Ocular Motility: Lecture 10: VOR

Question 1

Overview of VOR

1. What does VOR do?
2. The Function of VOR?
3. The drive for this reflex is what?
   a. When does it operate?

Answer 1

1. Stabilizes Retinal Images during Head motion. (Counter-rotates the eyes at the SAME speed as the head but in the opposite direction)
2. Generates Eye Orientation that best compensates for changes in position and orientation of the head
3. It’s VESTIBULAR rather than Visual.
   a. Works even in the DARK

Question 2

Overview of VOR (2)

1. Damage to Vestibular system often causes what?
2. Damage to the Vestibular Sensors on one side UPSETS the Balance b/w what?
3. 2 Types of Head Motion?
   a. What do each refer to?

Answer 2

1. Oscillopsia
2. B/w Vestibular Signals Generated from Both Sides
3. ROTATION and TRANSLATION
   a. Rotation: Change in ORIENTATION; Translation: Change in POSITION

Question 3

Overview of VOR (3)

1. Motion of the head is DETECTED by what?
   a. Composed of what 2 things?
2. Semicircular Canals Detect Head Rotation (rotational/Angular VOR)
   a. Horizontal
   b. Vertical
   c. Torsional
3. Translation (Otolith Organs)
   a. Heave
   b. Bob
   c. Surge
   d. Otolith Organs also detect what?

Answer 3

1. the Peripheral Vestibular Apparatus or Labyrinth
   a. 3 Semicircular Canals and Otolith Organs (consist of Utricle and Saccule)
2. a. Yaw
   b. Pitch
   c. Roll
3. a. Side-to-side
   b. up and down
   c. fore and aft
   d. Static Head Tilt (position of the head w/respect to gravity)

Question 4

Overview of VOR (4)

1. VOR Gain varies with what?
   a. It has to Approximate -1.0 to PREVENT what?
2. Horizontal and Vertical VOR Gains approximate what in the DARK?
   a. In the LIGHT? why is this?

Answer 4

1. with Frequency of Head Motion
   a. to prevent Retinal Images from Slipping
2. -0.9
   a. close to -1.0 due to Visual Enhancement

Question 5

Overview of VOR (5)

1. During Dynamic Head Roll: Compensatory Eye Movements are generated by what?
   a. This is Mediated PREDOMINANTLY by what?
2. Static Head Roll Evokes Compensatory Changes in what?
   a. These are MEDIATED by what?
3. Dynamic Torsional VOR has a LOWER GAIN than what 2 things?
   a. Range
4. Static Torsional VOR has what?
   a. Range?

Answer 5

1. by TORSIONAL VOR
   a. by the VERTICAL SEMICIRCULAR CANALS (Anterior and Posterior Canals)
2. in TORSIONAL EYE POSITION
   a. by the Otolith-Ocular Reflex from Inputs of the UTRICLES
3. a LOWER GAIN than Horizontal or Vertical VOR
   a. -0.4 to -0.7 depending on the frequency of Head Roll
4. (AKA Ocular Counter-roll) has a LOWER GAIN than its DYNAMIC COUNTERPART
   a. -0.1 to -0.24

Question 6

Overview of VOR (6)

1. IF the Gain is TOO MUCH ABOVE or BELOW its Ideal Value of UNITY, A Target image remains where?
   a. Although it may be Transiently what?
2. VOR Gain Decreases with what?
3. VOR Latency is what?

Answer 6

1. Remains OFF the FOVEA
   a. stable on the retina
2. with age
3. 16 msec

Question 7

Anatomy of Semicircular Canal

1. There are 3 pairs of Semicircular Ducts, and they’re Oriented roughly what?
   a. Purpose?
2. A Turn of the Head EXCITES the receptors in one AMPULLA and inhibits receptors in what?
3. When the head turns, fluid in one or more semicircular ducts pushes against what 2 things?
   a. Fluid in the Corresponding semicircular duct on the opposite side of the head moves in what direction?

Answer 7

1. 90 degrees to each other
   a. For Max ability to detect Angular Rotation of the Head
2. in the Ampulla on the other Side
3. the Cupula and Bends the Cilia of the Hair Cells
   a. moves in the Opposite Direction

Question 8

Anatomy of Semicircular Ducts

1. When the Head turns, what causes the fluid to move more slowly than the head?
   a. This generates RELATIVE FLUID MOTION in the Semicircular Duct in what direction?
2. The Stereocilia are Bent toward their what?
3. Shearing of the Stereocilia TOWARD Kinocilium causes what?

Answer 8

1. Inertia
   a. in the Opposite Direction of the Head Turn
2. their Kinocilium on one side and away from their Kinocilium on the Other Side
3. Causes DEPOLARIZATION of the Receptor Potential and an Increase in Afferent Action Potentials

Question 9

1. The receptors are called what?
   a. They are PATCHES of Hair Cells topped by SMALL, CALCIUM CARBONATE CRYSTALS called what?
   b. The SACCULE and UTRICLE lie how far from each other?
2. Any position of the head, Gravity will bend the CILIA of one Patch of Hair Cells, due to the weight of what?
3. This bending of the Cilia produces what?

Answer 9

1. MACULAE
   a. OTOCONIA
   b. 90 Degrees to each other
2. of OTOCONIA
3. AFFERENT ACTIVITY going thru the VIIIth Nerve to the Brainstem

Question 10

Horizontal Canal

1. PRimary Afferents of the Horizontal VOR pathway originate from what?
2. 2 Projections for Horizontal Angular VOR
   a. First is a DIRECT EXCITATORY PROJECTION from what 2 things?

b. Axons of these 2nd order Neurons then project to what?

3. What are the 2 populations of neurons lie w/in the Abducens Nucleus?
   a. They Cross the Midline and Ascend w/in what?
   b. To innervate what?
4. The Horizontal Canal Sends RECIPROCAL INHIBITORY PROJECTIONS to what?

Answer 10

1. Horizontal (Lateral) Canals
2. a. from Horizontal Canal to 2nd Order Neurons in the MVN
   b. to the CONTRALATERAL ABDUCENS NUCLEUS
3. Abducens Motoneurons (Innervate the LATERAL RECTUS on that side: Forming a 3-neuron arc; and the ABDUCENS INTERNUCLEAR NEURONS (cross midline)

a. w/in the Medial Longitudinal Fasciculus (MLF):
b. the Medial Rectus Motoneurons in the Oculomotor Nucleus on the Opposite Side

4. to Antagonist Muscles (Ipsilateral Lateral Rectus and Contralateral Medial Rectus)

Question 11

1. Stimulate Right Horizontal Canal (RHC)

2. Stimulate LHC

Answer 11

1. Both Eyes Turn Left

2. Both Eyes Turn Right

Question 12

1. Stimulate Right Anterior Canal (RAC)

2. Stimulate LAC

Answer 12

1. Both eyes Rotate up and COUNTERCLOCKWISE (from patients point of view)
   a. Right Eye INCLYCLOTORTS (Right SR) and Left Eye Excyclotorts (Left Inferior Oblique)
2. Both Eyes Rotate up and CLOCKWISE (Right Eye Excyclotorts (right inferior oblique); (LEft Eye Incyclotorts (Left SR))

Question 13

1. Stimulate Right Posterior Canal (RPC)

2. Stimulate LPC

Answer 13

1. Both Eyes Rotate Down and COUNTERCLOCKWISE (right eye Incyclotorts (Right Superior Oblique) and Left eye Excyclotorts (LIR)
2. Both Eyes Rotate Down and CLOCKWISE (right eye excyclotorts (RIR) and Left Eye Inclyclotorts (Left Superior Oblique)

Question 14

Caloric Nystagmus

1. Cold water is put in the right ear…20 ml is injected over about 30 seconds. Cold water cools what?
   a. This primarily affects what?

Answer 14

1. the Tympanic Membrane, which cools the air in the Middle ear, and finally the Endolymph.
   a. The Horizontal Semicircular Canal cuz it’s close to the middle ear space

Question 15

Caloric Nystagmus

1. IF water is WARM (about 44 degrees Celsius) Endolymph in the Ipsilateral Horizontal Canal does what?
   a. What does this cuase?
   b. This situation mimics what?
   c. Both eyes will do what?

Answer 15

1. will RISE
   a. an INCREASED Rate of Firing in the Vestibular Afferent Nerve

b. a HEAD TURN to the IPSILATERAL SIDE
c. turn toward the Contralateral Ear, with Horizontal Nystagmus to the Ipsilateral Ear

Question 16

Caloric Nystagmus

1. If water is COLD, relative to body temperature, what happens to the ENDOLYMPH?
   a. What does this DECREASE?

b. What do they eyes do?

Answer 16

1. It Falls w/in the Semicircular Canal
   a. the Rate of Vestibular Afferent Firing and the HEAD TURN to the CONTRALATERAL SIDE
   b. turn toward IPSILATERAL EAR, with Horizontal Nystagmus (quick horizontal Eye movements) to the Contralateral Ear

Question 17

VOR Features

1. The Endolymph Motion is Proportional to what?
   a. This produces the Velocity Signal and is INTEGRATED to produce what?
2. The VOR GAIN is defined as the RATIO of what 2 things?
3. The VOR Gain INCREASES with DECREASED what?
   a. This compensates for what?

Answer 17

1. to the HEAD VELOCITY
   a. the Head Displacement Signal
2. of the Amplitude of Eye Rotation to the Amplitude of Head Rotation
3. Viewing Distance
   a. for the Difference in Axis of Rotation of the Head Versus the Eye

Question 18

Velocity Storage of the VOR

1. During Sustained Constant-Velocity Rotation, the Hair Cells are INITIALLY what?
   a. What do they do after that?
   b. When Hair cells return to Resting Position, and the Decline in Activity of the Vestibular Nerve has a TIME CONSTANT of about how long?

c. A Central Vestibular Mechanism is called what?

Answer 18

1. Deflected
   a. soon return to their resting position
   b. about 5 seconds (time constant is defined as the time required for a response to decline to 37% of its initial value)

c. VELOCITY STORAGE. Must have stored the activity from the hair cells to Prolong VOR duration threefold

Question 19

VOR Adaptation

1. VOR may show what?
   a. What is this?
2. Changes may occur how long?
   a. A Reduction of Response after what?
3. The VOR is what kind of System?
   a. This means that the Labyrinthine Receptors, which provide the INPUT of the Reflex, and Receive what?

Answer 19

1. HABITUATION
   a. A REDUCTION of Response after Repetitive stimulation in Complete Darkness
2. Immediately or After Several days to weeks and are classified as HABITUATION and ADAPTATION
   a. after REPETITIVE STIMULATION in COMPLETE DARKNESS
3. an Open-Loop Control System
   a. no info about eye movements (the output of the reflex)

Question 20

VOR Adaptation: Recalibration

1. Magnifying and minifying Glasses
   a. The Retinal image Slip caused by MAGNIFYING GLASSES INCREASES what of the eye?

b. Due to ROTATIONAL MAGNIFICATION, a Farsighted (hyperopic) Person who Habitually wears Plus Lenses (Magnified Visual Field) has a HIGHER what?
c. A Near Sighted person who habitually wear minus Lenses has what?
d. Peeps who habitually wear Contact Lenses have what?
2. When the Magnifying Glasses are Removed, the VOR Gain is readapted w/in what time?

Answer 20

1. a. the AMPLITUDE of the EYE movement relative to that of the head.
   b. Higher VOR Gain than an Emmetropic Person
   c. Lower VOR Gain
   d. Have NO CHANGES in Gain cuz there’s no ROTATIONAL Magnification
2. w/in 30 Minutes

Question 21

VOR Adaptation

1. Reversing Prisms
   a. Laterally Invert the World such that a Head Turn Causes the Environment to appear to move how?

b. After a SHORT PERIOD of ADAPTATION, the Eyes Rotate in what?

Answer 21

1. a. in the SAME DIRECTION as the HEAD TURN

b. in the SAME DIRECTION as the HEAD

Question 22

Abnormal Vestibular System

1. Peripheral and Central Vestibular Lesions cause what?
   a. Static Imbalance of Canal Inputs or Connections Leads to what?
   b. Dynamic Imbalance AFFECTS what?
2. Amblyopic Eye: 2 things?

Answer 22

1. static and dynamic imbalance of the VOR
   b. to Spontaneous Nystagmus
   c. the Gain and Phase of the VOR
2. 1. Asymmetric and Reduced Responses for Caloric-Induced Nystagmus in patients w/Strabismus Induced Amblyopia.
      and Vestibular Imbalance in the Dark