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| | '''For patient information, click [[Myopia (patient information)|here]]''' |
| | {{Myopia}} |
| | {{CMG}} {{AE}} {{SME}} |
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| {{SI}} | | {{SK}} Shortsightedness; Refractive error - nearsightedness |
| | ==[[Myopia overview|Overview]]== |
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| {{CMG}}
| | ==[[Myopia historical perspective|Historical Perspective]]== |
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| ==Overview== | | ==[[Myopia classification|Classification]]== |
| [[Image:Uploadwontworktryin325034503509.jpg|frame|Normal vision. Courtesy [[National Institutes of Health|NIH]] [[National Eye Institute]]]]
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| [[Image:Fileisnotcorruptedactuallyupload3453405.jpg|frame|The same view with myopia. (Camera lens was adjusted in a way to physically simulate myopia.)]]
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| [[Image:Myopia.svg|thumb|250 px|right|Compensating for myopia using a corrective lens.]] | |
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| '''Myopia''' (from [[Greek language|Greek]]: μυωπία ''myopia'' "near-sightedness"<ref>http://www.etymonline.com/index.php?term=myopia</ref>), also called '''near-''' or '''short-sightedness''', is a [[Refractive error|refractive defect]] of the [[eye]] in which [[collimated light]] produces image [[focus (optics)|focus]] in front of the [[retina]] when [[accommodation (eye)|accommodation]] is relaxed.
| | ==[[Myopia pathophysiology|Pathophysiology]]== |
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| Those with myopia [[Visual perception|see]] nearby objects clearly but distant objects appear [[Focus (optics)|blurred]]. With myopia, the eyeball is too long, or the [[cornea]] is too steep, so images are focused in the vitreous inside the eye rather than on the [[retina]] at the back of the eye. The opposite defect of myopia is [[hyperopia]] or "farsightedness" or "long-sightedness" — this is where the cornea is too flat or the eye is too short.
| | ==[[Myopia causes|Causes]]== |
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| Mainstream [[ophthalmologist]]s and [[optometrist]]s most commonly correct myopia through the use of [[corrective lens]]es, such as [[glasses]] or [[contact lens]]es. It may also be corrected by [[refractive surgery]], such as [[LASIK]]. The corrective [[lens (optics)|lenses]] have a negative [[optical power]] (i.e. are concave) which compensates for the excessive positive diopters of the myopic eye. In some cases, [[pinhole glasses]] are used by patients with low-level myopia. These work by reducing the blur circle formed on the retina.
| | ==[[Myopia differential diagnosis|Differentiating Myopia from other Diseases]]== |
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| ==Classification== | | ==[[Myopia epidemiology and demographics|Epidemiology and Demographics]]== |
| Myopia has been classified in various manners.<ref name="Grosvenor">Grosvenor T. "A review and a suggested classification system for myopia on the basis of age-related prevalence and age of onset." ''Am J Optom Physiol Opt.'' 1987 Jul;64(7):545-54. PMID 3307441</ref><ref name="Borish">Borish, Irvin M. (1949). ''Clinical Refraction''. Chicago: The Professional Press.</ref><ref name="Duke-Elder">Duke-Elder, Sir Stewart (1969). ''The Practice of Refraction'' (8th ed.). St. Louis: The C.V. Mosby Company. ISBN 0-7000-1410-1.</ref> | |
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| ===Etiology=== | | ==[[Myopia risk factors|Risk Factors]]== |
| [[Ivan Borish|Borish]] and [[Sir Stewart Duke-Elder|Duke-Elder]] classified myopia by cause:<ref name="Borish"/><ref name="Duke-Elder"/>
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| *'''Axial myopia''' is attributed to an increase in the eye's axial length.<ref name="Cline">{{cite book|last=Cline|first=D|coauthors=Hofstetter HW; Griffin JR|authorlink=|title=Dictionary of Visual Science|edition=4th ed|publisher=Butterworth-Heinemann|location=Boston|year=1997|isbn=0-7506-9895-0|series=}}</ref>
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| *'''Refractive myopia''' is attributed to the condition of the refractive elements of the eye.<ref name="Cline"/> Borish further subclassified refractive myopia:<ref name="Borish"/>
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| :*'''Curvature myopia''' is attributed to excessive, or increased, curvature of one or more of the refractive surfaces of the eye, especially the cornea.<ref name="Cline"/> In those with [[Cohen syndrome]], myopia appears to result from high corneal and lenticular power.<ref>{{cite journal|last=Summanen|first=P|coauthors=Kivitie-Kallio, S; Norio, R; Raitta, C; Kivelä, T|title=Mechanisms of myopia in Cohen syndrome mapped to chromosome 8q22|journal=Invest. Ophthalmol. Vis. Sci.|volume=43|issue=5|pages=1686–1693|year=2002|pmid=11980891}}</ref>
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| :*'''Index myopia''' is attributed to variation in the [[index of refraction]] of one or more of the ocular media.<ref name="Cline"/>
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| ===Clinical entity=== | | ==[[Myopia screening|Screening]]== |
| Various forms of myopia have been described by their clinical appearance:<ref name="Duke-Elder"/><ref name="Goss">{{cite book|last=Goss|first= DA|coauthors=Eskridge JB|chapter=Myopia|editor=Amos, JB (ed)|title=Diagnosis and management in vision care|edition=|publisher=Butterworths|location=Boston|year=1988|isbn=0409950823|pages=445|oclc=14967262}}</ref>
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| *'''Simple myopia''' is more common than other types of myopia and is characterized by an eye that is too long for its [[optical power]] (which is determined by the [[cornea]] and [[lens (anatomy)|crystalline lens]]) or optically too powerful for its axial length.<ref name="AOA">American Optometric Association. ''[http://www.aoa.org/documents/CPG-15.pdf Optometric Clinical Practice Guideline: Care of the patient with myopia.]'' 1997.</ref> Both genetic and environmental factors, particularly significant amounts of near work, are thought to contribute to the development of simple myopia.<ref name="AOA"/>
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| *'''Degenerative myopia''', also known as '''malignant, pathological, or progressive myopia''', is characterized by marked fundus changes, such as posterior staphyloma, and associated with a high refractive error and subnormal visual acuity after correction.<ref name="Cline"/> This form of myopia gets progressively worse over time. Degenerative myopia has been reported as one of the main causes of [[visual impairment]].<ref>Li CY, Lin KK, Lin YC, Lee JS. [http://www.cgmh.org.tw/cgmj/2503/250302.pdf "Low vision and methods of rehabilitation: a comparison between the past and present."] ''Chang Gung Med J.'' 2002 Mar;25(3):153-61. PMID 12022735.</ref> Myopia with degenerative changes has been described as being very common in certain races and cultures, such as Chinese, Japanese, Arab, and Jewish people.<ref name="Verma">Verma A, Singh D. [http://www.emedicine.com/oph/topic668.htm "Myopia, Phakic IOL."] eMedicine.com. August 19, 2005.</ref>
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| *'''Nocturnal myopia''', also known as ''night myopia'' or ''twilight myopia'', is a condition in which the eye has a greater difficulty seeing in low illumination areas, even though its daytime vision is normal. Essentially, the eye's far point of an individual's focus varies with the level of light. Night myopia is believed to be caused by pupils dilating to let more light in, which adds aberrations resulting in becoming more nearsighted. A stronger prescription for myopic night drivers is often needed. Younger people are more likely to be affected by night myopia than the elderly.<ref>The Eyecare Trust. ''[http://www.eye-care.org.uk/item_view.php?item_id=52&content_id=3 Night Driving - The Facts.]'' January 26, 2005.</ref>
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| *'''Pseudomyopia''' is the blurring of distance vision brought about by spasm of the [[ciliary muscle]].<ref name="Cassin">Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainsville, Florida: Triad Publishing Company, 1990.</ref>
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| *'''Induced myopia''', also known as '''acquired myopia''', results from exposure to various [[pharmaceutical]]s, increases in [[glucose]] levels, [[nuclear sclerosis]], or other anomalous conditions.<ref name="AOA"/> The encircling bands used in the repair of retinal detachments may induce myopia by increasing the axial length of the eye.<ref>{{cite journal|last=Vukojević|first=N|coauthors=Sikić J, Curković T, Juratovac Z, Katusic D, Saric B, Jukic T|title=Axial eye length after retinal detachment surgery|journal=Collegium antropologicum|volume=29|issue=Suppl 1|pages=25–27|year=2005|pmid=16193671 |doi=}}</ref>
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| :*'''Index myopia''' is attributed to variation in the index of refraction of one or more of the ocular media.<ref name="Cline"/> Cataracts may lead to index myopia.<ref>{{cite journal|last=Metge|first=P|coauthors=Donnadieu M |title=[Myopia and cataract]|language=French|journal=La Revue du praticien|volume=43|issue=14|pages=1784–1786|year=1993|pmid=8310218 |doi=}}</ref>
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| :*'''Form deprivation myopia''' is a type of myopia that occurs when the eye is deprived of clear form vision.<ref name="Shen">{{cite journal|last=Shen|first=W|coauthors=Vijayan M, Sivak JG |title=Inducing form-deprivation myopia in fish|url=http://www.iovs.org/cgi/content/full/46/5/1797|journal=Invest. Ophthalmol. Vis. Sci.|volume=46|issue=5|pages=1797–1803|year=2005|pmid=15851585|doi=10.1167/iovs.04-1318}}</ref> Myopia is often induced this way in various animal models to study the pathogenesis and mechanism of myopia development.<ref name="Shen"/>
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| ===Degree=== | | ==[[Myopia natural history, complications and prognosis|Natural History, Complications and Prognosis]]== |
| Myopia, which is measured in [[diopters]] by the strength or [[optical power]] of a corrective lens that focuses distant images on the retina, has also been classfied by degree or severity:<ref name="Grosvenor"/>
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| *'''Low myopia''' usually describes myopia of −3.00 diopters or less.<ref name="Cline"/>
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| *'''Medium myopia''' usually describes myopia between −3.00 and −6.00 diopters.<ref name="Cline">Cline D; Hofstetter HW; Griffin JR. ''Dictionary of Visual Science''. 4th ed. Butterworth-Heinemann, Boston 1997. ISBN 0-7506-9895-0</ref> Those with moderate amounts of myopia are more likely to have [[pigment dispersion syndrome]] or [[glaucoma|pigmentary glaucoma]].<ref>[http://www.eyemdlink.com/Condition.asp?ConditionID=2 "Glaucoma."] EyeMDLink.com. Retrieved August 27, 2006.</ref>
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| *'''High myopia''' usually describes myopia of −6.00 or more.<ref name="Cline">Cline D; Hofstetter HW; Griffin JR. ''Dictionary of Visual Science''. 4th ed. Butterworth-Heinemann, Boston 1997. ISBN 0-7506-9895-0</ref> People with high myopia are more likely to have [[retinal detachment]]s<ref>Larkin GL. [http://www.emedicine.com/EMERG/topic504.htm "Retinal Detachment."] eMedicine.com. April 11, 2006.</ref> and [[glaucoma|primary open angle glaucoma]].<ref>[http://www.agingeye.net/glaucoma/glaucomainformation.php "More Information on Glaucoma."] AgingEye Times. Retrieved August 27, 2006.</ref> They are also more likely to experience [[floater]]s, shadow-like shapes which appear singly or in clusters in the [[visual field|field of vision]]. Roughly 30% of myopes have high myopia.<ref name="Verma"/>
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| ===Age of onset===
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| Myopia is sometimes classified by the age of onset:<ref name="Grosvenor"/>
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| *'''Congenital myopia''', also known as '''infantile myopia''', is present at birth and persists through infancy.<ref name="AOA"/>
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| *'''Youth onset myopia''' occurs prior to age 20.<ref name="AOA"/>
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| :*'''School myopia''' appears during childhood, particularly the school-age years.<ref name="Morgan 1">Morgan I, Rose K. "How genetic is school myopia?" ''Prog Retin Eye Res.'' 2005 Jan;24(1):1-38. PMID 15555525.</ref> This form of myopia is attributed to the use of the eyes for close work during the school years.<ref name="Cline"/>
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| *'''Adult onset myopia'''
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| :*'''Early adult onset myopia''' occurs between ages 20 and 40.<ref name="AOA"/>
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| :*'''Late adult onset myopia''' occurs after age 40.<ref name="AOA"/>
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| ==Epidemiology==
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| The global prevalence of refractive errors has been estimated from 800 million to 2.3 billion.<ref>Dunaway D, Berger I. [http://www.infocusonline.org/WORLDWIDE%20DISTRIBUTION%20OF%20VISUAL%20REFRACTIVE%20ERROR1.doc "Worldwide Distribution of Visual Refractive Errors and What to Expect at a Particular Location."] Retrieved August 31,2006.</ref> The incidence of myopia within sampled population often varies with [[age]], country, [[sex]], [[race]], [[ethnicity]], occupation, environment, and other factors.<ref name="Verma"/><ref name="Fredrick">Fredrick DR. [http://bmj.bmjjournals.com/cgi/content/full/324/7347/1195#B15 "Myopia."] ''BMJ.'' 2002 May 18;324(7347):1195-9. PMID 12016188.</ref> Variability in testing and data collection methods makes comparisons of prevalence and progression difficult.<ref>National Research Council Commission. [http://darwin.nap.edu/books/0309040817/html "Myopia: Prevalence and Progression."] Washington, D.C. : National Academy Press, 1989. ISBN 0-309-04081-7</ref>
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| In some areas, such as [[Japan]], [[Singapore]] and [[Taiwan]], up to 44% of the adult population is myopic.
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| A recent study involving first-year undergraduate students in the United Kingdom found that 50% of [[United Kingdom|British]] whites and 53.4% of British Asians were myopic.<ref>Logan NS, Davies LN, Mallen EA, Gilmartin B. Ametropia and ocular biometry in a UK university student population. Optom Vis Sci. 2005 Apr;82(4):261-6. PMID 15829853.</ref>
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| In [[Australia]], the overall prevalence of myopia (worse than −0.50 diopters) has been estimated to be 17%.<ref>Wensor M, McCarty CA, Taylor HR. Prevalence and risk factors of myopia in Victoria, Australia. Arch Ophthalmol. 1999 May;117(5):658-63. PMID 10326965.</ref> In one recent study, less than 1 in 10 (8.4%) Australian children between the ages of 4 and 12 were found to have myopia greater than −0.50 diopters.<ref>Junghans BM, Crewther SG. [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15705207 "Little evidence for an epidemic of myopia in Australian primary school children over the last 30 years."] ''BMC Ophthalmol.'' 2005 Feb 11;5(1):1. PMID 15705207.</ref> A recent review found that 16.4% of Australians aged 40 or over have at least −1.00 diopters of myopia and 2.5% have at least −5.00 diopters.<ref>Kempen JH, Mitchell P, Lee KE, Tielsch JM, Broman AT, Taylor HR, Ikram MK, Congdon NG, O'Colmain BJ; Eye Diseases Prevalence Research Group. "The prevalence of refractive errors among adults in the United States, Western Europe, and Australia." ''Arch Ophthalmol.'' 2004 Apr;122(4):495-505. PMID 15078666.</ref>
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| In [[Brazil]], a 2005 study estimated that 6.4% of Brazilians between the ages of 12 and 59 had −1.00 diopter or myopia or more, compared with 2.7% of the indigenous people in northwestern Brazil.<ref>Thorn F, Cruz AA, Machado AJ, Carvalho RA. "Refractive status of indigenous people in the northwestern Amazon region of Brazil." ''Optom Vis Sci.'' 2005 Apr;82(4):267-72. PMID 15829854.</ref> Another found nearly 1 in 8 (13.3%) of the students in one city were myopic.<ref>Garcia CA, Orefice F, Nobre GF, Souza Dde B, Rocha ML, Vianna RN. [http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0004-27492005000300009&tlng=en&lng=en&nrm=iso "Prevalence of refractive errors in students in Northeastern Brazil."] ''Arq Bras Oftalmol.'' 2005 May-Jun;68(3):321-5. Epub 2005 Jul 26. PMID 16059562.</ref>
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| In [[Greece]], the prevalence of myopia among 15 to 18 year old students was found to be 36.8%.<ref name="Mavracanas">Mavracanas TA, Mandalos A, Peios D, Golias V, Megalou K, Gregoriadou A, Delidou K, Katsougiannopoulos B. [http://www.blackwell-synergy.com/doi/abs/10.1034/j.1600-0420.2000.078006656.x#search=%22myopia%2C%20prevalence%22 "Prevalence of myopia in a sample of Greek students."] ''Acta Ophthalmol Scand.'' 2000 Dec;78(6):656-9. PMID 11167226.</ref>
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| In [[India]], the prevalence of myopia in the general population has been reported to be only 6.9%.<ref>Mohan M, Pakrasi S, Zutshi R. "Myopia in India." ''Acta Ophthalmol Suppl.'' 1988;185:19-23. PMID 2853533.</ref><ref name="Mavracanas"/>
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| A recent review found that 26.6% of Western Europeans aged 40 or over have at least −1.00 diopters of myopia and 4.6% have at least −5.00 diopters.<ref>Kempen JH, Mitchell P, Lee KE, Tielsch JM, Broman AT, Taylor HR, Ikram MK, Congdon NG, O'Colmain BJ; Eye Diseases Prevalence Research Group. "The prevalence of refractive errors among adults in the United States, Western Europe, and Australia." ''Arch Ophthalmol.'' 2004 Apr;122(4):495-505. PMID 15078666.</ref>
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| In the [[United States]], the prevalence of myopia has been estimated at 20%.<ref name="Verma"/> Nearly 1 in 10 (9.2%) American children between the ages of 5 and 17 have myopia.<ref>Kleinstein RN, Jones LA, Hullett S, Kwon S, Lee RJ, Friedman NE, Manny RE, Mutti DO, Yu JA, Zadnik K; Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study Group. [http://archopht.ama-assn.org/cgi/content/abstract/121/8/1141 "Refractive error and ethnicity in children."] ''Arch Ophthalmol.'' 2003 Aug;121(8):1141-7. PMID 12912692.</ref> Approximately 25% of Americans between the ages of 12 and 54 have the condition.<ref name="Sperduto">Sperduto RD, Seigel D, Roberts J, Rowland M. "Prevalence of myopia in the United States." ''Arch Ophthalmol.'' 1983 Mar;101(3):405-7. PMID 6830491.</ref> A recent review found that 25.4% of Americans aged 40 or over have at least −1.00 diopters of myopia and 4.5% have at least −5.00 diopters.<ref>Kempen JH, Mitchell P, Lee KE, Tielsch JM, Broman AT, Taylor HR, Ikram MK, Congdon NG, O'Colmain BJ; Eye Diseases Prevalence Research Group. "The prevalence of refractive errors among adults in the United States, Western Europe, and Australia." ''Arch Ophthalmol.'' 2004 Apr;122(4):495-505. PMID 15078666.</ref>
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| A study of Jordanian adults aged 17 to 40 found that over half (53.7%) were myopic.<ref>Mallen EA, Gammoh Y, Al-Bdour M, Sayegh FN. "Refractive error and ocular biometry in Jordanian adults." ''Ophthalmic Physiol Opt.'' 2005 Jul;25(4):302-9. PMID 15953114.</ref>
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| ===Ethnicity and race===
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| The prevalence of myopia in has been reported as high as 70-90% in some [[Asia]]n countries. 30-40% in Europe and the United States, and 10-20% in Africa.<ref name="Fredrick"/>
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| Myopia is less common in [[Black people|black]], [[Nubian]]s, and [[Sudanese]] people.<ref name="Verma"/> In Americans between the ages of 12 and 54, myopia has been found to affect whites less than blacks.<ref name="Sperduto"/>. Asians had the highest prevalence (18.5%), followed by Hispanics (13.2%). Whites had the lowest prevalence of myopia (4.4%), which was not significantly different from African Americans (6.6%). For hyperopia, whites had the highest prevalence (19.3%), followed by Hispanics (12.7%). Asians had the lowest prevalence of hyperopia (6.3%) and were not significantly different from African Americans (6.4%). For [[astigmatism]], Asians and Hispanics had the highest prevalences (33.6% and 36.9%, respectively) and did not differ from each other ([[P-value|P]] = .17). African Americans had the lowest prevalence of astigmatism (20.0%), followed by whites (26.4%)<ref>{{cite journal|last=Kleinstein|first=RN|coauthors=Jones LA, Hullett S, Kwon S, Lee RJ, Friedman NE, Manny RE, Mutti DO, Yu JA, Zadnik K|title=Refractive error and ethnicity in children |journal=Arch. Ophthalmol. |volume=121 |issue=8 |pages=1141–1147 |year=2003 |pmid=12912692 |doi=10.1001/archopht.121.8.1141}}</ref>.
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| ===Education, intelligence, and IQ===
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| A number of studies have shown that the prevalence of myopia increases with level of education <ref name="Sperduto"/><ref name="Mavracanas"/> and many studies have shown a relationship between myopia and [[IQ]]. However, care must be taken in interpreting these results as [[correlation does not imply causation]].
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| According to [[Arthur Jensen]], myopes average 7-8 IQ points higher than non-myopes. The relationship also holds within families, and siblings with a higher degree of [[refraction error]] average higher IQs than siblings with less refraction error. Jensen believes that this indicates myopia and IQ are [[pleiotropic|pleiotropically]] related as they are caused or influenced by the same genes. The mechanism that has caused a relationship between myopia and IQ is not yet known with certainty.
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| ==Etiology and pathogenesis==
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| Because in the most common, "simple" myopia, the eye length is too long, any [[etiologic]] explanation must account for such axial elongation. To date, no single [[theory]] has been able to satisfactorily explain this elongation.
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| In the early [[1900s]], [[William Bates]] controversially asserted that myopia, as with all refractive errors, resulted from a particular type of "eyestrain" that was itself a result of "mental strain".<ref>[http://www.iblindness.org/books/bates/ch10.html "Chapter X: Strain."]</ref> He stated that the shape of the eyeball responded instantaneously to the action of the [[extraocular muscles]] upon it<ref>[http://www.iblindness.org/books/bates/ch7.html "Chapter VII: The Variability of the Refraction of the Eye."]</ref> and that myopia was produced due to contraction of the [[inferior oblique muscle|inferior oblique]] and [[superior oblique muscle]]s which lengthened the eye.<ref>[http://www.iblindness.org/books/bates/ch4.html Chapter IV : The Truth about Accommodation as Demonstrated by Experiments on the Eye Muscles of Fish, Cats, Dogs, Rabbits and Other Animals."]</ref> According to Bates, myopia was associated with a "strain" to see distance objects rather than near work.<ref>[http://www.iblindness.org/books/bates/ch1.html "Chapter I: Introductory."]</ref> Bates theories were rejected by mainstream ophthalmologists of his time and remain so today. <ref name="Bradley">{{cite news
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| | author=Robyn E. Bradley
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| | title=ADVOCATES SEE ONLY BENEFITS FROM EYE EXERCISES
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| | publisher=The Boston Globe (MA)
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| |date=September 23, 2003
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| | url=http://visioneducators.com/articles/advocates_see_only_benefits_from_eye_exercises.pdf }}</ref><ref name="Rawstron">{{cite journal
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| | author=Rawstron JA, Burley CD, Elder MJ
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| | journal=J Pediatr Ophthalmol Strabismus
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| | year=2005
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| | volume=42
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| | issue=2
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| | pages=82-8
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| | title=A systematic review of the applicability and efficacy of eye exercises.
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| | url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=15825744&query_hl=13&itool=pubmed_DocSum}}</ref>
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| In the mid-1900s, mainstream ophthalmologists and optometrists believed myopia to be primarily hereditary; the influence of near work in its development seemed "incidental" and the increased prevalence of the condition with increasing age was viewed as a "statistical curiosity".<ref name="Borish"/><ref name="Duke-Elder"/><ref name="Mutti">Mutti D. [http://www.revoptom.com/index.asp?ArticleType=SiteSpec&page=osc/apr01/lesson_0401.htm "Can We Conquer Myopia?"] ''Review of Optomery.'' Optometric Study Center: April, 2001.</ref>
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| Among mainstream researchers and [[eye care professional]]s, myopia is now thought to be a combination of genetic and environmental factors.<ref name="AOA"/><ref name="Morgan 1"/>
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| There are currently two basic mechanisms believed to cause myopia: [[form deprivation]] (also known as pattern deprivation<ref>http://arapaho.nsuok.edu/~salmonto/VSIII_2006/Lecture27.pdf </ref>) and [[defocus aberration|optical defocus]].<ref name="Saw 1">Saw SM, Gazzard G, Au Eong KG, Tan DT. [http://bjo.bmjjournals.com/cgi/content/short/86/11/1306 "Myopia: attempts to arrest progression."] ''Br J Ophthalmol.'' 2002 Nov;86(11):1306-11. PMID 12386095.</ref> Form deprivation occurs when the image quality on the [[retina]] is reduced; optical defocus occurs when light focus in front of or behind the retina. Numerous experiments with animals have shown that myopia can be artificially generated by inducing either of these conditions. In animal models wearing negative spectacle lenses, axial myopia has been shown to occur as the eye elongates to compensate for optical defocus.<ref name="Saw 1"/> The exact mechanism of this image-controlled elongation of the eye is still unknown. It has been suggested that [[accommodative lag]] leads to blur (i.e. optical defocus) which in turn stimulates axial elongation and myopia.<ref>Schor C. "The influence of interactions between accommodation and convergence on the lag of accommodation." ''Ophthalmic Physiol Opt.'' 1999 Mar;19(2):134-50. PMID 10615449.</ref>
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| ===Theories===
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| *'''Combination of genetic and environmental factors''' — In China, myopia is more common in those with higher education background<ref name="Xu">Xu L, Li J, Cui T, Hu A, Fan G, Zhang R, Yang H, Sun B, Jonas JB. "Refractive error in urban and rural adult Chinese in Beijing." ''Ophthalmology.'' 2005 Oct;112(10):1676-83. PMID 16111755.</ref> and some studies suggest that near work may exacerbate a genetic predisposition to develop myopia.<ref name="Wolffsohn">Wolffsohn JS, Gilmartin B, Li RW, Edwards MH, Chat SW, Lew JK, Yu BS.
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| [http://www.iovs.org/cgi/content/full/44/5/2284 "Nearwork-induced transient myopia in preadolescent Hong Kong Chinese."]
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| ''Invest Ophthalmol Vis Sci.'' 2003 May;44(5):2284-9. PMID 12714672.</ref> Other studies have shown that near work (reading, computer games) may not be associated with myopic progression, however<ref>{{cite journal | author = Saw S, Tong L, Chua W, Chia K, Koh D, Tan D, Katz J | title = Incidence and progression of myopia in Singaporean school children. | journal = Invest Ophthalmol Vis Sci | volume = 46 | issue = 1 | pages = 51-7 | year = 2005 | id = PMID 15623754}}</ref>. A "genetic susceptibility" to environmental factors has been postulated as one explanation for the varying degrees of myopia among individuals or populations,<ref name="Hammond">Hammond CJ, Andrew T, Mak YT, Spector TD. [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15307048 "A susceptibility locus for myopia in the normal population is linked to the PAX6 gene region on chromosome 11: a genomewide scan of dizygotic twins."] ''Am J Hum Genet.'' 2004 Aug;75(2):294-304. Epub 2004 Jun 24. PMID 15307048</ref> but there exists some difference of opinion as to whether it exists.<ref name="Morgan 1"/><ref name="Morgan 2">Morgan I, Megaw P. Using natural STOP growth signals to prevent excessive axial elongation and the development of myopia. Ann Acad Med Singapore. 2004 Jan;33(1):16-20. PMID 15008556</ref> High heritability simply means that most of the variation in a particular population at a particular time is due to genetic differences. If the environment changes — as, for example, it has by the introduction of televisions and computers — the incidence of myopia can change as a result, even though heritability remains high. From a slightly different point of view it could be concluded that — determined by heritage — some people are at a higher risk to develop myopia when exposed to modern environmental conditions with a lot of extensive near work like reading. In other words, it is often not the myopia itself which is inherited, but the reaction to specific environmental conditions — and this reaction can be the onset and the progression of myopia.
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| *'''Genetic factors''' — The wide variability of the prevalence of myopia in different ethnic groups has been reported as additional evidence supporting the role of genetics in the development of myopia.<ref>Saw SM, Katz J, Schein OD, Chew SJ, Chan TK. [http://epirev.oxfordjournals.org/cgi/reprint/18/2/175.pdf?ijkey=4b53ec70497f8fb9e4972067851564674f1a6f08 "Epidemiology of myopia."] ''Epidemiol Rev.'' 1996;18(2):175-87. PMID 9021311.</ref> Measures of the [[heritability]] of myopia have yielded figures as high as 89%, and recent research has identified [[gene]]s that may be responsible: defective versions of the [[PAX6]] gene seem to be associated with myopia in [[twin studies]] [http://www.sciencenews.org/articles/20040710/fob1.asp]. Under this theory, the eye is slightly elongated front to back as a result of faults during development, causing images to be [[Focus (optics)|focused]] in front of the [[retina]] rather than directly on it. It is usually discovered during the pre-teen years between eight and twelve years of age. It most often worsens gradually as the eye grows during [[adolescence]] and then levels off as a person reaches adulthood. Genetic factors can work in various biochemical ways to cause myopia, a weak or degraded [[connective tissue]] is a very essential one. Genetic factors include an inherited, increased susceptibility for environmental influences like excessive near work, and the fact that some people do not develop myopia in spite of very adverse conditions is a clear indication that heredity is involved somehow in any case.
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| *'''Environmental factors''' — It has been suggested that a genetic susceptibility to myopia does not exist.<ref name="Morgan 1"/> A high heritability of myopia (as for any other condition) does not mean that environmental factors and lifestyle have no effect on the development of the condition. Some recommend a variety of [[Bates Method|eye exercises]] to strengthen the [[ciliary muscle]]. Other theories suggest that the eyes become strained by the constant extra work involved in "nearwork" and get stuck in the near position, and eye exercises can help loosen the muscles up thereby freeing it for far vision. These primarily mechanical models appear to be in contrast to research results, which show that the myopic elongation of the eye can be caused by the image quality, with biochemical processes as the actuator. Common to both views is, however, that extensive near work and corresponding accommodation can be essential for the onset and the progression of myopia.
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| :One Austrian study confirmed that the axial length of the eye does mildly increase while reading, but attributed this elongation due to contraction of the ciliary muscle during [[Accommodation (eye)|accommodation]] (the process by which the eye increases optical power to maintain a clear image focus), not “squeezing” of the extraocular muscles.<ref>Drexler W, Findl O, Schmetterer L, Hitzenberger CK, Fercher AF. "Eye elongation during accommodation in humans: differences between emmetropes and myopes." ''Invest Ophthalmol Vis Sci.'' 1998 Oct;39(11):2140-7. PMID 9761293.</ref>
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| :Near work and nightlight exposure in childhood have been hypothesized as environmental risk factors for myopia.<ref name="Saw 2">Saw SM, Wu HM, Hong CY, Chua WH, Chia KS, Tan D. [http://bjo.bmjjournals.com/cgi/content/full/85/5/527 "Myopia and night lighting in children in Singapore."] ''Br J Ophthalmol.'' 2001 May;85(5):527-8. PMID 11316706.</ref> Although one initial study indicated a strong association between myopia and nightlight exposure,<ref>Quinn GE, Shin CH, Maguire MG, Stone RA. "Myopia and ambient lighting at night." ''Nature.'' 1999 May 13;399(6732):113-4. PMID 10335839.</ref> recent research has found none.<ref name="Saw 2"/><ref>Zadnik K, Jones LA, Irvin BC, Kleinstein RN, Manny RE, Shin JA, Mutti DO. "Myopia and ambient night-time lighting. CLEERE Study Group. Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error." ''Nature.'' 2000 Mar 9;404(6774):143-4. PMID 10724157.</ref><ref>Gwiazda J, Ong E, Held R, Thorn F. "Myopia and ambient night-time lighting." ''Nature.'' 2000 Mar 9;404(6774):144. PMID 10724158.</ref><ref>Guggenheim JA, Hill C, Yam TF. [http://bjo.bmjjournals.com/cgi/content/full/87/5/580#R13 "Myopia, genetics, and ambient lighting at night in a UK sample."] ''Br J Ophthalmol.'' 2003 May;87(5):580-2. PMID 12714399.</ref>
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| :*Near work. Near work has been implicated as a contributing factor to myopia in some studies, but refuted in others<ref>{{cite journal | author = Saw S, Tong L, Chua W, Chia K, Koh D, Tan D, Katz J | title = Incidence and progression of myopia in Singaporean school children. | journal = Invest Ophthalmol Vis Sci | volume = 46 | issue = 1 | pages = 51-7 | year = 2005 | id = PMID 15623754}}</ref>. One recent study suggested that students exposed to extensive "near work" may be at a higher risk of developing myopia, whereas extended breaks from near work during summer or winter vacations may retard myopic progression [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15926878&query_hl=11]. Near work in certain cultures (e.g. [[Vanuatu]]) does not result in greater myopia[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=3875961&query_hl=2&itool=pubmed_docsum][http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=2853534&query_hl=2&itool=pubmed_docsum][http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=3259077&query_hl=2&itool=pubmed_docsum][http://www.newscientist.com/article.ns?id=dn2120]. It has been hypothesized that this outcome may be a results of genetics or environmental factors such as diet or [[over-illumination]], changes in which seem to occur in Asian, Vanuatu and Inuit cultures acclamating to intensive early studies[http://www.newscientist.com/article.ns?id=dn2120].
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| :*Diet and nutrition - One 2002 [http://news.bbc.co.uk/1/hi/health/1909075.stm article] suggested that myopia may be caused by over-consumption of bread in childhood, or in general by diets too rich in [[carbohydrates]], which can lead to chronic [[hyperinsulinemia]]. Various other components of the diet, however, were made responsible for contributing to myopia as well, as summarized in a [http://www.myopia-manual.de documentation].
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| :*Stress has been postulated as a factor in the development of myopia.<ref>Bowan M. [http://www.nb.net/%7Esparrow/stressandeye.html "Stress and Eye: New Speculations on Refractive Error."] ''J. Behavioral Optom.'' 7(5)115-22, 1996.</ref>
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| ===Relevant research===
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| *A Turkish study found that [[accommodative convergence]], rather than accommodation, may be a factor in the onset and progression of myopia in adults.<ref>Bayramlar H, Cekic O, Hepsen IF. "Does convergence, not accommodation, cause axial-length elongation at near? A biometric study in teens." ''Ophthalmic Res.'' 1999;31(4):304-8. PMID 10325546.</ref>
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| *A recent Polish study revealed that "with-the-rule astigmatism" may lead to the creation of myopia.<ref>Czepita D, Filipiak D. [The effect of the type of astigmatism on the incidence of myopia]. ''Klin Oczna.'' 2005;107(1-3):73-4. PMID 16052807.</ref>
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| ==Presbyopia and the 'payoff' for the nearsighted==
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| Many people with myopia are able to read comfortably without eyeglasses. Myopes considering [[refractive surgery]] are advised that this may be a disadvantage after the age of 40 when the eyes become [[presbyopia|presbyopic]] and lose their ability to [[accommodation (eye)|accommodate]] or change focus.
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| ==Diagnosis== | | ==Diagnosis== |
| A diagnosis of myopia is typically confirmed during an [[eye examination]] by an [[ophthalmologist]] or an [[optometrist]]. Frequently an [[autorefractor]] or [[retinoscope]] is used to give an initial objective assessment of the refractive status of each eye, then a [[phoropter]] is used to subjectively refine the patient's [[eyeglass prescription]].
| | [[Myopia history and symptoms|History and Symptoms]] | [[Myopia physical examination|Physical Examination]] | [[Myopia other imaging findings|Other Imaging Findings]] | [[Myopia other diagnostic studies|Other Diagnostic Studies]] |
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| ==Treatment, management, and prevention==
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| [[Image:Briller2.JPG|right|thumb|Glasses are commonly used to address short-sightedness.]]
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| [[Eyeglasses]], [[contact lenses]], and [[refractive surgery]] are the primary options to treat the visual symptoms of those with myopia. [[Orthokeratology]] is the practice of using special rigid contact lenses to flatten the cornea to reduce myopia.
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| ===Eye-exercises and biofeedback===
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| Practitioners and advocates of [[alternative medicine|alternative therapies]] often recommend eye exercises and relaxation techniques such as the [[Bates method]]. However, the efficacy of these practices is disputed by scientists and eye care practitioners. <ref name="Bradley"/> A 2005 review of scientific papers on the subject concluded that there was "no clear scientific evidence" that eye exercises were effective in treating myopia. <ref name="Rawstron"/>
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| In the eighties and nineties, there was a flurry of interest in [[biofeedback]] as a possible treatment for myopia. A [[1997]] review of this biofeedback research concluded that "controlled studies to validate such methods ... have been rare and contradictory." <ref name=Rupolo>{{cite journal | author=G Rupolo, M Angi, E Sabbadin, S Caucci, E Pilotto, E Racano and C de Bertolini | journal=Psychosomatic Medicine | volume=59 | issue=3 | pages=313-317 | year=1997 | title=Treating myopia with acoustic biofeedback: a prospective study on the evolution of visual acuity and psychological distress}}</ref> It was found in one study that [[Myopia|myopes]] could improve their visual acuity with biofeedback training, but that this improvement was "instrument-specific" and did not generalise to other measures or situations. <ref name=Randle>{{cite journal | author=Randle RJ | title=Responses of myopes to volitional control training of accommodation. | journal=Ophthalmic Physiol Opt | volume=8 | pages=333-340 | year=1988}}</ref> In another study an "improvement" in visual acuity was found but the authors concluded that this could be a result of subjects learning the task <ref name=Gallaway>{{cite journal | author=Gallaway M, Pearls SM, Winkelstein AM, et al. | title=Biofeedback training of visual acuity and myopia: A pilot study. | journal=Am J Optom Physiol Opt | volume=64 | pages=62-71 | year=1987}}</ref> Finally, in an evaluation of a training system designed to improve acuity, "no significant difference was found between the control and experimental subjects" <ref name=Koslowe>{{cite journal | author=Koslowe KC, Spierer A, Rosner M, et al. | title=Evaluation of accommotrac biofeedback training for myopia control. | journal=Optom Vis Sci | volume=68 | year=1991 | pages=252-4}}</ref>
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| ===Prevention===
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| There is no universally accepted method of preventing myopia.<ref name="AOA"/> Some clinicians and researchers recommend plus power (convex) lenses in the form of single vision reading lenses or [[bifocal]]s. <ref name="AOA"/> <ref name="Rehm">Rehm, Donald "The Myopia Myth-The Truth About Nearsightedness And How To Prevent It" Chapter 6 Published by The International Myopia Prevention Assn., 1054 Gravel Hill Road, Ligonier, PA 15658. 1981 ISBN 0-9608476-0-X</ref> A recent Malaysian study reported in ''[[New Scientist]]''<ref name=NS>{{cite news | url=http://www.newscientist.com/article.ns?id=dn3082 | title=Eye correction is seriously short sighted | date=20 November 2002 | author=Andy Coghlan and Michael Le Page | publisher=New Scientist}}</ref> suggested that undercorrection of myopia caused more rapid progression of myopia,<ref>Chung K, Mohidin N, O'Leary DJ. "Undercorrection of myopia enhances rather than inhibits myopia progression." ''Vision Res.'' 2002 Oct;42(22):2555-9. PMID 12445849.</ref> However, the reliability of this data has been called into question.<ref name=Wildoset>{{cite web | title=Controlling Myopia Progression - A Confusing Story | author=The Wildoset Lab. | url=http://vision.berkeley.edu/wildsoet/myopiaNews/controllingMyopia.html | accessdate=September 1, 2006}}</ref> Many myopia treatment studies suffer from any of a number of design drawbacks: [[sample size|small numbers]], lack of adequate [[control (experiment)|control]] group, failure to [[blinding|mask examiners]] from knowledge of treatments used, etc.
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| [[Pirenzepine]] eyedrops had a limited effect on retarding myopic progression in a recent, placebo-control, double-blinded [[prospective study|prospective]] controlled study <ref name="Siatkowski">{{cite journal | author = Siatkowski R, Cotter S, Miller J, Scher C, Crockett R, Novack G | title = Safety and efficacy of 2% pirenzepine ophthalmic gel in children with myopia: a 1-year, multicenter, double-masked, placebo-controlled parallel study. | journal = Arch Ophthalmol | volume = 122 | issue = 11 | pages = 1667-74 | year = 2004 | id = PMID 15534128}}</ref>. | | ==Treatment== |
| | | [[Myopia management|Management]] | [[Myopia medical therapy|Medical Therapy]] | [[Myopia surgery|Surgery]] | [[Myopia primary prevention|Primary Prevention]] | [[Myopia cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[Myopia future or investigational therapies|Future or Investigational Therapies]] |
| ===Myopia control===
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| Various methods have been employed in an attempt to decrease the progression of myopia.<ref name="Saw 1"/> Altering the use of eyeglasses between full-time, part-time, and not at all does not appear to alter myopia progression.<ref>Ong E, Grice K, Held R, Thorn F, Gwiazda J. "Effects of spectacle intervention on the progression of myopia in children." ''Optom Vis Sci.'' 1999 Jun;76(6):363-9. PMID 10416930.</ref><ref>Parssinen O, Hemminki E, Klemetti A. Effect of spectacle use and accommodation on myopic progression: final results of a three-year randomised clinical trial among schoolchildren. Br J Ophthalmol. 1989 Jul;73(7):547-51. PMID 2667638.</ref> Bifocal and [[progressive lenses]] have not shown significant differences in altering the progression of myopia.<ref name="Saw 1"/>
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| ==Myopia as metaphor==
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| The terms ''myopia'' and ''myopic'' have also been used [[metaphor]]ically to refer to cognitive thinking and decision making that is narrow sighted or lacking in concern for long-term consequence.
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| | == Case Studies == |
| | [[Myopia case study one|Case #1]] |
| == Related Chapters == | | == Related Chapters == |
| *[[Astigmatism (eye)]] | | *[[Astigmatism (eye)]] |
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| *[[Relaxed selection]] | | *[[Relaxed selection]] |
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| ==References==
| | ==External Links== |
| {{Reflist|2}}
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| ==External links== | |
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| *[http://www.pupileyes.com/index.php?content=myopia&lang=english pupilEyes - Learn how Myopia happens] | | *[http://www.pupileyes.com/index.php?content=myopia&lang=english pupilEyes - Learn how Myopia happens] |
| *[http://www.myopia-manual.de/ ''Myopia Manual — an impartial documentation of all the reasons, therapies and recommendations''] — summary of scientific publications, status February 2007
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| *[http://www.VisionSimulations.com/ VisionSimulations.com |What the world looks like to people with various diseases and conditions of the eye]
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| *[http://vision.berkeley.edu/wildsoet/index.html The Wildsoet Lab] - Myopia research at the University of California, Berkeley
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| *[http://www.ssc.education.ed.ac.uk/resources/vi&multi/eyeconds/Myop.html Scottish Sensory Centre - Medical Info on Myopia] | | *[http://www.ssc.education.ed.ac.uk/resources/vi&multi/eyeconds/Myop.html Scottish Sensory Centre - Medical Info on Myopia] |
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| {{Eye pathology}} | | {{Eye pathology}} |
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