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Physiology of vision and the visual system > Physiology of EOM > Flashcards

Physiology of EOM Flashcards

1
Q

What is binocular viewing important for?

A

Depth perception/steropsis

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2
Q

Where in the visual pathway does stereopsis/depth perception occur?

A

cortex, involves the fusion of both retinal images

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3
Q

In what condition can a false macula/pseudofovea develop?

A

Squint

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4
Q

What is a horopter?

A

Charting of corresponding points in the retina projecting to single points in space within the field of binocular vision

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5
Q

What is the minimum binocular single vision for drivers vehicle license?

A

BSV field of 20 degrees above and below horizontal meridian

BSV field 60 degrees either side of vertical meridian

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6
Q

What is retinal rivalry?

A

Simultaneous perception by each eye individually without fusion of the images

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7
Q

what is ocular dominance?

A

preferential use of one eye when performing monocular activities

e.g. if the same image is presented to both eyes but each at difference brightness, it may register as the image perceived only by one of the eyes (i.e. dim if the left eye is the side of lower illumination and if it is the more dominant eye)

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8
Q

In which area of the cortex is the coloured stimuli registered?

A

V4

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9
Q

In which region of the cortex are moving targets registered?

A

V5

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10
Q

Which areas of the cortex is the V1 cortex directly related to?

A

V3-V8

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11
Q

How is the V1 cortex INDIRECTLY connected to V3-V8?

A

Via V2

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12
Q

How is the V2 cortex organised?

A

Into thin and thick stripes separated by inter-stripes.

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13
Q

What do the thin stripes of V2 cortex detect?

A

colour detection

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14
Q

What do the thick stripes of V2 cortex detect?

A

motion detection

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15
Q

What is ‘Listing’s plane’?

A

rotation of the eye in either the vertical (z) or horizontal axis (x) plane

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16
Q

What is ‘Hering’s rule’?

A

The extent of movement in one eye is equal and symmetrical to the movement of the other eye

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17
Q

In what direction do conjugate eyes move?

A

Both eyes move in parallel

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18
Q

In what direction do dysjunctive eyes move?

A

They move in opposite directions (convergent and divergent directions)

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19
Q

Which EOM are involved in convergent movements?

A

Both medial recti

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20
Q

What are the different types of conjugate movements of the eye?

A

Saccades: short, sharp movements

Smooth pursuit: continuous tracking movements

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21
Q

What is ‘microsaccades’?

A

When the eye is steadily, fixated on something, there are still small conjugates movements

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22
Q

What are the features of saccades?

A
  1. Rapid voluntary relocation of fixation
  2. under supranuclear contralateral control
  3. Latency of 100ms
  4. Velocity of 800-1000degrees/s
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23
Q

What are the features of pursuit?

A
  1. Slower tracking movements
  2. Under supranuclear ipsilateral control
  3. Latency of 150ms
  4. Velocity of 30-50 degrees/s
24
Q

In the primary position, are the EOM in a state of tonic acitivity?

A

Yes

25
Q

What controls the voluntary action of EOM?

A

Frontal cortex

26
Q

What are the ‘coordinating centres’ for the voluntary movements of the EOM?

A

Occipital cortex

Superior colliculus

27
Q

Where does fine tuning of eye movements occur?

A

paramedian pontine reticular formation (PPRF)

rostral interstitial nucleus of median longitudinal fasciculus in the midbrain

28
Q

What is optikinetic nystagmus?

A

Nystagmus has a slow phase when the eyes follow a target and a fast flick when they readjust to a new target position

29
Q

What is the optikinetic nystagmus useful for?

A

Demonstrating the fixating reflex

30
Q

Where is the pathology that will lead to a loss in the optokinetic nystagmus?

A

Temporal lobe

31
Q

Is the optikinetic nystagmus lost in parietal lobe lesions?

A

No

32
Q

What is the ‘oculovestibular reflex’?

A

Eye movement responses due to a change in the position of the head and trunk

33
Q

Which parts of the vestibular apparatus provide position information of the head and trunk when static?

A

Utricle and saccule

34
Q

Which parts of the vestibular apparatus provide position information of the head and trunk when accelerating or decelerating?

A

Semicircular canals

35
Q

How are the semicircular canals stimulated?

A

Ampullae of semicircular canals are stimulated via inertial forces in the endolymph surrounding the hair cells (viscous drag)

36
Q

How is the utricle and saccule of the vestibular apparatus stimulated?

A

Via movement of the head

37
Q

How is the oculo-vestibular reflex demonstrated?

A

The observer is rotated whilst their gaze remains fixated on a stationary object

38
Q

What type of movement is an example of oculo-vestibular movement?

A

Dolls head movement

39
Q

A lack of doll’s head movement suggests infarct of the…

A

Brainstem

40
Q

What is the midbrain a coordinating centre for?

A

Reflex eye movement

41
Q

Where is voluntary eye movements initiated?

A

In the contralateral motor strip of the frontal cortex

42
Q

Describe the neuronal pathway for voluntary horizontal eye movement (saccades).

A
  • Initiated in the contralateral motor strip of the frontal cortex
  • signal passes down the midbrain via the anterior limb of the internal capsule
  • Synapses in the horizontal gaze centre in the PPRF
  • Neurones then pass to ipsilateral CN6 and interneurones cross to the opposite median longitudinal fasciculus to subserve the contralateral CN3
43
Q

What type of cells are with the PPRF?

A

Burst cells

44
Q

What is the rate of discharge of Burst cells?

A

1000Hz/s

45
Q

Is the discharge from burst cells continuous or transient?

A

transient

46
Q

How are burst cells continuously inhibited?

A

normally burst cells, are continuously inhibited by ‘pause cells’, until the pause cells are inhibited by neurones from the frontal eye field

47
Q

once saccade has been generated, how does the eye remain in fixation?

A

maintained via tonic neuronal integrators within the PPRF

48
Q

How does the PPRF carry out fine, accurate gaze control?

A

It received input from vestibular nuclei, cerebellum, basal ganglia, cervical proprioceptors to make fine, small changes to gaze

49
Q

How does the vertical gaze centre differ from the horizontal gaze centre?

A

It does not have any identifiable cortical control

50
Q

Where is the vertical gaze centre located?

A

In the reticular medial longitudinal fasciculus (opposite the superior colliculus and above the level of CN3n nucleus)

51
Q

What does the medial longitudinal fasciculus carry fibres for?

A
  • conjugate horizontal eye movement
  • holding vertical position of eye
  • vertical smooth pursuit
  • vertical vestibulo-ocular reflexes
52
Q

In which condition is the medial longitudinal fasciculus affected and what ocular pathology arises as a result?

A

Multiple sclerosis- the MLF is affected and results in abnormal horizontal saccades

53
Q

Which nerve carries afferent input from the EOM?

A

Trigeminal nerve

54
Q

What are the three different types of proprioceptors in the EOM?

A
  • muscle spindles
  • Golgi tendon organs
  • palisade endings
55
Q

where are the muscle spindles restricted to?

A

outer orbital layer of EOM

56
Q

where are the golgi tendons restricted to?

A

inner global layer of EOM

57
Q

What are the palisade endings restricted to?

A

marginal layer of EOM

Physiology of vision and the visual system (5 decks)

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