L31. Eye and Head Movements

Question 1

What are the two components required to stablise an image of an object on the retina and thus maintain control of gaze?

Answer 1

1. Oculomotor system - moving the eyes while the head remains still
2. Head-movement system - moving the head while the eyes stay still

Question 2

What group of muscles are involved in the oculomotor system?

Answer 2

Extraocular muscles and neural pathways that coordinate movement of the eye within the orbit

Question 3

What two major systems are involved in the head-movement process to move the eye sockets as a whole?

Answer 3

1. Vestibular system
2. Oculomotor system

Question 4

What are the five different types of eye movements?

Answer 4

1. Saccidic
2. Smooth pursuits
3. Vergence
4. Vestibular ocular
5. Optokinetic

Question 5

What is saccadic eye movement? Give an example

Answer 5

Where the fovea rapidly shifts to a new visual target. Eg. looking at a new environment or image, from one spot/focus to another.

Question 6

What are smooth pursuit eye movements? Give an example

Answer 6

When there is moving target you are following, it keeps the moving image on the fovea.

Eg. watching your dog run across a park

Question 7

What is vergence eye movement? Give an example

Answer 7

It is movement of the eyes in opposite directions. The most common is converging movement (movement towards each other) to focus on a near by object.

Eg. reading a book

Question 8

What is vestibular ocular eye movement? Give an example

Answer 8

Movements that enable you to hold an object still on the retina during brief head movements

Eg. Shaking your head while looking at a stationary object

Question 9

What is optokinetic eye movement? Give an example

Answer 9

Holding an image stationary during a sustained head rotation or translation

Eg. sitting in a moving car and looking outside the window to a fixed object

Question 10

What are the six extraocular muscles?

Answer 10

4 Rectus Muscles:

• Superior Rectus
• Inferior Rectus
• Medial Rectus
• Lateral Rectus

2 Oblique Muscles:

• Superior Oblique
• Inferior Oblique

Question 11

Define the 6 movements of the eyeballs

Answer 11

1. Elevation: looking up
2. Depression: looking down
3. Abduction: eyeballs moving laterally
4. Adduction: eyeballs moving towards the nose
5. Intorsion: eyeballs rotating towards the nose
6. Extorson: eyeballs rotating away from the nose

Question 12

What does the actions of the extraocular muscles depend on? Why is this so?

Answer 12

The action depends on the insertion because the muscles insert at an angle and thus have primary, secondary and tertiary actions

Question 13

What are the primary actions of the 4 Rectus muscles?

Answer 13

1. Superior rectus = elevation
2. Inferior rectus = depression
3. Medial rectus = adduction
4. Lateral rectus = abduction

Question 14

Describe the position of the eyes that the rectus muscles attach to compared to the oblique muscles

Answer 14

Rectus muscles all attach to the sclera of the eye at angles to the eye ball. They all attach in the same plane to one another called the equator.

The oblique muscles attach/insert to the eyeball also at an angle but at a point behind the equator

Question 15

Do all the extraocular muscles have primary, secondary and tertiary movements?

Answer 15

NO

• Lateral rectus only has the primary movement of abduction
• Medial rectus only has the primary movement of adduction

Question 16

Where to all the extraocular muscles arise from?

Answer 16

From the apex of the orbit from a common tendinous ring

Question 17

Where does the superior oblique muscle insert into?

What is special about its course to get to the attachment site?

Answer 17

It inserts well behind the equator at an oblique angle close to the lateral rectus muscle.

The tendon of the muscle runs through a fibrocartilage pulley called the trochlea on the medial side of the skull

Question 18

What is the primary action of the superior oblique muscle?

Answer 18

Torsion (rotation) of the eye towards the nose (intorsion)

Question 19

Where does the inferior oblique insert?

What is its main action?

Answer 19

It inserts behind the equator close to the lateral rectus

Its primary action is torsion/rotation away from the nose (extratorsion)

Question 20

What is special about the origin of the inferior oblique muscle?

Answer 20

Unlike most of the other extraocular muscles, it does not originate from the common tendinous ring, but rather originates from the orbital surface of the maxillary bone

Question 21

Describe what is meant by the insertion of muscles at an angle to the eyeball? (Use SR as the example)

What is the major consequence of this insertion?

Answer 21

The muscles doesn’t sit perfectly aligned with the midline of the eyeball. Its attachment it about 23 degrees away from the axis of the eye.

This means that MULTIPLE MUSCLES work together to elevate and depress the eye

Question 22

Describe the double H test, to test each muscle in isolation.

Draw the H superimposed on the eyes

Answer 22

The only muscle that is able to elevate the eye when it is abducted is superior rectus and the only that can depress it is inferior rectus

The only muscle that is able to elevate the eye when it is adducted is inferior oblique and the only that can depress it is superior oblique.

Question 23

What nerves innervate each extraocular muscle?

Answer 23

1. Oculomotor Nerve CN III: Superior rectus, Inferior rectus, Medial rectus and Inferior oblique
2. Trochlear Nerve CN IV: Superior oblique
3. Abducens Nerve CN VI: Lateral rectus

Question 24

If there was a lesion impacting CN VI, what problem would be seen in the eyes?

Answer 24

Lesion on the abducens nerve impacts the eyeball’s ability to abduct (look laterally to the side of the face).

Question 25

What is meant by the heirarchial control of eye movement?

Answer 25

Multiple levels of control exist to allow for eye movement

1. Lower motor neurons (cranial nerves)
2. Brainstem eye movement centres (reticular formation)
3. Higher cortical areas (frontal eye fields)

Question 26

Why is there a need to coordinate movements of one eye to the other? What does this involve?

What visual problem occurs if eye movements are not coordinated?

Answer 26

To ensure focusing on one object for the two eyes. This requires coordinated contraction and opposing relaxation in both eyes.

If eye movements weren’t coordinated, then a person would experience double vision (diplopia)

Question 27

What is the Medial Longitudinal Fasciculus (MLF)?

Answer 27

It is a very important white matter tract that connects the important cranial nerve nuclei that innervate the extraocular muscles together

It is especially important in coordinating horizontal eye movements (requiring differential lateral/medial rectus coordiation)

Question 28

What are the gaze centres of the brainstem involved with coordination of movement from one eye to the other?

Answer 28

They are in the Reticular Formation

1. Pontine paramedian reticular formation (Pons)
2. Mesencephalic paramedian reticular formation (Midbrain)

Question 29

Describe the two centres of eye movement control in the brainstem and what movements and nerves they are resonsible for

Answer 29

1. Pontine paramedian reticular formation is also known as the HORIZONTAL GAZE CENTRE for coordination of the medial rectus and lateral rectus muscles of each eye. They thus include CN III and CNVI
2. Mesancephalic paramedian reticular formation is also known as the VERCAL GAZE CENTRE for coordination of the superior oblique and superior rectus muscles of the eye. Thus include CN IV and CN III