Muscles of the eye

Question 1

What is the basic difference between intrinsic eye muscles and Extraocular muscles (extrinsic)

Answer 1

Intrinsic - control pupil diameter & helps alter lens curvature to enable us to see near objects

Extrinsic - Move the actual eye

Question 2

Identify these extra-ocular muscles

Answer 2

Question 3

Where do the recti muscles of the eye originate?

Answer 3

They arise from the apex of the orbit from an annular fibrous ring

Question 4

Where do the oblique eye muscles arise from?

Answer 4

Superior oblique:

• Lesser wing of the Sphenoid
  
  • Although it goes through a sling thingy

Inferior oblique:

• medial part of the orbit floor
  
  • Only one that originates kinda forwardish

Question 5

What extraocular muscle in the orbit doesn’t actually interact with the eye?

Answer 5

LPS (levator palpebrae superioris)

• a muscle running to the upper eyelid to elevate it

Question 6

How does the attachment of oblique muscles compare to the attachment of rectus muscles?

Answer 6

Rectus - attach to sclera Anteriorly

Oblique - attach to sclera posteriorly

Question 7

Describe the innervation of the extrinsic eye muscles

Answer 7

Trochlear (IV) nerve supplies superior oblique

• Think –> The muscle with a sling (trochlea)

Abducent (VI) nerve supplies Lateral rectus

• Think –> The muscle which abducts

Everything else – Oculomotor (III) nerve

Question 8

Describe the primary movements permitted by the extrinsic eye muscles

Answer 8

Superior & Inferior Rectus

• Elevation & Depression

Lateral & Medial Rectus

• Abduction & Adduction

Superior & Inferior Oblique

• Intorsion & Extorsion

Question 9

Complete the tables of the actions of extraocular muscles

Use RADSIN as a pneumonic to help

RADSIN (Recti ADductors, Superiors INtortors)

Answer 9

Question 10

For each label; describe the corresponding muscle and the nerve that innervates it

Answer 10

Question 11

What is Strabismus?

Answer 11

Squint (misalignment of the eyes)

2 types:

• Esotropia (manifest convergent squint)
• Exotropia (manifest divergent squint)

Question 12

What are the functional consequences of having a squint?

Answer 12

Amblyopia (lazy eye)

• where 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

Diplopia (double vision)

• usually occurs in squints occuring as a result of nerve palsies.

Question 13

What are the intrinsic eye muscles?

Describe their motor innervation

Answer 13

Ciliaris

• muscle in ciliary body
• Parasympathetic innervation via IIIn

Constrictor pupillae

• in iris at pupillary border
• Parasympathetic innervation via IIIn

Dilator pupillae

• radially running muscle in iris
• Sympathetic innervation via plexus around its blood vessels

Question 14

Describe how you would test the pupillary reflex of a patient

Answer 14

*in dimly lit room*

• Pen torch in front of one eye
  
  • check for both pupils constricting (Direct and consensual reflex)
• Swing light to other side
  
  • should remain both pupils constricted

Question 15

In basics, describe why the light reflex causes constriction of both pupils and not just one

Answer 15

Most impulses from the single eye’s retina travel to the LGB (a relay centre) in the thalamus

However - pupillary fibres instead fuck off to the midbrain to a part called the IIIn nucleus

• This contains the Edinger-Westphal nucleus (EWN) for parasympathetic fibres

EWN sends Parasympathetic stimulation to both eyes in response to unilateral stimulus

Question 16

Describe the efferent pathway for the pupillary reflex (from the EWN part of the IIIn nucleus)

Answer 16

Question 17

What is Anisocoria?

Answer 17

Pupils are different sizes

Many causes eg Horner’s syndrome, injury etc

Question 18

What are some causes of abnormal light reflexes of the pupils?

Answer 18

Diseases of Retina:

• detachment/ degenerations or dystrophies

Diseases of Optic nerve:

• optic neuritis (frequently seen in MS)

Diseases of the III cranial nerve (efferent limb)

Question 19

Why is it important to check someone with CN III palsy for their pupillary reflex?

Answer 19

In CN III nerve palsy due to a medical cause such as diabetes, there is usually no damage to parasympathetic fibres so the reflex should be normal

If reflex is absent then suspect a cerebral artery aneurysm (emergency)

Question 20

Describe the effects of Horner’s syndrome on the eye

Answer 20

Anisocoria (pupil sizes different) due to damage to the sympathetic innervation to the pupil on one side

You might also see ptosis (drooping of the eyelid) on the affected side

Other signs – Miosis, anhidrosis (loss of sweating on the affected side)

Question 21

Describe the basic route for sympathetic innervation of the eye

Answer 21

Thoracolumbar outflow of the sympathetic nerves

Travel up sympathetic chain and cervical ganglia

In the head and neck – postganglionic sympathetic fibres travel along with blood vessels to reach the eye

Horner’s syndrome can be caused by disruption at any point - eg from pancoast tumours