Editing Vestibulo-ocular reflex (section)

{{Short description|Reflex where rotation of the head causes eye movement to stabilize vision}}
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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]] that acts to stabilize [[Gaze (physiology)|gaze]] during head movement, with [[eye movement]] due to activation of the [[vestibular system]], it is also known as the cervico-ocular reflex. The reflex acts to [[image stabilization|stabilize images]] on the [[retina]]s of the [[eye]] during head movement. Gaze is held steadily on a location by producing eye movements in the direction opposite that of head movement. For example, when the head moves to the right, the eyes move to the left, meaning the image a person sees stays the same even though the head has turned. Since slight head movement is present all the time, VOR is necessary for stabilizing vision: people with an impaired reflex find it difficult to read using print, because the eyes do not stabilise during small head tremors, and also because damage to reflex can cause [[nystagmus]].<ref>{{cite web|url=http://www.dizziness-and-balance.com/practice/nystagmus/vestibular.html|title=Vestibular nystagmus|website=www.dizziness-and-balance.com}}</ref>

The VOR does not depend on what is seen. It can also be activated by hot or cold stimulation of the [[inner ear]], where the vestibular system sits, and works even in total darkness or when the eyes are closed. However, in the presence of light, the [[fixation reflex]] is also added to the movement.<ref name="eb">"Sensory Reception:  Human Vision: Structure and function of the Human Eye" vol. 27, p. 179  Encyclopædia Britannica,  1987</ref> Most features of VOR are present in kittens raised in complete darkness.<ref>{{Cite journal |last1=Berthoz |first1=A. |last2=Jeannerod |first2=M. |last3=Vital-Durand |first3=F. |last4=Oliveras |first4=J. L. |date=1975-10-01 |title=Development of vestibulo-ocular responses in visually deprived kittens |url=https://doi.org/10.1007/BF00238024 |journal=Experimental Brain Research |language=en |volume=23 |issue=4 |pages=425–442 |doi=10.1007/BF00238024 |pmid=1183513 |issn=1432-1106}}</ref>

In lower animals, the organs that coordinate balance and movement are not independent from eye movement. A fish, for instance, moves its eyes by reflex when its tail is moved.  Humans have [[semicircular canals]], neck muscle  "stretch" receptors, and the [[Utricle (ear)|utricle]] (gravity organ).  Though the semicircular canals cause most of the reflexes which are responsive to acceleration, the maintaining of balance is mediated by the stretch of neck muscles and the pull of gravity on the utricle (otolith organ) of the inner ear.<ref name="eb"/>

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 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 | s2cid = 15755814 }}</ref>