The Eye Muscles

Question 1

What are the two types of muscles in the eye?

Answer 1

Intrinsic and extrinsic

Question 2

What is the action of the intrinsic muscles?

Answer 2

Controls pupil diameter and helps alter lens curvature to enable us o see near objects

Question 3

What is the action of the extrinsic muscles?

Answer 3

Movement of the eye

Question 4

Name the four recti muscles?

Answer 4

• Medial rectus
• Lateral rectus
• Superior rectus
• Inferior rectus

Question 5

Name the two oblique muscles?

Answer 5

• Superior oblique

* Inferior oblique

Question 6

Describe the orbital and optical axes

Answer 6

• Orbital - are not parallel to each other they are slightly divergent
• Optical - parallel axis

Question 7

What axis do the extrinsic muscle pull on the eyeball?

Answer 7

Orbital axis, giving the muscle more than one action

Question 8

What are the actions of the oblique muscles?

Answer 8

They are attached that the posterior part of the sclera, so they pull the posterior part of the eyeball up/down

SO depresses eye and IO causes elevation

Question 9

When the eye is abducted what is the action of the superior and inferior rectus muscles?

Answer 9

• SR - elevation

* IF - depression

Question 10

When the eye is adducted what is the action of the superior and inferior rectus muscles?

Answer 10

• SR - intorsion

* IR - extorsion

Question 11

When the eye is adducted what is the action of the superior and inferior oblique muscles?

Answer 11

• SO - depression

* IO - elevation

Question 12

When the eye is abducted what is the action of the superior and inferior oblique muscles?

Answer 12

• SO - intorsion

* IO - extorsion

Question 13

What are the principles of testing the action of the EOMs?

Answer 13

The obliques elevate/ depress when the eye is adducted.

The recti (SR and IR) elevate/depress when the eye is abducted.

Question 14

Do the medial and lateral rectus muscles have more than one action?

Answer 14

No, only one:
• MR - adducts
• LR - adducts

Question 15

What are the actions of the superior rectus muscle?

Answer 15

• Elevation
• Adduction
• Intorsion

Question 16

What are the actions of the inferior rectus muscle?

Answer 16

• Depression
• Adduction
• Extorsion

Question 17

What are the actions of superior oblique muscle?

Answer 17

• Intorsion
• Depression
• Abduction

Question 18

What are the actions of the inferior oblique muscle?

Answer 18

• Extorsion
• Elevation
• Abduction

Question 19

What are two types of misalignments of the eyes (strabismus)?

Answer 19

• Esotropia -> convergent squint

* Exotropia -> divergent squint

Question 20

What are two consequences of the squint?

Answer 20

1. Amblyopia (lay eye)

2. Diplopia (double vision)

Question 21

What happens in amblyopia?

Answer 21

Lazy eye - Brain supresses the image of one eye leading to poor vision in that eye without any pathology (correctable in early years using eye patches to stimulate the ‘lazy’ eye to work)

Question 22

What happens in diplopia?

Answer 22

Double vision - Usually occurs in squints occurring as a result of nerve palsies

Question 23

Name three different intrinsic muscles

Answer 23

• Ciliaris
• Constrictor pupillae
• Dilator pupillae

Question 24

How are the intrinsic muscle innervated?

Answer 24

Ciliaris and constrictor papillae - innervated by oculomotor nerve (CN III)

Dilator pupillae - sympathetic innervation (from plexus around blood vessels)

Question 25

What can pathology of the nerves innervating the intrinsic muscles cause?

Answer 25

Pupillary abnormalities

Question 26

Describe the pupillary reaction to light

Answer 26

* Increased illumination -> parasympathetic -> both pupils constrict * Decreased illumination -> sympathetic -> pupils dilate

Question 27

Describe how you would elicit a pupillary reflex

Answer 27

Start in a dimly lit room (pupils dilate): | Pen torch in front of one eye -> check for both pupils constricting (direct and consensual reflex)

Question 28

Describe the afferent limb of the light (pupillary) reflex

Answer 28

Light on retina -> impulse travels along optic nerve -> optic chiasma -> optic tract Fibres destined for pupillary reflex do not enter LGB, but travel to the midbrain (where CN III nucleus is situated)

Question 29

What is the Edinger-Westphal nucleus (EWN)?

Answer 29

Parasympathetic preganglionic nucleus body of CN III

Question 30

Describe the efferent limb of the light (pupillary) reflex

Answer 30

1. From EWN (part of CN III nucleus) 2. Preganglionis pass through CN III into orbit 3. Parasympathetic fibres synapse in the ciliary ganglion 4. Post-ganglionic fibres go through short ciliary to constrictor pupillae 5. Pupillary constriction on both sides

Question 31

Name abnormalities with pupils that can occur

Answer 31

* Pupils maybe of different sizes – anisocoria i.e. Horner’s syndrome * Pupils may look normal but react abnormally to light (abnormal light reflex)

Question 32

Name three common cause of absent/abnormal pupillary reflex

Answer 32

* Disease of the retina - detachment or dystrophies * Diseases of the optic nerve - i.e. optic neuritis * Disease of the CN III (efferent)

Question 33

What must you check in a patient with CN III palsy?

Answer 33

Check pupillary reflex as usually due to diabetes, not by damage to parasympathetic fibres

Question 34

What does an absent reflex indicate?

Answer 34

Suspect cerebral artery aneurysm -> emergency

Question 35

Name the features of Horner's Syndrome

Answer 35

* Anisocoria (unequal size of pupil) due to damage to the sympathetic innervation to the pupil * May see ptosis (drooping eyelid) or anhidrosis (loss of sweating)