S8) Binocular vision, Extra-ocular muscles, axes and terminology Flashcards
1
Q
Why do we have binocular vision? (why do we have two eyes?)
A
- Allows for wider field of vision and depth perception → enabling 3D vision (stereoscopic vision)
2
Q
What needs to be ensured for binocular vision?
A
- visual axis of both eyes need to be aligned
- eyes need to co-ordinate and move together → called conjugate eye movement
- This is vital so that 2 images that reach the cortex are ‘fused’ so perceived as one by the brain
3
Q
What can misalignment of visual axes cause and why?
A
- Diplopia
- Misalignment of two visual axes image focuses on different area of each retina (usually they should hit the same point of the retina in both eyes)
- .: brain is unable to ‘fuse’ - thus we see 2 seperate images
- → Diplopia (double-vision)
4
Q
What is diplopia?
A
- double vision - where 2 images seen
- can be displaced horizontal, vertically and/ or diagonally depending on misalignment between the 2 eyes.
5
Q
If a pt covers over one of his eyes e.g. by closing his eyelid, or covering with a hand, his double vision immediately improves: explain why this happens.
A
- Sensory only from one eye .: there is no misalignment of the visual axis as 2 eyes are not involved .: nothing to confuse with between the 2 eyes as there is only one sensory input.
6
Q
There are two types of muscles of the eye and orbit. They are extrinsic and intrinsic muscles.
What are the extrinsic muscles? What is their innervation?
A
7
Q
There are two types of muscles of the eye and orbit. They are extrinsic and intrinsic muscles.
What are the intrinsic muscles? What is their innervation?
A
8
Q
Identify the 6 extra-ocular muscles of the eye.
A
- Superior recti
- Inferior recti
- Medial recti
- Lateral recti
- Superior oblique
- Inferior oblique
9
Q
What are the 4 recti muscles?
A
- Superior
- Inferior
- Medial
- Lateral
10
Q
What are the 2 oblique muscles in the eye?
A
- Superior oblique
- Inferior oblique
11
Q
Where do the extra -ocular muscles originate?
A
Apex of the orbit, except inferior oblique arises from the floor of the orbital cavity anteriorly
12
Q
What is the common tendinous ring?
A
a fibrous cuff that surrounds the optic canal
13
Q
Which muscles arise from a common tendinous ring?
A
The 4 recti muscles
14
Q
Where do the extra-ocular muscles insert?
A
sclera of the eye
15
Q
What are the extra-ocular muscles innervated by?
A
- LR6SO4
- Lateral rectus → CN VI
- Superior oblique → CN IV
- Rest of the muscles by CN III
16
Q
Observe this picture. Appreciate it ;)
A
17
Q
When looking at the eye, we see 2 axis. What are they?
A
- Visual axis (axis of the eyeball) - in resting gaze, when we look straight ahead, the visual axis of our eyeball is straight ahead
- Axis of the orbit - relates to the angle in which the extra-ocular muscles insert into the eye
18
Q
Why are there several actions of movements on the globe and not just simply up and down for some of the extra-ocular muscles?
A
- The extra-ocular muscles run in line with axis of orbit
- Therefore some muscles attach at an oblique angle - those attaching to superior and inferior surfaces of globe
19
Q
Identify the labels on the 3D model of the right eye.
A
20
Q
The primary resting gaze (position at rest) depends on …
A
- equal and opposite pull of all extra-ocular muscles
- read picture
21
Q
When we change the position of our gaze, what is occurring muscles wise?
A
- exert greater pull through action of certain extraocular muscles, while antagonists relax
- read slide
22
Q
How would you..
- Abduct
- Adduct
- Internally rotate
- Externally rotate
- Elevate
- Depress
the eye….
A
23
Q
What muscles are causing these eye movements?
A
Eye adduction → Medial rectus muscle - inserts at the medial aspect of the sclera
Eye abduction → Lateral rectus muscle - inserts at the lateral aspect of the sclera
24
Q
What muscle causes eye abduction?
A
Lateral rectus muscle
25
What muscle causes eye adduction?
Medial rectus muscle
26
What is the origin and insertion of superior rectus muscle?
* Origin: Apex of the orbit
* Inserts: obliquely into superior anterolateral surface of globe
27
What is the action of superior rectus muscle at primary resting gaze?
* **Elevate**
* slightly adducts (pulls eye medially)
* slightly intorts (internally rotates)
28
What is the action of superior rectus muscle when the eye is positioned laterally i.e. abducted?
* More powerful **elevator**
29
What is the origin and insertion of the Inferior rectus muscle?
* Origin: Apex of the orbit
* Insertion: antero-inferior surface of globe
30
What is the action of inferior rectus muscle at primary resting gaze?
* **Depress**
* slightly adducts (pulls eye medially)
* Slightly exorts (externally rotates)
31
What is the action of inferior rectus muscle when eye is positioned laterally i.e. abducted?
* More powerful **depressor**
32
What is the origin and insertion of Superior Oblique muscle?
* Origin: apex of orbit, passes through trochlea
* Insertion: Superior-posterior aspect of globe
33
What is the action of superior oblique muscle at primary resting gaze?
* **Intort (internally rotate)**
* **Depress**
* Slightly abducts (pull eye laterally)
34
What is the action of superior oblique muscle when the eye is positioned medially i.e. adducted?
* more powerful **depressor**
35
What is the origin and insertion of the inferior oblique muscle?
* Origin: Antero-medial surface of floor of orbit
* Insertion: Infero-posterior aspect of globe
36
What is the action of inferior oblique muscle at primary resting gaze?
* **Extort**
* **Elevate**
* Slightly abduct (pulls eye laterally)
37
What is the action of inferior oblique muscle when the eye is positioned medially i.e. adducted?
* More powerful **elevator**
38
Summary image actions of SR, IR, Obliques (starting from primary resting gaze)
39
Which extra-ocular muscles have an action in elevating the eyeball?
* Superior rectus muscle
* Inferior oblique muscle
40
Which extra-ocular muscles have an action in depressing the eyeball?
* Inferior rectus muscle
* Superior oblique muscle
41
Which extra-ocular muscles are stronger elevators and depressors of the eyeball when the eye is in the **adducted** position?
* Strong elevator → inferior oblique muscle
* Strong depressor → superior oblique muscle
42
Which extra-occular muscles are stronger elevators and depressors of the eyeball when the eye is in the **abducted** position?
* Superior rectus muscle → strongest elevators
* Inferior rectus muscle → strongest depressors
43
Consistency of activity in all extra-ocular muscles on the eyeball - at resting gaze, there is equal and opposite pull.
If a muscle (s) weakened, what influence will it have?
It's ‘influence’ is lost/ reduced
Other muscle actions no longer antagonised
.: resting position of eyeball may deviate → resulting in **strabismus (squint)** due to actions of remaining working muscles
There may also be difficulties with moving eye in certain directions of gaze depending on the muscle weakness.
44
45
46
How would you clinically test for the lateral rectus muscle?
Ask patient to follow your finger
Test abduction of the eye
47
How would you clinically test for medial rectus muscle?
Ask patient to follow your finger
Test adduction of the eye
48
How do we test for superior rectus muscle?
1. Bring eye laterally first (abducted) - starting position of the eye
2. Then ask patient to look up and down.
3. Look up → superior rectus muscle
49
How do we test for inferior rectus muscle?
1. Bring eye laterally first (abducted) - starting position of the eye
2. Then ask patient to look up and down.
3. Look down → inferior rectus muscle
50
How do we test for inferior oblique muscle?
1. Bring eye medially first (adducted) - starting position of the eye
2. Then ask patient to look up and down.
3. Look up → inferior oblique muscle
51
How do we test for superior oblique muscle?
1. Bring eye medially first (adducted) - starting position of the eye
2. Then ask patient to look up and down.
3. Look down → superior oblique muscle
52
Ocular misalignment can result in **strabismus.** Who is it commonly seen in and why?
* common in **children** (congenital or develops in infancy)
* idiopathic
53
What is the cause of strabismus in adults?
* In adults → ‘acquired’ due to pathology or disease involving no. of different structures
* e.g Neuromuscular junctions e..g Myasthenia gravis
* Nerves supplying the muscles ( CNIII, IV, VI)
54
Cranial nerve in the eye, can be affected by….
55
56
CNIII palsies can be due to 2 categories. What are they and what happens to the pupil?
1. **Vasculopathic** (microvascular) lesions e.g. diabetes/ hypertension - **PUPIL SPARED**
2. **Compressive lesions** (raised ICP, tumour, posterior communicating artery aneurysm) - **PUPIL INVOLVED**
57
What does the trochlear nerve supply in the eye?
* innervates the superior oblique muscle .: intort, and depress and abduct eye
58
If there is a trochlear nerve palsy, what happens?
* in resting gaze, **EXTORTED, slightly elevated and abducted** (unopposed actions)
* extortion of eyeball compensated by head tilt (not seen in image)
59
What might someone say with a trochlear nerve palsy when they **look down and medially? Why?**
* worsening **diplopia** esp walking downstairs, reading
* because SO is main depressor of the eyeball when in adduction → SO is weak .: this action is affected !!!
60
What happens in an abducens nerve palsy?
* lateral rectus muscle weakness .: abduction lost .: unopposed adduction by the medial rectus muscle
61
In an abducens nerve palsy, when would diplopia worsen?
* made worse on **horizontal gaze towards eye affected**
62
What is the most likely cause of CNIII, IV, and VI lesions?
**vasculopathic**
– pts will be otherwise asymptomatic - apart from signs/ symptoms directly relating to CN lesion
– lesions usually self-resolve within few months
63
History will help give a clearer indication for more concerning underlying cause …such as
64
There are two types of muscles of the eye and orbit. They are extrinsic and intrinsic muscles.
What are the extrinsic muscles? What is their innervation?
65
Fill this table out.
66
SUMMARY OF EXTRA-OCULAR MUSCLES, INNERVATION, CLINICAL TESTING
