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Physiology of the Eye > Ocular Mobility > Flashcards

Ocular Mobility Flashcards

1
Q

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

A

decreases rapidly

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2
Q

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

A

anterior body and neck muscles

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3
Q

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

A

trigeminal semilunar ganglion

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4
Q

Which extraocular muscle do birds lack?

A

retractor bulbi muscles

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5
Q

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

A

brain

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6
Q

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

A
  • dog, cat and bird lack them

- ruminants and pigs possess them

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7
Q

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

A

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)

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8
Q

What are the two fundamental laws that govern eye movement?

A
  • reciprocal innervation

- yokes muscle pairs

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9
Q

Describe reciprocal innervation as it applies to extraocular muscle movement?

A

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

discovered by Sherrington

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10
Q

Describe yoked muscle pairs as they apply to extraocular muscle movement

A

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

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11
Q

Characterize saccadic eye movements.

A
  • 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.
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12
Q

What are smooth pursuit eye movements?

A

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

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13
Q

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

A

optokinetic nystagmus

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14
Q

What do vergence eye movements do?

A
  • 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
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15
Q

How fast are vergence movements?

A

typically slow (<21 degrees/s)

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16
Q

What are the two function of vergence movements?

A
  • aid in visualizing nearby objects (combined with mitosis and accommodation)
  • resolve small misalignments between the two visual axes
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17
Q

What are the two afferent stimuli for eye movement?

A
  • the visualized object

- movement of the head

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18
Q

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

A

otoliths

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19
Q

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

A

hair cells of the semicircular canals

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20
Q

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

A

vestibulo-ocular

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21
Q

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

A

cat

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22
Q

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

A
  • 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
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23
Q

Name 10 types/categories of nystagmus.

A
  • optokinetic
  • rotary
  • postrotary
  • ocular
  • caloric
  • galvanic
  • anesthetic
  • brainstem
  • cerebellar
  • vestibular
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24
Q

Characterize optokinetic nystagmus.

A
  • 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
25
Q

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

A
  • same direction as the rotation of the head

- acceleration is the stimulus

26
Q

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

A
  • 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
27
Q

How long does postrotary nystagmus last after rotation stops?

A

approximately 10 seconds

28
Q

What is ocular nystagmus?

A

wandering or searching movement of the eyes associated with congenital blindness

29
Q

What is caloric nystagmus?

A
  • 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
30
Q

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

A
  • cold water causes nystagmus to the opposite side

- warm water cause nystagmus to the same side

31
Q

What is galvanic nystagmus?

A

direct current stimulation of the vestibular nerve

32
Q

Why is nystagmus generated during induction of anesthesia?

A

general anesthesia decreases inhibition of the brains centers that initiate nystagmus

33
Q

What causes brainstem, cerebellar, and vestibular nystagmus?

A

pathologic changes to those respective ares.

34
Q

The direction of nystagmus is indicated by what?

A

direction of the fast phase

35
Q

What is the stimulus for optokinetic nystagmus?

A

visual stimulus

36
Q

What are the receptors for optokinetic nystagmus?

A

photoreceptors (rods and cones)

37
Q

What is the afferent pathway for optokinetic nystagmus?

A

optic nerve to occipital visual cortex and frontal visual cortex

38
Q

What is the efferent pathway for optokinetic nystagmus?

A

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

39
Q

What are the effectors for optokinetic nystagmus?

A

extraocular muscles (except retractor bulb)

40
Q

What is the response for optokinetic nystagmus?

A

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

41
Q

What is the stimulus for rotary and postrotary nystagmus?

A

movement of endolymph in the semicircular canals

42
Q

What are the receptors for rotary and postrotary nystagmus?

A

hair cells of the cupula

43
Q

What is the afferent pathway for rotary and postrotary nystagmus?

A

vestibular nerve (CN 8) to vestibular nuclei and cerebellum

44
Q

What is the efferent pathway for rotary and postrotary nystagmus?

A

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

45
Q

What are the effectors for rotary and postrotary nystagmus?

A

extraocular muscles (except retractor bulb)

46
Q

What is the response for rotary and postrotary nystagmus?

A

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

47
Q

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

A

5-60 minutes

numerous bursts may occur dying a single episode of sleep

48
Q

What are position maintenance eye movements?

A

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

49
Q

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

A
  • low magnitude (several minutes per arc)

- high frequency (1-50/second)

50
Q

What is another term for position maintenance eye movements?

A

microsaccades or micornystagmus

51
Q

Kittens are born with what type of strabismus?

52
Q

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

A
  • depends on visual stimuli

- develops during the second postnatal month

53
Q

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

A

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

54
Q

What type of stimuli may lead to the oculocardiac reflex?

A
  • pressure on the globe
  • tension on the extraocular muscles or the iris
  • increased infraorbital pressure from injection, hemorrhage or a foreign body
55
Q

What species has the oculocardiac reflex been demonstrated in?

A
  • humans
  • dog
  • cat
  • horse
  • rabbit
  • mice
  • cockatiel
56
Q

Describe the neroanatomic pathway of the oculocardica reflex

A
  • 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)
57
Q

What are the clinically significant effects of the oculocardiac reflex?

A
  • bradycardia (most common)
  • ventricular fibrilation
  • cardiac arrest
58
Q

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

A

false (can be elicited in both situations)

59
Q

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

A
  • heart rate increases as IOP increases

- indicates the possibility of an intraocular-sympathetic-cardiac reflex

Physiology of the Eye (10 decks)

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