Editing Amblyopia (section)

==Cause==
Amblyopia, often referred to as "lazy eye," can be categorized into three types:

# '''Deprivation Amblyopia''': This occurs when something obstructs light from entering the eye, preventing proper vision development. A congenital cataract is an example of such a condition.
# '''Strabismic Amblyopia''': The most common form, this type arises when the eyes are not properly aligned, leading to double vision. To avoid confusion, the brain compensates by ignoring the visual input from the misaligned eye.
# '''Refractive Amblyopia''': This type is caused by a significant difference in uncorrected refractive errors, such as nearsightedness or farsightedness, between the two eyes.

===Strabismus===
{{Further|Strabismus}}
Strabismus, sometimes also incorrectly called lazy eye, is a condition in which the eyes are misaligned.<ref name=handbook>{{cite book|title=Handbook of Pediatric Strabismus and Amblyopia | last1 = Wright | first1 = Kenneth W. | last2 = Spiegel | first2 = Peter H. | last3 = Thompson | first3 = Lisa S. | name-list-style = vanc |year=2006|isbn=978-0-387-27924-4|publisher=[[Springer Science+Business Media|Springer]]|location=New York, New York}}</ref> Strabismus usually results in normal vision in the preferred sighting (or "fellow") eye (the eye that the person prefers to use), but may cause abnormal vision in the deviating or strabismic eye due to the difference between the images projecting to the brain from the two eyes.<ref>{{cite journal | vauthors = Levi DM | title = Visual processing in amblyopia: human studies | journal = Strabismus | volume = 14 | issue = 1 | pages = 11–9 | date = March 2006 | pmid = 16513566 | doi = 10.1080/09273970500536243 | s2cid = 29190763 }}</ref>
Adult-onset strabismus usually causes double vision ([[diplopia]]), since the two eyes are not fixed on the same object.
Children's brains are more [[Neuroplasticity|neuroplastic]], so can more easily adapt by [[Suppression (eye)|suppressing images]] from one of the eyes, eliminating the double vision. This plastic response of the brain interrupts the brain's normal development, resulting in the amblyopia.{{citation needed|date=July 2018}} Recent evidence points to a cause of infantile strabismus lying with the input 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>

Those with strabismic amblyopia tend to show ocular motion deficits when reading, even when they use the nonamblyopic eye. In particular, they tend to make more [[saccade]]s per line than persons with normal stereo vision, and to have a reduced [[reading speed]], especially when reading a text with small [[font size]].<ref name="pmid24370829">{{cite journal | vauthors = Kanonidou E, Gottlob I, Proudlock FA | title = The effect of font size on reading performance in strabismic amblyopia: an eye movement investigation | journal = Investigative Ophthalmology & Visual Science | volume = 55 | issue = 1 | pages = 451–9 | date = January 2014 | pmid = 24370829 | doi = 10.1167/iovs.13-13257 | doi-access = free | hdl = 2381/38991 | hdl-access = free }}</ref><ref name="pmid20207968">{{cite journal | vauthors = Kanonidou E, Proudlock FA, Gottlob I | title = Reading strategies in mild to moderate strabismic amblyopia: an eye movement investigation | journal = Investigative Ophthalmology & Visual Science | volume = 51 | issue = 7 | pages = 3502–8 | date = July 2010 | pmid = 20207968 | doi = 10.1167/iovs.09-4236 | doi-access =  }}</ref>{{primary source inline|date=February 2019}}

Strabismic amblyopia is treated by clarifying the visual image with glasses, or encouraging use of the amblyopic eye with an [[eyepatch]] over the dominant eye or [[Atropine#Ophthalmic use|pharmacologic penalization]] of the better eye. Penalization usually consists of applying [[atropine]] drops to temporarily paralyze the accommodation reflex, leading to the blurring of vision in the good eye. It also dilates the [[pupil]]. This helps to prevent the bullying and teasing associated with wearing a patch, although sometimes application of the eye drops is challenging. The ocular alignment itself may be treated with surgical or nonsurgical methods, depending on the type and severity of the strabismus.<ref name="Holmes">{{cite journal | vauthors = Holmes JM, Repka MX, Kraker RT, Clarke MP | title = The treatment of amblyopia | journal = Strabismus | volume = 14 | issue = 1 | pages = 37–42 | date = March 2006 | pmid = 16513568 | doi = 10.1080/09273970500536227 | s2cid = 31165871 }}</ref>

===Refractive===
Refractive amblyopia may result from [[anisometropia]] (unequal refractive error between the two eyes).<ref>{{cite journal | first1 = Robert F.| last1 = Rutstein | first2 = David | last2 = Corliss | name-list-style = vanc |title=Relationship between Anisometropia, Amblyopia, and Binocularity|journal=Optometry & Vision Science|date=April 1999|volume=76|issue=4| pages = 229–33 | doi = 10.1097/00006324-199904000-00026 | pmid = 10333185}}</ref><ref>{{cite journal | vauthors = Weakley DR | title = The association between nonstrabismic anisometropia, amblyopia, and subnormal binocularity | journal = Ophthalmology | volume = 108 | issue = 1 | pages = 163–71 | date = January 2001 | pmid = 11150283 | doi = 10.1016/s0161-6420(00)00425-5 }}</ref> Anisometropia exists when there is a difference in the [[refractive error|power]] between the two eyes. The eye which provides the brain with a clearer image typically becomes the dominant eye. The image in the other eye is blurred, which results in abnormal development of one half of the visual system. Refractive amblyopia is usually less severe than strabismic amblyopia and is commonly missed by [[primary care physician]]s because of its less dramatic appearance and lack of obvious physical manifestation, such as with strabismus.<ref name=AAFP>{{cite journal | vauthors = Simon JW, Kaw P | title = Commonly missed diagnoses in the childhood eye examination | journal = American Family Physician | volume = 64 | issue = 4 | pages = 623–8 | date = August 2001 | pmid = 11529261 | url = http://www.aafp.org/afp/20010815/623.html | access-date = 28 August 2005 | archive-date = 12 September 2005 | archive-url = https://web.archive.org/web/20050912000156/http://www.aafp.org/afp/20010815/623.html | url-status = dead }}</ref> Given that the refractive correction of anisometropia by means of spectacles typically leads to different image magnification for the two eyes, which may in turn prevent binocular vision, a refractive correction using [[contact lens]]es is to be considered. Also [[Refractive surgery#Children|pediatric refractive surgery]] is a treatment option, in particular if conventional approaches have failed due to [[aniseikonia]] or lack of compliance or both.<ref>{{cite journal | vauthors = Astle WF, Rahmat J, Ingram AD, Huang PT | title = Laser-assisted subepithelial keratectomy for anisometropic amblyopia in children: outcomes at 1 year | journal = Journal of Cataract and Refractive Surgery | volume = 33 | issue = 12 | pages = 2028–34 | date = December 2007 | pmid = 18053899 | doi = 10.1016/j.jcrs.2007.07.024 | s2cid = 1886316 }}</ref>

Frequently, amblyopia is associated with a combination of anisometropia and strabismus. In some cases, the vision between the eyes can differ to the point where one eye has twice average vision while the other eye is completely blind.

=== Deprivation and occlusion ===
Deprivation amblyopia (amblyopia ex anopsia) results when the ocular media become [[Opacity (optics)|opaque]], such as is the case with [[congenital cataract]] or [[cornea]]l haziness.<ref name=Angell>{{cite journal | vauthors = Angell LK, Robb RM, Berson FG | title = Visual prognosis in patients with ruptures in Descemet's membrane due to forceps injuries | journal = Archives of Ophthalmology | volume = 99 | issue = 12 | pages = 2137–9 | date = December 1981 | pmid = 7305711 | doi = 10.1001/archopht.1981.03930021013004 }}</ref> These opacities prevent adequate visual input from reaching the eye, and disrupt development. If not treated in a timely fashion, amblyopia may persist even after the cause of the opacity is removed. Sometimes, drooping of the [[eyelid]] ([[ptosis (eyelid)|ptosis]]) or some other problem causes the upper eyelid to physically occlude a child's vision, which may cause amblyopia quickly.  Occlusion amblyopia may be a complication of a [[hemangioma]] that blocks some or all of the eye. Other possible causes of deprivation and occlusion amblyopia include obstruction in the vitreous and [[aphakia]].<ref name=":0">{{Cite journal|last1=Antonio-Santos|first1=Aileen|last2=Vedula|first2=S. Swaroop|last3=Hatt|first3=Sarah R.|last4=Powell|first4=Christine|date=23 March 2020|title=Occlusion for stimulus deprivation amblyopia|journal=The Cochrane Database of Systematic Reviews|volume=3|issue=3 |pages=CD005136|doi=10.1002/14651858.CD005136.pub4|issn=1469-493X|pmc=7089638|pmid=32203629}}</ref> Deprivation amblyopia accounts for less than 3% of all individuals affected by amblyopia.<ref name=":0" />