VOR

**OVERVIEW **
The vestibulo-ocular reflex (VOR) is a [|reflex] [|eye movement] that [|stabilizes images] on the [|retina] during head movement by producing an eye movement in the direction opposite to head movement in order to preserve the target image on the center of the visual field, or fovea. The VOR is effective up to a head rotation speed of 50 ͦ/sec. This allows us to comfortably adjust to everyday head movements and to see clearly when moving our head. For example, when you move your head to the right your eyes move to the left to compensate for the initial head rotation and focus the image on the fovea of your eye. Since humans are constantly moving their heads, the VOR is very important for stabilizing visions. People who have VOR dysfunction find it difficult to focus their eyes while they move their heads. Reading print and looking out a car window becomes almost impossible to them because they cannot stabilize their eyes during small and slight head tremors. The VOR does not depend on visual input, however, only on the vestibular system detecting head rotation. Because of this it works even in total darkness or when eyes are closed.  There are two different types of head movements that the vestibular system detects: rotational and translational movement. Both rotational and translational movement stimulate the vestibule-ocular reflex. With a rotational movement, the head moves relative to the body. Examples of this include turning the head back and forth, nodding, and bringing the ear in contact with the shoulder. Translational movements occur when the entire body (including the head) is moved in tandem. Thus, rotational vestibuloocular reflex (r-VOR) responds to angular motion of the head and results from stimulation of the semicircular canals, whereas translational vestibuloocular reflex (t-VOR) responds to linear motion of the head and results from stimulation of the otolithic organs. Some head movements may involve a combination of both translational VOR and rotational VOR.

In this wikispace we will discuss rotational VOR which responds to angular motion of the head and results from stimulation of the semicircular canals.


 * FUNCTIONAL ANATOMY **

 The VOR works on all three muscle pairs in the eye. However, we will focus only on rotational (r-VOR) which includes the medial-lateral rectus pair, and the horizontal semicircular canals.

The diagram to the left shows the six eye muscles responsible for eye movement. These six muscles work in pairs, producing 3 muscle pairs that work together to allow for specific eye movement. In rotational VOR (r-VOR), the lateral and medial rectus work together to respond and compensate for left and right head rotation and keep the eye focused on an image.

__//<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Innervations of the Extraocular Muscles: //__ <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The eyes are rotated by the action of six extraocular muscles, which act as three agonist/antagonist pairs allowing rotations in horizontal, vertical and torsional directions. The six extraocular muscles are controlled by three cranial nerves:
 * 1) <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">1. Oculomotor nerve (III)
 * 2) <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">2. Trochlear nerve (IV)
 * 3) <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">3. Abducens nerve (VI).

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The Oculomotor nerve (III) innervates the superior and inferior recti, the inferior oblique, and the **medial rectus**. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The Trochlear nerve (IV) innervates the superior oblique. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The Abducens nerve (VI) innervates the **lateral rectus**. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The Oculomotor and Trochlear nerves originate from the midbrain. The Abducens nerve originates from the pons.

<span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">This diagram shows the medial and lateral recti and the semicircular canals. The semicircular canals are responsible for detecting movement of the endolymph <span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">and decoding the direction of head rotation ultimately activating or inhibiting the medial-lateral recti to produce side to side eye movement and thus compensate for the initial head rotation.

<span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">The horizontal canals in each ear are responsible for detecting side to side rotational movement of the head. Depending on the direction of the head rotation (either to the left or to the right), the horizontal canals in each ear will either be activated or inhibited. This will ultimately send signals to the medial and lateral eye muscles to compensate for the initial head movement and keep eyes fixed on the object (pathway is discussed in a later section). The lateral rectus muscle will pull the eye lateral towards the ear, and the medial rectus will pull the eye medially towards the nose, both in the horizontal plane.

__//<span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">The semicircular canals: //__ <span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">There are 3 canals, corresponding to the three dimensions in which you move, so that each canal detects motion in a single plane. Each canal is a loop filled with a gelatinous liquid called endolymph. At the base of each canal are clusters of hair cells that sit in a small swelling called the ampula. The hair cells are arranged as a single clump that pertrudes up into the cupula.

<span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">The pathway begins as a result of the initial head rotation. The head moves, either to the left or to the right, and this brings about a series of responses and signals in the vestibular system due to the movement of the endolymph in the horizontal canals. <span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">When you turn your head, the inertia of the endolymph causes it to slosh against the cupula, deflecting the hair cells. Now, if you were to keep turning in circles, eventually the fluid would catch up with the movement of the head, and there would be no more pressure on the cupula. And the endolymph would stop deflecting the hair cells. If all of a sudden you stopped spinning, the moving fluid would slosh up against a suddenly still cupula, and you would feel as though you were turning in the other direction. Thus sudden change in head rotation will affect the endolymph and cause it to slosh against the hair cells, deflecting them and activating them. This initiates the signals that encode for head rotation. <span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">Naturally, you have the same but mirrored arrangement on both sides of the hea, in each ear. Hair cells in the cupula will be polarized depending on which way you deflect them. If you push them one way, they will be excited, but if you push them the other way, they will be inhibited. <span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">This means that the canals on either side of the head will generally be operating in a **push-pull** rhythm; when one side is excited, the other side is inhibited (see diagram below).
 * <span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">OVERVIEW of PATHWAY **

<span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">It is important that both sides agree as to what the head is doing. If there is disagreement and both sides are activated or inhibited at the same time, then you will feel debilitating vertigo and nausea. This is the reason that infections of the endolymph or damage to the inner ear can cause vertigo. However, if one vestibular nerve is cut, the brain will gradually get used to only listening to one side - this can actually be a treatment for intractable vertigo.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Rotational vestibuloocular reflex
 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">GENERAL PATHWAY **

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">1. During rotational movements of the head, the endolymphatic fluid within the semicircular canals shifts because of its inertia, which deflects the hair cells on the cupula


 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Endolymphatic flow toward the ampulla (called ampullopetal) is excitatory in the horizontal canals and increases firing
 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Endolymphatic flow away the ampulla is inhibitory (called ampullofugal) is inhibitory in the horizonatal canals and decreases firing

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">2. Afferent nerves from the ampulla carry both excitatory and inhibitory signals to the 4 major vestibular nuclei: medial vestibular nucleus, lateral vestibular nucleus, inferior or descending vestibular nucleus, and superior vestibular nucleus <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">3. Different regions within each of the nuclei project to the oculomotor nuclei and abducens nuclei <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">4. Efferent signals from these nuclei then result in contraction and relaxation of the appropriate ocular muscles.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Excitation of one lateral canal, let’s say in the left ear, results in contraction of the ipsilateral medial rectus and contralateral lateral rectus muscles and relaxation of the contralateral medial rectus and ipsilateral lateral rectus muscles. This results in a horizontal eye movement toward the opposite ear, the right ear. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The vestibulocerebellum compares input from visual and vestibular sensors and mediates necessary changes in the vestibuloocular reflex.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">**SPECIFIC EXAMPLE** //<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Left Head Rotation // <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">If you __move your head to the left, you will excite the left horizontal canal__, inhibiting the right. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">In order to keep your eyes fixed on a stationary point, you need to fire the right lateral rectus and the left medial rectus, to contract these muscle and move the eyes to the right.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The pathway is as follows:

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">1. Head rotation to left causes endolymph to flow in the opposite direction (right), this stimulates the hair cells in the cupula, exciting the left horizontal canal. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">2. The vestibular nerve picks up the signals coming from the hair cells, enters the brainstem and synapses in the vestibular nucleus. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">3. Fibers from the vestibular nucleus cross over to the contralateral side and project to the abducens nucleus (VI) on the right side, to stimulate the <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">contralateral (right) lateral rectus. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">4. They also project to the occulomotor nucleus (III) on the ipsilateral side, to stimulate the ipsilateral (left) medial rectus.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The same vestibular cells also inhibit the opposing muscles (in this case, the right medial rectus, and the left lateral rectus).

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">On the other side, the right horizontal canal is wired to the complementary set of muscles. Since it is inhibited, it will not excite its target muscles (the right medial <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">rectus and the left lateral rectus), nor will it inhibit the muscles you want to use (the right lateral rectus and the left medial rectus).


 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">NORMAL VOR **

//<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">-Neurological Exam: Normal Cranial Nerves and VOR response // <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">[|Normal VOR Video] <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Video shows a neurological exam showing a normal VOR. In a neurological exam the VOR is obtained by having the patient visually fixate on an object straight ahead, then rapidly turning the patient’s head from side to side and up and down. In a healthy and normal VOR, the eyes should stay fixed on the object and turn in the opposite direction of the head movements.

//<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">-University of Utah Videos of Normal and Abnormal Neurological Exams // <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">[|Normal and Abnormal Neurological Exam Videos] <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Website lists a good number of videos showing abnormal neurological exams, and abnormal eye movement control including abnormal VOR, nystagmus and other vestibular related dysfunctions.

//<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">-Normal VOR // <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The top picture shows a normal VOR response to head rotation to the right and left. When head is rotated to the left (picture on the left), eyes turn in the opposite direction, towards the right. When head rotates to the right (picture on the right), eyes turn to the left to compensate for head movements and keep the

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">The importance of the VOR mechanism is vital for everyday life. A recent study discussed the <span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">importance of this mechanism to everyday life and tasks. In this article, the VOR and its necessity were described by a physician whose inner ear had been severely damaged by excessive streptomycin therapy.He could read in bed only by bracing his head against the headboard; otherwise the printed page jumped with each heartbeat. When walking he was unable to recognize faces or read signs unless he stood still. We experience what it must be like for those afflicted in this way when watching a movie shot from a vehicle being jolted by a bad road; viewers of the movie, unlike those doing the shooting, are not assisted by their VORs so that their gaze is constantly having to jump about to recapture the target with a succession of saccades.
 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">DYSFUNCTION **

__//<span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">Abnormalities in Comatose Patients: //__ <span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">Once it has been determined that the cervical spine is not damaged, a test of the VOR can be performed in comatose patients. This is done by turning the head to one side and observing the reactive movements of the eyes in response to the head movement. If the brainstem is intact, the eyes will move conjugately away from the direction of the head movement (as if they were still looking at the examiner rather than the fixed object straight ahead). This is called “Doll’s Eyes”, simply because it is how a doll’s eyes would move.

<span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">Having “Doll’s Eyes” is thus a sign that a comatose patient’s brainstem is still intact.

<span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">[|Abnormal VOR Video]
 * <span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">Table A. Manifestations of Vestibuloocular Reflex Dysfunction **[|Dysfunction]

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">__// VOR Testing //__

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">// Rapid head impulse test // or //Halmagyi-Curthoys-test// <span style="color: black; font-family: 'Times New Roman',Times,serif; font-size: 120%;">Head is rapidly moved to the side with force. If eyes succeed to remain looking in the same direction and fixate on one object in front of them then VOR is normal. When the function of the VOR system is damaged, by a disease or by an accident, quick head movement can no longer be sensed properly any more. When no reactive eye movement is generated to compensate for the head movement, and the patient cannot fixate a point in space during this rapid head movement then VOR is abnormal.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">// Caloric Reflex test // <span style="color: black; font-family: 'Times New Roman',Times,serif; font-size: 120%;">The Caloric Reflex test is an attempt to induce nystagmus by pouring cold or warm water into the ear. Nystagmus produced by water irrigation is then observed and compared to normal VOR response

<span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">Acute VOR dysfunction is disturbing and constant to a patient, present and noticed every time the head is moved. With time and as patients learn to compensate, the dysfunction becomes less debilitating and noticeable. Patients can actively promote compensation through a series of rehabilitation exercises.
 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">REHABILITATION **

<span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">VOR disturbances are treated with different forms of rehabilitation exercises. For example, patients are asked to hold an index card 1 foot from their eyes and to focus on a word or object on the index card as they rotate their head.

<span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">Other types of rehabilitation are mostly to make the patients more comfortable and make adjustments to their everyday lives and tasks to allow them to carry out a normal life, as much as possible.

<span style="color: black; font-family: 'Times New Roman','serif'; font-size: 16px;">A large role of the semicircular canal system is to keep your eyes still in space while your head moves around them. The reason is that the semicircular canals exert direct control over the eyes, so they can directly compensate for head movements. The three pairs of muscles that control eye movements are: the medial and lateral rectus, the superior and inferior rectus, and the inferior and superior oblique. These muscles respond to the signals sent from the semicircular canals and produce compensatory reflex to keep the eyes fixed on an image during head movements. This is called the vestibulo-ocular reflex (VOR).
 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">SUMMARY **

<span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">The human brain is one of the most organized and complex structure in the universe. The system as a whole with its subsystems, allows us to function. In this discussion, we focused on the brain and vestibular system and in their direct control over eye muscles to compensate for head rotation, by use of the vestibule-ocular reflex

<span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">Lesions, diseases and old age can cause a gradual breakdown of the vestibular system and disrupt the VOR. This causes us to begin to lose control over our compensatory eye movements and become unable to focus an image. Dizziness, nystagmus and vertigo become potential symptoms, making it impossible to see clearly. It is usually not until something goes wrong and VOR becomes abnormal, that we start to notice it. It is not until we notice something wrong with our balance, vision and perception of motion that we begin to admire the complexity of the elaborate systems that are constantly working and the importance of the vestibule-ocular reflex.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">__** Vestibular system **__ : a complex sensory system located in the inner ear consisting of the saccule, utricle, and semicircular canals that contributes to the sense of balance, sense of spatial orientation and allows for coordinated movement.
 * <span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">GLOSSARY **

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">__** Conjugate **** eye movements **__ : the eyes moving in unison together

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">** __Vestibulo-occular reflex (VOR__): ** controls eye movements to stabilize images on the fovea during head movements

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">__** Semicircular canals **__ : 3 canals (horizontal, posterior and anterior) <span style="color: black; font-family: 'times new roman',times,serif; font-size: 120%;">corresponding to the three dimensions in which you move, detect angular acceleration.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">** __A__ **__** mpulla **__ : a flask-like dilatation of a tubular structure <span style="color: black; font-family: 'times new roman',times,serif; font-size: 120%;">

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">__** Cupula **__ : located within the ampullae of each of the three semicircular canals. As fluid <span style="color: black; font-family: 'times new roman',times,serif; font-size: 120%;">rushes by the cupula, hair cells within it sense rotational acceleration and transmit the corresponding signal to the brain the vestibulocochlear nerve (CN VIII)



<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">__** Occulomotor nerve **__ : CN III, controls ipsilateral medial recti of the eyes <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">** __Abducens nerve__: ** CN VI, controls contralateral lateral recti of the eyes <span style="color: black; font-family: 'times new roman',times,serif; font-size: 120%;">

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">__**Caloric reflex test**__: in medicine, is a test of the vestibule-ocular reflex that involves irrigating cold or warm water or air into the external auditory canal. It is done to produce nystagmus and see if the body’s response to the test is normal.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">__**Nystagmus**__: abnormal eye movements to the left and the right when vestibular system is damaged; compensatory eye movement in the absence of head motion

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">QUIZ

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">1. TRUE/FALSE: The horizontal semicircular canals are involved in directing rotational VOR. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">2. TRUE/FALSE: When the head rotates to the right, the endolymph in the horizontal canal flows in the same direction. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">3. TRUE/FALSE: The occulomotor nerve innervates the ipsilateral medial rectus. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">4. TRUE/FALSE: The six extraocular muscles are controlled by three nerves: III, IV, V. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">5. TRUE/FALSE: The oculomotor and abducens nerves are involved in lateral eye movement to compensate for head rotation. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">6. TRUE/FALSE: The abducens nerve innervates the contralateral lateral rectus.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">7. All of the follow cranial nerves are involved in controlling the six extraocular muscles of the eye, EXCEPT: <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">A) VI <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">B) V <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">C) IV <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">D) III

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">8. The oculomotor nerve (III) innervates all of the following muscles, EXCEPT: <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">A) Superior recti <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">B) Medial recti <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">C) Inferior recti <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">D) Inferior oblique <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">E) Lateral recti

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">9. What region of the cereballum compares input from <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">visual and vestibular sensors and mediates necessary changes in the vestibuloocular reflex? <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">A) Vestibulocerebellum <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">B) Spinocerebellum <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">C) Cerebrocerebellum <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">D) Thalamus

__<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">Short Answer Questions: __ <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">10. Define the terms ampullopetal and ampullofugal and describe how the direction of the flow of the endolymph affects neural firing. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">11. Describe some symptoms or signs of VOR dysfunction. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">12.How are comatose patients tested for VOR function? Describe the term "Doll's eyes".

__<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">Essay: __ <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">13. Describe and draw the pathway in right head rotation.


 * <span style="color: black; font-family: 'times new roman','serif'; font-size: 16px;">LINKS/SUGGESTED READINGS **

//<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">-Article: Neural Learning Rules for the Vestibulo-Ocular Reflex // <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">[]

//<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">-Article: Vestibulo-ocular Function during Coordinated Head and Eye Movements to Acquire Visual Targets // <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">h[|ttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC1281486/] <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Article discusses VOR function during head and eye movements to focus visual targets on the fovea and produce <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">clear images.

//<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">-University of Utah Video of Neurological Exam // <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">[|http://library.med.utah.edu/neurologicexam/html/cranialnerve_abnormal.html#21] <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Website lists a good number of videos showing abnormal neurological exams, and abnormal eye movement <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">control including abnormal VOR, nystagmus and other vestibular related dysfunctions.

//<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">-Caloric Test Video // <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">[] <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Video shows the VOR response after ear is irrigated with water during a caloric test. //<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">-Video on Anatomy of Vestibular System // <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">[] <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Video discusses and describes the vestibular system.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">1. T <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">2. F <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">3. T <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">4. F <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">5. T <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">6. T <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">7. B <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">8. E <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">9. A
 * <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">ANSWERS **

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">**REFERENCES** <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">1. Gurney, Peter. Our Eye Movement and Their Control: Part 2. [Online]. Answersingenesis.org. []. [April 1, 2003]

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;"> 2. [|Lincoln Gray, Ph.D. Chapter 10: Vestibular System: Structure and Function. [Online. Department of Communication Sciences and Disorders]], [|James Madison University.] []. [1997-Present].

<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">3. Manali, Amin. "Vestibuloocular Reflex Testing: EMedicine Clinical Procedures." EMedicine-Medical Reference. Medscape, 2010. Web. 01 May 2010. <[]>.

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