Vision Flashcards
(149 cards)
1
Q
Where is the supraorbital notch? What passes through the notch?
A
half way of the supraorbital margin
supraorbital artery, vein and nerve
2
Q
What forms the roof of the orbit?
A
frontal bone, lesser wing of sphenoid
3
Q
what forms the floor of the orbit
A
maxilla, zygomatic and tiny pit of palatine
4
Q
What forms the lateral wall of the orbit?
A
zygomatic, greater wing of sphenoid
5
Q
what forms the medial wall of the orbit
A
maxilla, lacrimal bone, ethmoid, body of the sphenoid
6
Q
Which bones are very susceptible to fracture
A
ethmoid and lacrimal
7
Q
How much of the eyeball is formed by the sclera?
A
5/6
8
Q
What is the function of the sclera
A
maintain shape of globe
offer resistance to internal and external forces
provide attachments for extra-ocular muscles
9
Q
why is sclera so hard to dissect?
A
there is a lot of collagen laid down in whirls to offer extra strength
10
Q
What is the function of the cornea? Where is it in the eyeball?
A
does 60% of the refraction for the eye
it’s found on the anterior 1/6th of the eye
11
Q
What makes the cornea ideal for vision?
A
it’s avascular and transparent
12
Q
how many layers are in the cornea? What are the names of the layers
A
five epithelium Bowman's Stroma descemet's membrane endothelium
13
Q
the epithelium is a ______ membrane
the stroma is full of _______ and is continuous with _______
the endothelium is very specialised because it does not _____ or _______. It controls _________, and any damage will cause the cornea to _______
A
mucus collagen sclera divide regenerate water balance swell
14
Q
What is the makeup of the cornea? How does it make the cornea transparent?
A
packets of collagen laid down in organised layers
adjacent lamellae lie at angles to each other but fibrils within a lamella run in parallel
this creates “destructive interference”, where there is no interruption for light to pass
15
Q
The collage fibrils of cornea are _______ spaced and ______ in diameter. There are about ________ lamellae in the stroma.
A
evenly
uniform
200-300
16
Q
why is the sclera is opaque
A
all collagen fibres are at different size and length
the layers are not organised
17
Q
When there is damage to the cornea, to what extent will there be scarring?
A
if the stroma is damaged, the ordered layers might be disrupted, so you may get corneal scar
damage to endothelium is irreversible
18
Q
Where is the anterior chamber angle
A
it’s at the junction of iris and cornea
19
Q
what is the function of anterior chamber angle?
A
it’s the draining site for the aqueous humour of the eye
20
Q
what happens if the fluid is not drained?
A
pressure builds up inside the orbit
21
Q
How is the aqueous humour produced and where does it travel to?
A
It is produced in the ciliary body, passes through the pupil, and drains via the anterior chamber angle, through trabecular meshwork, into the canal of Schlemm then to the exterior
22
Q
what is the uvea made of?
A
ciliary body, iris, and choroid
23
Q
What are the functions of ciliary body
A
formation of aqueous humour
tethers lens via ciliary process
accommodation via ciliary muscle
24
Q
what are ciliary processes
A
epithelial-like cells that form aqueous humour
the most medial area has ligaments that attach to the lens
25
What are the ligaments of ciliary processes called?
zonules
26
what is the most important fibre of ciliary muscle? What is it innervated by?
circular muscle, innervated by PNS from CNIII
27
When we try to look close up, the ciliary muscle ______, and the ______ in the zonules is lost, making the lens ______
When we try to look in the distance, the ciliary muscle _____, providing tension on the ________, which ______ the lens
contracts
tension
bulgy
relaxes
zonules
flattens
28
What is presbyopia
the loss of accommodation with age because the lens is inflexible and cannot change shape as well
29
Iris is the ________ of the eye which forms the _______. There are two muscles - SNS innervates __________, which ______ the pupil, and PNS innervates ___________, which _______ the pupil
```
aperture
pupil
dilator pupillae
dilates
sphincter pupillae
constricts
```
30
What is the function of choroid?
has blood supply and provides nutrition for mostly the outer retina
31
How many layers are there in the choroid? Which layer is the most important layer
3 layers
| choriocapillaris
32
what is the edge of the retina called?
Orra serrata
33
what is the relationship between the fovea and macula
macula is a yellow colour spot in the retina, whereas fovea is an area within the macula which has highest density of cones
34
T/F the retina is made of layers of neurons
True, with 6 principle types of neurons
35
List 4 properties of the fovea
high visual acuity
avascular
high density of cones
no rods
36
T/F The fovea contains layers of neurons
False, everything is shuffled aside except for photoreceptors
37
What is the lamina cribosa?
A patchy section of sclera that crosses the path of the optic nerve
38
How much sclera continues as the lamina cribosa? How much continues parallel with the optic nerve
1/3 forming the lamina cribosa
| 2/3 parallel to optic nerve
39
how is lamina cribosa related to eye pathology?
Because the sclera is patchy, it is more sensitive to change in intra-ocular pressure, hence can contribute to optic nerve damage where there is increased pressure
40
Which arterial branch gives tributaries for the blood supply of the eye
opthalmic artery, first branch of the internal carotid
41
What are the main arteries supplying the eye?
central retinal artery
long and short posterior ciliary artery
anterior ciliary artery
42
Which artery pierces the optic nerve? Which arteries pierces the globe?
central retinal artery
central retinal, long and short posterior ciliary artery
43
where the the anterior ciliary artery pierce the globe?
travels with a muscle and pierces at the conjunctiva
44
Describe the dual blood supply of the retina
the inner retina is supplied by the central retinal artery
| the outer retina is supplied by the posterior ciliary artery
45
what structures can be found on the eyelids?
```
skin
glands and eyelashes
conjuntiva
muscles
lacrimal apparatus
```
46
what are the muscles of the eyelid and what are their function?
orbicularis oculi - sphincter muscle to depress upper lid
| levator palpebrae superosis - elevates upper lid
47
What are the two muscles of the eyelid supplied by? Do they ever work with each other?
LPS supplied by CNIII
Orbicularis Oculi supplied by CNVII
No, when one contracts, the other always relaxes
48
What is the macula densa important for?
central vision
49
What are the two fundamental factors affecting visual acuity?
neural and optical factors
50
What is visual acuity
the ability to see fine detail
51
How is visual acuity tested?
by the Snellen or LogMAR chart
52
What does a Snellen result of 6/12 mean?
what a normal person sees at 12m distance, a 6/12 person needs to be at 6m to see it
53
What are the optical factors affecting visual acuity?
pupil size
clarity of optical media
refractive error
54
What is cataract?
clouding of the lens
55
```
Define each term
Myopia
Hypermetropia
Astigmatism
Presbyopia
```
```
Myopia = short-sighted
Hypermetropia = long-sighted
astigmatism = deviation from spherical curvature
presbyopia = long-sightedness due to ageing and lack of elasticity of the lens
```
56
# Define
1) photopic
| 2) scotopic
1) related to daytime
| 2) related to night time
57
What is vision at the fovea determined by?
the number of cones
58
where is the
1) cones
2) rods
most concentrated?
1) at the fovea
| 2) at ~8 degrees off the centre of retina
59
What are the six principle retinal neurons?
rods, cones, bipolar, horizontal, amacrine, ganglion cells
60
What cells are found in the outer and inner plexiform layer of the retina
outer: photoreceptors and horizontal cells
inner: bipolar cells and amacrine cells
61
Why do cones provide better visual acuity when rods outnumber cones 20:1
connectivity - cones have one to one relationship with ganglion cells, whereas many rods integrate signals onto a ganglion cell
62
Which cells are responsible for lateral interactions
horizontal and amacrine cells
63
How many types of bipolar cells can be found in the retina?
10 - 1 type of rod bipolar, and 9 types of cone bipolar
64
There are two broad types of bipolar cells - the off BCs ________ when excited, and the on BCs _______ when excited
hyperpolarise
| depolarise
65
Horizontal cell is important for _________ . It receives inputs and outputs to the _________ and signals via the neurotransmitter ________. Hence, HC is mostly _______
lateral inhibition
photoreceptors
GABA
inhibitory
66
There are many types of amacrine cells, but structurally, they are ________ and is important for ________ . They use neurotransmitters like _____ and _____ , and is important for detecting ________
```
axonless
lateral inhibition
GABA
glycine
movements
```
67
There are many types of Ganglion cells, but _____ and ______ are the most important types. _______ is the main neurotransmitter. GCs are the first cell of visual pathway to __________
magnocellular
parvocellular
glutamate
fire action potentials
68
T/F the retina is purely a light detector
False, it also detects contrast
69
How do ganglion cells respond to light?
increase or decrease the rate of firing action potentials
70
Do neuro signals differ when light is shown onto different parts of the receptive field? If so, how does it differ?
Yes
light on the centre of receptive field will increase AP rate
light on the surrounding of receptive field will decrease AP rate
71
How does light get transduced to neural impulse?
the opsin, attaching to retinal, is activated by light. This changes the conformation of cis-retinal to trans-retinal, and dissociates the opsin so it activates transducin, which activates phosphodiesterase
phosphodiesterase decreases cGMP level, and closes Na channel and reduces Na influx, so the cell hyperpolarises
72
T/F Only ON bipolar cells activate with light signal
False, OFF and ON both get switched on at the same synapse
73
When light is on, the photoreceptor will be ________, leading to a _______ of glutamate release. Glutamate is _______ to the ON cell and _______ to the OFF cell. Therefore, the _______ of glutamate will lift the _______ on the ON cell, and it will ________. The opposite will occur to OFF cell, and it will _________ .
```
hyperpolarised
reduction
inhibitory
excitatory
reduction
inhibition
depolarise
hyperpolarise
```
74
When light shines on the surrounding photoreceptor, the photoreceptor _______ and there is a _______ in glutamate. Glutamate is ________ to horizontal cell, so a ______ of glutamate will _______ the horizontal cell and ______ the amount of GABA released, therefore further _______ the ON bipolar cell
```
hyperpolarises
reduction
excitatory
reduction
hyperpolarise
reduce
depolarise
```
75
what is glaucoma
group of ocular disorder that ultimately leads to increased intra-ocular pressure
76
What do M cells look like and what do they detect?
they have large cell body and large dendritic tree
| it detects motion
77
what do P cells like look like? What proportion of GCs are P cells? What do they detect?
P cells are small cells with small dendrites. 80% of the GCs are P cells. They detect colour and visual acuity
78
Where do most of the GCs go to make synaptic connection?
the lateral geniculate nucleus in the thalamus
79
Where is the optic chiasm?
at the base of the brain anterior to the pituitary, with internal carotid arteries on either side
80
where do information from the temporal visual field go to in the retina?
the photoreceptors on the nasal side
81
where GCs cross at the optic chiasm?
the nasal GCs, carrying information for the temporal visual fields
82
What is the most common cause of optic chiasm lesion? What happen to the visual field?
pituitary macroadenoma
| bitemporal hemianopia
83
What does the LGN act as for the visual neurons?
a relay station
84
What is the segregation of visual information at the LGN based on 1) L/R eyes 2) types of cells
1) Left side goes to layers 1,4,6, right side to 2,3,5
| 2) P cells to 3,4,5,6 M cells to 1,2
85
What is the name of the axon tract after the LGN? Where does it go to?
optic radiation to the occipital lobe primary visual cortex
86
What area number is V1?
area 17
87
Where is the occipital lobe? Where is V1 in particular?
occipital lobe is around the calcarine fissure
| V1 is in the medial occipital lobe, the most posterior area of the brain
88
What does each contralateral visual cortex represent?
one half of the visual field
89
What is the most posterior part of the primary visual cortex for?
Macula cortex for central vision
| The more anterior it gets, the more peripheral the vision
90
Is the visual signal inverted in the visual cortex?
Yes, the top left quadrant of the visual field is encoded in the bottom right part of the visual cortex (V1)
91
What is occipital sparring
When there is avascular problem in the visual cortex, resulting in homonymous peripheral hemianopia and the central vision is sparred
This is because the macula cortex is supplied by a separate artery
92
What will happen if lesion occurs in
1) before the chiasm
2) at the chiasm
3) post chiasm
1) unilateral blindness
2) bitemporal hemianopia
3) homonymous hemianopia
93
Can GC cells still fire AP when the subject is blind? What do these cells target?
A proportion of the cells can (~4000 cells) as long as the retina is intact
There isn't enough of them for vision, but they project to areas other than LGN
94
What is the name of the GC that projects to areas other than the LGN?
Melanopsin ganglion cells, which contains photosensitive melanopsin which depolarises the GC
They are the visual pigments in invertebrates
95
Why does migraine pain get worst with light exposure
Because of the intrinsically photosensitive melanopsin GCs that increases the sensitive of pain fibres
96
Where do the GCs related to migraine project to?
posterior nucleus of the thalamus
97
What is the pain sensation in migraine carried by?
from the dura, carried by CNV, which project to brainstem, and to posterior nucleus of thalamus (where GCs act)
98
Is the pupil reflex lost in a blind person?
No, not if the retina is intact and the ipGCs are still present
99
What is the pathway of the pupil reflex?
ipGCs leaves half way to the LGN, runs infero-medially to optical pretectal nucelus (OPN)
OPN sends two secondary interneurons to Edinger-westfal nuclei on both sides, and a third neuron carries info back anteriorly to the ciliary ganglion
Finally, an efferent neuron leaves the CG to control the Iris
100
What is the function of the GCs that project to the suprachiasmatic nucleus of the hypothalamus?
driving circadian rhythm
101
what is gaze?
stabilising an image of an object on the retina
102
What are the two components controlling gaze?
oculomotor and head-movement systems
103
What is saccadic eye movement
shifts the fovea rapidly to a new visual target
104
what is smooth pursuit?
keeps the image of a moving target on the fovea in a slower fashion
105
What is intorsion
movement that involves twisting the eyeball to nose
106
What is extorsion
movement that involves twisting the eyeball away from nose
107
What is the course of superior oblique muscle
projects medially from the tendinous ring, runs through the trochlea and turns laterally, goes under the superior rectus muscle and insert close to the lateral rectus
108
What is the primary action of oblique muscles?
torsion, which is something that we can't see. We see either elevation of depression
109
how can ocular muscle actions be divided into primary, secondary, and tertiary?
because of the insertion angle. For example, the superior rectus inserts at a 23 degrees angle, which allows elevation and also a twisting action
110
How do we isolate the movement of superior and inferior rectus muscles?
test the movement in eye abduction
111
How do we isolate the movement of superior and inferior oblique muscles?
test the movement in eye adduction
112
What is the action of superior oblique?
depress the eyeball (note that the insertion is posterior to the trochlea, so the pulley system depresses the eyeball)
113
Describe the course of the inferior oblique
runs laterally from the trochlea. There is no pulley system for IO, and it inserts medially near the medial rectus
114
How is the course of CNIV different to the two other ocular lower motor neurons?
CNIV crosses the midline before exiting the brainstem, hence innervates the contralateral lateral rectus muscle
115
What is the function of medial longitudinal fasciculus
it is a white matter tract that connects the various cranial nerve nuclei
116
If you can't coordinate eye movement in the vertical direction, where would the lesion be?
in mesencephalic paramedian reticular formation of the midbrain
117
What would happen if you have a lesion in the pontine paramedian reticular formation (PPRF)
lose coordination between medial and lateral rectus, thus cannot move in the horizontal direction
118
What is the pattern of action potential for burst neurons
they fire at high frequency just before movements in saccade
Burst neurons drive movements
119
what is the pattern of action potential for omnipause neurons
fires continuously during saccade. They fire all the time unless burst neurons are firing
120
What is the role of omnipause neurons?
Omnipause neurons are GABA inhibitory. They tonically inhibit the action of lower motor neurons in order to fix the eye on a target
121
When moving the eye to the left in saccade, the cortical neuron first reaches the burst neurons in _______, which further projects to ______ on the ipsilateral side. From there, one lower motor neuron will excite the _______ on the ________ eye, while another neuron will project to ________ oculomotor nucleus via ________, which excites the __________ medial rectus
```
PPRF
abducent nucleus
lateral rectus
ipsilateral (left)
contralateral
medial longitudinal fasticulus
contralateral
```
122
T/F the left cortex controls the right brainstem in terms of eye movement
True, the decussation occurs just under the inferior colliculus.
123
Which system provides information about the position of the head
vestibular system
124
What is the role of
1) semicircular canal
2) otolith
1) send information regarding head position
| 2) send information regarding linear acceleration
125
T/F with acceleration, the neurons of the vestibular centre will decrease firing rate
False, it will increase the firing rate
126
When the head is turn to the right, the right vestibular system will ______ firing rate, while the left vestibular system will ______ firing rate
increase
| decrease
127
Which muscles do we want to contract in order to maintain central eye field if we move our head to the right? Which vestibular nucleus will be excited? Which abducens nucleus inhibited?
left lateral rectus and right medial rectus
right vestibular nucleus (in the direction of head movement)
left abducens nucleus (in the direction of excited lateral rectus)
128
Where do LGN neurons project to?
the primary visual cortex
129
Which zone is the major input zone of V1
layer 4
130
which zone do M cells terminate at?
layer 4Ca
131
which zone do P cells terminate at?
layer 4Cb
132
Where do cells in layer 4Ca (motion) project to?
to layer 4B, which has special cells tuned for motion
133
What special property do cells of layer 4B have?
some neurons show preference for directional movement. They respond best to bars of light moving in a specific directly
134
What's the proportion of the cortex responsible for vision?
40%
135
Where does the dorsal stream project to and what does it process?
Where does it receive information from?
projects to area MT (middle temporal lobe), specialised for processing object motion
V2, V3, and 4B of V1
136
In area MT, neurons have ________ receptive field and respond to _________. Almost all cells in area MT are ________, which respond to ________ or ________. A lesion in area MT will cause the visual images to be _______, and can only see ______ motion
```
large
movement
directional selective
drifting spots
waves of light
intermittent
slow
```
137
Which three primary colours create the images we see?
red, green, blue
138
What determines the colour we see?
how much of each kind of photoreceptors are activated
139
Red is always compared with ______
| _______ is always compared with yellow
green
| blue
140
How do we maximally inhibit a red photoreceptor signal?
shine green light in the periphery
141
T/F Shining blue light in central vision will maximally inhibit yellow from peripheral vision
True, blue and yellow are contrasting colours, and brain detects colour based on contrast
142
What happens when red light is shone onto both central and peripheral visual fields?
red is detected and peripheral signals are deleted
143
Area V4 is part of the ________ stream which receives inputs from _____ and V3 via _______. Neurons of V4 have ______ receptive fields that are both _______ and _______ selective. It is important for recognising object's _____ and ____
```
ventral
V2
V1 (4Cb)
large
orientation
colour
shape
colour
```
144
Where is area V4?
in the medial aspect of inferior temporal lobe
145
Where do neurons from V4 project to? What is this area important for?
area IT
important for visual memory and perception of faces
neurons here are tuned to see faces
146
What are the three groups of colour blindness?
Monochromacy - patient only has one type of cone
Dichromacy - patient has two functional cones
Anomalous trichromacy - most common, all cones working but one is problematic
147
What is protanope? What is protanomal?
protanope - no red cone
| protanomal - abnormal red cone
148
What is deutanope?
no green cone
149
what is tritanope?
no blue cone
