mymedschool.orgM01.02.021 Extra-ocular

Learning Objective: At the end of this session, the learner should be able to identify and describe the attachments, innervation, and actions of the extraocular muscles and recognize the clinical features of cranial nerve palsies and Horner’s syndrome.

Overview

The extraocular muscles are seven muscles located within the orbit, external to the eyeball. They are responsible for the movement of the eyeball and upper eyelid, ensuring precise visual focus and gaze coordination.

Functional Groups

Eye Movement (6 muscles):
- Recti group: Superior, Inferior, Medial, and Lateral Rectus
- Oblique group: Superior and Inferior Oblique
Eyelid Movement (1 muscle):
1. Levator palpebrae superioris

Levator Palpebrae Superioris (LPS)

Function: Elevates the upper eyelid. A small smooth muscle portion, the superior tarsal muscle, assists in maintaining eyelid elevation and is under sympathetic control.

Feature	Description
Origin	Lesser wing of the sphenoid (above the optic foramen)
Insertion	Superior tarsal plate of the upper eyelid
Innervation	CN III (oculomotor nerve) for LPS; sympathetic fibers for the superior tarsal muscle
Action	Elevates the upper eyelid

Muscles of Eye Movement

Recti Muscles

All four recti muscles originate from the common tendinous ring, surrounding the optic canal, and attach directly to the sclera in a straight path (Latin rectus = straight).

Muscle	Origin	Insertion	Action	Innervation
Superior Rectus	Common tendinous ring (superior part)	Superior anterior sclera	Elevation, adduction, medial rotation	CN III
Inferior Rectus	Common tendinous ring (inferior part)	Inferior anterior sclera	Depression, adduction, lateral rotation	CN III
Medial Rectus	Common tendinous ring (medial part)	Medial sclera	Adduction	CN III
Lateral Rectus	Common tendinous ring (lateral part)	Lateral sclera	Abduction	CN VI (Abducens)

Mnemonic:
👉 “LR6, SO4, All the Rest by 3” (Lateral Rectus – CN VI, Superior Oblique – CN IV, the rest – CN III)

Oblique Muscles

Unlike the recti, the oblique muscles take an angled course and attach posteriorly on the sclera.

Muscle	Origin	Path & Insertion	Action	Innervation
Superior Oblique	Body of the sphenoid	Tendon passes through trochlea → inserts posterior to the superior rectus	Depresses, abducts, and medially rotates the eyeball	CN IV (Trochlear)
Inferior Oblique	Anterior floor of the orbit	Passes posteriorly to insert near the lateral rectus	Elevates, abducts, and laterally rotates the eyeball	CN III

Clinical Relevance

Cranial Nerve Palsies

Nerve	Muscle(s) Affected	Clinical Findings
CN III (Oculomotor)	All except LR & SO	Eye deviated down and out, ptosis, dilated pupil
CN IV (Trochlear)	Superior Oblique	Diplopia (worse when looking down), compensatory head tilt opposite the lesion
CN VI (Abducens)	Lateral Rectus	Inability to abduct, eye deviated medially

🩺 Mnemonic Reminder: LR6 – SO4 – R3

Horner’s Syndrome

Caused by damage to the sympathetic trunk in the neck. Triad of symptoms:

Ptosis: Due to paralysis of the superior tarsal muscle
Miosis: Pupil constriction from denervation of the dilator pupillae
Anhidrosis: Loss of sweating on the affected side

Common causes: Pancoast tumor (lung apex), carotid dissection, or thyroid carcinoma.

Summary Table

Muscle	Primary Action	Nerve Supply
Levator palpebrae superioris	Elevates the upper eyelid	CN III
Superior rectus	Elevates & adducts the eye	CN III
Inferior rectus	Depresses & adducts the eye	CN III
Medial rectus	Adducts eye	CN III
Lateral rectus	Abducts eye	CN VI
Superior oblique	Depresses & abducts	CN IV
Inferior oblique	Elevates & abducts	CN III