Extraocular muscles

The extraocular muscles are responsible for controlling precise movements of the eyeball within the orbit. There are six muscles in total — four recti and two obliques — working together to move the eyes smoothly and maintain binocular vision.

Muscle Origins

• The four recti muscles — superior, inferior, medial, and lateral rectus — all arise from the common tendinous ring (annulus of Zinn) at the apex of the orbit.

• The superior oblique originates from the body of the sphenoid bone, above and medial to the optic canal.

• The inferior oblique is unique — it originates anteriorly from the orbital surface of the maxilla in the anteromedial floor of the orbit.

Nerve Supply

• Oculomotor nerve (cranial nerve III): supplies all extraocular muscles except two.

• Trochlear nerve (cranial nerve IV): supplies the superior oblique.

• Abducens nerve (cranial nerve VI): supplies the lateral rectus.

Mnemonic: “LR6 SO4, all the rest by 3.”

Functional Note

• The recti muscles primarily move the eye up, down, or medially/laterally.

• The oblique muscles fine-tune these movements by rotating (torsioning) the eyeball and assisting with elevation or depression when the eye is adducted.

• Acting together, the extraocular muscles ensure precise, coordinated eye movements for stable and aligned vision.