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{{Short description|Reflex where rotation of the head causes eye movement to stabilize vision}}
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{{more citations needed|date=August 2020}}
[[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 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.{{Citation needed|date=October 2016}} 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>
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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>{{
==Function==
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=== VOR suppression ===
When a person tracks the movement of something with both their eyes and head together, the VOR is counterproductive to the goal of keeping the gaze and head angle aligned. Research indicates that there exists mechanisms in the brain to suppress the VOR using the active visual (retinal) feedback obtained by watching the object in motion.<ref>{{
===Gain===
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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>{{
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. Also available is bi-thermal air caloric irrigations, in which warm and cool air is administered into the ear.{{Citation needed|date=May 2020}}
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>{{
==Related terms==
===Cervico-ocular reflex===
Summary: Cervico-ocular reflex, also known by its acronym COR, involves the achievement of stabilization of a visual target,<ref>Schubert, Michael C. (December 2010) "The cervico-ocular reflex". Handbook of Clinical Neurophysiology. [https://www.researchgate.net/publication/251466086_The_cervico-ocular_reflex]
</ref> and image on the retina, through adjustments of gaze impacted by neck and, or head movements or rotations. The process works in conjunction with the vestibulo-ocular reflex (VOR).<ref>Kelders, W P A ; Kleinrensink; G J , van der Geest, J N ; Feenstra, L ; de Zeeuw, C I ; Frens, M. (November 2003). Compensatory increase of the cervico-ocular reflex with age in healthy humans. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2343479/]</ref> It is conspicuous in certain animals that cannot move their eyes much, such as owls.<ref>{{
== See also ==
{{Portal|Medicine}}
* [[Pursuit movement]]▼
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* [[Vestibulocerebellar syndrome]]▼
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* {{Annotated link |Cerebellum}}
* {{Annotated link |Eyeblink conditioning}}
* {{Annotated link |Physiologic nystagmus|Nystagmus}}
* {{Annotated link |Saccade}}
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<!-- alphabetical order please [[WP:SEEALSO]] -->
== References ==
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