M01.02.033 The Extraocular Muscles

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Learning Objective: To understand the anatomy, attachments, actions, and innervation of the extraocular muscles, and recognise the clinical consequences of nerve lesions affecting eye movement and eyelid elevation.

The extraocular muscles are located within the orbit but are extrinsic to the eyeball itself. Their primary roles include controlling eye movement and elevating the upper eyelid.

There are seven extraocular muscles:

  • Levator palpebrae superioris (LPS)
  • Four recti muscles: superior rectus, inferior rectus, medial rectus, lateral rectus
  • Two oblique muscles: the superior oblique and, inferior oblique

Functionally, they are divided into:

  1. Muscles responsible for eye movement – recti + oblique muscles
  2. Muscle responsible for superior eyelid elevation – LPS

ACTIVITY

Levator Palpebrae Superioris (LPS)

The primary muscle that raises the upper eyelid.

  • Attachments: Originates from the lesser wing of the sphenoid above the optic foramen → inserts into the superior tarsal plate.
  • Actions: Elevates the upper eyelid.
  • Innervation:
    • LPS: Oculomotor nerve (CN III)
    • Superior tarsal muscle: Sympathetic fibres

Recti Muscles

All four recti originate from the common tendinous ring and run straight to insert on the anterior sclera.

Superior Rectus

  • Action: Elevation + adduction + medial rotation
  • Innervation: CN III

Inferior Rectus

  • Action: Depression + adduction + lateral rotation
  • Innervation: CN III

Medial Rectus

  • Action: Pure adduction
  • Innervation: CN III

Lateral Rectus

  • Action: Pure abduction
  • Innervation: CN VI

Oblique Muscles

Superior Oblique

  • Origin: Body of sphenoid → tendon passes through trochlea → inserts posterior to superior rectus
  • Action: Depression + abduction + medial rotation
  • Innervation: CN IV

Inferior Oblique

  • Origin: Anterior orbital floor → posterior sclera
  • Action: Elevation + abduction + lateral rotation
  • Innervation: CN III

ACTIVITY

Clinical Relevance

Cranial Nerve Palsies

  • CN III palsy: Eye rests “down and out”, ptosis, dilated pupil
  • CN IV palsy: Affects the superior oblique → vertical diplopia, compensatory head tilt
  • CN VI palsy: Loss of lateral rectus → medial deviation of the eye

(Helpful mnemonic: LR6 – SO4 – R3)

Horner’s Syndrome

Results from the disruption of the sympathetic supply.

Triad:

  • Ptosis (superior tarsal muscle)
  • Miosis
  • Anhidrosis

ACTIVITY

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