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Strabismus
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=== Other considerations === Strabismus can be further classified as follows: * Paretic strabismus is due to paralysis of one or several [[extraocular muscles]]. * Nonparetic strabismus is not due to paralysis of extraocular muscles. * Comitant (or ''concomitant'') strabismus is a deviation that is the same magnitude regardless of gaze position. * Noncomitant (or ''incomitant'') strabismus has a magnitude that varies as the person shifts his or her gaze up, down, or to the sides. Nonparetic strabismus is generally concomitant.<ref>{{cite web |url=http://medical-dictionary.thefreedictionary.com/concomitant+strabismus |title=concomitant strabimus |website=TheFreeDictionary |publisher=Farlex }}</ref> Most types of infant and childhood strabismus are comitant.<ref name="Wright-etal-2003-p155">{{cite book |first1 = Kenneth Weston |last1 = Wright |first2 = Peter H. |last2 = Spiegel |title = Pediatric Ophthalmology and Strabismus |url = https://books.google.com/books?id=ydim6J7sFS4C&pg=PA155 |date = January 2003 |publisher = Springer Science & Business Media |isbn = 978-0-387-95478-3 |page = 155 |via = Google Books |url-status = live |archive-url = https://web.archive.org/web/20160507063427/https://books.google.com/books?id=ydim6J7sFS4C&pg=PA155 |archive-date = May 7, 2016 |df = mdy-all }}</ref> Paretic strabismus can be either comitant or noncomitant. Incomitant strabismus is almost always caused by a limitation of ocular rotations that is due to a restriction of extraocular eye movement (ocular restriction) or due to [[extraocular muscle paresis]].<ref name="Wright-etal-2003-p155" /> Incomitant strabismus cannot be fully corrected by [[Prism (optics)|prism]] glasses, because the eyes would require different degrees of prismatic correction dependent on the direction of the gaze.<ref>{{cite web|url=http://one.aao.org/clinical-statement/adult-strabismus-surgery--january-2007 |title=Adult Strabismus Surgery β 2013 |date=April 2013 |website=ONE Network |publisher=American Association of Ophthalmology |access-date=September 6, 2014 |archive-date=September 7, 2014 |archive-url=https://web.archive.org/web/20140907005412/http://one.aao.org/clinical-statement/adult-strabismus-surgery--january-2007 |url-status=dead }}</ref> Incomitant strabismus of the eso- or exo-type are classified as "alphabet patterns": they are denoted as A- or V- or more rarely [[lambda|Ξ»]]-, Y- or X-pattern depending on the extent of convergence or divergence when the gaze moves upward or downward. These letters of the alphabet denote ocular motility pattern that have a similarity to the respective letter: in the A-pattern there is (relatively speaking) more convergence when the gaze is directed upwards and more divergence when it is directed downwards, in the V-pattern it is the contrary, in the Ξ»-, Y- and X-patterns there is little or no strabismus in the middle position but relatively more divergence in one or both of the upward and downward positions, depending on the "shape" of the letter.<ref>{{cite web |first1=James L. |last1=Plotnik |first2=Michael J. |last2=Bartiss |date=October 13, 2015 |url=http://emedicine.medscape.com/article/1199714-overview |title=A-Pattern Esotropia and Exotropia |website=Medscape |access-date=September 8, 2014 |url-status=live |archive-url=https://web.archive.org/web/20140908181215/http://emedicine.medscape.com/article/1199714-overview |archive-date=September 8, 2014 }}</ref> Types of incomitant strabismus include: [[Duane syndrome]], [[horizontal gaze palsy]], and [[congenital fibrosis of the extraocular muscles]].<ref>{{cite journal | vauthors = Engle EC | title = Genetic basis of congenital strabismus | journal = Archives of Ophthalmology | volume = 125 | issue = 2 | pages = 189β95 | date = February 2007 | pmid = 17296894 | doi = 10.1001/archopht.125.2.189 | df = mdy-all | doi-access = }}</ref> When the misalignment of the eyes is large and obvious, the strabismus is called large-angle, referring to the angle of deviation between the lines of sight of the eyes. Less severe eye turns are called small-angle strabismus. The degree of strabismus can vary based on whether the person is viewing a distant or near target. Strabismus that sets in after eye alignment had been surgically corrected is called ''consecutive strabismus''.
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