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Z MD1 neurology > Vision > Flashcards

Vision Flashcards

1
Q

what forms the supraorbital and infraorbital margins

A

supraorbital margin - frontal bone

infraorbital margin - zygomatic bone (laterally) and maxilla (medially)

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2
Q

what forms the roof of the orbit

A

frontal bone and the lesser wing of sphenoid

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3
Q

what forms the floor of the orbit

A

the maxilla, zygomatic bone and palantine bone

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4
Q

what forms the lateral wall of the orbit

A

the zygomatic bone and the greater wing of sphenoid

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5
Q

what forms the medial wall of the orbit

A

the maxilla, the lacrimal bone, ethmoid bone and body of sphenoid

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6
Q

which parts of the orbit are the most vulnerable to fracture

A

lacrimal bone and the ethmoid bone

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7
Q

what are the functions of the sclera

A
  • maintains the shape of the globe
  • offers resistance to internal and external formces
  • provides attachments for the EOMs
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8
Q

what gives the sclera the resistance and structure it has

A

the way that the collagen is laid down within - laid down in whirls = tough

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9
Q

where is the cornea

A

the most anterior part of the sclera

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10
Q

what is the function of the cornea

A

principal refracting component of the eyes

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11
Q

what is the special function of the endothelial layer of the corne

A

it controls the water balance in the eye

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12
Q

why is the cornea transparent while the sclera is not

A

because the corneal collagen is laid down in a very organised way, uniform in diameter and evenly spaced - where each layer is laid down at slightly different angles

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13
Q

what determines the opacity of the sclera

A
  • the composition of the stroma
  • the hydration of the stroma
  • the size and distribution of the collagen
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14
Q

where is the anterior chamber angle

A

the junction between the iris and the cornea

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15
Q

what is the function of the anterior chamber angle

A

it is the outflow for the aqueus humour to drain out of the eye

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16
Q

what are the key components of the anterior chamber angle that are involved in the drainage of the aqueous humour

A

the trabecular meshwork and the canal of schlemm

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17
Q

what are the functions of the ciliary body and which parts of the body do each function

A
  • forms the aqueous humour (ciliary epithelium
  • tethers lens (ciliary processes)
  • accomodation (ciliary muscle)
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18
Q

what is the importance of aqueous humour

A
  • maintains the health of the lens and cornea

- creates intraoccular pressure

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19
Q

which to structures are used for eye accomodation (focussing)

A

ciliary muscle

zonules

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20
Q

what are zonules

A

the ligaments that attach between the ciliary processes and the lens

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21
Q

how does the eye focus

A

the ciliary muscle changes the tension on the zonules that attach to the lens –> influences the shape of the lens
(contraction of muscle - less tension on the ligaments and vice versa)

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22
Q

innervation of the ciliary muscle

A

innervated by the PNS - non-voluntary muscle

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23
Q

what is presbyopia

A

refers to the loss of accomodation that occurs with age

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24
Q

what causes presbyopia

A

the reduction in flexibility in the lens, capsule and zonules (has become quite inflexible)

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25
Q

what are the two muscles that control the iris? What are their function and what are there innervation?

A

spincter pupillae - constricts the pupil - innervated by the PNS in CNIII
dilator pupillae - dilates pupil - innervated by the SNS

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26
Q

explain the structure and function of the choroid

A

3 layers of blood vessels underneath the retina - supplies nutrients to the retina

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27
Q

what is the optic disc

A

it is where the optic nerve enters the back of the eye and where the BVs exit

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28
Q

function of the fovea and macula

A

allows you to see centralls

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29
Q

what is the orra serrata

A

the edge of the retina

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30
Q

explain the structure of the fovea

A

avascular region of the retina where there is a high density of cones and no rods

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31
Q

the optic nerve is formed by….

A

the axons of ganglion cells as they exit the retina

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32
Q

what is the lamina cribosa

A

band of dense connective tissue made of collagen fibres that forms a sieve like structure that is part of the slcera that provide some structure as the axons pass out of the eye

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33
Q

all of the blood supply of the eye comes from which vessel

A

the opthalmic artery (first branch of the carotid artery)

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34
Q

what is the first branch of the opthalmic artery

A

the central retinal artery - pierces the optic nerve and spans out across the retina

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35
Q

what are the other main arteries of the eye other than the central retinal artery and where are they

A
  • long posterior ciliary artery - travel around to the front of the eyeball
  • short posterior ciliary artery - dont travel very far - supplies the optic nerve head and the photoreceptors
  • anterior ciliary artery - dont pierce the globe, just come forward with one of the muscular arteries and feed the anterior structures when they get close to the conjunctivae
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36
Q

explain the dual blood supply of the retina

A

central retinal artery supplies the inner retina

posterior ciliary artery supplies the outer retina (photoreceptors)

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37
Q

what are the 2 muscles of the eyelids and explain their function and innervated

A
  • orbicularis oculi - innervated by facial nerve - depresses the upper lid
  • levator palpebrae superiosis - elevates the upper lid - innervated by CNIII
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38
Q

what forms the outer, middle and inner coats of the eye, and what are their general functions?

A

outer - cornea and sclera –> strength
middle - uvea –> nutrition
inner - retina –> vision

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39
Q

what is visual acuity

A

the ability to resolve fine detail

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40
Q

what are the optical factors affecting visual acuity

A
  • pupil size (smaller the aperture, the better the VA)
  • clarity of optical media
  • refractive errors (sually determined by the legnth of the eyeball
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41
Q

what is the visual acuity across the retina? And why is there a change?

A

fovea - 6/6 - due to the high level of cones
at 5 minutes of arc away from the fovea –> demostrable VA loss- due to the very low level of cones and the high number of cones

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42
Q

what are the 6 neurons of the retina

A 
rods
cons
horizontal cells
bipolar cells
amacrine cells
ganglion cells
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43
Q

which, rods or cones, allow colour signals

A

cones

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44
Q

what is the ratio of rods and cones at the retina

A

rods:cones = 20:1

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45
Q

why is it that even though the rods outnumber the cones that our night vision is poor and our vision through cones is so good

A

because of the connectivity - how the retina is wired up

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46
Q

what is the “pathway” through the retina?

A

go through photoreceptors –> bipolar cells –> ganglion cells
(has modulation by the horizontal cells and the amacrine cells)

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47
Q

what are the two main types of bipolar cells

A

OFF-bipolar cells –> hyperpolarizing

ON-bipolar cells –> depolarizing

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48
Q

how do horizontal cells modulate the optic pathway

A

they respond to light by using inhibitory neurotransmitter GABA to cause hyperpolarization

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49
Q

how do amacrine cells modulate the optic pathway

A

release inhibitory NT for lateral inhibition

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50
Q

What is the only cell in the retina that fires action potentials?

A

the ganglion cells

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51
Q

what is the function of the ganglion cells

A

the axon asses down the optic nerve to higher brain centres

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52
Q

how do ganglion cells respond to light

A

by increasing or decreasing their action potential firing rate

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53
Q

what is the receptive filed of a ganglion cell or bipolar cell

A

the area of retina that when stimulated with light changes the cells membrane potential

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54
Q

what is the photopigment in rods and cones

A

rods - rhodpsin
cones - cone-opsins
(both attached to vitamin A molecule)

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55
Q

what happens to photoreceptors with light

A

they are hyperpolarized –> releasing less glutamate

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56
Q

in the dark… explain how the RMP is maintained in the photoreceptors

A

open cGMP gated sodium channels causing continuous influx of Na ions into the cell –> depolarisation

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57
Q

in the light…. explain the RMP in photoreceptors

A

light activates rhodopsin –> cascade of events that activates PDE –> cGMP breaks down to GMP - no longer keeps the sodium gate open –> flow of Na ions ceases –> cell is hyperpolarised

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58
Q

what determines the central response and the surround response of the retina

A

central response - the “through pathway” - Ph-BC-GCs

surround response - determined by inputs from horizontal cells

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59
Q

other than the classification of ON and OFF ganglion cells, what is the other classification of ganglion cells and what are their projections and functions

A

M ganglion cells –> project to the M layers of the LGN and give information regarding motion
P ganglion cells –> project to the P layers of the LGN and give information regarding colour and visual acuity

60
Q

where does the optic nerve travel to

A

the lateral geniculate nucleus of the thalamus

61
Q

where is the optic chiasm

A

lies over the sella turcica and pituitary at the base of the brain

62
Q

which optic fibres cross at the optic chiasm

A

the nasal fibres taking information from the peripheral visual fields

63
Q

what other important structures lie around the optic chiasm

A

pituitary gland
cavernous sinus
internal carotids

64
Q

explain the layering system of the lateral geniculate nucleus

A

layers 1 and 2 = magnocellular layers - where M ganglionic cells terminate
layers 3-6 = parvocellular layers - where P ganglionic cells terminate

layers encode different eyes - do not mix information here

65
Q

what are the optic radiations

A

the white matter tracts that project from the lateral geniculate nucleus of the thalamus to the visual cortex

66
Q

where anatomically is the primary visual cortex (V1)

A

on the medial surface of the occipital lobe around the calcarine fissure

67
Q

what is the organisation of the primary visual cortex

A

central vision is encoded on the most occipital/posterior part of V1
As you go more anterior it is encoding more peripheral vision

68
Q

what visual field defect will you have with a lesion before the chiasm

A

defect of one eye only

69
Q

what visual field defect will you have with a lesion at the chiasm

A

defect in both eyes on the temporal sides (bitemporal)

70
Q

what visual field defect will you have with a lesion in the optic radiation

A

affects both eyes on the same side

71
Q

how is it that if someone is blind, some cells in the retina are still activated

A

some ganglion cells are intrinsically photosensitive (dont rely on photoreceptor activation) and depolarise in response to light )due to containing melanopsin)

72
Q

what are melanopsin ganglion cells responsible for

A
  • circadian rhythm
  • sleep regulation
  • pupil responses
  • general information about light levels in the environment
  • light allodynia
73
Q

what is the pathway for pupil constriction

A

light detected by melanopsin ganglion cells –> through the optic chiasm –> leaves the pathway before the LGN, goes to the pretectal nucleus in the midbrain –> sends out a process to each side of the brainstem to the Edinger-Westfall nuclei –> process goes to the ciliary ganglion and then to the intraoccular eye muscle that controls constriction of the pupils

74
Q

where will the lesion be if you have an afferent or an efferent pupillary defect

A

afferent - in the optic nerve or the eyeball

efferent - somewhere between the EW nucleus and the eye

75
Q

which nucleus of the hypothalamus receives information from the melanopsin ganglion cells

A

the suprachiasmatic nucleus

76
Q

what is the importance of melanopsin ganglion cells projecting to the suprachiasmatic nucleus

A

important for driving circadian rhythms

77
Q

what is the pain pathway for migraine

A

dura –> trigeminal nerve –> brainstem –> posterior nucleus of the thalamus

78
Q

two components of the control of our eye gaze

A

occulomotor system -moves the eyes in the orbit (whilst head is still)
head-movement system -moves the eye sockets as a whole (whilst head moves)

79
Q

what are the 5 types of eye movements

A 
saccadic eye movements
smooth pursuits
vergence
vestibular ocular
optokinetic
80
Q

what is saccadic eye movements

A

shift the fovea very quickly from one place to another

81
Q

what is smooth pursuits eye movements

A

keeps the image of a moving target on the fovea

82
Q

what is vestibular ocular eye movements

A

holds the image still on the retina during brief head movements

83
Q

what is optokinetic eye movements

A

holds the image still on the retina during sustained head rotation or translation

84
Q

what are the 6 eye extraocular eye muscles

A 
superior rectus
inferior rectus
lateral rectus
medial rectus
superior oblique
inferior oblique
85
Q

what are the primary actions of the recti muscles of the eye

A

superior rectus - elevation
inferior rectus - depression
medial rectus - adduction
lateral rectus - abduction

86
Q

where is the insertion of superior oblique

A

close to the lateral rectus

87
Q

what is the primary action of superior oblique

A

torsion (rotation inwards and downwards)

88
Q

where is the insertion of inferior oblique

A

close to the lateral rectus

89
Q

what is the primary action of inferior oblique

A

torsion (rotation outwards and upwards)

90
Q

why is that all extraoccular muscles have secondary and tertiary actions

A

because they insert at an angle

91
Q

which muscles are tested during horizontal eye movement

A

medial and lateral rectus muscle

92
Q

what muscles are testing during vertical eye movements while abducted

A

Superior rectus (upwards) and inferior rectus (downwards)

93
Q

what movement tests the superior and inferior oblique muscles

A

vertical eye movements while the eyes are adducted

superior (downward), inferior (upward)

94
Q

which cranial nerves are involved in eye movements

A

III - SR, IR, MR, IO
VI - LR
IV - SO

95
Q

what is special about the trochlear nerve

A

it is the only nerve that crosses the midline and it exits the brainstem from the dorsal surface –> innervates the SO on the contralateral side

96
Q

what two structures are involved in the coordination of one eye with the other

A

medial longitudinal fasiculus (MLF) - white matter tract that connects the various cranial nerve nuclei
reticular formation

97
Q

what two parts of the reticular formation are involved in the coordination of one eye with the other, and what are their main functions

A

pontine paramedian reticular formation - horizontal gaze centre (coordination of MR and LR - CNIII and CNVI)
mesencephalic paramedian reticular formation - vertical gaze centre (coordination of SO and SR - IV an CNIII)

98
Q

what are the two types of neurons in the pontine paramedian reticular formation and when are they activated

A

burst neruons - fire at high frequency just before movement

omnipause neurons - fires continuously except for when burst neurons are firing

99
Q

where do the burst neurons project to?

A

provide:

  • excitatory connections with ipsilateral abducens nucleus
  • inhibitory connections to the suppress the activity of the contralateral abducens
100
Q

where do the omnipause neurons project to?

A

the contralateral abducens nucleus

101
Q

what is the order of steps of abduction of the R eye beginning from cortical stimulation

A
  • cortical stimulation of the burst neurons in the pontine paramedian reticular formation
  • burst neurons stimulate the R abducens nucleus while inhibiting the L abducens nucleus –> R lateral rectus contraction and L lateral rectus relaxation
  • PPRF stimulation of contralateral occulomotor nucleus via the medial longitudinal fasiculus while inhibiting ipsilateral occulomotor nucleus via the MLF –> L medial rectus contraction and R medial rectus relaxation
102
Q

where does the cortical control of eye movements come from

A
  • contralateral frontal eye fields
  • posterior parietal cortex
  • superior colliculus
  • basal ganglia
103
Q

what is the function of the vestibular system of the ears

A
  • provides info about the position of the head in space

- coordinates the position of the head and eyes

104
Q

what are the two parts of the vestibular system involved in coordination of eye and head movements

A

semicircular canals: head position

otolith: linear acceleration

105
Q

how is the vestibular system activated

A

movement of the head moves the fluid within towards one direction –> increasing the firing rate in the vestibular system in one ear and decreasing the firing rate in the other

106
Q

where does the information go to from the vestibular system

A

carried by the vestibulocohlear nerve to the vestibular nuclei in the medulla

107
Q

for coordination of head and eye movements.. the vestibular nuclei needs to coordinate with which cranial nerves

A

III and VI

108
Q

explain the communication of the vestibular nuclei with cranial nerve nuclei III and VI

A

vestibular nuclei stimulates contralateral abducens nucleus (which itself stimulates contralateral (again) occulomotor nucleus)

109
Q

what is the “pathway” for colour vision

A

P ganglion cells –> optic nerve –> optic chiasm –> optic tract –> LGN –> 4Cb layer of visual cortex –> ventral stream –> area IT

110
Q

what is the “pathway” for motion vision

A

M ganglion cells –> optic nerve –> optic chiams –> optic tract –> LGN –> 4Ca layer of visual cortex –> 4Blayer of visual cortex –> dorsal stream –> area MT

111
Q

which cells are directionally selective

A

the cells in layer 4B of the visual cortex

cells in area MT

112
Q

which information travels down the dorsal and ventral streams from the primary visual cortex

A 
dorsal = motion
ventral = colour
113
Q

where does the dorsal stream project to

A

area MT (middle temporal lobe)

114
Q

function of area MT

A

specialised for processing object motion

115
Q

how is “colour” determined

A

by the relative activity of the 3 different “coloured” cones in the retina

116
Q

where does the ventral stream project to

A

area IT (inferior temporal lobe)

117
Q

function of area IT

A

important for visual memory and perception

important for perception of faces

118
Q

what is anomalous trichromacy

A

person has all 3 cones, but one expresses an abnormal pigment and doesnt work the same as normal cones

119
Q

what are the types of colour vision deficiencies

A

protan - red cone problem
deutan - green cone problem
tritan - blue cone problem

120
Q

what test is used to check for colour blindness

A

pseudoisochromatic plates

121
Q

what is the part of the eye called that is the intersection between the sclera and the iris

A

the limbus

122
Q

what gland keeps the anterior surface of the eye moist

A

the lacrimal gland (innervated via the superior salivatory nucleus)

123
Q

when looking at a fundoscopy… how can you tell if it is a R or L eye

A

the optic disc is on the medial side of the retina

the fovea is on the lateral side of the retina

124
Q

where is the conjunctiva

A

anteriorly covers the sclera

125
Q

what is the anterior CHAMBER

A

the cavity between the cornea and the iris

126
Q

what can a blockage of the canal of Schlemm cause

A

glaucoma (increase in pressure)

127
Q

what is the relative size of the lens of the eye during close and distant accomodation

A

close - thicker lens

distant - thin lens

128
Q

what are 8 layers of the retina

A 
choroid
photoreceptors
outer nuclear layer
outer plexiform layer
inner nuclear layer
inner plexiform layer
ganglion cell layer
nerve fibre layer
129
Q

what is in the outer nuclear layer

A

contains photoreceptor nuclei

130
Q

what is in the outer plexiform layer

A

contains synapses between the photoreceptors, bipolar cells and Horizontal cells
(synapses here are glutamate)

131
Q

what is in the inner nuclear layer

A

contains nuclei of horizontal cells, bipolar cells and amacrine cells

132
Q

what is in the inner plexiform layer

A

contains synapses between biplar cells, amacrine cells and ganglion cells

133
Q

what is in the ganglion cell layer

A

contains nuclei of ganglion cells and displaced amacrine cells

134
Q

what is in the nerve fibre layer

A

contains axons of ganglion cells

135
Q

what is the NT used by photoreceptors

A

glutamate

136
Q

what happens with retinitis pigmentosa

A

usually a mutation in rhodopsin gene –> causes gradual loss of rods, night blindness and development of tunnel vision

137
Q

what type of receptors do ON and OFF bipolar cells have

A

ON - metabotropic glutamate Rs

OFF - ionotropic glutamate Rs

138
Q

what type of receptor do ganglion cells have

A

ionotropic glutamate Rs

139
Q

how does sympathetic innervation get to the dilator pupllae muscle for dilation of the pupil

A

via the long ciliary nerves (come with the nasociliary branch of V1)

140
Q

What causes Horner’s syndrome

A

interruption of the SNS supply to the eye

141
Q

what is the clinical “triad” of symptoms of a patient with Horner’s syndrome

A
  • miosis (constricted pupil)
  • partial ptosis
  • loss of hemifacial sweating
142
Q

what part of the visual pathway is split into upper and lower visual fields

A

optic radiations

  • temporal white matter convey upper visual field
  • parietal white matter convey lower visual field
143
Q

what is papilloedema

A

swelling of the optic disc

144
Q

what causes internuclear opthalmoplegia

A

lesion in the medial longitudinal fasiculus (connecting CNIII and CNVI nuclei)

145
Q

explain the pathway onto off and on bipolar cells in the dark

A

dark:
OFF: glutamate released onto OFF bipolar cells –> releases NT onto off ganglion cells –> brain (dark)
ON: glutamate released onto ON bipolar cells–> inhibits release of NT

146
Q

explain the pathway from photoreceptor to OFF and ON bipolar cell in the light

A

light:
OFF - less glutamate released from photoreceptor –> OFF bipolar cell no longer stimulated
ON - less glutamate therefore ON bipolar cells no longer told not to fire –> releases NT onto ON ganglion cell –> light

Z MD1 neurology (17 decks)

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