Editing Refractive error (section)

{{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>