Extraocular Muscle Cone

Overview

There are seven extraocular muscles, six of which control movements of the eye (four recti muscles and two oblique muscles) and one which controls movements of the upper eyelid (levator palpebrae superioris). The recti muscles originate from the common tendinous ring, whereas the oblique muscle does not. 

Superior Rectus

• Origin: Superior part of tendinous ring
• Inserts: Anterior superior surface of the eye
• Actions:
  • Primary – elevation during abduction.
  • Other – Incyclotorsion during adduction, and adduction
• Innervation: Superior branch of oculomotor nerve

Inferior Rectus

• Origin: Inferior part of tendinous ring
• Inserts: Inferior surface of the eye
• Actions:
  • Primary – depression during abduction
  • Other – extorsion and adduction
• Innervation: Inferior branch of oculomotor nerve
• Blood supply: Branches of infraorbital artery

Medial Rectus

• Origin: Medial part of tendinous ring
• Inserts: Anteromedial surface of the eye
• Actions:
  • Primary – adduction in neutral position
• Innervation: Inferior branch of oculomotor nerve

Lateral Rectus

• Origin: Superior part of tendinous ring
• Inserts: Anterior lateral surface of the eye
• Actions:
  • Primary – abduction in neutral position
• Innervation: Abducens nerve
• Blood supply: Lacrimal artery (branch of ophthalmic artery)

Superior Oblique

• Origin: Body of the sphenoid bone. Tendon passes through a trochlea
• Inserts: Sclera of eye, posterior to the superior rectus
• Actions:
  • Primary – incyclotorsion
  • Other – depresses, abducts and medially rotates the eyeball
• Innervation: Trochlear nerve

Inferior Oblique

• Origin: Anterior aspect of the orbital floor of the maxillary bone
• Inserts: Sclera of eye, posterior to the lateral rectus
• Actions:
  • Primary – excylcotorsion
  • Other – elevates, abducts and laterally rotates the eyeball
• Innervation: Inferior branch of oculomotor nerve
• Blood supply: Branches of infraorbital artery

Common Tendinous ring (Annulus of Zinn)

A ring of fibrous tissue surrounding the optic nerve at its entrance at the apex of the orbit, also known as the annulus of Zinn or common tendinous ring.  It is the common origin of the four rectus muscles.

Structures

Structures passing through from superior to inferior:

• Superior division of the oculomotor nerve
• Nasociliary nerve – the only branch of the ophthalmic nerve (2nd division of trigeminal nerve) which passes through the common tendinous ring
• Inferior division of the oculomotor nerve
• Abducens nerve
• Optic nerve

Relations

• Circle of Zinn: arterial vascular structure which surrounds the optic nerve