Editing Myopia (section)

==Mechanism==
Because myopia is a refractive error, the physical cause of myopia is comparable to any optical system that is out of focus. [[Irvin Borish|Borish]] and [[Stewart Duke-Elder|Duke-Elder]] classified myopia by these physical causes:<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>
* Axial myopia is attributed to an increase in the eye's axial length.<ref name="Cline">{{cite book| vauthors = Cline D, Hofstetter HW, Griffin JR |title=Dictionary of Visual Science|edition=4th|publisher=Butterworth-Heinemann |location=Boston|year=1997|isbn=978-0-7506-9895-5}}</ref>
* Refractive myopia is attributed to the condition of the [[Refraction|refractive]] elements of the eye.<ref name="Cline" /> Borish further subclassified refractive myopia:<ref name="Borish" />
** 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 | vauthors = Summanen P, Kivitie-Kallio S, Norio R, Raitta C, Kivelä T | title = Mechanisms of myopia in Cohen syndrome mapped to chromosome 8q22 | journal = Investigative Ophthalmology & Visual Science | volume = 43 | issue = 5 | pages = 1686–93 | date = May 2002 | pmid = 11980891 }}</ref>
** Index myopia is attributed to variation in the [[Refractive index|index of refraction]] of one or more of the ocular media.<ref name="Cline" />

As with any optical system experiencing a [[defocus aberration]], the effect can be exaggerated or masked by changing the [[F-number|aperture size]]. In the case of the eye, a large pupil emphasizes refractive error and a small pupil masks it. This phenomenon can cause a condition in which an individual has a greater difficulty seeing in low-illumination areas, even though there are no symptoms in bright light, such as daylight.<ref>The Eyecare Trust. ''[http://www.eye-care.org.uk/item_pdf.php?item_id=477 Night Driving – The Facts.]'' OR ''[http://www.eyecaretrust.org.uk/pdf/night_driving_final.pdf Eye care advice for driving in the dark] {{webarchive|url=https://web.archive.org/web/20120320054904/http://www.eyecaretrust.org.uk/pdf/night_driving_final.pdf|date=20 March 2012}}'' 26 January 2005.'<!--
ORIGINAL SOURCE WAS (but this didn't work as of 2011.10.01): http://www.eye-care.org.uk/item_view.php?item_id=52&content_id=3 Night Driving – The Facts.
--></ref>

Under rare conditions, edema of the [[ciliary body]] can cause an anterior displacement of the lens, inducing a myopia shift in refractive error.<ref name="Panday2007"/>