Eyeball muscles with image

Reading File

Finding Sources

Searching Images

extraocular eye muscles anatomy diagram

This composite educational graphic features a contrast-enhanced computerized tomography (CT) scan and a corresponding anatomical schematic of the left orbit in the coronal plane. The CT image displays the soft tissue window, highlighting the retrobulbar space and extraocular muscles (EOM) within the orbital fat. The accompanying diagram provides labeled identification of the orbital contents, including the superior rectus, inferior rectus, medial rectus, and lateral rectus muscles. Additionally, the schematic delineates the superior oblique, levator palpebrae superioris, ophthalmic artery, and the central optic nerve. The visual focus is on the cross-sectional morphology of the EOMs, particularly demonstrating a larger cross-sectional area of the inferior rectus compared to the superior rectus. This comparison is relevant for assessing Thyroid Eye Disease (TED) or other orbital pathologies involving muscle hypertrophy. The material is designed for intermediate to advanced medical education, specifically within ophthalmology and radiology, to teach orbital anatomy and the diagnostic interpretation of CT scans for muscle-sparing or involvement patterns.

Reading File

Searching Images

rectus oblique eye muscle actions movement

Loading Image

Reading File

Loading Image

Reading File

I now have everything needed for a comprehensive, well-illustrated answer. Let me compile it.

Extraocular Muscles of the Eyeball

There are 6 extraocular muscles (EOMs) that control eye movement - 4 rectus muscles and 2 oblique muscles.

Anatomy Overview

Fig. 18.4A - Superior view of the orbit (Kanski's Clinical Ophthalmology):

Superior view of extraocular muscles - trochlea, superior oblique, medial rectus, superior rectus, lateral rectus

Fig. 18.4B - Lateral view of the orbit:

Lateral view - all 6 extraocular muscles labeled including inferior oblique, inferior rectus, levator palpebrae

CT coronal section + diagram of the orbit:

CT coronal + labeled orbital diagram showing all 4 rectus muscles, superior oblique, optic nerve, levator palpebrae

The 6 Extraocular Muscles

All 4 rectus muscles originate from the annulus of Zinn (common tendinous ring) at the orbital apex.

1. Medial Rectus (MR)

Origin: Annulus of Zinn
Insertion: 5.5 mm behind the nasal limbus (closest to the limbus)
Primary action: Adduction (moves eye nasally/inward)
Nerve: CN III (Oculomotor)

2. Lateral Rectus (LR)

Origin: Annulus of Zinn
Insertion: 6.9 mm behind the temporal limbus
Primary action: Abduction (moves eye temporally/outward)
Nerve: CN VI (Abducens)

3. Superior Rectus (SR)

Origin: Upper part of the annulus of Zinn
Insertion: 7.7 mm behind the superior limbus (farthest from limbus among recti)
Primary action: Elevation
Secondary actions: Adduction + Intorsion
Nerve: CN III (Oculomotor)
Testing tip: The SR acts as a pure elevator when the eye is abducted 23° (visual and orbital axes align)

4. Inferior Rectus (IR)

Origin: Lower part of the annulus of Zinn
Insertion: 6.5 mm behind the inferior limbus
Primary action: Depression
Secondary actions: Adduction + Extorsion
Nerve: CN III (Oculomotor)
Testing tip: Acts as a pure depressor when the eye is abducted 23°

5. Superior Oblique (SO)

Origin: Superomedial to the optic foramen (sphenoid bone)
Course: Passes anteriorly through the trochlea (a fibrocartilaginous pulley at the superomedial orbital rim), then reflected backwards and laterally
Insertion: Posterior upper temporal quadrant of the globe (behind the equator)
Angle with visual axis: 51°
Primary action: Intorsion
Secondary actions: Depression + Abduction
Nerve: CN IV (Trochlear)
Testing tip: Acts as a pure depressor when the eye is adducted 51°; weakness manifests as failure of depression in adduction

6. Inferior Oblique (IO)

Origin: Small depression just behind the orbital rim, lateral to the lacrimal sac (anterior medial orbital wall - unique: no trochlea)
Insertion: Posterior lower temporal quadrant of the globe (near the macula)
Angle with visual axis: 51°
Primary action: Extorsion
Secondary actions: Elevation + Abduction
Nerve: CN III (Oculomotor)
Testing tip: Acts as a pure elevator when the eye is adducted 51°

Spiral of Tillaux

The insertions of the 4 recti form the Spiral of Tillaux - an imaginary line joining their scleral insertions, progressively further from the limbus:

Muscle	Insertion from limbus
Medial rectus	5.5 mm
Inferior rectus	6.5 mm
Lateral rectus	6.9 mm
Superior rectus	7.7 mm

This is an important surgical landmark.

Nerve Supply Summary

Muscle	Cranial Nerve
Lateral rectus	CN VI (Abducens)
Superior oblique	CN IV (Trochlear)
All others (MR, SR, IR, IO) + Levator palpebrae + ciliary + sphincter pupillae	CN III (Oculomotor)

Memory aid: "LR6 SO4 rest 3" - Lateral Rectus = CN 6, Superior Oblique = CN 4, the remaining 4 muscles = CN 3.

Actions (Summary Table)

Muscle	Primary	Secondary
Medial rectus	Adduction	-
Lateral rectus	Abduction	-
Superior rectus	Elevation	Adduction, Intorsion
Inferior rectus	Depression	Adduction, Extorsion
Superior oblique	Intorsion	Depression, Abduction
Inferior oblique	Extorsion	Elevation, Abduction

Superior Rectus Actions (Intorsion + Elevation Diagram)

Superior rectus muscles of both eyes showing intorsion and elevation

Muscle Pulleys

The 4 rectus muscles pass through connective tissue and smooth muscle condensations just posterior to the equator. These pulleys act as the functional origins of the rectus muscles, minimizing off-axis movements and coordinating eye movements. Pulley displacement can cause V- and A-pattern strabismus.

Sources: Kanski's Clinical Ophthalmology 10th Ed., p. 723-726; Neuroanatomy through Clinical Cases 3rd Ed., p. 594

This is a shared conversation. Sign in to Orris to start your own chat.