers from it.^[4]^[5]^[6] The prevalence of astigmatism increases with age.^[7] Although a person may not notice mild astigmatism, higher amounts of astigmatism may cause blurry vision, squinting, asthenopia, fatigue, or headaches.^[8]^[9]^[10]

There are a number of tests that are used by ophthalmologists and optometrists during eye examinations to determine the presence of astigmatism and to quantify the amount and axis of the astigmatism.^[11] A Snellen chart or other eye chart may initially reveal reduced visual acuity. A keratometer may be used to measure the curvature of the steepest and flattest meridians in the cornea's front surface.^[12] Corneal topography may also be used to obtain a more accurate representation of the cornea's shape.^[13] An autorefractor or retinoscopy may provide an objective estimate of the eye's refractive error and the use of Jackson cross cylinders in a phoropter may be used to subjectively refine those measurements.^[14]^[15]^[16] An alternative technique with the phoropter requires the use of a "clock dial" or "sunburst" chart to determine the astigmatic axis and power.^[17]^[18]

Astigmatism may be corrected with eyeglasses, contact lenses, or refractive surgery. The planning and analysis of astigmatism treatment in corneal, cataract, and refractive surgery has been outlined by the American National Standards Institute, and was originally described by Australian ophthalmologist Noel A. Alpins in his Alpins Method of astigmatism analysis. Various considerations involving ocular health, refractive status, and lifestyle frequently determine whether one option may be better than another. In those with keratoconus, toric contact lenses often enable patients to achieve better visual acuities than eyeglasses. If the astigmatism is caused by a problem such as deformation of the eyeball due to a chalazion, treating the underlying cause will resolve the astigmatism.

Misaligned or malformed lenses and mirrors

Grinding and polishing of precision optical parts, either by hand or machine, typically employs significant downward pressure, which in turn creates significant frictional side pressures during polishing strokes that can combine to locally flex and distort the parts. These distortions generally do not possess figure-of-revolution symmetry and are thus astigmatic, and slowly become permanently polished into the surface if the problems causing the distortion are not corrected. Astigmatic, distorted surfaces potentially introduce serious degradations in optical system performance.

Surface distortion due to grinding or polishing increases with the aspect ratio of the part (diameter to thickness ratio). To a first order, glass strength increases as the cube of the thickness. Thick lenses at 4:1 to 6:1 aspect ratios will flex much less than high aspect ratio parts, such as optical windows, which can have aspect ratios of 15:1 or higher. The combination of surface or wavefront error precision requirements and part aspect ratio drives the degree of back support uniformity required, especially during the higher down pressures and side forces during polishing. Optical working typically involves a degree of randomness that helps greatly in preserving figure-of-revolution surfaces, provided the part is not flexing during the grind/polish process.

Deliberate astigmatism in optical systems

Compact disc players use an astigmatic lens for focusing. When one axis is more in focus than the other, dot-like features on the disc project to oval shapes. The orientation of the oval indicates which axis is more in focus, and thus which direction the lens needs to move. A square arrangement of only four sensors can observe this bias and use it to bring the read lens to best focus, without being fooled by oblong pits or other features on the disc surface.

Some telescopes use deliberately astigmatic optics.^[19]

References

^ Harper, Douglas (2001). "Online Etymology Dictionary". Retrieved 2007-12-29.
^ Frederic Eugene Wright (1911). The Methods of Petrographic-microscopic Research, Their Relative Accuracy and Range of Application. Carnegie institution of Washington.
^ "Astigmatism Laser Eye Surgery". The Irish Times.
^ Kleinstein RN, Jones LA, Hullett S, Kwon S, et al. (2003). "Refractive Error and Ethnicity in Children". Arch Ophthalmol. 121 (8): 1141–7. doi:10.1001/archopht.121.8.1141. PMID 12912692.
^ Garcia CA, Oréfice F, Nobre GF, Souza Dde B, Rocha ML, Vianna RN (2005). "[Prevalence of refractive errors in students in Northeastern Brazil.]". Arq Bras Oftalmol (in Portuguese) 68 (3): 321–5. doi:10.1590/S0004-27492005000300009. PMID 16059562.
^ Bourne RR, Dineen BP, Ali SM, Noorul Huq DM, Johnson GJ (June 2004). "Prevalence of refractive error in Bangladeshi adults: results of the National Blindness and Low Vision Survey of Bangladesh". Ophthalmology 111 (6): 1150–60. doi:10.1016/j.ophtha.2003.09.046. PMID 15177965.
^ Asano K, Nomura H, Iwano M, et al. (2005). "Relationship between astigmatism and aging in middle-aged and elderly Japanese". Jpn. J. Ophthalmol. 49 (2): 127–33. doi:10.1007/s10384-004-0152-1. PMID 15838729.
^ Eyetopics.com
^ Medicinenet.com
^ Hipusa.com
^ Hipusa.com
^ Stlukeseye.com
^ Emedicine.com
^ Graff T (June 1962). "[Control of the determination of astigmatism with the Jackson cross cylinder.]". Klin Monatsblatter Augenheilkd Augenarztl Fortbild (in German) 140: 702–8. PMID 13900989.
^ Del Priore LV, Guyton DL (November 1986). "The Jackson cross cylinder. A reappraisal". Ophthalmology 93 (11): 1461–5. doi:10.1016/s0161-6420(86)33545-0. PMID 3808608.
^ Brookman KE (May 1993). "The Jackson crossed cylinder: historical perspective". J Am Optom Assoc 64 (5): 329–31. PMID 8320415.
^ Quantumoptical.com
^ Nova.edu
^ Sacek, Vladimir (July 14, 2006). "Telescope astigmatism". Amateur Telescope Optics. Archived from the original on 19 September 2008. Retrieved Oct 16, 2008.

Greivenkamp, John E. (2004). Field Guide to Geometrical Optics. SPIE Field Guides vol. FG01. SPIE. ISBN 0-8194-5294-7.
Hecht, Eugene (1987). Optics (2nd ed.). Addison Wesley. ISBN 0-201-11609-X.

External links

Astigmatism Articles
Paul van Walree's Astigmatism and field curvature

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 成人における視覚障害：屈折障害と老視 visual impairment in adults refractive disorders and presbyopia
2. 小児における屈折異常 refractive errors in children
3. レーザー屈折矯正手術 laser refractive surgery
4. Overview of contact lenses
5. Amblyopia in children: Classification, screening, and evaluation

English Journal

Intravitreal bevacizumab for retinopathy of prematurity: refractive error results.

Harder BC, Schlichtenbrede FC, von Baltz S, Jendritza W, Jendritza B, Jonas JB.SourceDepartment of Ophthalmology, Medical Faculty Mannheim, Ruprecht-Karls-University Heidelberg, Heidelberg, Germany.
American journal of ophthalmology.Am J Ophthalmol.2013 Jun;155(6):1119-1124.e1. doi: 10.1016/j.ajo.2013.01.014. Epub 2013 Mar 12.
PURPOSE: To evaluate refractive error in infants who underwent intravitreal bevacizumab injection for treatment of threshold retinopathy of prematurity (ROP).DESIGN: Retrospective nonrandomized interventional comparative study.METHODS: The study group included all infants who consecutively received
PMID 23490192

Racial variations in the prevalence of refractive errors in the United States: the multi-ethnic study of atherosclerosis.

Pan CW, Klein BE, Cotch MF, Shrager S, Klein R, Folsom A, Kronmal R, Shea SJ, Burke GL, Saw SM, Wong TY.SourceSaw Swee Hock School of Public Health, National University of Singapore, Singapore.
American journal of ophthalmology.Am J Ophthalmol.2013 Jun;155(6):1129-1138.e1. doi: 10.1016/j.ajo.2013.01.009. Epub 2013 Feb 27.
PURPOSE: To describe racial variations in the prevalence of refractive errors among adult white, Chinese, Hispanic, and black subjects in the United States.DESIGN: Cross-sectional data from a prospective cohort study-the Multi-Ethnic Study of Atherosclerosis (MESA).METHODS: A total of 6000 adults ag
PMID 23453694

Cocaine-assisted epithelial debridement for the treatment of anterior basement membrane dystrophy.

Sayegh RR, Kouyoumjian PB, Vedula GG, Nottage JM, Nirankari VS.Source*Department of Ophthalmology and Visual Sciences, University of Maryland School of Medicine, Baltimore, MD; †Massachusetts Eye & Ear Infirmary, Harvard Medical School, Boston, MA; ‡Private Practice, Hawthorne, CA; §Cleveland Clinic Florida, Weston, FL; and ¶Eye Consultants of Maryland, Baltimore, MD.
Cornea.Cornea.2013 Jun;32(6):889-92. doi: 10.1097/ICO.0b013e318288ad4d.
PURPOSE: : To describe a method of epithelial debridement with the adjunctive use of topical cocaine for the treatment of symptomatic anterior basement membrane dystrophy (ABMD).METHODS: : Retrospective consecutive chart review. Symptomatic patients with ABMD were treated with 4% topical cocaine fol
PMID 23591147

Agreement between refractive and corneal astigmatism in pseudophakic eyes.

Tejedor J, Guirao A.Source*Department of Ophthalmology, Hospital Ramón y Cajal, Madrid, Spain †Faculty of Medicine, Universidad Autónoma de Madrid, Madrid, Spain ‡Department of Physics, Universidad de Murcia, Murcia, Spain.
Cornea.Cornea.2013 Jun;32(6):783-90. doi: 10.1097/ICO.0b013e31826dd44b.
PURPOSE: : To examine the agreement and relationship between refractive and corneal astigmatism in a population of pseudophakic eyes.METHODS: : Patients of age at least 40 years, visual acuity 20/40 or better, and no ocular disease were included (n = 111). Refractive astigmatism was obtained by subj
PMID 23132451

Japanese Journal

CLINICAL INVESTIGATION : Effects of corneal irregular astigmatism on visual acuity after conventional and femtosecond laser-assisted Descemet's stripping automated endothelial keratoplasty

Tomida Daisuke,Yamaguchi Takefumi,Ogawa Akiko [他]
Japanese journal of ophthalmology : the official international journal of the Japanese Ophthalmological Society 59(4), 216-222, 2015-07
NAID 40020527507

Development of high-power, 6 kHz, single-mode Ti:sapphire laser at 904 nm for generating 193 nm light

Tsuboi Mizuki,Nakazato Tomoharu,Onose Takashi,Tanaka Yuichi,Sarukura Nobuhiko,Kakizaki Kouji,Watanabe Shuntaro
Jpn. J. Appl. Phys. 54(4), 042702, 2015-03-18
… The thermal lens in the Ti:sapphire crystal having a focal length down to 10 mm along with strong astigmatism was compensated by distributing thermal load to three amplifiers with an even number of passes, resulting in a nearly diffraction limited beam. …
NAID 150000110458

レチノスコピーで観察されるscissors movementの臨床的意義

岩見千丈,妹尾佳平,山下あさひ
眼科 57(3), 279-286, 2015-03
NAID 40020397872

円錐角膜,屈折矯正術後の不正乱視の治療 (特集役に立つ角膜疾患診療の知識)

東原尚代,稗田牧
あたらしい眼科 32(1), 39-45, 2015-01
NAID 40020345452

Related Pictures

★リンクテーブル★

リンク元	「羞明」「非点収差」「乱視」

「羞明」

v; t; e; Optical aberration
	Distortion; Spherical aberration; Coma; Astigmatism; Petzval field curvature; Chromatic aberration; Defocus; Tilt

　　[★]

英: photophobia
同: まぶしがり症
関: 光感受性

眼に限局する疾患でも全身性疾患でも起こる。どちらも炎症が原因だけど例外が3つある。白皮症 albinism, 片頭痛 migraine, 眼精疲労 eye strain from astigmatism and hyperopia。眼に限局する疾患で結膜炎、角膜炎、角膜への外来異物、虹彩炎、網膜炎、脈絡網膜炎、視神経炎が羞明を起こす。全身性疾患では熱性の疾患、特に結膜を介して感染症と関連した熱性の疾患が羞明を起こす。麻疹、髄膜炎、脳炎、hay fever、インフルエンザ、感冒、旋毛虫症が羞明を起こすことは少ない(just a few)。毒物(特に、ヨード、臭素、アトロピン誘導体)も羞明を起こす。暗所にいるだけでも羞明は起こる。ヒステリーと恐怖症・群集不安も羞明の原因となる。(DIF 354)

「非点収差」

　　[★]

英: astigmatism, astigmatic aberration
ラ: astigmatismus
関: 乱視

「乱視」

　　[★]

英: astigmatism
ラ: astigmatismus
関

[1] Harper, Douglas (2001). "Online Etymology Dictionary". Retrieved 2007-12-29.

[2] Frederic Eugene Wright (1911). The Methods of Petrographic-microscopic Research, Their Relative Accuracy and Range of Application. Carnegie institution of Washington.

[3] "Astigmatism Laser Eye Surgery". The Irish Times.

[4] Kleinstein RN, Jones LA, Hullett S, Kwon S, et al. (2003). "Refractive Error and Ethnicity in Children". Arch Ophthalmol. 121 (8): 1141–7. doi:10.1001/archopht.121.8.1141. PMID 12912692.

[5] Garcia CA, Oréfice F, Nobre GF, Souza Dde B, Rocha ML, Vianna RN (2005). "[Prevalence of refractive errors in students in Northeastern Brazil.]". Arq Bras Oftalmol (in Portuguese) 68 (3): 321–5. doi:10.1590/S0004-27492005000300009. PMID 16059562.

[6] Bourne RR, Dineen BP, Ali SM, Noorul Huq DM, Johnson GJ (June 2004). "Prevalence of refractive error in Bangladeshi adults: results of the National Blindness and Low Vision Survey of Bangladesh". Ophthalmology 111 (6): 1150–60. doi:10.1016/j.ophtha.2003.09.046. PMID 15177965.

[7] Asano K, Nomura H, Iwano M, et al. (2005). "Relationship between astigmatism and aging in middle-aged and elderly Japanese". Jpn. J. Ophthalmol. 49 (2): 127–33. doi:10.1007/s10384-004-0152-1. PMID 15838729.

[8] Eyetopics.com

[9] Medicinenet.com

[10] Hipusa.com

[11] Hipusa.com

[12] Stlukeseye.com

[13] Emedicine.com

[14] Graff T (June 1962). "[Control of the determination of astigmatism with the Jackson cross cylinder.]". Klin Monatsblatter Augenheilkd Augenarztl Fortbild (in German) 140: 702–8. PMID 13900989.

[15] Del Priore LV, Guyton DL (November 1986). "The Jackson cross cylinder. A reappraisal". Ophthalmology 93 (11): 1461–5. doi:10.1016/s0161-6420(86)33545-0. PMID 3808608.

[16] Brookman KE (May 1993). "The Jackson crossed cylinder: historical perspective". J Am Optom Assoc 64 (5): 329–31. PMID 8320415.

[17] Quantumoptical.com

[18] Nova.edu

[19] Sacek, Vladimir (July 14, 2006). "Telescope astigmatism". Amateur Telescope Optics. Archived from the original on 19 September 2008. Retrieved Oct 16, 2008.

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