The Extraocular Muscles

Original Author: Oliver Jones
Last Updated: January 27, 2017
Revisions: 29

The extraocular muscles are located within the orbit, but are extrinsic and separate from the eyeball itself. They act to control the movements of the eyeball and the superior eyelid.

There are seven extraocular muscles – the levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, lateral rectus, inferior oblique and superior oblique. Functionally, they can be divided into two groups:

  • Responsible for eye movement: Recti and oblique muscles.
  • Responsible for superior eyelid movement: Levator palpebrae superioris.

In this article, we shall look at the attachments, innervations and movements of the extraocular muscles of the eye. We shall also consider the clinical implications of denervation of these muscles.


Levator Palpebrae Superioris

Fig 1.0 - Attachment of the levator palpebrae superiors to the superior tarsal plate.

Fig 1.0 – Attachment of the levator palpebrae superiors to the superior tarsal plate.

The levator palpebrae superioris (LPS) is the only muscle involved in raising the superior eyelid. A small portion of this muscle contains a collection of smooth muscle fibres – known as the superior tarsal muscle. In contrast to the LPS, the superior tarsal muscle is innervated by the sympathetic nervous system.

  • Attachments: Originates from the lesser wing of the sphenoid bone, immediately above the optic foramen. It attaches to the superior tarsal plate of the upper eyelid (a thick plate of connective tissue).
  • Actions: Elevates the upper eyelid.
  • Innervation: The levator palpebrae superioris is innervated by the oculomotor nerve (CN III). The superior tarsal muscle (located within the LPS) is innervated by the sympathetic nervous system.

Clinical Relevance: Horner’s Syndrome

Fig 1.1 - Left sided Horner's syndrome. Note the partial ptosis.

Fig 1.1 – Left sided Horner’s syndrome. Note the partial ptosis.

Horner’s syndrome refers to a triad of symptoms produced by damage to the sympathetic trunk in the neck:

  • Partial ptosis (drooping of the upper eyelid) – Due to denervation of the superior tarsal muscle.
  • Miosis (pupillary constriction) – Due to denervation of the dilator pupillae muscle.
  • Anhydrosis (absence of sweating) on the ipsilateral side of the face – Due to denervation of the sweat glands.

Horner’s syndrome can represent serious pathology, such as a tumour of the apex of the lung (Pancoast tumour), aortic aneurysm or thryoid carcinoma.

Muscles of Eye Movement

There are six muscles involved in the control of the eyeball itself. They can be divided into two groups; the four recti muscles, and the two oblique muscles.

Recti Muscles

There are four recti muscles; superior rectus, inferior rectus, medial rectus and lateral rectus. 

These muscles characteristically originate from the common tendinous ring. This is a ring of fibrous tissue, which surrounds the optic canal at the back of the orbit. From their origin, the muscles pass anteriorly to attach to the sclera of the eyeball.

The name recti is derived from the latin for ‘straight’ – this represents the fact that the recti muscles have a direct path from origin to attachment. This is in contrast with the oblique eye muscles, which have an angular approach to the eyeball.

Superior Rectus

  • Attachments: Originates from the superior part of the common tendinous ring, and attaches to the superior and anterior aspect of the sclera.
  • Actions: Main movement is elevation. Also contributes to adduction and medial rotation of the eyeball.
  • Innervation: Oculomotor nerve (CN III).

Inferior Rectus

  • Attachments: Originates from the inferior part of the common tendinous ring, and attaches to the inferior and anterior aspect of the sclera.
  • Actions: Main movement is depression. Also contributes to adduction and lateral rotation of the eyeball.
  • Innervation: Oculomotor nerve (CN III).

Medial Rectus

  • Attachments: Originates from the medial part of the common tendinous ring, and attaches to the anterio-medial aspect of the sclera.
  • Actions: Adducts the eyeball.
  • Innervation: Oculomotor nerve (CN III).

Lateral Rectus

  • Attachments: Originates from the lateral part of the common tendinous ring, and attaches to the anterio-lateral aspect of the sclera.
  • Actions: Abducts the eyeball.
  • Innervation: Abducens nerve (CN VI).
Fig 1.1 - Lateral view of the extraocular muscles.

Fig 1.2 – Lateral view of the extraocular muscles.


Oblique Muscles

There are two oblique muscles – the superior and inferior obliques. Unlike the recti group of muscles, they do not originate from the common tendinous ring.

From their origin, the oblique muscles take an angular approach to the eyeball (in contrast to the straight approach of the recti muscles). They attach to the posterior surface of the sclera.

Superior Oblique

  • Attachments: Originates from the body of the sphenoid bone. Its tendon passes through a trochlear, and then attaches to the sclera of the eye, posterior to the superior rectus.
  • Actions: Depresses, abducts and medially rotates the eyeball.
  • Innervation: Trochlear nerve (CN IV).

Inferior Oblique

  • Attachments: Originates from the anterior aspect of the orbital floor. Attaches to the sclera of the eye, posterior to the lateral rectus
  • Actions: Elevates, abducts and laterally rotates the eyeball.
  • Innervation: Oculomotor nerve (CN III).

Clinical Relevance: Cranial Nerve Palsies

The extraocular muscles are innervated by three cranial nerves. Damage to one of the cranial nerves will cause paralysis of its respective muscles. This will alter the resting gaze of the affected eye. Thus, a lesion of each cranial nerve has its own characteristic appearance:

  • Oculomotor nerve (CN III)  – A lesion of the oculomotor nerve affects most of the extraocular muscles. The affected eye is displaced laterally by the lateral rectus and inferiorly by the superior oblique. The eye adopts a position known as ‘down and out’.
  • Trochlear nerve (CN IV) – A lesion of CN IV will paralyse the superior oblique muscle. There is no obvious affect of the resting orientation of the eyeball. However, the patient will complain of diplopia (double vision), and may develop a head tilt away from the site of the lesion.
  • Abducens nerve (CN VI) – A lesion of CN VI will paralyse the lateral rectus muscle. The affected eye will adducted by the resting tone of the medial rectus.

(A good tool to remember the innervation of the extraocular muscles is LR6 – SO– R3)

Fig 1.3 - Oculomotor nerve palsy. Note the 'down and out' position of the eye.

Fig 1.3 – Oculomotor nerve palsy. Note the ‘down and out’ position of the eye.

 

 

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Question 1 / 8
Which nerve innervates the levator palpebrae superioris?

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Question 2 / 8
Which of the following is not a typical symptom of Horners syndrome?

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Question 3 / 8
What is the main action of the superior rectus muscle?

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Question 4 / 8
Which nerve innervates the medial rectus muscle?

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Question 5 / 8
Which nerve innervates the lateral rectus muscle?

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Question 6 / 8
Which of the following is not an action of the superior oblique muscle?

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Question 7 / 8
Which nerve innervates the inferior oblique muscle?

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Question 8 / 8
Which of the following signs would be present in a patient with an oculomotor nerve palsy?

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