Ocular Mobility

Question 1

What happens to visual acuity and color perception in the more peripheral retina?

Answer 1

decreases rapidly

Question 2

In sheep, afferent nerves entering the brainstem through the oculomotor nerve carry impulses (especially from the conjunctiva) to the brainstem, where the influence what?

Answer 2

anterior body and neck muscles

Question 3

In sheep, where are the cell bodies of the afferent oculomotor nerve fibers located?

Answer 3

trigeminal semilunar ganglion

Question 4

Which extraocular muscle do birds lack?

Answer 4

retractor bulbi muscles

Question 5

In birds, the two eyes weight almost as much as what other cranial structure?

Answer 5

brain

Question 6

Which species possess spindles in their extra ocular muscles, and which do not?

Answer 6

• dog, cat and bird lack them

- ruminants and pigs possess them

Question 7

How is the motor axon innervation different between the extraocular muscles ands skeletal muscle?

Answer 7

a single motor axon in EO muscles typically innervates 5-10 muscle fibers, where a single axon in skeletal muscle innervates thousands of fibers. (this provides for more precise control of EO muscle movement by the central nervous system)

Question 8

What are the two fundamental laws that govern eye movement?

Answer 8

• reciprocal innervation

- yokes muscle pairs

Question 9

Describe reciprocal innervation as it applies to extraocular muscle movement?

Answer 9

antagonistic muscles in the same eye have reciprocal innervation (stimulation of the medial rectus leads to relaxation of the lateral rectus)

discovered by Sherrington

Question 10

Describe yoked muscle pairs as they apply to extraocular muscle movement

Answer 10

yokes muscle pairs are always equally innervated so that a lateral movement of the left eye will lead to an identical medial movement of the right.

discovered by Hering

Question 11

Characterize saccadic eye movements.

Answer 11

• rapid (1000 degrees/s) and brief (<0.1 s) eye movements that are intended for rapid correction of eye position to bring the image of interest onto the areas centralis.
• mostly used when tracking a fast-moving object, or to begin suite of a formerly stationary object.

Question 12

What are smooth pursuit eye movements?

Answer 12

movements used to match the speed of an object once it has been placed on the area centralis to help keep it there

Question 13

The combination of saccadic and smooth pursuit eye movements is called what?

Answer 13

optokinetic nystagmus

Question 14

What do vergence eye movements do?

Answer 14

• change the angel of intersection between the two eyes.
• convergent increase the angle between the visual axis
• divergent decreases the angle between the visual axis

Question 15

How fast are vergence movements?

Answer 15

typically slow (<21 degrees/s)

Question 16

What are the two function of vergence movements?

Answer 16

• aid in visualizing nearby objects (combined with mitosis and accommodation)
• resolve small misalignments between the two visual axes

Question 17

What are the two afferent stimuli for eye movement?

Answer 17

• the visualized object

- movement of the head

Question 18

Linear acceleration of the head stimulates what component of the vestibular apparatus?

Answer 18

otoliths

Question 19

Angular acceleration of the head stimulates what component of the vestibular apparatus?

Answer 19

hair cells of the semicircular canals

Question 20

The otoliths and semicircular canals provide the afferent impulse for what reflex?

Answer 20

vestibulo-ocular

Question 21

Which species makes greater use of the vestibule-ocular reflex, dog or cat?

Answer 21

cat

Question 22

Characterize the eye movements generated from the vestibule-ocular reflex.

Answer 22

• immediate but slow movements that compensate for movement of the head, helping to keep the image focused on the area centralis
• when the head moves up, the VOR moves the eyes down, and the same for medial/later movements

Question 23

Name 10 types/categories of nystagmus.

Answer 23

• optokinetic
• rotary
• postrotary
• ocular
• caloric
• galvanic
• anesthetic
• brainstem
• cerebellar
• vestibular

Question 24

Characterize optokinetic nystagmus.

Answer 24

• eyelids must be open
• when stimuli is moving and head is stationary, fast phase is opposite the direction of the moving stimuli
• when head is moving and stimuli is stationary, fast phase is the same direction as the movement of the head
• usually occurs in the horizontal plane

Question 25

What direction is the fast phase in rotary nystagmus, and what is the stimulus for rotary nystagmus?

Answer 25

- same direction as the rotation of the head | - acceleration is the stimulus

Question 26

What is postrotary nystagmus, what direction is the fast phase, and what is the stimulus?

Answer 26

- rotation that occurs after rotation of the head stops - fast phase is in the opposite direction to rotation of the head - deceleration is the stimulus

Question 27

How long does postrotary nystagmus last after rotation stops?

Answer 27

approximately 10 seconds

Question 28

What is ocular nystagmus?

Answer 28

wandering or searching movement of the eyes associated with congenital blindness

Question 29

What is caloric nystagmus?

Answer 29

- nystagmus elicited by poring hot (48C) or cold (18C) water into the ear canal, leading to expansion (hot) or contraction (cold) of endolymph in the semicircular canals

Question 30

In caloric nystagmus, how does the temperature of water typically affect the direction of nystagmus?

Answer 30

- cold water causes nystagmus to the opposite side | - warm water cause nystagmus to the same side

Question 31

What is galvanic nystagmus?

Answer 31

direct current stimulation of the vestibular nerve

Question 32

Why is nystagmus generated during induction of anesthesia?

Answer 32

general anesthesia decreases inhibition of the brains centers that initiate nystagmus

Question 33

What causes brainstem, cerebellar, and vestibular nystagmus?

Answer 33

pathologic changes to those respective ares.

Question 34

The direction of nystagmus is indicated by what?

Answer 34

direction of the fast phase

Question 35

What is the stimulus for optokinetic nystagmus?

Answer 35

visual stimulus

Question 36

What are the receptors for optokinetic nystagmus?

Answer 36

photoreceptors (rods and cones)

Question 37

What is the afferent pathway for optokinetic nystagmus?

Answer 37

optic nerve to occipital visual cortex and frontal visual cortex

Question 38

What is the efferent pathway for optokinetic nystagmus?

Answer 38

corticotectal and corticotegmental tract to oculomotor; abducens and trochlear nerve via medial longitudinal fasciculus

Question 39

What are the effectors for optokinetic nystagmus?

Answer 39

extraocular muscles (except retractor bulb)

Question 40

What is the response for optokinetic nystagmus?

Answer 40

saccadic eye movement (slow phase followed by a fast phase)

Question 41

What is the stimulus for rotary and postrotary nystagmus?

Answer 41

movement of endolymph in the semicircular canals

Question 42

What are the receptors for rotary and postrotary nystagmus?

Answer 42

hair cells of the cupula

Question 43

What is the afferent pathway for rotary and postrotary nystagmus?

Answer 43

vestibular nerve (CN 8) to vestibular nuclei and cerebellum

Question 44

What is the efferent pathway for rotary and postrotary nystagmus?

Answer 44

vestibular nuclei to oculomotor, abducens and trochlear nerve via medial longitudinal fasciculus

Question 45

What are the effectors for rotary and postrotary nystagmus?

Answer 45

extraocular muscles (except retractor bulb)

Question 46

What is the response for rotary and postrotary nystagmus?

Answer 46

saccadic eye movement (slow phase followed by a fast phase)

Question 47

rapid eye movements (REM) occur during sleep in burst that typically last how long?

Answer 47

5-60 minutes | numerous bursts may occur dying a single episode of sleep

Question 48

What are position maintenance eye movements?

Answer 48

movements that maintain eye position while gazing at a stationary object (used even when the observer is stationary)

Question 49

What is the magnitude and frequency of position maintenance eye movements?

Answer 49

- low magnitude (several minutes per arc) | - high frequency (1-50/second)

Question 50

What is another term for position maintenance eye movements?

Answer 50

microsaccades or micornystagmus

Question 51

Kittens are born with what type of strabismus?

Answer 51

divergent

Question 52

Normal interocular alignment is dependent on what, and when does it typically develop?

Answer 52

- depends on visual stimuli | - develops during the second postnatal month

Question 53

What is the underlying cause for the crossed eyes (convergent strabismus) seen in siamese cats and some ablino mammals?

Answer 53

results form a genetic neuroanatomic defect in the primary visual pathway that involves the retinogeniculate and geniculocortical projections.

Question 54

What type of stimuli may lead to the oculocardiac reflex?

Answer 54

- pressure on the globe - tension on the extraocular muscles or the iris - increased infraorbital pressure from injection, hemorrhage or a foreign body

Question 55

What species has the oculocardiac reflex been demonstrated in?

Answer 55

- humans - dog - cat - horse - rabbit - mice - cockatiel

Question 56

Describe the neroanatomic pathway of the oculocardica reflex

Answer 56

- stimuli: eye and orbital areas - afferent: sensory branches of the ophthalmic division of the trigeminal nerve to its sensory nucleus, which then stimulates the vagal nucleus - efferent: vagus nerve to the heart (slowing)

Question 57

What are the clinically significant effects of the oculocardiac reflex?

Answer 57

- bradycardia (most common) - ventricular fibrilation - cardiac arrest

Question 58

Ture of false: the oculocardiac reflex can be elicited in conscious animals, but not lightly anesthetized animals?

Answer 58

false (can be elicited in both situations)

Question 59

In the dog, as the IOP increases, what also increases, and what might this indicate?

Answer 59

- heart rate increases as IOP increases | - indicates the possibility of an intraocular-sympathetic-cardiac reflex