refractive error

File:Refractive error.jpg

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.{{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}}

Types of refractive error include myopia, hyperopia, presbyopia, and astigmatism.

• 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.{{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}}
• 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.{{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}}
• 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.{{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}}
• 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.{{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}}

Children are typically born hyperopic and shift toward emmetropia or myopia as their eyes lengthen through childhood.{{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}}

Other terminology include anisometropia, when the two eyes have unequal refractive power,{{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}} and aniseikonia which is when the magnification power between the eyes differ.{{cite web |title=Aniseikonia - EyeWiki |url=https://eyewiki.aao.org/Aniseikonia |access-date=10 February 2020 |website=eyewiki.aao.org}}

Refractive errors are typically measured using three numbers: sphere, cylinder, and axis.{{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}}

• 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.{{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}}

File:Fundus of patient with retinitis pigmentosa, early stage.jpg, 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.

The Online Mendelian Inheritance in Man (OMIM) database has listed 261 genetic disorders in which myopia is one of the symptoms.{{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}} 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). Myopia has also been reported in X-linked disorders caused by mutations in loci involved in retinal photoreceptor function (NYX, RP2, MYP1) such as: autosomal recessive congenital stationary night blindness (CSNB; OMIM 310500); retinitis pigmentosa 2 (RP2; OMIM 312600); Bornholm eye disease (OMIM 310460).{{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}}

Many genes that have been associated with refractive error are clustered into common biological networks involved in connective tissue growth and extracellular matrix organization. Although a large number of chromosomal localisations have been associated with myopia (MYP1-MYP17), few specific genes have been identified.

In studies of the genetic predisposition of refractive error, there is a correlation between environmental factors and the risk of developing myopia.{{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}} Myopia has been observed in individuals with visually intensive occupations. 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. 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.{{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 }}{{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 }} Socioeconomic status and higher levels of education have also been reported to be a risk factor for myopia.{{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 }} Blepharoptosis can also induce refractive errors.{{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 }}

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, which are located at the front of the eye, the anterior segment.{{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}}

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, and is accomplished by the eye thickening the lens.

File:Refrarction error test.JPG

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

An automated refractor is an instrument that is sometimes used in place of retinoscopy to objectively estimate a person's refractive error.{{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}} Shack–Hartmann wavefront sensor and its inverse{{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}} 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.{{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 }}

When refractive errors in children are not treated, the child may be at risk of developing ambylopia, where vision may remain permanently blurry.{{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}} 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.{{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 }}

The management of refractive error is done post-diagnosis of the condition by either optometrists, ophthalmologists, refractionists, or ophthalmic medical practitioners.{{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}}

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.

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.{{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}}

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.{{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}}

; 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.{{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}}

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.

There are a number of complication associated with contact lenses. Typically the ones that are used daily.{{cn|date=September 2024}}

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.

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.{{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}}{{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}}

Atropine has believed to slow the progression of near-sightedness and is administered in combination with multifocal lenses. These, however, need further research.{{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}}{{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}}

Strategies being studied to slow worsening include adjusting working conditions, increasing the time children spend outdoors, and special types of contact lenses.{{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}} In children special contact lenses appear to slow worsening of nearsightedness.{{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}}

A number of questionnaires exist to determine quality of life impact of refractive errors and their correction.{{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}}{{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}}

File:Refractive errors world map - DALY - WHO2004.svg per 100,000 people due to refractive errors in 2004.{{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 }}{{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. The number of people globally with refractive errors that have not been corrected was estimated at 660 million (10 per 100 people) in 2013.

Refractive errors are the first common cause of visual impairment and second most common cause of visual loss .{{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}} The assessment of refractive error is now done in DALY (Disability Adjusted Life Years) which showed an 8% increase from 1990 to 2019.{{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}}{{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. Rates vary between regions of the world with about 25% of Europeans and 80% of Asians affected. Near-sightedness is one of the most prevalent disorders of the eye. Rates among adults are between 15 and 49% while rates among children are between 1.2 and 42%. 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 system. Presbyopia affects most people over the age of 35, and nearly 100% of people by the ages of 55–65. Uncorrected refractive error is responsible for visual impairment and disability for many people worldwide. It is one of the most common causes of vision loss along with cataracts, macular degeneration, and vitamin A deficiency.

The yearly cost of correcting refractive errors is estimated at 3.9 to 7.2 billion dollars in the United States.{{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}}

{{Clear}}

• Dioptre
• Focal length
• Optical power

{{Reflist}}

{{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

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