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Neuro > Visual system > Flashcards

Visual system Flashcards

1
Q

What are the three layers of the eye?

A

Sclera - hard, opaque
Choroid - pigmented, vascular
Retina - neurosensory tissue

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2
Q

What is the sclera?

A

Tough, opaque protective tissue (white of the eye), high water content

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3
Q

What is the uvea, and where is it located?

A

Vascular coat of eyeball,
lies between sclera and retina

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4
Q

What are the three parts of the uvea?

A

Iris, Ciliary Body, Choroid

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5
Q

Why can a disease in one part of the eye affect other portions?

A

Uvea is intimately connected so disease can travel between parts of the eye

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6
Q

What is the retina and what is its function?

A

Thin layer of tissue on the inner part of the eye, captures light rays and sends impulse to the brain via optic nerve

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7
Q

What is the visible part of the optic nerve called?

A

Optic disc

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8
Q

What is the optic nerve?

A

Transmits impulses from retina to the brain
connects to the back of the eye, near the macula

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9
Q

What is the macula?

A

Small, highly sensitive part of retina for detailed central vision

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10
Q

Where is the macula located?

A

Roughly in centre of retina, temporal (ie lateral) to the optic nerve

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11
Q

What is the very centre of the macula called?

A

Fovea, responsible for even finer detail

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12
Q

Blind spot in the eye

A

Where optic nerve meets retina (optic disc) - there are no light sensitive cells here

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13
Q

What is the difference between central vision and peripheral vision?

A

Central vision is directly in front of you, peripheral is what you can see in the edges without turning your head

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14
Q

Central vision

A

Detail day vision, colour, reading, facial recognition

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15
Q

How can you assess central vision?

A

Visual acuity assessment (reading letters eye test)

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16
Q

Peripheral vision

A

Shape, movement, night vision
aids with navigation

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17
Q

How can you assess peripheral vision?

A

Visual field assessment

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18
Q

What is the effect of losing visual field even with perfect visual acuity?

A

Unable to navigate, may even need white stick

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19
Q

What concentrations of cells does the fovea?

A

High concentration of cones, - colour receptors
low concentration of rods

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20
Q

What are the three layers of the retinal structure?

A

Outer, Middle, Inner Layer

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21
Q

What cells does the outer retinal layer contain and what is its function?

A

Photoreceptors (act as 1st order neurons - detection of light)

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22
Q

What cells does the middle retinal layer contain and what is its function?

A

Bipolar cells (act as second order neurons) - local signal processing to regulate sensitivity

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23
Q

What cells does the inner retinal layer contain and what is its function?

A

Retinal ganglion cells (act as third order neurons) - transmission of signal from eye to brain
axons converge to form the optic nerve

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24
Q

Retinal pigment epithelium

A

transports nutrients from the choroid to the retina and metabolites back to the choroid

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25
Q

What are the two main photoreceptors?

A

Rods and Cones

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26
Q

What is the difference between rod cells and cone cells?

A

Rod cells detect light, more sensitive to light than cnes but slow response
Cone cells detect colour, less sensitive to light but fast response

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27
Q

Why are rods slower to respond to light?

A

More photoreceptors, higher spatial and temporal summation of stimuli before response

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28
Q

What type of vision are rods responsible for?

A

Night vision - scotopic vision

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29
Q

What type of vision are cones responsible for?

A

Daylight fine vision and colour vision - photopic

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30
Q

What is refraction?

A

When light enters a new medium, changing its velocity and path

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31
Q

What are the two basic types of lenses?

A

Convex (CONVErging - brings rays together at focal point, + prescription),
Concave (diverging - spreads rays apart, - prescription)

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32
Q

What is Emmetropia

A

Adequate correlation btw refractive power of lens and cornea and axial length (size of the eye) to retina - parallel light rays fall on the retina

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33
Q

What is Ametropia

A

mismatch between refractive power and axial length, causes parallel lines miss the retina
e.g. myopia, hyperopia, presbyopia

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34
Q

What is myopia?

A

Parallel rays converge at a focal point anterior to the retina
Near sightedness

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35
Q

What are the two types of myopia?

A

Axial Myopia (more common - long globe, aka eye is long),
Refractive Myopia (excessive refractive power - lens is too strong)

36
Q

What are the symptoms of myopia?

A

Blurred long distance vision,
squinting to improve visual acuity,
headache

37
Q

What is hyperopia?

A

Parallel rays of light converge at a focal point posterior (behind) retina
Far sightedness

38
Q

What are the two types of hyperopia?

A

Axial Hyperopia (more common - short globe, aka eye is short),
Refractive Hyperopia (insufficient refractive power - lens is too weak)

39
Q

What are the symptoms of hyperopia?

A

Blurred short distance vision (can vary, worsens when person is tired or low light)
Asthenopic symptoms (aka eye strain symptoms - eye pain, headache, burning sensation of the eye)

40
Q

How does the eye adapt for near vision?

A

Using the near response triad

41
Q

What are the three parts of the near response triad?

A

Pupillary miosis (sphincter pupillae - pupil constricts to increase depth of field)
Convergence (medial recti from both eyes bring eyes towards near object)
Accommodation (circular ciliary muscle - contraction increases refractive power of lens)

42
Q

What is presbyopia?

A

Natural loss of accommodation (focus on near objects) from 40 years+
Distant vision intact

43
Q

How to correct presbyopia

A

Reading glasses (convex lenses) to increase the refractive power of the eye

44
Q

What is the function of the visual pathway?

A

Transmits signals from eye to visual cortex

45
Q

What are the landmarks of the visual pathway?

A

Eye
Optic Nerve (ganglion nerve fibres)
Optic chiasm, nerves from both eyes converge (53% decussate)
Optic tract
Lateral Geniculate Nucleus (ganglion nerves synapse here and relay with the thalamus)
Optic Radiation (4th order neuron relays the signal btw LGN + PVC)
Primary Visual Cortex or Striate Cortex (occipital lobe to the extra-striate cortex which has even higher visual processing)

46
Q

What are the landmarks of the visual pathway in the retina?

A

First order (rod and cones),
Second order (retinal bipolar),
Third Order (retinal ganglion)

47
Q

What fibres cross at the optic chiasma?

A

Crossed Fibres - from nasal retina (medial retina), responsible from temporal (lateral) visual field

48
Q

What fibres do not cross at the optic chiasma?

A

Uncrossed fibres - from temporal (lateral retina), responsible from nasal (medial) visual field

49
Q

What parts of the retina does left visual field stimulate?

A

Nasal retina of left eye, temporal retina of right eye (just vice versa for other one)

50
Q

How many eyes do lesions anterior to the optic chiasma affect?

A

One eye only

51
Q

How many eyes do lesions posterior to the optic chiasma affect?

A

Both eyes (due to crossover)

52
Q

What does a lesion at the optic chiasma cause?

A

Damage to nasal retina from both eyes - leads to temporal field deficit in both eyes so
BITEMPORAL HEMIANOPIA

53
Q

What does a lesion posterior to the optic chiasm cause?

A

Contralateral HOMONYMOUS HEMIANOPIA
(right sided lesion causes left homonymous hemianopia in both eyes)

54
Q

What does a lesion to a unilateral optic nerve cause?

A

Monocular blindness

55
Q

What does a lesion to the primary visual cortex cause?

A

Contralateral Homonymous Hemianopia with Macular Sparing
(right sided lesion causes left sided visual defect, but avoids macula region)

56
Q

What is a typical cause of homonymous hemianopia?

A

stroke (cerebrovascular accident)

57
Q

Why does macular sparing occur?

A

Macula receives blood supply from posterior cerebral arteries from BOTH sides - one damaged will not stop the other

58
Q

What is the pupil response to light?

A

Constriction

59
Q

How does the pupil constrict?

A

Circular muscles contract innervated by parasympathetic nerves within oculomotor nerve

60
Q

What are the effects of pupil constriction?

A

Decrease glare
Increases depth of field (recall near response triad), Decrease bleaching of photopigments

61
Q

What is the pupil response to dark?

A

Dilation

62
Q

How does the pupil dilate?

A

Radial muscles contract innervated by sympathetic nerve

63
Q

What is the effect of pupil dilation?

A

Increases light sensitivity in the dark by allowing more light to enter the eye

64
Q

Describe the afferent pathway of the pupillary reflex

A

THINK SENSORY: rod and cone photoreceptors > bipolar cells > retinal ganglion, exits at posterior third of optic tract > enters lateral geniculate nucleus > brainstem pretectal nucleus > synapse at Edinger-Westphal Nuclei in both sides of the brainstem
(stimuli from one eye affects both due to synapse system)

65
Q

Describe the efferent pathway of the pupillary reflex

A

THINK MOTOR: common for both eyes - oculomotor nerve efferents leave Edinger-Westphal nucleus, synapse at ciliary ganglion, follows short posterior ciliary nerve, to pupillary sphincter

66
Q

What is the direct pupillary reflex

A

Constriction of the light stimulated eye

67
Q

Consensual pupillary reflex

A

Constriction of the eye that is not light stimulated

68
Q

What is the neurological explanation for the consensual pupillary reflex?

A

Afferent pathway on one side will stimulate common efferent pathway on both sides

69
Q

What is an example of a right afferent defect?

A

Damage to right optic nerve

70
Q

In a Right Afferent Defect, what will happen when the right eye is light-stimulated?

A

Neither pupil will constrict

71
Q

In a Right Afferent Defect, what will happen when the left eye is light-stimulated?

A

Both pupils will constrict

72
Q

Example of right efferent defect

A

Damage to the right 3rd nerve

73
Q

In a Right Efferent Defect, what will happen when either eye is light-stimulated?

A

No right pupil constriction
Left eye constriction

74
Q

How can you assess an Afferent Pupillary Defect?

A

Swinging Torch Test - alternating light stimulation of right and left eye

75
Q

What are the 6 extraocular muscles?

A

Straight muscles: Superior Rectus, Inferior Rectus, Lateral Rectus, Medial Rectus,
Superior Oblique, Inferior Oblique

76
Q

Where is the attachment of the superior rectus and what is its function?

A

Attaches at 12 o’clock, elevation

77
Q

Where is the attachment of the inferior rectus and what is its function?

A

Attaches at 6 o’clock, depression

78
Q

Where is the attachment of the lateral rectus and what is its function?

A

Attaches on temporal side of the eye, abduction (away from midline)

79
Q

Where is the attachment of the medial rectus and what is its function?

A

Attaches on nasal side, adduction (towards midline)

80
Q

What is the origin and attachment for the superior oblique?

A

Originates at the apex of the orbit, passes through the trochlea of the nasal bone, attaches on the superior temporal side of eye, underneath superior rectus

81
Q

What is the function of the superior oblique?

A

Depression and Adduction

82
Q

What is the origin and attachment for the inferior oblique?

A

Originates at the base of the orbit, passes through the trochlea of the nasal bone, attaches on the inferior nasal side of the eye, over the inferior rectus

83
Q

What is the function of the inferior oblique?

A

Elevation and Adduction

84
Q

What muscles does the oculomotor nerve innervate?

A

superior branch:
Superior Rectus, Levator Palpebrae Superioris (raises eyelid),

Inferior branch:
Inferior Rectus, Medial Rectus, Inferior Oblique, Circular Muscles of Iris

85
Q

What muscles does the trochlear nerve innervate?

A

Superior Oblique

86
Q

What muscle does the abducens innervate?

A

Lateral rectus

Neuro (12 decks)

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