The Orbit and Eye - 2 Flashcards
1
Q
When do we get contraction of the ciliary muscle?
A
When we have a shift from long to short vision. This is a way of focusing on near objects.
2
Q
When focusing on closer objects, as well as contraction of the ciliary muscle what else happens?
A
We get constriction of the pupil.
3
Q
What do you notice about contraction of the ciliary muscle and constriction of the pupil?
A
They are both parasympathetic effects.
4
Q
What is the 3rd thing that happens to both eyes when close objects are observed?
A
The eyes converge when close objects are observed.
5
Q
What is it called when the eyes change focus from long to short vision?
A
This is called accomodation.
6
Q
What is the largest part of the middle coat of the eye?
A
The choroid.
7
Q
What does the choroid have many of?
A
The choroid has many blood vessels.
8
Q
What is the inner layer of the eye called?
A
The inner layer is called the retina.
9
Q
How can we study the retina?
A
By using an opthalmoscope.
10
Q
What is the fundus?
A
This is a whole view of the back of the retina that can be seen by an ophthalmoscope.
11
Q
What 3 things can we see using an ophthalmoscope?
A
- optic disc
- macula lutea
- retinal arteries
12
Q
Where is the optic disc found?
A
It is found 3mm to the nasal side of the anteroposterior axis of the eye.
13
Q
What happens at the optic disc?
A
This is where the optic nerve fibers and the blood vessels leave the eye.
The optic nerve fibres build up into a circular zone as they leave and this gives the optic disc a raised edge. the central part of the disc is depressed.
14
Q
What artery enters at the optic disc?
A
The central artery of the retina enters at the disc and its branches can easily be seen here.
Retinal veins are also easily seen here.
15
Q
What is the macula?
A
The macula is a small yellowish spot that lies exactly in the visual axis.
This is the area of most distinct vision.
16
Q
What is the fovea centralis?
A
This is a small depression in the centre of the macula.
17
Q
What is the significance of the fovea centralis?
A
This is the point where the resolving power of the retina is maximal and it is therefore the point of most accurate central vision.
18
Q
What happens to the margins of the optic disc when the intracranial pressure increases?
A
The margins of the optic disc become swollen.
19
Q
Why is the state of retinal vessels extremely important to note?
A
It is the one place in the body where blood vessels can be viewed directly. In patient with high blood pressure, the vessels with have thick walls and appear rigid. Where arteries cross veins, they will compress the veins.
Sometimes there can be a haemorrhage into the retina from the vessels or white fluffy areas of exudate from vessels.
Diabetes also gives characteristics when the fundus is examined.
20
Q
What is contained in the cavity behind the lens?
A
Vitreous humour.
21
Q
What is the vitreous humour like?
A
This is like jelly.
22
Q
What is the hyaloid fossa?
A
In front, the posterior surface of the lens and the ciliary processes form a concavity in the jelly which is called the hyaloid fossa.
23
Q
What is the hyaloid canal?
A
This is a minute disc that runs from the optic disc to the posterior surface of the lens.
24
Q
What does the hyaloid canal represent?
A
This represents the remains of a small branch of the central artery of the retina that degenerates before birth and it can only be seen with special optical instruments.
25
What is the vitreous membrane?
The vitreous body is condensed superficially to form an envelope called the vitreous membrane.
26
The vitreous membrane is thickened in front to form the ...................... .........................
capillary zonule.
27
What is the posterior layer of the capillary zonule like?
The posterior layer is very thin.
28
What is the anterior layer of the capillary zonule like?
It is thick and it forms the suspensory ligament of the lens.
29
What is the function of the suspensory ligament of the lens?
This ligament holds the lens in the hyaloid fossa and maintains tension on the periphery of the lens when the eye is at rest or focused on distant objects.
30
How does contraction of the ciliary muscle cause the lens to take up a fat shape?
When the ciliary muscle contracts, it pulls the ciliary processes, zonule and suspensory ligaments forwards.
This releases tension in these ligaments.
The lens takes up a flat shape by its own elasticity and its focal length is shortened.
31
In the orbit, what separates the eyeball from the orbital muscles and fat?
The orbit is surrounded by a fascial sheath in which it rotates and in which it is separated from the orbital muscles and fat.
32
What is the diameter of the eyeball?
About 2.5 cm but the cornea is more curved than the globe.
33
Where is the fascial sheath deficient?
The fascial sheath is deficient in front over the cornea.
34
What does the fascial sheath fuse with posteriorly?
It fuses with the dura over the optic nerve.
35
As each extra-ocular muscle passes to the eyeball, what does it have to do before it inserts into the sclera?
It has to pierce the fascial sheath before it can insert into the sclera.
It does this close to the equator of the eye and the sheath is carried over the muscles for a short distance.
36
What are check ligaments?
At the point where the fascial sheath continues over the muscle for a short while, the sleeves of the medial and lateral rectus muscles are attached to the walls of the bony orbit by small fascial slings or **check ligaments**.
37
What is the function of check ligaments?
* They help to stabilise the eye in the orbital cavity.
* Resist compression of the globe of the eye when the muscles act.
38
Describe the suspensory ligament and its attachments.
* hammack shape band
* stretched between lacrimal and zygomatic bones
* attached to the fascial sheath of the eyeball since it blends with the sheaths covering the extra-ocular muscles that lie beneath the eye
39
What surrounds the apex of the orbit?
A tendinous ring.
40
What does the tendinous ring enclose?
It encloses the optic foramen and the medial part of the superior orbital fissure.
41
How many muscles arise from the tendinous ring?
4
42
Where do the 4 muscles that arise from the tendinous ring insert?
They insert in front of the coronal equator of the globe of the eye.
43
What are the 4 muscles that arise from the tendinous ring?
Lateral, medial, superior and inferior rectus muscles.
As these pass forwards from their origins they form a cone of muscles around the eye.
44
What 2 muscles arise from the bony orbit outside the cone?
2 oblique muscles arise from the bony orbit outside the cone - one above and one below.
45
Where does the superior oblique muscle arise from?
Arises from the bone above the tendinous ring.
46
Describe the path of the superior oblique muscle.
It passes forwards along the upper border of the medial rectus to reach a fibrous pulley or trochlea which is attached to the roof of the bony orbit.
When the muscle fibres reach the trochlea they change course and is then directed posteriorly to its insertion behind the coronal equator of the eye.
47
Where does the inferior oblique muscle arise from?
It arises well forwards on the orbital floor.
48
Where does the inferior oblique muscle insert?
It runs backwards from the point of origin to insert into the eye behind the coronal equator.
49
Where does the levator palpebrae superioris muscle arise from?
It arises from the bony orbit above the origin of the superior rectus and it passes forwards to insert into the structures of the upper eyelid.
50
What is the function of the levator palpebrae superioris muscle?
Its action is to raise the upper eyelid.
51
What is the function of the lateral and medial recti?
These muscles rotate the eye around a vertical axis through the globe so that the cornea points laterally and medially.
52
When we look directly forwards, what plane does the visual axis lie in?
The visual axis lies in the sagittal plane.
This is parallel to the medial wall but not to the lateral wall.
53
In what position of the eye does the visual axis correspond to the line of pull of the superior and inferior rectus muscles?
When the eye is turned laterally.
Therefore when the eye is turned laterally their pull is powerfully and directly up and down.
54
What happens to the function of the superior and inferior recti when the eye looks medially?
The pull of these muscles is ineffectual in elevation and depression and these muscles have a tendency to rotate the globe only around a transverse anteroposterior axis -- this movement is called torsion. Torsion means twisting.
55
Which muscles are powerful elevators and depressors when the eye is medially placed?
The obliques.
56
What is the function of the superior oblique muscle when the eye is placed medially?
The superior oblique pulls the eye down.
57
What is the function of the inferior oblique muscle when the eye looks medially?
This pulls the eye up.
58
When is elevation and depression via the superior and inferior oblique muscles maximally effective?
When the eye is directed medially.
59
What happens to the obliques when the eye is laterally directed?
They become muscles of torsion and have a tendency to rotate the globe only around a transverse anteroposterior axis.
60
How can you test the action of the medial and lateral recti?
By asking the patient to look at their nose and then away.
61
How can we test the action of the obliques and the superior and inferior recti together?
By asking the patient to look forwards and then up and down.
62
How can we test the individual actions of the obliques and superior and inferior recti?
* We can put the eye into medial/ lateral gaze and test elevation and depression
* When eye is looking medially the oblique muscles are most suited to elevate and depress.
* When the eye is looking laterally, the superior and inferior recti are most suited to elevate and depress.
63
What is required to keep the eyes parallel at all times?
This involved fine control of muscles of both eye.
The pure movements of elevation, depression, lateral and medial motion are important but it is also important for constant corrections for torsional movements.
64
How do neurovascular structures enter and leave the orbit?
Through the optic foramen or the superior orbital fissure.
65
Where do structures passing through the optic foramen and the medial end of the superior orbital fissure enter the orbit?
They enter the orbit within the cone of muscles
66
Where do structures that pass through the lateral part of the superior orbital fissure enter the orbit?
They enter the orbit outside the cone of muscles.
67
Once we remove the bony roof of the orbit what do we see?
We see 3 nerves that are lying just deep to the periosteum.
68
Where do the 3 nerves that lie deep to the periosteum of the roof of the bony orbit enter the orbit?
They entire the orbit through the lateral part of the fissure and they lie outside the cone of muscles.
69
What are the 3 nerves that can be seen that lie deep to the roof the bony orbit?
* 2 of these are the branches of the ophthalmic division of the 5th cranial nerve;
* lacrimal nerve
* frontal nerve
* 4th cranial nerve -- trochlear nerve
70
What is the function of the ophthalmic division of 5th cranial nerve and its branches?
This nerve and its branches are purely sensory.
71
Where does the lacrimal branch of the opthalmic branch of the 5th cranial nerve carry impulses from?
It carries sensory impulses from the conjunctiva and the eyelids.
72
What does the frontal branch of the ophthalmic divison divide into?
It divides into 2 branches which are the supraorbital and supratrochlear branches.
73
Where does the frontal branch of the 5th nerve carry sensation from?
It carries sensation from a wide area of skin that extends from the side of the eye upwards over the scalp tp the top of the head.
74
What is the function of the trochlear nerve?
This is the 4th cranial nerve and it is entirely motor in function.
75
Describe the trochlear nerve.
It is a small thread like nerve.
76
What muscle does the trochlear nerve supply?
It supplies the superior oblique muscle.
77
What are the 4 nerves that pass through the optic foramen and the medial end of the superior orbital fissure and therefore run within the cone of muscles?
* optic nerve = second cranial nerve
* nasociliary branch of the ophthalmic division of the 5th cranial nerve
* oculomotor nerve = 3rd cranial nerve
* abducent nerve = 6th cranial nerve.
78
How does the optic nerve reach the eyeball?
It reaches the eyeball by passing through the optic foramen and the tendinous ring to reach the eyeball about 3mm medial to its posterior pole (it is important to know the relation of the optic nerve from the posterior pole when examining the interior of the eye with an ophthalmoscope.
79
What does the entrance of the optic nerve look like?
The entrance of the optic nerve looks like a saucer like depression called the optic disc.
80
What is the function of the nasociliary branch of the opthalmic division of the 5th cranial nerve?
This is entirely sensory.
81
Describe the path of the nasociliary branch?
* crosses above the optic nerve and passes towards the medial wall of the orbit
* at the medial wall of the orbit it divides into branches that carry sensation from the **surface and the bridge of the nose** and from **air sinuses in the ethmoid bone.**
* in the orbit, several important branches leave the main trunk of the nasociliary nerve
82
What are some of the important branches that leave the main trunk of the nasociliary branch?
* long ciliary nerve
* short ciliary nerve
83
What is the function of the long ciliary nerves?
* sensory nerves from the eyeball
* carry sympathetic fibres to the eye
84
What happens when there is sympathetic activity to the muscles that control the pupil?
Sympathetic activity causes the pupil to dilate.
85
What fibres are present in the short ciliary nerves?
Some sensory neurones of the nasociliary nerve and some sympathetic neurones take another course to the eye through the short ciliary nerves,
86
Describe the path of the short ciliary nerve.
* fibres first pass through the parasympathetic ciliary ganglion
* sympathetic and sensory fibres DONT synapse here
* sensory fibres continue through the ganglion and join up with the nasociliary nerve
* therefore the ciliary ganglion looks like it is suspended from the nasociliary nerve and hangs down just to the lateral side of the optic nerve.
87
What happens to the oculomotor nerve?
It divides into 2 divisions that supply all the extraocular muscles *except superior oblique which is supplied by the trochlear nerve which is the 4th cranial nerve and the lateral rectus muscle that is supplied by the 6th cranial nerve or the abducent nerve.*
88
What does the oculomotor nerve also carry?
It also carries parasympathetic motor fibres from the brain.
89
What is the path of the parasympathetic motor fibres that come from the brain and are carried by the oculomotor nerve?
* the fibres leave the nerve and jump into the ciliary ganglion
* at the ciliary ganglion the fibres synapse
* post ganglionic parasympathetic fibres pass to the eye within the short ciliary nerves.
90
What does activity of the parasympathetic fibres to the eye cause?
It causes the pupil to constrict and the ciliary muscle to contract.
91
What is the abducent nerve the motor nerve to?
It is the motor nerve to the lateral rectus muscle.
92
What is the path of the abducent nerve?
It passes through the medial end of the superior orbital fissure within the fibrous ring and it quickly enters the lateral rectus muscle.
93
How can we detect strabismus of the eye due to lesions of the 3rd, 4th and 6th cranial nerves?
By testing the movements of each eye.
94
What happens when we stimulate sympathetic neurones to the eye?
This causes the pupils to dilate.
95
What is the path of sympathetic neurones that leave the thoracic spinal cord?
Preganglionic -- They ascend in the trunks to the upper cervical sympathetic ganglion where they synapse.
Postganglionic -- climb along the carotid arteries and the ophthalmic branch to reach the orbit. At the orbit they pass without synapsing through the ciliary ganglion to the eye, or simply hitch hike along the short and long ciliary branches of the nasociliary nerve.
96
What is a consequence of the fact that the sympathetic fibres have a long course?
This means that a lesion as far away as the apex of the lung in the thorax could affect the sympathetic trunk and the sympathetic supply to the eye.
Therefore the pupil of the eye will be unable to dilate and it will remain small and constricted.
97
What is a common pathology during or following a severe injury to the head?
The parasympathetic neurones in the oculomotor nerve may be compressed or injured.
As a result of swelling and oedema of the brain the pressure within the cranial cavity increases and the oculomotor nerve is easily compressed.
The pupil on the side of raised pressure is therefore unable to constrict and it remains dilated and sluggish or even unresponsive to a light shone in the eye,
98
Where does arterial blood supply to the eye and orbit come from?
It comes from the ophthalmic artery.
99
When does the opthalmic nerve enter the orbit?
It enters the orbit below the optic nerve through the optic foramen.
100
What is the path of the opthalmic artery after it passes through the optic foramen?
It spiral around the lateral side of the optic nerve and supplies many branches to the muscles, eyelids and conjunctiva and other orbital structures.
