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▲}}[[Image:Simple vestibulo-ocular reflex.PNG|thumb|300px|right|The vestibulo-ocular reflex. A rotation of the head is detected, which triggers an inhibitory signal to the [[extraocular muscles]] on one side and an excitatory signal to the muscles on the other side. The result is a compensatory movement of the eyes.]]
The '''vestibulo-ocular reflex''' ('''VOR''') is a [[reflex]]
The VOR does not depend on
In animals other
The VOR has both rotational and translational aspects. When the head rotates about any axis (horizontal, vertical, or torsional) distant visual images are stabilized by rotating the eyes about the same axis, but in the opposite direction.<ref name="Crawford1991">{{cite journal | vauthors = Crawford JD, Vilis T | title = Axes of eye rotation and Listing's law during rotations of the head | journal = Journal of Neurophysiology | volume = 65 | issue = 3 | pages = 407–23 | date = March 1991 | pmid = 2051188 | doi = 10.1152/jn.1991.65.3.407 }}</ref> When the head translates, for example during walking, the visual fixation point is maintained by rotating [[Gaze (physiology)|gaze]] direction in the opposite direction<ref>{{Cite web|url=https://collections.lib.utah.edu/details?id=187678|title=VOR (Slow and Fast) {{!}} NOVEL - Daniel Gold Collection|website=collections.lib.utah.edu|language=en|access-date=2019-10-03}}</ref>, by an amount that depends on distance.<ref name="Angelaki2004">{{cite journal | vauthors = Angelaki DE | title = Eyes on target: what neurons must do for the vestibuloocular reflex during linear motion | journal = Journal of Neurophysiology | volume = 92 | issue = 1 | pages = 20–35 | date = July 2004 | pmid = 15212435 | doi = 10.1152/jn.00047.2004 }}</ref>
==
[[Image:Vestibulo-ocular reflex EN.svg|thumb|300px]]
The
▲The main "direct path" neural circuit for the horizontal rotational VOR is fairly simple. It starts in the [[vestibular system]], where semicircular canals get activated by head rotation and send their impulses via the [[vestibular nerve]] (cranial nerve VIII) through the [[vestibular ganglion]] and end in the [[vestibular nuclei]] in the [[brainstem]]. From these nuclei, fibers cross to the contralateral cranial nerve VI nucleus ([[abducens nucleus]]). There they synapse with 2 additional pathways. One pathway projects directly to the [[lateral rectus]] of the eye via the [[abducens nerve]]. Another nerve tract projects from the abducens nucleus by the [[medial longitudinal fasciculus]] to the contralateral [[oculomotor nucleus]], which contains [[motor neuron|motorneurons]] that drive eye [[muscle]] activity, specifically activating the [[medial rectus]] muscle of the eye through the [[oculomotor nerve]] (cranial nerve III).
Another pathway (not in picture) directly projects from the vestibular nucleus through the [[ascending tract of Dieters]] to the
Similar pathways exist for the vertical and torsional components of the VOR.
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In addition to these direct pathways, which drive the velocity of eye rotation, there is an indirect pathway that builds up the position signal needed to prevent the eye from rolling back to center when the head stops moving. This pathway is particularly important when the head is moving slowly because here position signals dominate over velocity signals. David A. Robinson discovered that the eye muscles require this dual velocity-position drive, and also proposed that it must arise in the brain by mathematically integrating the velocity signal and then sending the resulting position signal to the motoneurons. Robinson was correct: the 'neural integrator' for horizontal eye position was found in the nucleus prepositus hypoglossi<ref name="Cannon1987">{{cite journal | vauthors = Cannon SC, Robinson DA | title = Loss of the neural integrator of the oculomotor system from brain stem lesions in monkey | journal = Journal of Neurophysiology | volume = 57 | issue = 5 | pages = 1383–409 | date = May 1987 | pmid = 3585473 | doi = 10.1152/jn.1987.57.5.1383 }}</ref> in the medulla, and the neural integrator for vertical and torsional eye positions was found in the interstitial nucleus of Cajal<ref name="Crawford1991#2">{{cite journal | vauthors = Crawford JD, Cadera W, Vilis T | title = Generation of torsional and vertical eye position signals by the interstitial nucleus of Cajal | journal = Science | volume = 252 | issue = 5012 | pages = 1551–3 | date = June 1991 | pmid = 2047862 | doi = 10.1126/science.2047862 | bibcode = 1991Sci...252.1551C }}</ref> in the midbrain. The same neural integrators also generate eye position for other conjugate eye movements such as saccades and smooth pursuit.
===
For instance, if the head is turned
Furthermore, some neurons from the right vestibular nucleus directly stimulate the right
===Speed===
The vestibulo-ocular reflex needs to be fast: for clear vision, head movement must be compensated almost immediately; otherwise, vision corresponds to a photograph taken with a shaky hand.
=== VOR suppression ===
During head-free pursuit of moving targets{{Clarify|reason=|date=May 2020}}, the VOR is counterproductive to the goal of reducing retinal offset. Research indicates that there exists mechanisms to suppress VOR using active visual feedback.<ref>{{Cite web|url=http://psycnet.apa.org/record/1980-24636-001|title=PsycNET|website=psycnet.apa.org|language=en|access-date=2018-05-15}}</ref> In the absence of visual feedback, such as during occlusions, we use anticipatory (extra-retinal) signals to supplement our pursuit movements by VOR suppression.<ref>{{cite journal | vauthors = Ackerley R, Barnes GR | title = The interaction of visual, vestibular and extra-retinal mechanisms in the control of head and gaze during head-free pursuit | journal = The Journal of Physiology | volume = 589 | issue = Pt 7 | pages = 1627–42 | date = April 2011 | pmid = 21300755 | pmc = 3099020 | doi = 10.1113/jphysiol.2010.199471 }}</ref>
===Gain===
The "gain" of the VOR is defined as the change in the eye angle divided by the change in the head angle during the head turn. Ideally the gain of the rotational VOR is 1.0. The gain of the horizontal and vertical VOR is usually close to 1.0, but the gain of the torsional VOR (rotation around the line of sight) is generally low.<ref name="Crawford1991"/> The gain of the translational VOR has to be adjusted for distance, because of the geometry of motion parallax. When the head translates, the angular direction of near targets changes faster than the angular direction of far targets.<ref name="Angelaki2004"/>
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[[Ethanol]] consumption can disrupt the VOR, reducing dynamic visual acuity.<ref>{{cite journal | vauthors = Schmäl F, Thiede O, Stoll W | title = Effect of ethanol on visual-vestibular interactions during vertical linear body acceleration | journal = Alcoholism, Clinical and Experimental Research | volume = 27 | issue = 9 | pages = 1520–6 | date = September 2003 | pmid = 14506414 | doi = 10.1097/01.ALC.0000087085.98504.8C | url = http://cat.inist.fr/?aModele=afficheN&cpsidt=15155766 }}</ref>
==Clinical significance==
==Testing== <!--Rapid head impulse test and Halmagyi-Curthoys redirect here-->▼
This reflex can be tested by the ''rapid head impulse test'' or ''Halmagyi–Curthoys test'', in which the head is rapidly moved to the side with force, and is controlled if the eyes succeed to remain to look in the same direction. When the function of the right balance system is reduced, by a disease or by an accident, a quick head movement to the right cannot be sensed properly anymore. As a consequence, no compensatory eye movement is generated, and the patient cannot fixate a point in space during this rapid head movement.
The head impulse test can be done at the bed side and used as a screening tool for problems with a person's vestibular system.<ref>{{Cite web|url=https://collections.lib.utah.edu/ark:/87278/s63b97tz|title=VOR (Slow and Fast)|last=Gold|first=Daniel|date=|website=Neuro-Ophthalmology Virtual Education Library (NOVEL): Daniel Gold Collection. Spencer S. Eccles Health Sciences Library.|url-status=live|archive-url=|archive-date=|access-date=20 November 2019}}</ref> It can also be diagnostically tested by doing a video-head impose test (VHIT). In this diagnostic test, a person wears highly sensitive goggles that detect rapid changes in eye movement. This test can provide site-specific information on vestibular system and its function.<ref>{{cite journal | vauthors = McGarvie LA, MacDougall HG, Halmagyi GM, Burgess AM, Weber KP, Curthoys IS | title = The Video Head Impulse Test (vHIT) of Semicircular Canal Function - Age-Dependent Normative Values of VOR Gain in Healthy Subjects | journal = Frontiers in Neurology | volume = 6 | pages = 154 | date = 2015-07-08 | pmid = 26217301 | pmc = 4495346 | doi = 10.3389/fneur.2015.00154 }}</ref>
Another way of testing the VOR response is a [[caloric reflex test]], which is an attempt to induce [[physiologic nystagmus|nystagmus]] (compensatory eye movement in the absence of head motion) by pouring cold or warm water into the ear.
The vestibulo-ocular reflex can be tested by the aforementioned [[caloric reflex test]]; this plays an important part in confirming diagnosis of brainstem death. A code of practice must be followed in this process, namely that of the Academy of Medical Royal Colleges.<ref>{{Cite journal|last=Oram|first=John|last2=Murphy|first2=Paul|date=2011-06-01|title=Diagnosis of death|url=https://academic.oup.com/bjaed/article/11/3/77/257231|journal=Continuing Education in Anaesthesia Critical Care & Pain|language=en|volume=11|issue=3|pages=77–81|doi=10.1093/bjaceaccp/mkr008|issn=1743-1816}}</ref>
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== See also ==
*[[Pursuit movement]]
*[[Vestibulocerebellar syndrome]]
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* [https://web.archive.org/web/20160304073046/http://headimpulse.com/ (Video) Head Impulse Testing site] (vHIT) Site with thorough information about vHIT
* [https://web.archive.org/web/20160303232050/http://edboyden.org/03.09.boyden.html Motor Learning in the VOR in Mice] at edboyden.org
▲* {{MeshName|Vestibulo-Ocular+Reflex}}
* [http://www.cimit.org Center for Integration of Medicine and Innovative Technology - Testing device development]
* {{eMedicine|ent|482}} - "Vestibuloocular Reflex Testing"
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