View source for Refractive error

{{Short description|Problem with focusing light accurately on the retina due to the shape of the eye}}
{{Use dmy dates|date=March 2025}}
{{Infobox medical condition (new)
| name            = Refractive error
| image           = File:Refractive Errors of the Eye.jpg
| caption         = A correctly-focused eye (top), and two showing refractive error: In the middle image, the [[light]] is focused too far forward; in the bottom image, the focal point is behind the eye.
| synonyms        = Refraction error
| field           = [[Ophthalmology]], [[optometry]]
| symptoms        = [[Blurry vision]], [[double vision]], [[headaches]], [[eye strain]]
| complications   = [[Blindness]], [[amblyopia]]<ref>{{cite web |title=Care of the Patient with Amblyopia |url=https://www.aoa.org/documents/optometrists/QRG-4.pdf |access-date=17 February 2020 |archive-date=19 August 2016 |archive-url=https://web.archive.org/web/20160819153508/https://www.aoa.org/documents/optometrists/QRG-4.pdf |url-status=dead }}</ref><ref>{{cite journal |last1=Dandona |first1=R |last2=Dandona |first2=L |title=Refractive error blindness. |journal=Bulletin of the World Health Organization |date=2001 |volume=79 |issue=3 |pages=237–43 |pmid=11285669|pmc=2566380 }}</ref>
| onset           =
| duration        =
| types           = [[myopia|Near-sightedness]], [[hyperopia|far-sightedness]], [[astigmatism]], [[presbyopia]]<ref name=NIH2010/>
| causes          = [[Eyeball]] length, problems with [[cornea]] shape, aging of the [[lens]]<ref name=NIH2010/>
| risks           =
| diagnosis       = [[Eye examination]]<ref name=NIH2010/>
| differential    =
| prevention      =
| treatment       = [[Eyeglass]]es, [[contact lenses]], [[refractive surgery]]<ref name=NIH2010/>
| medication      =
| prognosis       =
| frequency       = ~1.5&nbsp;billion<ref name=OUP2014/>
| deaths          =
}}
<!-- Definition and symptoms -->

'''Refractive error''' is a problem with [[focus (optics)|focus]]ing light accurately on the [[retina]] due to the shape of the [[eye]] and/or [[cornea]].<ref name=NIH2010>{{cite web |title=Facts About Refractive Errors |url=https://nei.nih.gov/health/errors/errors |website=NEI |access-date=29 July 2016 |date=October 2010 |url-status=dead |archive-url=https://web.archive.org/web/20160728000730/https://nei.nih.gov/health/errors/errors |archive-date=28 July 2016}}</ref> The most common types of refractive error are [[myopia|near-sightedness]], [[hyperopia|far-sightedness]], [[astigmatism]], and [[presbyopia]]. Near-sightedness results in far away objects being [[blurred vision|blurry]], far-sightedness and presbyopia result in close objects being blurry, and astigmatism causes objects to appear stretched out or blurry. Other symptoms may include [[double vision]], [[headaches]], and [[eye strain]].<ref name=NIH2010/>

<!-- Cause and diagnosis -->
Near-sightedness is due to the length of the eyeball being too long; far-sightedness the eyeball too short; astigmatism the cornea being the wrong shape, while presbyopia results from aging of the [[lens of the eye]] such that it cannot change shape sufficiently.<ref name=NIH2010/> Some refractive errors occur more often among those whose parents are affected. Diagnosis is by [[eye examination]].

<!-- Treatment -->
Refractive errors are corrected with [[eyeglass]]es, [[contact lenses]], or [[surgery]].<ref name=NIH2010/> Eyeglasses are the easiest and safest method of correction. Contact lenses can provide a wider [[field of vision]]; however they are associated with a risk of infection. [[Refractive surgery]] may consist of either permanently changing the shape of the cornea or, alternatively, implanting [[intraocular lens]]es.<ref name=NIH2010/><ref>{{cite book |first1=Daniel |last1=Kook |first2=Thomas |last2=Kohnen |chapter=31 - Refractive lens exchange |editor1-first=George L. |editor1-last=Spaeth |editor2-first=Helen V. |editor2-last=Danesh-Meyer |editor3-first=Ivan |editor3-last=Goldberg |editor4-first=Anselm |editor4-last=Kampik |title=Ophthalmic Surgery: Principles and Practice |edition=Fourth |publisher=W.B. Saunders |date=2012 |pages=187–191 |isbn=978-1-4377-2250-5 |doi=10.1016/B978-1-4377-2250-5.00031-X |chapter-url=https://www.sciencedirect.com/science/article/pii/B978143772250500031X }}</ref>

<!-- Epidemiology and prognosis -->
The number of people globally with refractive errors has been estimated at one to two billion.<ref name=OUP2014/> Rates vary between regions of the world with about 25% of Europeans and 80% of Asians affected.<ref name=OUP2014>{{cite book|last1=Denniston|first1=Alastair|last2=Murray|first2=Philip|title=Oxford Handbook of Ophthalmology|date=2018|publisher=OUP Oxford|isbn=978-0-19-881675-1|page=926|edition=4}}</ref> Near-sightedness is the most common disorder.<ref name=Fos2014>{{cite journal|last1=Foster|first1=PJ|last2=Jiang|first2=Y|title=Epidemiology of myopia.|journal=Eye|date=February 2014|volume=28|issue=2|pages=202–8|pmid=24406412|doi=10.1038/eye.2013.280|pmc=3930282}}</ref> Rates among adults are between 15 and 49% while rates among children are between 1.2 and 42%.<ref name=Pan2012>{{cite journal|last1=Pan|first1=CW|last2=Ramamurthy|first2=D|last3=Saw|first3=SM|title=Worldwide prevalence and risk factors for myopia.|journal=Ophthalmic & Physiological Optics|date=January 2012|volume=32|issue=1|pages=3–16|pmid=22150586|doi=10.1111/j.1475-1313.2011.00884.x|s2cid=32397628|doi-access=}}</ref> Far-sightedness more commonly affects young children and the elderly.<ref name=Cas2014>{{cite journal|last1=Castagno|first1=VD|last2=Fassa|first2=AG|last3=Carret|first3=ML|last4=Vilela|first4=MA|last5=Meucci|first5=RD|title=Hyperopia: a meta-analysis of prevalence and a review of associated factors among school-aged children.|journal=BMC Ophthalmology|date=23 December 2014|volume=14|pages=163|pmid=25539893|doi=10.1186/1471-2415-14-163|pmc=4391667 |doi-access=free }}</ref><ref name=Gro2007>{{cite book|last1=Grosvenor|first1=Theodore|title=Primary care optometry|date=2007|publisher=Butterworth Heinemann, Elsevier|location=St. Louis (Miss.)|isbn=978-0-7506-7575-8|page=70|edition=5|url=https://books.google.com/books?id=uEmQKPAOwccC&pg=PA70|url-status=live|archive-url=https://web.archive.org/web/20160815211218/https://books.google.ca/books?id=uEmQKPAOwccC&pg=PA70|archive-date=2016-08-15}}</ref> Presbyopia affects most people over the age of 35.<ref name=NIH2010/>

The number of people with refractive errors that have not been corrected was estimated at 660 million (10 per 100 people) in 2013.<ref name=GBD2015>{{cite journal|last1=Vos|first1=Theo|last2=Barber|first2=Ryan M|last3=Bell|first3=Brad|last4=Bertozzi-Villa|first4=Amelia|last5=Biryukov|first5=Stan|last6=Bolliger|first6=Ian|collaboration=Global Burden of Disease Study 2013 Collaborators|title=Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013.|journal=Lancet|date=22 August 2015|volume=386|issue=9995|pages=743–800|pmid=26063472|doi=10.1016/s0140-6736(15)60692-4|pmc=4561509}}</ref> Of these 9.5&nbsp;million were [[Blindness|blind]] due to the refractive error.<ref name=GBD2015/> It is one of the most common causes of [[vision loss]] along with [[cataract]]s, [[macular degeneration]], and [[vitamin A deficiency]].<ref name=Pan2015>{{cite journal|last1=Pan|first1=CW|last2=Dirani|first2=M|last3=Cheng|first3=CY|last4=Wong|first4=TY|last5=Saw|first5=SM|title=The age-specific prevalence of myopia in Asia: a meta-analysis.|journal=Optometry and Vision Science|date=March 2015|volume=92|issue=3|pages=258–66|pmid=25611765|doi=10.1097/opx.0000000000000516|s2cid=42359341|doi-access=free}}</ref>

==Classification==
[[File:Refractive error.jpg|thumb|upright=1.3|Top: farsighted corrected using convex lens Bottom: nearsighted corrected using concave lens.]]
Refractive error – sometimes called "ametropia" – is when the refractive power of an eye does not match the length of the eye, so the image is focused away from the central retina, instead of directly on it.<ref>{{Cite journal |last=Lawrenson |first=John G. |last2=Huntjens |first2=Byki |last3=Virgili |first3=Gianni |last4=Ng |first4=Sueko |last5=Dhakal |first5=Rohit |last6=Downie |first6=Laura E. |last7=Verkicharla |first7=Pavan K. |last8=Kernohan |first8=Ashleigh |last9=Li |first9=Tianjing |last10=Walline |first10=Jeffrey J. |date=2025-02-13 |title=Interventions for myopia control in children: a living systematic review and network meta-analysis |url=https://pubmed.ncbi.nlm.nih.gov/39945354 |journal=The Cochrane Database of Systematic Reviews |volume=2 |issue=2 |pages=CD014758 |doi=10.1002/14651858.CD014758.pub3 |issn=1469-493X |pmc=11822883 |pmid=39945354}}</ref>

Types of refractive error include myopia, hyperopia, presbyopia, and astigmatism.
* '''[[Near-sightedness|Myopia]] or [[Nearsightedness]]''': When the refractive power is too strong for the length of the eyeball, this is called [[myopia]] or nearsightedness. People with myopia typically have blurry vision when viewing distant objects because the eye is refracting more than necessary. Myopia can be corrected with a concave lens, which causes the divergence of light rays before they reach the cornea.<ref>{{Cite journal |last= |date=2016-08-22 |title=Vision and Optical Instruments: Vision Correction |url=https://pressbooks-dev.oer.hawaii.edu/collegephysics/chapter/26-2-vision-correction/ |journal=College Physics: OpenStax |language=en-ca |pages=26-2}}</ref>
* '''[[Far-sightedness|Hyperopia]] or [[Farsightedness]]''': When the refractive power is too weak for the length of the eyeball, one has [[hyperopia]] or farsightedness. People with hyperopia have blurry vision when viewing near objects because the eye is unable to focus the light sufficiently. This can be corrected with convex lenses, which cause light rays to converge prior to hitting the cornea.<ref>{{cite book |last=Grosvenor |first=Theodore |title=Primary care optometry |date=2007 |publisher=Butterworth Heinemann, Elsevier |location=St. Louis (Miss.) |isbn=978-0-7506-7575-8 |page=17 |edition=5|url=https://books.google.com/books?id=uEmQKPAOwccC&pg=PA17}}</ref>
* '''[[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.<ref>{{cite book |last=Khurana |first=AK |title=Theory and practice of optics and refraction |publisher=Elsevier |isbn=978-81-312-1132-8 |pages=100–103 |edition=2nd |chapter=Asthenopia, anomalies of accommodation and convergence |date=September 2008 |chapter-url=https://books.google.com/books?id=qYeD3VHi8OsC&pg=PA100}}</ref>
* '''[[Astigmatism]]''' is when the refractive power of the eye is not uniform across the surface of the cornea because of asymmetry. In other words, the eye focuses light more strongly in one direction than another, leading to distortion of the image.<ref>{{cite book |last=Grosvenor |first=Theodore |title=Primary care optometry |date=2007 |publisher=Butterworth Heinemann, Elsevier |location=St. Louis (Miss.) |isbn=978-0-7506-7575-8 |pages=17–19 |edition=5|url=https://books.google.com/books?id=uEmQKPAOwccC&pg=PA17}}</ref>

Children are typically born hyperopic and shift toward emmetropia or myopia as their eyes lengthen through childhood.<ref>{{Citation |last1=Saluja |first1=Gunjan |title=Childhood Myopia and Ocular Development |date=2023 |url=http://www.ncbi.nlm.nih.gov/books/NBK587350/ |work=StatPearls |access-date=2023-10-31 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=36508524 |last2=Kaur |first2=Kirandeep}}</ref>

Other terminology include [[anisometropia]], when the two eyes have unequal [[refractive power]],<ref>{{cite web |title=Anisometropia - American Association for Pediatric Ophthalmology and Strabismus |url=https://aapos.org/glossary/anisometropia |access-date=10 February 2020 |website=aapos.org |language=en}}</ref> and [[aniseikonia]] which is when the [[magnification]] power between the eyes differ.<ref>{{cite web |title=Aniseikonia - EyeWiki |url=https://eyewiki.aao.org/Aniseikonia |access-date=10 February 2020 |website=eyewiki.aao.org}}</ref>

Refractive errors are typically measured using three numbers: sphere, cylinder, and axis.<ref name=":2">{{Cite web |date=2023-04-18 |title=How to Read an Eyeglasses Prescription |url=https://www.aao.org/eye-health/glasses-contacts/how-to-read-eyeglasses-prescription |access-date=2023-10-31 |website=[[American Academy of Ophthalmology]] |last=Porter |first=Daniel}}</ref>
* '''Sphere:''' This number denotes the strength of the lens needed to correct your vision. A "–" indicates nearsightedness while a "+" indicates farsightedness. Higher numbers indicate more power in either direction.
* '''Cylinder:''' This number denotes the amount of astigmatism, if any.
* '''Axis:''' This number notes the direction of the astigmatism and is written in degrees between 1 and 180.

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 located beyond 6 meters, or 20 feet, from the eye, since the light from those objects arrives as essentially parallel rays when considering the limitations of human perception.<ref>{{cite book|last1=Bope|first1=Edward T.|last2=Kellerman|first2=Rick D.|title=Conn's Current Therapy 2016|date=2015|publisher=Elsevier Health Sciences|isbn=978-0-323-35535-3|page=354|url=https://books.google.com/books?id=_x_mCgAAQBAJ&pg=PT390|language=en}}</ref>

==Risk factors==

===Genetics===
[[File:Fundus of patient with retinitis pigmentosa, early stage.jpg|thumb|upright=1.3|Fundus of person with [[retinitis pigmentosa]], early stage]]
There is evidence to suggest genetic predilection for refractive error. Individuals that have parents with certain refractive errors are more likely to have similar refractive errors.<ref name="NIH2010" />

The Online Mendelian Inheritance in Man ([[OMIM]]) database has listed 261 genetic disorders in which myopia is one of the symptoms.<ref name="Morgan 1739–1748">{{cite journal|last=Morgan|first=Ian|author2=Kyoko Ohno-Matsui |s2cid=208793136|title=Myopia|journal=The Lancet|date=May 2012|volume=379|issue=9827|pages=1739–1748|doi=10.1016/S0140-6736(12)60272-4|pmid=22559900}}</ref> Myopia may be present in heritable connective tissue disorders such as: [[Knobloch syndrome]] (OMIM 267750); [[Marfan syndrome]] (OMIM 154700); and [[Stickler syndrome]] (type 1, OMIM 108300; type 2, OMIM 604841).<ref name="Wojciechowski 301–320"/> Myopia has also been reported in [[X-linked recessive inheritance|X-linked disorders]] caused by mutations in [[Locus (genetics)|loci]] involved in retinal [[Photoreceptor cell|photoreceptor]] function ([[NYX (gene)|NYX]], [[RP2 (gene)|RP2]], MYP1) such as: autosomal recessive [[congenital stationary night blindness]] ([[CSNB]]; OMIM 310500); [[retinitis pigmentosa]] 2 (RP2; OMIM 312600); Bornholm eye disease (OMIM 310460).<ref name="Wojciechowski 301–320">{{cite journal|last=Wojciechowski|first=Robert|title=Nature and Nurture: the complex genetics of myopia and refractive error|journal= Clinical Genetics|date=April 2011|volume=79|issue=4|pages=301–320|doi=10.1111/j.1399-0004.2010.01592.x|pmid=21155761|pmc=3058260}}</ref>
Many genes that have been associated with refractive error are clustered into common biological networks involved in connective tissue growth and extracellular matrix organization.<ref name="Wojciechowski 301–320"/> Although a large number of chromosomal localisations have been associated with myopia (MYP1-MYP17), few specific genes have been identified.<ref name="Morgan 1739–1748"/>

===Environmental===
In studies of the genetic predisposition of refractive error, there is a correlation between environmental factors and the risk of developing myopia.<ref name=":0">{{cite journal|last=Barnes|first=Katherine|date=Feb 2013|title=Genome-wide meta-analyses of multiancestry cohorts identify multiple new susceptibility loci for refractive error and myopia|journal=Clinical Genetics|volume=45|issue=3|pages=314–8|doi=10.1111/j.1399-0004.2010.01592.x|pmc=3740568|pmid=23396134}}</ref> Myopia has been observed in individuals with visually intensive occupations.<ref name="Wojciechowski 301–320"/> [[Reading]] has also been found to be a predictor of myopia in children. It has been reported that children with myopia spent significantly more time reading than non-myopic children who spent more time playing outdoors.<ref name="Wojciechowski 301–320"/> Additionally, focusing on near objects for long periods of time - such as when reading, looking at close screens, or writing - has been associated with myopia.<ref>{{Cite journal |last1=Huang |first1=Hsiu-Mei |last2=Chang |first2=Dolly Shuo-Teh |last3=Wu |first3=Pei-Chang |date=2015-10-20 |editor-last=Jhanji |editor-first=Vishal |title=The Association between Near Work Activities and Myopia in Children—A Systematic Review and Meta-Analysis |journal=PLOS ONE |language=en |volume=10 |issue=10 |pages=e0140419 |doi=10.1371/journal.pone.0140419 |pmid=26485393 |pmc=4618477 |bibcode=2015PLoSO..1040419H |issn=1932-6203|doi-access=free }}</ref><ref>{{Cite journal |last1=Dutheil |first1=Frédéric |last2=Oueslati |first2=Tharwa |last3=Delamarre |first3=Louis |last4=Castanon |first4=Joris |last5=Maurin |first5=Caroline |last6=Chiambaretta |first6=Frédéric |last7=Baker |first7=Julien S. |last8=Ugbolue |first8=Ukadike C. |last9=Zak |first9=Marek |last10=Lakbar |first10=Ines |last11=Pereira |first11=Bruno |last12=Navel |first12=Valentin |date=2023-01-03 |title=Myopia and Near Work: A Systematic Review and Meta-Analysis |journal=International Journal of Environmental Research and Public Health |language=en |volume=20 |issue=1 |pages=875 |doi=10.3390/ijerph20010875 |pmid=36613196 |pmc=9820324 |issn=1660-4601|doi-access=free }}</ref> [[Socioeconomic status]] and higher levels of education have also been reported to be a risk factor for myopia.<ref>{{Cite journal |last1=Foster |first1=P J |last2=Jiang |first2=Y |date=February 2014 |title=Epidemiology of myopia |journal=Eye |language=en |volume=28 |issue=2 |pages=202–208 |doi=10.1038/eye.2013.280 |pmid=24406412 |pmc=3930282 |issn=0950-222X|doi-access=free }}</ref> [[Ptosis (eyelid)|Blepharoptosis]] can also induce refractive errors.<ref>{{cite journal |last1=Owji |first1=N |last2=Khalili |first2=MR |last3=Bazrafkan |first3=H |last4=Heydari |first4=M |title=Long-term outcome of refractive errors in patients with congenital blepharoptosis who have undergone ptosis surgery. |journal=Clinical & Experimental Optometry |date=September 2022 |volume=105 |issue=7 |pages=715–720 |doi=10.1080/08164622.2021.1973344 |pmid=34538220|s2cid=237573319 }}</ref>
== Normal refraction ==
In order to see a clear image, the eye must focus rays of light on to the light-sensing part of the eye – the [[retina]], which is located in the back of the eye. This focusing – called [[refraction]] – is performed mainly by the [[cornea]] and the [[Lens (vertebrate anatomy)|lens]], which are located at the front of the eye, the [[Anterior segment of eyeball|anterior segment]].<ref name=":1">{{Cite web |date=2023-04-29 |title=Eye Anatomy: Parts of the Eye and How We See |url=https://www.aao.org/eye-health/anatomy/parts-of-eye |access-date=2023-10-31 |website=[[American Academy of Ophthalmology]] |last1=Boyd |first1=Kierstan |last2=Turbert |first2=David}}</ref>

When an eye focuses light correctly on to the retina when viewing distant objects, this is called ''[[emmetropia]]'' or being ''emmetropic.'' This means that the refractive power of the eye matches what is needed to focus parallel rays of light onto the retina. A distant object is defined as an object located beyond 6 meters (20 feet) from the eye.{{cn|date=September 2024}}

When an object is located close to the eye, the rays of light from this object no longer approach the eye parallel to each other. Consequently, the eye must ''increase'' its refractive power to bring those rays of light together on the [[retina]]. This is called [[Accommodation (vertebrate eye)|accommodation]], and is accomplished by the eye thickening the lens.<ref name=":1" />

==Diagnosis==
[[File:Refrarction error test.JPG|upright=1.3|thumb|A doctor uses a trial frame and trial lenses to measure the person'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 person views a distant spot while the clinician changes the lenses held before the person'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 person 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<ref name=":0" />

An [[automated refractor]] is an instrument that is sometimes used in place of retinoscopy to objectively estimate a person's refractive error.<ref>{{cite web|title = Frequently Asked Questions: How do you measure refractive errors?|work = The New York Eye And Ear Infirmary|url = http://www.nyee.edu/faqlist.html?tablename=faq&key=36|access-date = 2006-09-13|url-status = live|archive-url = https://web.archive.org/web/20060901064328/http://www.nyee.edu/faqlist.html?tablename=faq&key=36|archive-date = 2006-09-01}}</ref> [[Shack–Hartmann wavefront sensor]] and its inverse<ref>{{cite web|title = NETRA: Inverse Shack-Hartmann Wavefront Sensor using High Resolution Mobile Phone Display|work = Vitor F. Pamplona, Ankit Mohan, Manuel M. Oliveira, Ramesh Raskar|url = http://web.media.mit.edu/~pamplona/NETRA/|access-date = 2011-12-13|url-status = dead|archive-url = https://web.archive.org/web/20111221185852/http://web.media.mit.edu/~pamplona/NETRA/|archive-date = 2011-12-21}}</ref> can also be used to characterize [[Aberrations of the eye|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.<ref>{{Cite journal |last1=Schiefer |first1=Ulrich |last2=Kraus |first2=Christina |last3=Baumbach |first3=Peter |last4=Ungewiß |first4=Judith |last5=Michels |first5=Ralf |date=2016-10-14 |title=Refractive errors |journal=Deutsches Ärzteblatt International |volume=113 |issue=41 |pages=693–702 |doi=10.3238/arztebl.2016.0693 |pmid=27839543 |issn=1866-0452|pmc=5143802 }}</ref>
== Screening ==
When refractive errors in children are not treated, the child may be at risk of developing [[Amblyopia|ambylopia]], where vision may remain permanently blurry.<ref name=":02">{{Cite web |title=Refractive Errors in Children - American Association for Pediatric Ophthalmology and Strabismus |url=https://aapos.org/glossary/refractive-errors-in-children |access-date=2023-10-30 |website=aapos.org |language=en}}</ref> Because young children typically do not complain of blurry vision, the American Academy of Pediatrics recommends that children have yearly vision screening starting at three years old so that unknown refractive errors or other ophthalmic conditions can be found and treated if deemed necessary by healthcare professionals.<ref name=":02" /><ref>{{Cite journal |last=Adam |first=Henry |date=2020-04-02 |title=Vision Screening |url=https://doi.org/10.1542/aap.ppcqr.396022 |journal=Pediatric Care Online |doi=10.1542/aap.ppcqr.396022 |s2cid=263605231 |issn=2767-6617|url-access=subscription }}</ref>

==Management==
The management of refractive error is done post-diagnosis of the condition by either optometrists, ophthalmologists, refractionists, or ophthalmic medical practitioners.<ref name="Cochrane c1711">{{Cite journal|last1=Cochrane|first1=Gillian M.|last2=Toit|first2=Rènée du|last3=Mesurier|first3=Richard T. Le|date=2010-04-12|title=Management of refractive errors|url=https://www.bmj.com/content/340/bmj.c1711|journal=BMJ|language=en|volume=340|pages=c1711|doi=10.1136/bmj.c1711|issn=0959-8138|pmid=20385718|s2cid=8240093|url-access=subscription}}</ref>

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 person is asymptomatic. For those who are symptomatic, [[glasses]], [[contact lenses]], [[refractive surgery]], or a combination are typically used.<ref name=":1" /><ref name=":2" /><ref name="Morgan 1739–1748" />

=== Glasses ===
These are the most effective ways of correcting the refractive error. However, the availability and affordability of eyeglasses can present a difficulty for people in many low income settings of the world. Glasses also pose a challenge to children to whom they are prescribed to, due to children's tendency to not wear them as consistently as recommended.<ref>{{Cite journal|last1=Wedner|first1=S.|last2=Masanja|first2=H.|last3=Bowman|first3=R.|last4=Todd|first4=J.|last5=Bowman|first5=R.|last6=Gilbert|first6=C.|date=2008-01-01|title=Two strategies for correcting refractive errors in school students in Tanzania: randomised comparison, with implications for screening programmes|url=https://bjo.bmj.com/content/92/1/19|journal=British Journal of Ophthalmology|language=en|volume=92|issue=1|pages=19–24|doi=10.1136/bjo.2007.119198|issn=0007-1161|pmid=18156372|s2cid=2157969|url-access=subscription}}</ref>

As mentioned earlier refractive errors are because of the improper focusing of the light in the retina. Eyeglasses work as an added lens of the eye serving to bend the light to bring it to focus on the retina. Depending on the eyeglasses, they serve many functions.<ref>{{Cite web |title=Pediatric Ophthalmology, Optometry and Orthoptics |url=https://asianeyeinstitute.com/custom_services/pediatric-ophthalmology-orthoptics-strabismus/ |access-date=2022-08-03 |website=Asian Eye Institute}}</ref>

; Reading glasses: These are general over-the-counter glasses which can be worn for easier reading, especially for defective vision due to aging called presbyopia.
; Single vision prescription lenses: They can correct only one form of defective vision, either far-sightedness or near-sightedness.
; Multifocal lenses: The multifocal lenses can correct defective vision in multiple focus, for example: near-vision as well as far-vision. This are particularly beneficial for presbyobia.<ref>{{Cite web|title=Eyeglasses for Refractive Errors {{!}} National Eye Institute|url=https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/refractive-errors/eyeglasses-refractive-errors|access-date=2021-06-29|website=www.nei.nih.gov}}</ref>

=== Contact lenses ===
Alternatively, many people choose to wear contact lenses. One style is hard contact lenses, which can distort the shape of the cornea to a desired shape. Another style, soft contact lenses, are made of silicone or hydrogel. Depending on the duration they are designed for, they may be worn daily or may be worn for an extended period of time, such as for weeks.<ref name="Cochrane c1711"/>

There are a number of complication associated with contact lenses. Typically the ones that are used daily.{{cn|date=September 2024}}
{| class="wikitable"
|+
! Complications of contact lens wear
! Description
|-
| Conjunctivitis (giant papillary form)
| Caused in response to the allergen present in the material from which the contact lens is made from. There is often discomfort in the eye after wearing and vision may be affected. Choosing the right lens material and changing it regularly might prevent conjunctivitis.
|-
| Corneal abrasion
| Caused by a foreign body, dust, sand, or grit trapped under the lens.
|-
| Corneal edema
| Caused by decreased oxygen delivery to the tissue compressed by the lens. Usually resolved after the removal of the lenses. Discomfort upon lens removal may be seen.
|-
| Neovascularization
| New blood vessels may form in the iris region and the limbus. This may impair vision.
|-
| Infections
| Various viral, bacterial, and fungal infection may be seen in the eye post-contact-lens wear, if proper lens hygiene is not maintained. Acanthamoeba are the most common infections in the people using contact lenses.
|}

If redness, itching, and difficulty in vision develops, the use of the lenses should be stopped immediately and the consultation of ophthalmologists may be sought.

=== Surgery ===
Laser in situ keratomileusis (LASIK) and photo-refractive keratectomy (PRK) are popular procedures; while use of laser epithelial keratomileusis (LASEK) is increasing. Other surgical treatments for severe myopia include insertion of implants after [[clear lens extraction]] (refractive lens exchange). Full thickness corneal graft may be a final option for patients with advanced kerataconus although currently there is interest in new techniques that involve collagen crosslinking. As with any surgical procedure complications may arise post-operatively Post-operative monitoring is normally undertaken by the specialist ophthalmic surgical clinic and optometry services. Patients are usually informed pre-operatively about what to expect and where to go if they suspect complications. Any patient reporting pain and redness after surgery should be referred urgently to their ophthalmic surgeon.<ref>{{Cite web |date=2023-05-03 |title=10 Cataract Surgery Side Effects, and How to Cope |url=https://www.aao.org/eye-health/tips-prevention/side-effects-cataract-surgery-complications-cope |access-date=2023-11-06 |website=[[American Academy of Ophthalmology]] |last=Mukamal |first=Reena}}</ref><ref>{{Cite web |date=2023-07-26 |title=LASIK — Laser Eye Surgery |url=https://www.aao.org/eye-health/treatments/lasik |access-date=2023-11-06 |website=American Academy of Ophthalmology |language=en}}</ref>

=== Medical treatment ===
Atropine has believed to slow the progression of near-sightedness and is administered in combination with multifocal lenses. These, however, need further research.<ref>{{Cite journal|last1=Shih|first1=Yung-Feng|last2=Hsiao|first2=C. Kate|last3=Chen|first3=Chien-Jen|last4=Chang|first4=Ching-Wei|last5=Hung|first5=Por T.|last6=Lin|first6=Luke L.-K.|date=June 2001|title=An intervention trial on efficacy of atropine and multi-focal glasses in controlling myopic progression|journal=Acta Ophthalmologica Scandinavica|volume=79|issue=3|pages=233–236|doi=10.1034/j.1600-0420.2001.790304.x|pmid=11401629|issn=1395-3907|doi-access=free}}</ref><ref>{{Cite journal|last1=Lee|first1=Jong-Jer|last2=Fang|first2=Po-Chiung|last3=Yang|first3=I-Hui|last4=Chen|first4=Chih-Hsin|last5=Lin|first5=Pei-Wen|last6=Lin|first6=Sue-Ann|last7=Kuo|first7=Hsi-Kung|last8=Wu|first8=Pei-Chang|date=February 2006|title=Prevention of Myopia Progression with 0.05% Atropine Solution|url=http://dx.doi.org/10.1089/jop.2006.22.41|journal=Journal of Ocular Pharmacology and Therapeutics|volume=22|issue=1|pages=41–46|doi=10.1089/jop.2006.22.41|pmid=16503774|issn=1080-7683|url-access=subscription}}</ref>

=== Prevention ===
Strategies being studied to slow worsening include adjusting working conditions, increasing the time children spend outdoors,<ref name="Wojciechowski 301–320" /> and special types of contact lenses.<ref name="Li2017">{{cite journal|last1=Li|first1=X|last2=Friedman|first2=IB|last3=Medow|first3=NB|last4=Zhang|first4=C|title=Update on Orthokeratology in Managing Progressive Myopia in Children: Efficacy, Mechanisms, and Concerns.|journal=Journal of Pediatric Ophthalmology and Strabismus|date=1 May 2017|volume=54|issue=3|pages=142–148|doi=10.3928/01913913-20170106-01|pmid=28092397}}</ref> In children special contact lenses appear to slow worsening of nearsightedness.<ref name="Li2017" /><ref>{{cite journal|last1=Walline|first1=JJ|s2cid=24069302|title=Myopia Control: A Review.|journal=Eye & Contact Lens|date=January 2016|volume=42|issue=1|pages=3–8|doi=10.1097/ICL.0000000000000207|pmid=26513719}}</ref>

A number of questionnaires exist to determine [[quality of life]] impact of refractive errors and their correction.<ref>{{cite journal |last1=Kandel |first1=H |last2=Khadka |first2=J |last3=Goggin |first3=M |last4=Pesudovs |first4=K |date=2017 |title=Patient-reported outcomes for assessment of quality of life in refractive error: a systematic review|journal=Optometry and Vision Science |volume=94 |issue=12 |pages=1102–1119 |doi=10.1097/OPX.0000000000001143 |pmid=29095758 |s2cid=21512136 |name-list-style=vanc}}</ref><ref>{{cite journal |last1=Kandel |first1=H |last2=Khadka |first2=J |last3=Lundström |first3=M |last4=Goggin |first4=M |last5=Pesudovs |first5=K |date=2017 |title=Questionnaires for measuring refractive surgery outcomes |journal=Journal of Refractive Surgery |volume=33 |issue=6 |pages=416–424 |doi=10.3928/1081597X-20170310-01|pmid=28586503 |name-list-style=vanc}}</ref>

==Epidemiology==
[[File:Refractive errors world map - DALY - WHO2004.svg|thumb|upright=1.3|[[Disability-adjusted life year|DALYs]] per 100,000 people due to refractive errors in 2004.<ref>{{cite web |url=https://www.who.int/healthinfo/global_burden_disease/estimates_country/en/index.html |title=WHO Disease and injury country estimates |year=2009 |work=World Health Organization |access-date=Nov 11, 2009 |url-status=live |archive-url=https://web.archive.org/web/20091111101009/http://www.who.int/healthinfo/global_burden_disease/estimates_country/en/index.html |archive-date=2009-11-11 }}</ref>{{Div col|small=yes|colwidth=10em}}
{{legend|#b3b3b3|No data}}
{{legend|#ffff65|Less than 100}}
{{legend|#fff200|100–170}}
{{legend|#ffdc00|170–240}}
{{legend|#ffc600|240–310}}
{{legend|#ffb000|310–380}}
{{legend|#ff9a00|380–450}}
{{legend|#ff8400|450–520}}
{{legend|#ff6e00|520–590}}
{{legend|#ff5800|590–660}}
{{legend|#ff4200|660–730}}
{{legend|#ff2c00|730–800}}
{{legend|#cb0000|More than 800}}
{{div col end}}]]
It is estimated that at least 2 billion people in the world have refractive errors.<ref name="OUP2014" /> The number of people globally with refractive errors that have not been corrected was estimated at 660 million (10 per 100 people) in 2013.<ref name=GBD2015/>

Refractive errors are the first common cause of visual impairment and second most common cause of visual loss .<ref>{{Cite journal|last1=Hashemi|first1=Hassan|last2=Fotouhi|first2=Akbar|last3=Yekta|first3=Abbasali|last4=Pakzad|first4=Reza|last5=Ostadimoghaddam|first5=Hadi|last6=Khabazkhoob|first6=Mehdi|date=2017-09-27|title=Global and regional estimates of prevalence of refractive errors: Systematic review and meta-analysis|journal=Journal of Current Ophthalmology|volume=30|issue=1|pages=3–22|doi=10.1016/j.joco.2017.08.009|issn=2452-2325|pmc=5859285|pmid=29564404}}</ref> The assessment of refractive error is now done in DALY (Disability Adjusted Life Years) which showed an 8% increase from 1990 to 2019.<ref>{{Cite web|title=Global Disease Burden of Uncorrected Refractive Error Among Adolescents From 1990 to 2019|url=https://assets.researchsquare.com/files/rs-459379/v1/67274026-a654-4b9a-aa55-cb38e2d5c6b3.pdf|access-date=2023-03-21|url-status=dead|archive-url=https://web.archive.org/web/20210624205636/https://assets.researchsquare.com/files/rs-459379/v1/67274026-a654-4b9a-aa55-cb38e2d5c6b3.pdf|archive-date=2021-06-24}}</ref>{{Unreliable source?|reason=Source states it shouldn't be used as a reference for validated info.|sure=y|date=March 2023}}

The number of people globally with significant refractive errors has been estimated at one to two billion.<ref name=OUP2014/> Rates vary between regions of the world with about 25% of Europeans and 80% of Asians affected.<ref name=OUP2014 /> Near-sightedness is one of the most prevalent disorders of the eye.<ref name=Fos2014/> Rates among adults are between 15 and 49% while rates among children are between 1.2 and 42%.<ref name=Pan2012/> Far-sightedness more commonly affects young children, whose eyes have yet to grow to their full length, and the elderly, who have lost the ability to compensate with their [[Accommodation (eye)|accommodation system]].<ref name=Cas2014/><ref name=Gro2007/> Presbyopia affects most people over the age of 35, and nearly 100% of people by the ages of 55–65.<ref name=NIH2010/> Uncorrected refractive error is responsible for visual impairment and disability for many people worldwide.<ref name=GBD2015/> It is one of the most common causes of [[vision loss]] along with [[cataract]]s, [[macular degeneration]], and [[vitamin A deficiency]].<ref name=Pan2015/>

==Cost==
The yearly cost of correcting refractive errors is estimated at 3.9 to 7.2&nbsp;billion dollars in the United States.<ref name=Kuryan>{{cite journal |vauthors=Kuryan J, Cheema A, Chuck RS |title= Laser-assisted subepithelial keratectomy (LASEK) versus laser-assisted in-situ keratomileusis (LASIK) for correcting myopia |journal=Cochrane Database Syst Rev|volume=2017|pages= CD011080 |date=2017 |issue= 2 |pmid= 28197998 |doi= 10.1002/14651858.CD011080.pub2 |pmc=5408355}}</ref>
{{Clear}}
==See also==
*[[Dioptre]]
*[[Focal length]]
*[[Optical power]]

==References==
{{Reflist}}

== External links ==
{{Medical resources
|  ICD10      = {{ICD10|H|52|0|h|49}}-{{ICD10|H|52|4|h|49}}
|  ICD9       = {{ICD9|367.0}}-{{ICD9|367.2}}-{{ICD9|367.9}}
|  DiseasesDB = 29645
|  MeSH=D012030
}}

{{Eye pathology}}
{{Authority control}}

{{DEFAULTSORT:Refractive error}}
[[Category:Vision]]
[[Category:Disorders of ocular muscles, binocular movement, accommodation and refraction]]
[[Category:Refraction]]
[[Category:Wikipedia medicine articles ready to translate]]
[[Category:Wikipedia neurology articles ready to translate]]
[[Category:Corrective lenses]]