Extra-occular Eye Muscles, Actions And Diplopia

Question 1

Which muscle groups makes up the extrinsic and intrinsic muscles of the eye and orbit and what are their nerve innervations?

Answer 1

Extrinsic muscles somatic motor Ns

• muscles of the eyelid (also sympathetic innervation)
• extra ocular muscles that move the eyelid

Intrinsic muscles of the eye autonomic/ visceral Ns

• muscles of the iris dilate/ constrict pupil
• ciliary muscle controls thickness of lens

Question 2

What are the 7 extra-ocular muscles, from superior to inferior?

Answer 2

4 recti (S, M, L, I)
2 Obliques (S, I) 
LPS

7 S-> I

Superior oblique (onto side eyeball turns 45d) 
Levator palpebrae superioris
Superior rectus (onto front eyeball) 
Medial rectus (side eyeball) =
Lateral rectus (side eyeball)
Inferior oblique (side eyeball under M/LR & starts floor of orbit)
Inferior rectus (onto bottom eyeball) 

All origins from apex (bar IO)
Supplied by cranial nerves

Question 3

What occurs at primary resting gaze?

Answer 3

Equal and opposite pull of all extraoccular muscles

Each muscle has antagonist

Allows for forward gaze, visual axis both aligned , 2 images reach cortex then fused to be seen as one

Binocular vision - depth perception enabling ‘3D’ vision

Question 4

What occurs during changing position of gaze? What happens if this malfunctions?

Answer 4

Exert greater pull through action of certain extraoccular muscles while antagonists relax

Muscles moving both eyes must be highly co-ordinated & move simultaneously -> visual axis must remain aligned (conjugate gaze)

If visual axis maligned = diplopia

Question 5

What directions can the eyeball move in?

Answer 5

Elevation 
Depression 
Internal rotation 
External rotation 
Adduction 
abduction 

Some extraoccular muscles have one action some have several depending on starting position of eyeball

Question 6

How do some extraoccular muscles have several actions on the eye?

Answer 6

Run in line with axis of orbit

Some attach to globe at an oblique angle (those attach superior and inferior)

Confers some muscles several actions of movement on globe

Question 7

What are the anatomical actions of extraoccular eye muscles? Define

Answer 7

Action each individual muscle exerts on eyeball at resting gaze and when moving from primary resting gaze

Question 8

Which muscle aDduct and aBduct the eye and what is their nerve innervation?

Answer 8

Medial rectus aDducts - oCCulomotor

Lateral rectus - aBducts - ABDUcens

Question 9

What are the actions of superior rectus muscle?

Answer 9

SR (&IR) arise from apex of orbit

SR inserts into superior anterolateral surface of globe

If starting from primary resting gaze:
Elevate
Slightly aDducts
Slightly intorts/ internally rotates

Question 10

What are the actions of inferior rectus?

Answer 10

Arises from apex of orbit

Inserts into anteroinferior surface of globe

If starting from primary resting gaze:
Depress
Slightly aDducts
Slightly extorts/ externally rotates

Question 11

What are the actions of superior oblique?

Answer 11

Arises from apex of orbit passes through trochlea, turns 45d, and inserts superoposterior on globe

Action if starting from primary resting gaze:
Intort/ internal rotation
Depress
Slightly aBducts

Question 12

Actions of inferior oblique

Answer 12

Arises from anteromedial surface of floor orbit
Inserts inferoposterior globe

Action from primary resting gaze:
Extort/ externally rotate
Elevate
Slightly aBduct

Question 13

What can happen if an extraoccular eye muscle is weakened?

Answer 13

You can get abnormalities of gaze as one muscle action(s) is no longer antagonised e.g. resting position may deviate = strabismus (squint) or difficulties moving eye in certain directions

Can be congenital or acquired e.g. CN lesion

Question 14

If a person in resting gaze has their right eye looking to the left and their left eye looking forwards what has occurred?

Answer 14

• The right eye is aDducted
• the action of aBduction is lost
• the muscle which mostly aBducts is lateral rectus
• innervated by CN 6 so could be a CN6 lesion

Diplopia would improve if they looked left and worsen if they looked right

Question 15

If a person in resting gaze has their right eye elevated and looking left and their left eye looking forwards what has occurred?

Answer 15

• right eye is elevated and aDducted and (can’t see but) externally rotated
• muscular actions no longer acting are depression, aBduction and internal rotation
• superior oblique does all of the above
• Cn4 innervates so could be a lesion of this

May tilt head to correct rotation
Diplopia

Question 16

When clinically examining actions of extraoccular muscles which movements of the eye do you make a patient do and why?

Answer 16

Make the patient follow your fingers as you draw a H

Lateral and medial rectus only have one action so could test by looking straight and aBducting and aDducting but some muscles >1 action

• superior rectus and inferior oblique both elevate the eye
• inferior rectus and superior oblique both depress the eye

So test by changing starting position; starting position of eye medial (aDducting first):

• IO will elevate alone
• superior oblique will depress alone

Starting position of eye lateral (aBducting first):

• superior rectus will elevate alone
• inferior rectus will depress alone

Question 17

What can cause CN palsies of the eye? What signs might you find depending on what is causing the pathology?

Answer 17

CN 3/4/6 innervate muscles that move the eyeball

more concerning: Affected by raised intracranial pressure e.g. intracranial haemorrhage or tumour. Headache (+/- vomiting) suggests raised ICP, recent head injury, presence of pupil involvement = CN3 lesions

most likely cause for lesions is vascular disease (microvascular complications) from diabetes and hypertension - patients will otherwise by asymptomatic (apart from signs/ symptoms directly relating to CN lesion), usually self- resolves few months

Abnormalities of eye movements and diplopia, may be obvious from initial inspection

Question 18

What lesions May affect CN 3, what affect will they have on the eye?

Answer 18

Most extraoccular muscles innervated by oculomotor N (3) (except LR and SO). Innervates majority of muscle of eyelid (LPS) and sphincter papillae muscle.

So eye will be in ‘down and out position’ from depression SO and aBduction LR

• Vasculopathic (microvascular lesions) e.g. diabetes/ hypertension PUPIL spared
• compressive lesions (raised ICP, tumour, posterior communicating artery aneurysm) parasympathetics run on periphery CN3 often involved first = Pupil involved

Question 19

what effect will cranial nerve 4 palsies have on the eye? what are symptoms/ signs you should look for

Answer 19

Cranial nerve 4 = trochlear
innervates superior oblique muscle only
- acts to intort/ depress/ aBduct

Lose these actions so eye is extorted/ slightly elevated/ aDducted

Compensate for slight extortion by tilting head slightly

Abnormality in gaze v subtle and often missed

Worsening diplopia especially looking down and medially e.g. walking down stairs, reading bc SO main depressor when eye aDducted

Question 20

what effect will cranial nerve 6 palsies have on the eye?

Answer 20

Cranial nerve 6 = abducens

Innervates lateral rectus
So get unopposed pull of medial rectus = Unable to aBduct affected eye

Diplopia made worse on horizontal gaze