Visual System Flashcards
(104 cards)
1
Q
Why do we have 2 eyes
A
Stereopsis = able to see in 3D
Widens our visual field
2
Q
Number of layers of the eye
A
3
3
Q
3 layers of the eye
A
Outer layer = sclera and cornea
Middle layer = uvea
Inner layer = retina
4
Q
Sclera
A
Tough fibrous outer coat
Made of collagen
5
Q
Why must the outer layer of the eye be transparent - cornea
A
Light transmission
6
Q
Why must the outer layer of the eye be tough
A
Barrier to trauma and infection
Maintains shape of eye
7
Q
What is the cornea and sclera made out of
A
Collagen
8
Q
Outer layer of eye and refraction
A
Responsible for 2/3 refractive power of eye
9
Q
Number of layers in outer layer of eye
A
5
10
Q
5 layers of outer layer of eye
A
Epithelium
Bowman’s layer
Stroma
Descemet’s layer
Endothelium
11
Q
What makes up the middle layer of the eye
A
Iris
Ciliary body
Choroid
12
Q
Iris
A
Coloured part at front of eye
Contains dilator and sphincter pupillae muscles (pupillary reflexes)
13
Q
Ciliary body
A
Glandular epithelium produces aqueous humour
Ciliary (smooth) muscle controls accommodation
14
Q
Choroid
A
Blood supply to outer third of retina
Heat sink
Darkly pigmented so that it can absorb stray photons
15
Q
Retina
A
Specialised organ of phototransduction
16
Q
What makes up the retina
A
Macula lutea
Fovea centralis
Cones
Rods
17
Q
How are collagen fibres laid out in sclera
A
Cross-linked creating opacity
18
Q
How are collagen fibres in cornea laid out
A
Parallel - transparent
19
Q
What percentage of outer layer if cornea
A
1/6 (continuation of sclera)
20
Q
Limbus
A
forms the border between the transparent cornea and opaque sclera, contains the pathways of aqueous humour outflow, and is the site of surgical incisions for cataract and glaucoma
21
Q
Where are stem cells for the cornea found
A
Limbus
22
Q
What causes the choroid to be coloured
A
Contains melanocytes-
23
Q
Ora serrata
A
serrated junction between the retina and the ciliary body. This junction marks the transition from the simple non-photosensitive area of the retina to the complex, multi-layered photosensitive region.
24
Q
Intraocular lens
A
Suspended from cornea
1/3 refractive power
25
Which part of the eye never stops growing
Lens
26
Presbyopia
gradual loss of your eyes' ability to focus on nearby objects.
It's a natural, often annoying part of aging.
Presbyopia usually becomes noticeable in your early to mid-40s and continues to worsen until around age 65
27
What percentage of the corneal depth is the stroma
90%
28
Which layers of the outer layer of the eye can regenerate
Epithelium (not endothelium)
29
Role of endothelium in cornea
Keeps it dehydrated - fluid removed to keep it clear
Water actively pumped out of stroma so transparent
30
Thickness of cornea
550 micrometers
31
Role of ciliary muscles
Holds lens in place by suspensory ligaments
Contract/relax to control accommodation of lens
32
Function of iris
Changes aperture of pupil
33
What fluid fills the anterior chamber of the eye (between cornea and iris)
Aqueous humour
34
What produces the aqueous humour
Ciliary bodies
35
Function of aqueous humour
Maintain pressure in eye
36
Anterior chamber of eye
Between cornea and iris
37
Posterior chamber of eye
Between iris and ciliary processes
38
Pigmented outer layer of retina
formed by a single layer of cells. It is attached to the choroid and supports the choroid in absorbing light (preventing scattering of light within the eyeball). It continues around the whole inner surface of the eye.
39
Neural inner layer of retina
consists of photoreceptors, the light detecting cells of the retina. It is located posteriorly and laterally in the eye.
40
Macula lutea
part of the retina that is responsible for sharp, detailed central vision (also called visual acuity)
Very high concentration of cones
41
Sphincter muscles
Make pupil smaller
Parasympathetic
42
Dilator muscles
Make pupil larger
Sympathetic
43
Intraocular pressure
15 mmHg
44
Pars plana
Located near iris-sclera junction
45
Keratoconus
Abnormal shaped cornea
Results in a stigmatism and distorted light and visual focus
46
Coloboma
Left without uvea
Results in field defect in the affected area
47
Clinical links to retina
Central scotomas
Night blindness
Macular degeneration can lead to blindness
Humours - open angle glaucoma
Tunnel vision affects 2% of population
48
Vitreous humour
Acts as a collagen scaffold and helps maintain Intraocular pressure
49
What produces the vitreous humour
Retina
50
Fovea centralis
When light passes through pupil it projects an image of what you’re focused on to the fovea centralis
51
Retinal pigment epithelium
Contains photoreceptors (rods and cones)
52
Rods
Dim lighting
Sensitive
Peripheral vision
53
Cones
Colour vision
54
Photoelectric transducer
Converts light into electric impulses
55
Number of layers of tear film
3
56
3 layers of tear film
Anterior lipid
Middle aqueous
Posterior mucous
57
Anterior lipid layer
Secreted by meibomium glands
Provides hydrophobic barrier to prevent aqueous layer evaporating
58
Which glands secrete anterior lipid layer
Meibomium gland
59
Middle aqueous layer
Water, electrolytes and proteins
Secreted by lacrimal glands
Regulates transport through cornea and prevents infection
60
Which glands secrete middle aqueous layer
Lacrimal glands
61
Posterior mucous layer
Secreted by goblet cells
Provides hydrophilic layer
Allows for even distribution of tear film
62
Which cells secrete posterior mucous layer
Goblet cells
63
What does the vitreous humour contain
Hyaluronic acid and water
64
Blood supply to eye
Internal carotid artery- ophthalmic artery, central retinal artery and ciliary arteries
External carotid artery - facial artery supplies medial lid and orbit
65
Branches of internal carotid artery that supplies eye
Ophthalmic
Central retinal
Ciliary
66
Photon pathway
Tear film (transmission)
Cornea
Aqueous humour
Lens
Vitreous humour
Ganglion cell
Amacrine cell
Bipolar cell
Horizontal cell
Cone
Rods
Pigmented epithelium (absorption of excess photons)
67
Hypermetropia
Underpowered to focus near objects on retina
May be due to: - corneal curvature too shallow - lens not flexible enough - axial length of eyeball too short
68
Myopia
Overpowered so can’t focus far objects on retina
May be due to: - corneal curvature too steep - axial length of eyeball too long
69
Adenexae
Tear film
3 layers anterior lipid middle aqueous posterior mucous
Protective
Nutrition for cornea
70
Which veins drain the choroid
Vortex veins
71
Where do superior ophthalmic veins drain into
Cavernous sinus
72
Where do inferior ophthalmic veins drain into
pterygoid venous plexus
73
Lymphatics.
No lymphatic drainage of globe
Conjunctiva and lids drain into submandibular and pre-auricular nodes
74
Extra cranial visual pathway
Optic nerve formed by convergence of axons from retinal ganglion cells
Receive impulses from rods and cones
Optic nerve leaves via the optic canal through sphenoid bone
Enters the cranial cavity and runs along the middle cranial fossa
75
Intracranial visual pathway
In middle cranial fossa, optic nerves join = optic chiasm
At chiasm, fibres from the medial halves cross to the contralateral optic tract
Fibres from the lateral halves remain ipsilateral
Optic tracts then travel to lateral geniculate nucleus in the thalamus and fibres synapse
76
Where do optic tracts synapse
Lateral geniculate nucleus in thalamus
77
Optic radiation
Carry visual information to visual cortex from lateral geniculate nucleus
78
Upper optic radiation
Carries fibres from superior retinal quadrants (Baumans loop)
Travels through parietal lobe to visual cortex
79
Which optic radiation travels through the parietal lobe
Upper optic radiation
80
Lower optic radiation
Carries fibres from the inferior retinal quadrants
Travels through temporal lobe (via Meyer’s loop) to visual cortex
81
Which optic radiation travels through the temporal lobe
Lower optic radiation
82
Superior retinal quadrants correspond to
Inferior visual field quadratns
83
Inferior retinal quadrants correspond to
Superior visual field quadrants
84
Intorsion
Internal rotation
85
Extortion
External rotation
86
6 ocular muscles
Medial rectus
Lateral rectus
Superior oblique
Inferior oblique
Superior rectus
Inferior rectus
87
Damage to left optic nerve causes
No vision in left eye
88
Damage to optic chiasm
Loss of vision of the temporal visual fields = hemianopia
89
Damage to left optic tract
Loss of vision of temporal field of left eye and nasal field of right eye
90
Damage to left Meyer’s loop
Loss of vision in superior nasal field of left eye and superior temporal field of right eye
91
Damage to Baum’s loop
Loss of vision in inferior temporal field of right eye and inferior nasal field of left eye
92
Meyer’s loop
Lower optic radiation through temporal lobe
93
Baumans loop
Upper optic radiation through parietal lobe
94
Outer segments of rods and cones
contains discs containing light sensitive photopigment
95
Inner segments of rods and cones
made up of cell body, axon and synaptic terminals
96
Photopigment in rods
Rhodopsin
97
Photopigment in cones
Opsin
98
Opsins
transmembrane proteins which contain the light sensitive molecule retinal
Different opsin structures mean retinal absorbs different wavelengths of light
99
Effect of a photon on a rhodopsin molecule
Triggers conformation change to all-trans form
This change triggers changes in the opsin structure
This in turn triggers a cascade within the cell
100
Signals in the retina
Photoreceptor → bipolar cell → retinal ganglion cell
Horizontal and apocrine cells modulate signal
Retinal ganglion cells not graded response – action potential
101
Retinal blood supply outer 1/3
Choroid (posterior ciliary arteries)
102
Retinal blood supply inner 2/3
Central retinal artery
103
The visual pathway begins with the retina sending signals down the optic nerve towards the optic chiasm. After the optic chiasm, the optic tracts carry on the signal reaching the lateral geniculate nuclei. After this both the meyers loop and baums loop (optic radiations) carry the signal to the visual cortex. Lesions at any point in this pathway are known to cause various visual defects.
Which lobe does Baums loop pass through?
Parietal
104
The visual pathway begins with the retina sending signals down the optic nerve towards the optic chiasm. After the optic chiasm, the optic tracts carry on the signal reaching the lateral geniculate nuclei. After this both the meyers loop and baums loop (optic radiations) carry the signal to the visual cortex. Lesions at any point in this pathway are known to cause various visual defects.
Which lobe does meyers loop pass through?
Temporal
