関: ametropia

WordNet

(ophthalmology) faulty refraction of light rays in the eye as in astigmatism or myopia
(baseball) a failure of a defensive player to make an out when normal play would have sufficed (同)misplay
departure from what is ethically acceptable (同)wrongdoing
(computer science) the occurrence of an incorrect result produced by a computer (同)computer error
a misconception resulting from incorrect information (同)erroneous belief
part of a statement that is not correct; "the book was full of errors" (同)mistake
to make a mistake or be incorrect (同)mistake, slip
of or relating to or capable of refraction; "the refractive characteristics of the eye" (同)refractile

PrepTutorEJDIC

〈C〉『誤り』,『まちがい』 / 〈U〉思い違い,誤解 / 〈U〉〈C〉過ち,過失 / 〈U〉(計数の)誤差 / 〈C〉(野球で)エラー,失策
(判断・考え方・選択などで)『誤る』,まちがえる;過ちを犯す,罪を犯す《+『in』+『名』(do『ing』)》 / (正道・目的などから)それる,逸脱する《+『from』+『名』》

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/05/14 15:06:05」(JST)

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A refractive error, or refraction error, is an error in the focusing of light by the eye and a frequent reason for reduced visual acuity.

Classification

An eye that has no refractive error when viewing distant objects is said to have emmetropia or be emmetropic meaning the eye is in a state in which it can focus parallel rays of light (light from distant objects) on the retina, without using any accommodation. A distant object in this case is defined as an object 8 meters or further away from the eye. This proves to be an evolutionary advantage by automatically focusing the eye on objects in the distance because it allows an individual to be alert in, say, a prey-predator situation.

An eye that has refractive error when viewing distant objects is said to have ametropia or be ametropic. This eye, when not using accommodation, cannot focus parallel rays of light (light from distant objects) on the retina.

The word "ametropia" can be used interchangeably with "refractive error". Types of ametropia include myopia, hyperopia and astigmatism. They are frequently categorized as spherical errors and cylindrical errors:

Spherical errors occur when the optical power of the eye is either too large or too small to focus light on the retina. People with refractive error frequently have blurry vision.
- Myopia: When the optics are too powerful for the length of the eyeball one has myopia or nearsightedness. This can arise from a cornea or crystalline lens with too much curvature (refractive myopia) or an eyeball that is too long (axial myopia). Myopia can easily be corrected with a concave lens which causes the divergence of light rays before they reach the cornea.
- Hyperopia: When the optics are too weak for the length of the eyeball, one has hyperopia or farsightedness. This can arise from a cornea or crystalline lens with not enough curvature (refractive hyperopia) or an eyeball that is too short (axial hyperopia). This can be corrected with convex lenses which cause light rays to converge prior to hitting the cornea.

Cylindrical errors cause astigmatism, when the optical power of the eye is too powerful or too weak across one meridian, such as if the corneal curvature tends towards a cylindrical shape. The angle between that meridian and the horizontal is known as the axis of the cylinder.
- Astigmatism: A person with astigmatic refractive error sees lines of a particular orientation less clearly than lines at right angles to them. This defect can be corrected by refracting light more in one meridian than the other. Cylindrical lenses serve this purpose.
- Presbyopia: When the flexibility of the lens declines typically due to age. The individual would experience difficulty in near vision, often relieved by reading glasses, bifocal, or progressive lenses.

Diagnosis

A doctor uses a trial frame and trial lenses to measure the patient's refractive error.

Blurry vision may result from any number of conditions not necessarily related to refractive errors. The diagnosis of a refractive error is usually confirmed by an eye care professional during an eye examination using a large number of lenses of different optical powers, and often a retinoscope (a procedure entitled retinoscopy) to measure objectively in which the patient views a distant spot while the clinician changes the lenses held before the patient's eye and watches the pattern of reflection of a small light shone on the eye. Following that "objective refraction" the clinician typically shows the patient lenses of progressively higher or weaker powers in a process known as subjective refraction. Cycloplegic agents are frequently used to more accurately determine the amount of refractive error, particularly in children^[1]

An automated refractor is an instrument that is sometimes used in place of retinoscopy to objectively estimate a person's refractive error.^[2] Shack–Hartmann wavefront sensor and its inverse^[3] can also be used to characterize eye aberrations in a higher level of resolution and accuracy.

Vision defects caused by refractive error can be distinguished from other problems using a pinhole occluder, which will improve vision only in the case of refractive error.

Management

How refractive errors are treated or managed depends upon the amount and severity of the condition. Those who possess mild amounts of refractive error may elect to leave the condition uncorrected, particularly if the patient is asymptomatic. For those who are symptomatic, glasses, contact lenses, refractive surgery, or a combination of the three are typically used.

In the case of myopia, however, some believe that such treatments may also have the long-term effect of exacerbating that refractive error — i.e., making the patient even more nearsighted. This would be due to the very same prescription that is tailored for use at a 12-to-20-foot distance also commonly being used for close-up work as well, thus artificially amplifying the focusing stress that would normally be presented to the accommodation mechanisms of the eye at that distance.^{[citation needed]}

However, this exacerbating effect is not generally believed to exist in the general case, although in cases where the myopia is due to accommodative spasm, removing the corrective lenses for a time may lead to improvement.^{[citation needed]}

Epidemiology

DALYs per 100,000 people due to refractive errors in 2004.^[4]

no data

less than 100

100-170

170-240

240-310

310-380

380-450

450-520

520-590

590-660

660-730

730-800

more than 800

The global prevalence of refractive errors has been estimated from 800 million to 2.3 billion.^[5]

References

Notes

^ Roque, B. Refractive errors in children. November 2, 2005.
^ "Frequently Asked Questions: How do you measure refractive errors?". The New York Eye And Ear Infirmary. Retrieved 2006-09-13.
^ "NETRA: Inverse Shack-Hartmann Wavefront Sensor using High Resolution Mobile Phone Display". Vitor F. Pamplona, Ankit Mohan, Manuel M. Oliveira, Ramesh Raskar. Retrieved 2011-12-13.
^ "WHO Disease and injury country estimates". World Health Organization. 2009. Retrieved Nov 11, 2009.
^ http://www.infocusonline.org/WORLDWIDE%20DISTRIBUTION%20OF%20VISUAL%20REFRACTIVE%20ERROR1.doc

Sources

Saladin, Kenneth S., "Anatomy & Physiology: the Unity of Form and Function". Dubuque: McGraw-Hill, 2010. Print

UpToDate Contents

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1. 小児における屈折異常 refractive errors in children
2. 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
3. Amblyopia in children: Management and outcome
4. レーザー屈折矯正手術 laser refractive surgery
5. Amblyopia in children: Classification, screening, and evaluation

English Journal

Posterior corneal astigmatism in refractive lens exchange surgery.

Rydström E1, Westin O1, Koskela T1, Behndig A1.
Acta ophthalmologica.Acta Ophthalmol.2016 May;94(3):295-300. doi: 10.1111/aos.12965. Epub 2016 Jan 30.
PURPOSE: To assess the anterior, posterior and total corneal spherical and astigmatic powers in patients undergoing refractive lens exchange (RLE) surgery.METHODS: In 402 consecutive patients planned for RLE at Koskelas Eye Clinic, Luleå, Sweden, right eye data from pre- and postoperative subjectiv
PMID 26825986

Inverse relationship between sleep duration and myopia.

Jee D1,2, Morgan IG3, Kim EC4.
Acta ophthalmologica.Acta Ophthalmol.2016 May;94(3):e204-10. doi: 10.1111/aos.12776. Epub 2015 Jun 1.
PURPOSES: To investigate the association between sleep duration and myopia.METHODS: This population-based, cross-sectional study using a nationwide, systemic, stratified, multistage, clustered sampling method included a total of 3625 subjects aged 12-19 years who participated in the Korean National
PMID 26031352

Comparison of rates of retinal nerve fibre layer thinning between patients with non-myopic and myopic glaucoma.

Lee JY1, Sung KR1, Yun SC2.
The British journal of ophthalmology.Br J Ophthalmol.2016 May;100(5):699-703. doi: 10.1136/bjophthalmol-2015-307343. Epub 2015 Aug 28.
BACKGROUND/AIM: To compare the rates of retinal nerve fibre layer (RNFL) thinning in subgroups of patients with glaucoma based on spherical equivalent (SE).METHODS: In this retrospective study, patients were classified into three subgroups, namely, non-myopic glaucoma (NMG, >0 dioptres (D)), mild
PMID 26319947

Japanese Journal

臨床研究陸上自衛官における屈折矯正法の現状 : 東日本大震災後の経験を踏まえて

播本幸三,加藤直子,庄司拓平 [他]
日本眼科学会雑誌 118(2), 84-90, 2014-02
NAID 40019975491

CLINICAL INVESTIGATION : Influence of axial length on ganglion cell complex (GCC) thickness and on GCC thickness to retinal thickness ratios in young adults

Takeyama Asuka,Kita Yoshiyuki,Kita Ritsuko [他]
Japanese journal of ophthalmology : the official international journal of the Japanese Ophthalmological Society 58(1), 86-93, 2014-01
NAID 40019946974