Editing Strabismus (section)

== Pathophysiology ==
The [[extraocular muscles]] control the position of the eyes.  Thus, a problem with the muscles or the nerves controlling them can cause paralytic strabismus.  The extraocular muscles are controlled by cranial nerves [[Oculomotor nerve|III]], [[Trochlear nerve|IV]], and [[Abducens nerve|VI]]. An [[Oculomotor nerve palsy|impairment of cranial nerve III]] causes the associated eye to deviate down and out and may or may not affect the size of the pupil.  [[Fourth nerve palsy|Impairment of cranial nerve IV]], which can be [[Congenital fourth nerve palsy|congenital]], causes the associated eye to drift up and perhaps slightly inward. [[Sixth nerve palsy]] causes the associated eye to deviate inward and has many causes due to the relatively long path of the nerve.  [[Intracranial pressure|Increased cranial pressure]] can compress the nerve as it runs between the [[Clivus (anatomy)|clivus]] and [[brain stem]].<ref name=vaughan />{{Page needed|date=May 2017}}<ref name="pmid18258705">{{cite journal |vauthors=Adachi M, Kabasawa H, Kawaguchi E |title=Depiction of the cranial nerves within the brain stem with use of PROPELLER multishot diffusion-weighted imaging |journal=AJNR Am J Neuroradiol |volume=29 |issue=5 |pages=911–2 |date=May 2008 |pmid=18258705 |pmc=8128587 |doi=10.3174/ajnr.A0957}}</ref><ref>{{Cite web|url=https://www.merckmanuals.com/professional/neurologic-disorders/craniocervical-junction-abnormalities/craniocervical-junction-abnormalities|title=Craniocervical Junction Abnormalities - Neurologic Disorders|website=Merck Manuals Professional Edition}}</ref><ref>{{Cite book|url=https://doi.org/10.1007/978-1-60327-455-5_15|title=Neuroscience in Medicine|first=Harold H.|last=Traurig|editor-first=P. Michael|editor-last=Conn|date=February 6, 2008|publisher=Humana Press|pages=247–269|via=Springer Link|doi=10.1007/978-1-60327-455-5_15}}</ref>

Evidence indicates a cause for strabismus may lie with the input provided to the [[visual cortex]].<ref>{{cite journal | vauthors = Tychsen L | title = The cause of infantile strabismus lies upstairs in the cerebral cortex, not downstairs in the brainstem | journal = Archives of Ophthalmology | volume = 130 | issue = 8 | pages = 1060–1 | date = August 2012 | pmid = 22893080 | doi = 10.1001/archophthalmol.2012.1481 }}</ref>

Amblyopia may also cause strabismus.  If a great difference in clarity occurs between the images from the right and left eyes, input may be insufficient to correctly reposition the eyes.  Other causes of a visual difference between right and left eyes, such as asymmetrical cataracts, refractive error, or other eye disease, can also cause or worsen strabismus.<ref name=vaughan>{{cite book |first1=Emmett T. |last1=Cunningham |first2=Paul |last2=Riordan-Eva |title = Vaughan & Asbury's general ophthalmology. |publisher = McGraw-Hill Medical |isbn = 978-0-07-163420-5 |edition = 18th |date=May 17, 2011 }}</ref>{{Page needed|date=May 2017}}