Gross anatomy of the eyeball Flashcards
1
Q
where is the eyeball embedded
A
in orbital fat
2
Q
the eyeball is separated from the orbital fat by what
A
fascial sheath of the eyeball
3
Q
what are the 3 layers (tunics) of the eye
A
-outer fibrous coat
-middle vascular pigmented coat i.e. the uvea
-inner nervous coat i.e. the retina
4
Q
what is the outer fibrous coat like
A
its an inelastic coat
5
Q
what makes up the outer fibrous coat
A
-cornea (anteriorly)
-opaque sclera (posteriorly)
6
Q
what makes up the uvea
A
-choroid
-ciliary body
-iris
7
Q
where does the retina extends to
A
forwards to within 6mm of the limbus
8
Q
the opaque sclera is composed of what
A
dense fibrous tissue
9
Q
what colour is the sclera
A
white
10
Q
what pierces the sclera posteriorly
A
optic nerve
11
Q
the sclera is fused with what
A
dural sheath of the optic nerve
12
Q
what do you call the area of the sclera that is pierced by the nerve fibers of the optic nerve
A
lamina cribrosa
13
Q
what other things pierce the sclera
A
ciliary arteries and nerves and their associated veins
14
Q
the sclera is directly continuous with what in front
A
with the cornea at the corneoscleral junction/ limbus
15
Q
whats at the junction of the sclera and cornea
A
an opening i.e. the scleral venous sinus
16
Q
what colour is the cornea
A
transparent
17
Q
what does the cornea do
A
it refracts the light entering the eye
18
Q
what is the cornea in contact with posteriorly
A
the aqueous humor
19
Q
whats the blood supply of the cornea
A
it is avascular and devoid of lymphatic drainage.
20
Q
how is the cornea nourished
A
by diffusion from the aqueous humor and from the capillaries at its edge
21
Q
whats the nerve supply of the cornea
A
long ciliary nerves from the ophthalmic division of the trigeminal nerve
22
Q
why are cornea transplants common and successful
A
because the cornea has no blood vessels therefore there are no antibodies to cause rejection
23
Q
whats the limbus
A
the junction between the cornea and the sclera
24
Q
what does the limbus nourish
A
peripheral cornea
25
how is a cornea nourished in a cornea transplant
by tears and aqueous humor
26
what does the limbus assist in
corneal wound healing
27
the limbus has the pathway for what
aqueous outflow
28
whats the conjunctiva
the translucent mucous membrane that joins the eyeball to the lids ( it lines the posterior surface of the eyelids and anterior aspect of the eyeball)
29
whats the normal conjunctiva like
-pink
-smooth
-thin
-transparent
30
what runs within conjunctiva
large deep blood vessels that run vertically
31
what does the conjunctiva form at the upper and lower reflections between the eyeball and eyelid
2 sacs i.e. the superior and inferior fornices
32
whats the function of the conjunctiva
it helps lubricate the eye by producing mucus and tears (but a small volume of tears compared to the lacrimal gland)
it contributes to the immune surveillance and helps to prevent the entrance of microbes into the eye
33
what are the 3 parts of the conjunctiva
-bulbar conjunctiva
-palpebral conjunctiva
-forniceal conjunctiva
34
what does the conjunctiva contain
-stroma ( has no adenoid tissues until 3 months after birth)
-follicles and papillae
35
what are some conditions of the conjunctiva
-conjunctival injection
-chemosis
36
describe the palpebral conjunctiva
its richly vascular, extremely thin and strongly bound to the tarsal plate
37
the palpebral conjunctiva is subdivided into what
-marginal
-tarsal
-orbital
38
whats the extension of the marginal conjunctiva
it extends from the lid margin to about 2mm back of the lid upto the sulcus subtarsalis
39
whats the marginal conjunctiva
its actually a transitional zone between skin and the conjunctiva proper
40
what opens in the marginal zone
lacrimal puncta
41
whats the bulbar conjunctiva
its transparent and lies loose over the underlying structures ( so can be moved easily)
42
what separates the bulbar conjunctiva from the anterior sclera
episcleral tissue and tenons capsule
43
whats the blood supply of the conjunctiva
-marginal arcade of the eyelid
-peripheral arterial arcade of the eyelid
-anterior ciliary artery
44
what supplies the palpebral conjunctiva and the fornices
branches from the marginal and peripheral arcades of the artery
45
where do veins of the conjunctiva drain into
venous plexus of the eyelids which then drain into the superior and inferior ophthalmic veins
46
where does the cicumcorneal zone of the limbus drain into
the anterior ciliary veins
47
the lateral side of the conjunctiva drains into what lymph nodes
the periauricular lymph nodes
48
the medial side of the conjunctiva drains into what lymph nodes
the submandibular lymph nodes
49
whats the nerve supply of the bulbar conjunctiva
long ciliary nerve branches of nasociliary nerve from the ophthalmic division of the trigeminal nerve
50
whats the nerve supply of the superior palpebral and forniceal conjunctiva
frontal and lacrimal branches of V1
51
what are clinical correlates of the conjunctiva
-conjunctivitis
-malignant lymphoma
-conjunctival papilloma
52
what does the middle layer of the eye contain
blood vessels
53
what is the small opening in front of the middle layer
pupil
54
what is the choroid
its the vascular layer of the eye containing connective tissues
55
where does the choroid lie
between the retina and sclera
56
what is the choroid composed of
an outer pigmented layer and an inner highly vascular layer
57
what does the choroid do
provides oxygen and nourishment to the outer layers of the retina as well as the ciliary body and iris
58
whats the blood supply of the choroid
branches of the ophthalmic artery (which enter the eyeball without passing with the optic nerve)
59
what is the ciliary body continuous with
posteriorly with the choroid and anteriorly it lies behind the peripheral margin of the iris
60
what is the ciliary body composed of
-ciliary ring
-ciliary processes
-ciliary muscles
61
whats the ciliary ring
its the posterior part of the body and its surface has shallow grooves i.e. the ciliary striae
62
what are the ciliary processes
are radially arranged folds which are connected to the suspensory ligaments of the lens
63
whats the ciliary muscle composed of
meridional and circular fibers of smooth muscle
64
how do meridional fibers run
backward from the limbus to the ciliary processes
65
where do the circular fibers of the ciliary body lie
internal to the meridional fibers
66
whats the nerve supply of the ciliary body
-the ciliary muscle is supplied by parasympathetic fibers from the oculomotor nerve
67
whats the action of the ciliary body
contraction of the ciliary muscle especially the meridional fibers pulls the ciliary body forward, which relieves tension in the suspensory ligament causing the elastic lens to become more convex, increasing the refractive power of the lens
68
the tension on suspensory ligaments does what
changes the shape of the lens depending on the distance of the object being viewed, this process is called accommodation
69
whats the iris
its the coloured part of the eye and is the most anterior portion of the vascular tunic
70
what makes up the iris
radial and circular muscles
71
what does the iris do
controls the amount of light entering the eye
72
whats the opening in the middle of the iris
pupil
73
what happens to the iris in bright light
the parasympathetic nervous system causes the circular muscles to contract and the radial muscles to relax, causing the pupil to constrict and less light enters the eye.
74
what happens to the iris in dim light
the sympathetic nervous system causes the circular muscles to relax and radial muscles to contract, which causes the pupil to dilate and more light enters eye
75
what causes constriction of the pupils
contraction of the circular fibers because of parasympathetic control through the short ciliary nerves
76
what causes dilation of the pupils
contraction of the radial fibers because of sympathetic control through the long ciliary nerves
77
what does the drug atropine do
it inhibits the parasympathetic nervous system causing the pupil to dilate
78
what are the 3 chambers of the eye
-the anterior chamber
-the posterior chamber
-the vitreous cavity
79
where is the anterior and posterior chamber located
how do these 2 chambers communicate
what fills these 2 chambers
infront of iris and behind iris respectively
communicate through pupil
are filled with clear aqueous humour
80
what fills the vitreous cavity
a gel like structure i.e. the vitreous fluid
81
what makes aqueous humor
ciliary body
82
aqueous humor is continually drained by what
scleral venous sinus/ canal of schlemm
83
how often is aqueous humor replaced
90 mins
84
what is a glaucoma
its increased intraocular pressure that can cause blindness due to compression of the retina and its blood supply. It is caused by problems with drainage of aqueous humor
85
whats aqueous humor
its a clear liquid produced by the ciliary body and secreted onto the posterior chamber
86
how does the aqueous humor get into the anterior chamber
through the pupil
87
where is the scleral venous sinus located
junction between the cornea and the iris
88
what maintains the pressure within the eye
by continuous formation and drainage of aqueous
89
whats the normal intraocular pressure (IOP)
10-21mmHg
90
what causes high IOP
obstruction of aqueous outflow
91
whats the function of the aqueous humor
-supplies nutrients to avascular cornea and lens
-maintains intraocular pressure
92
what part of the eyeball is continuously growing throughout life
crystalline lens
93
what do lens do
-separates the anterior 1/5 of the eyeball and posterior 4/5
-its a changeable refractive media i.e. focuses image on retina
94
what controls the lenswhat is the lens composed of
-capsule
-epithelium
-lens fibers
95
what disease affects the lens
cataracts (opacity of the lens)
96
what controls the lens to focus images on the retina
suspensory ligaments and ciliary muscles
97
whats accommodation
it refers to the ability of the eye to alter its focus so that clear images of both close and distant objects can e formed on the retina
98
what are the light rays like for distant objects
they are almost parallel so dont need much refraction to focus on the retina
99
what should the lens for a distant object be like
thin and weak (have long focal length)
100
what are the light rays for a close object like
they are diverging so need more refraction to focus them onto the retina
101
what should the lens for close objects be like
thick and strong ( have a sort focal length)
102
what is the posterior cavity filled with
vitreous humor (its jelly like)
103
what does the posterior cavity do
holds retina in place
104
how often is vitreous humor formed
once during embryonic life
105
what are floaters
debris in vitreous of older individuals
106
the retina makes up what of the eye
posterior 3/4 of eyeball
107
anterior margin of retina contains what
ora serrata retina (rods only)
108
whats the optic disc
its where theres attachment of the optic nerve/ its the blind spot
109
optic disc has no what
photoreceptors
110
where is the fovea centralis
near the middle of the retina
111
whats does the fovea centralis contain
has high conc of cones
112
the fovea centralis is a region of high what
visual acuity
113
whats the blood supply of the retina
-central retinal artery
-choroid
114
how do the retinal vessels enter and leave the eye
through the optic nerve and run in the nerve fibre layer
115
what supplies each of the retinal quadrants
major arterial and venous branch that form an arcade
116
the retina has a superficial layer of what
pigment epithelium (melanin)
117
what is the superficial layer of pigment epithelium
-its a non visual portion
-it absorbs stray light and helps keep image clear
118
what are the layers of the retina
-photoreceptor layer
-bipolar neuron layer
-ganglion cell layer
119
what do rods do
-they are for nocturnal vision i.e. black and white vision, so give great sensitivity in dim light
-they discriminate shapes and movements distributed along the periphery retina
120
whats visual transduction
its when light initiates a nerve impulse
121
whats the structure of a rod cell
-it has an inner segment made up of synapse, nucleus, mitochondria
-outer segment made up of membrane disks
122
in visual transduction detection of light is carried out on what
the membrane disks
123
what do membrane disks contain
rhodopsin
124
what is rhodopsin
its a pigment of the photoreceptor cells in the retina
125
what does rhodopsin do
its responsible for the first events in the perception of light
126
what rhodopsin comprised of
-opsin
-retinal
127
retinal is made from what
vitamin A
128
which part of rhodopsin is the light sensitive part
retinal
129
retinal exists in what 2 forms
cis and trans
130
in the dark retinal is in what form
cis
131
what happens for retinal to switch to the trans form
it absorbs a photon of light and the shape of the opsin protein changes- a process called bleaching
132
what is the reverse reaction i.e. from trans to cis like
-its very slow
-it requires an enzyme reaction
- it requires ATP as rhodopsin has to be resynthesised
133
in visual transduction how does the impulse reach the brain
1. there is bleaching of the rhodopsin in a rod cell
2. this will alter the permeability of the membrane to Na+
3. this will create an nerve impulse that will travel down the sensory neuron in the optic nerve to the brain
134
what does rhodopsin control
sodium channels
135
which rhodopsin opens sodium channels
the rhodopsin with cis retinal (absence of light)
136
which rhodopsin closes sodium channels
the rhodopsin with trans retinal (light)
137
in visual transduction what happens in the dark
the cannel is open and Na+ flows in which causes rod cells to depolarise (so when in total darkness the membrane of a rod cell is polarised)
138
what do rod cells release in the dark
neurotransmitter
139
in visual transduction ,when in the dark, the synapse with bipolar cells is what
an inhibitory synapse (the neurotransmitter stops the impulse)
140
in visual transduction what happens in the light
1. cis retinal is converted to trans retinal and the Na+ channels begin to close
2. less neurotransmitter is produced , but if the threshold is reached the bipolar cell will be depolarised
3. this will then create an impulse which is then passed to the ganglion cells and then to the brain
141
what is the outer segment like for rods and cons
R- rod shaped
C- con shaped
142
where do you find rods and cones and what are they used for
R- are distributed throughout the retina so are for peripheral vision
C- are found mainly in the fovea, so they only detect images in the centre of retina
143
what is the sensitivity like for rods and cones
R- have good sensitivity
C- have poor sensitivity
144
what are the types of rods and cones and what vision do they provide
R- is only 1 type and gives monochromatic vision
C- has 3 types (R,G,B) and gives colour vision
145
what do rods and cones connect to
R- many of them connect to one bipolar cell, which results in poor acuity= poor resolution
C- each con is connected to 1 bipolar cell, which results in good acuity= good resolution
146
con cells have different what
forms of opsin but have the same retinal
147
red light stimulates which cones
R cones
148
yellow light stimulates which cones
R and G cones equally
149
cyan light stimulates which cones
B and G cones equally
150
white light stimulates which cones
all 3 cones equally
151
how are objects in the periphery of our field viewed
they are not seen in colour or detail
152
whats the pathway of light
ganglion cells- bipolar cells- photoreceptor cells
153
what is the pathway for visual impulses
photoreceptor cells- bipolar cells- ganglion cells- optic nerve
154
the optic nerve behind the eyeball is surrounded by what
CSF
155
behind the eyeball the optic nerve is protected by what
the meninges
156
what makes up the optic nerve
axons of the retinal ganglion cells
157
what 3 neurons make up the visual pathway and where do they lie
1. bipolar cell which lies within the retina
2. ganglion cell synapse in lateral geniculate body
3. the 3rd neuron terminates in the visual cortex
158
the left occipital lobe receives visual images from what
- nasal 1/2 of the right eye
-temporal 1/2 of the left eye
159
the right occipital lobe receives visual images from where
-nasal 1/2 of the left eye
- temporal 1/2 of the right eye
160
What’s the importance of the tear film
It maintains the normal environment for the corneal epithelial cells
