• Summary
• Introduction
• The recti
• The obliques
• The superior oblique muscle
• The inferior oblique muscle
• The nerve supply
• Ipsilateral and contralateral supply
• Trochlear nerve: contralateral supply
• Oculomotor nerve: contralateral supply
• The other functions of the oculomotor nerve
• Movements of the extraocular muscles
• Conjugate gaze
• Eye movement terminology and laws
• Yoked muscles
• Hering’s law
• Sherrington’s law
• Paired agonist muscles
• The eyelid muscles
• Levator palpebrae superioris
• Müller’s muscle (superior tarsal muscle)
• Orbicularis Oculi
• References
• Author(s)

Summary

The extraocular muscles function to move the eyes together. There are four recti muscles, two oblique muscles which make the movements of the eye possible. In this article, we will not only cover the muscles that move the eye, but also the accessory muscles of the eye involved in eyelid action.

Introduction

There are six muscles in each eye which function to move the eye around in the orbit in various directions. These are:

• Lateral rectus
• Medial rectus
• Superior rectus
• Inferior rectus
• Superior oblique
• Inferior oblique

The recti

The four recti are arranged at the top, bottom and sides of each eye as shown in the diagram below:

The four recti all converge at the back of the orbit on a common tendinous ring (also called the annulus of Zinn), as shown here:

The oblique muscles have a different origin, which will be discussed below.

The obliques

The superior oblique muscle

The superior oblique muscle originates on the lesser wing of the sphenoid bone, passes through a pulley called the trochlea and then changes its angle to attach onto the superolateral aspect of the eyeball, as shown in the diagram below.

The trochlea is a U-shaped piece of cartilage which attaches onto the orbital plate of the frontal bone.

The inferior oblique muscle

The inferior oblique muscle originates on the orbital surface of the maxilla and inserts into the inferolateral aspect of the eyeball, deep to the lateral rectus muscle.

The nerve supply

Three motor cranial neurons innervate the extraocular muscles. These are:

• The abducens nerve (CN 6)
• The trochlear nerve (CN 4)
• The oculomotor nerve (CN 3)

The abducens nerve (CN 6) originates in the abducens nucleus in the midbrain. It exits the brainstem at the pons-medullary junction and supplies the lateral rectus muscle (see diagram).

This can be remembered as ‘LR6’ (lateral rectus supplied by the 6th cranial nerve).

The trochlear nerve (CN 4) originates in the trochlear nucleus. It exits the posterior part of the midbrain (caudal midbrain) and supplies the superior oblique muscle.

This can be remembered as ‘SO4’ (superior oblique, supplied by the 4th cranial nerve).

The oculomotor nerve (CN 3) exits the front of the midbrain and supplies the remaining oculomotor muscles: the superior rectus, inferior rectus, medial rectus and inferior oblique.

The locations at which the cranial nerve exit the brainstem is shown below:

Thus, the innervation to the extraocular muscles can be summarised in the diagram below (note the exit from the brainstem isn’t anatomically accurate in the diagram):

Ipsilateral and contralateral supply

Some extraocular muscles are supplied by the contralateral nucleus. These are the trochlear nerve and some parts of the oculomotor nerve.

Trochlear nerve: contralateral supply

Note that the trochlear nerve (CN 4) supplies the contralateral superior oblique muscle due to its course in which it crosses the midline to the contralateral side.

Oculomotor nerve: contralateral supply

Each superior rectus muscle is innervated by contralateral oculomotor neurons. This is because of the arrangement of the oculomotor nerve nuclei.

The levator palpebrae superioris muscle receives bilateral innervation from a single dorsal caudal nucleus located in the midline.

The other muscles supplied by the oculomotor nerve (medial rectus, inferior rectus and inferior oblique) are supplied by the ipsilateral oculomotor neurons.

The abducens nerve (CN 6) supplies the ipsilateral lateral rectus muscle. Thus, to summarise:

The other contralateral innervation of the extraocular muscle is the superior rectus muscle, supplied by the superior division of the oculomotor nerve.

The other functions of the oculomotor nerve

In addition to supplying the above mentioned extraocular muscles, the oculomotor nerve also supplies the levator palpebrae superioris and carries parasympathetic fibres from the Edinger-Westphal nucleus which are responsible for pupillary constriction, as shown in the diagram below.

Clinical correlates: damage to the oculomotor nerve therefore results in three deficits: impairment of eye movement, ptosis and mydriasis (pupillary dilation).

Movements of the extraocular muscles

The extraocular muscles allow the eyes to move in certain directions. Let’s examine each extraocular muscle individually, before learning about conjugate gaze, which is the ability of the eyes to work together.

The actions produced by the extraocular muscles are described in the table below:

The actions produced by the extraocular muscles are summarised in the diagram below:

The rotary action of the eyeball is called torsion. Movements either bring the top of the eye towards the nose (intorsion) or away from the nose (extorsion).

Conjugate gaze

Conjugate gaze describes both eyes moving together in a single direction.

When testing the function of the extraocular muscles, these directions of gaze are assessed:

• Looking left
• Looking right and up
• Looking left and up
• Looking right and down
• Looking left and down
• Looking straight down
• Looking straight up
• Crossing the eyes

The terminology used for these movements are introduced below:

• Looking left → levoversion
• Looking right and up → dextroelevation
• Looking left and up → levoelevation
• Looking right and down → dextrodepression
• Looking left and down → levodepression
• Looking straight down → infraversion
• Looking straight up → supraversion
• Crossing the eyes → convergence

These eye movements are summarised in the diagram below:

Producing these directions of gaze require the action of multiple extraocular muscles. The extraocular muscles required to make these movements are described in the table below:

Convergence is when the left and right medial recti muscles contract simultaneously. When this happens, the eyes move horizontally towards the nose. Convergence occurs in order to focus on close-up objects.

These conjugate eye movements are summarised in the diagram below:

Eye movement terminology and laws

Yoked muscles

These are muscles that work together to move the eyes in the same direction at the same time. We have already learned these when examining the eye movements above.

Hering’s law

This is the principle that yoked muscles get the same amount of innervation and at the same time.

For example, the left lateral rectus and right medial rectus the same amount of innervation at the same time when looking to the left.

Hering’s law explains why eye movements are yoked.

Sherrington’s law

This is the principle that any increase in innervation to an agonist muscle must result in a decrease in innervation to the antagonist muscle.

For example, when looking to the left, you want your left lateral rectus to fire. Its antagonist muscle on the left eye is the left medial rectus, which must have a decrease in innervation to allow the eye to look to the left.

Paired agonist muscles

These are muscles in both eyes that move the eye a certain direction. For example, when looking to the left, you use the right medial rectus and the left lateral rectus.

The paired agonist muscles are summarised in the table below:

The eyelid muscles

There are three important muscles involved in opening and closing the eyelid. They are:

• Levator palpebrae superioris
• Müller’s muscle (superior tarsal muscle)
• Orbicularis oculi

We will discuss each of the above muscles.

Levator palpebrae superioris

The levator palpebrae superioris muscle originates from the lesser wing of the sphenoid bone, just above the optic foramen. It inserts onto the superior tarsus as well as the skin of the upper eyelid. At the insertion point, the muscle broadens and becomes the levator aponeurosis.

Müller’s muscle (superior tarsal muscle)

The Müller’s muscle originates from the deep aspect of levator palpebrae superioris. It inserts onto the upper margin of the superior tarsus of the eyelid.

To be more specific, the nerve supply to Müller’s muscle arises from the post-ganglionic sympathetic fibres from the superior cervical ganglion and from the internal carotid plexus around the internal carotid artery.

When the sympathetic nerve supply to the face and eye is damaged, it can lead to Horner’s syndrome. This is characterised by partial ptosis, miosis and loss of hemifacial sweating (anhidrosis). Sometimes, there may also be posterior displacement of the eyeball within the orbit (enophthalmos).

Orbicularis Oculi

The orbicularis oculi muscle originates from three bones of the orbit. These are the frontal bone, maxilla and lacrimal bone. It also arises from the soft tissue structures around the orbit. It inserts to the skin of the orbital region, the lateral palpebral raphe and the superior and inferior tarsal plates.

References

1. Superior Oblique Muscle - an Overview | ScienceDirect Topics. https://www.sciencedirect.com/topics/neuroscience/superior-oblique-muscle. Accessed 27 June 2022.
2. Anderson, B. C., and L. K. McLoon. ‘Cranial Nerves and Autonomic Innervation in the Orbit’. Encyclopedia of the Eye, edited by Darlene A. Dartt, Academic Press, 2010, pp. 537–48. ScienceDirect, https://doi.org/10.1016/B978-0-12-374203-2.00285-2.
3. Purves, Dale, et al. ‘The Actions and Innervation of Extraocular Muscles’. Neuroscience. 2nd Edition, 2001. www.ncbi.nlm.nih.gov, https://www.ncbi.nlm.nih.gov/books/NBK10793/.

Author(s)

Dr Abhiyan Bhandari

Abhiyan is the Co-Founder and Radiology & Imaging Lead of Ophtnotes. He is a doctor who graduated from UCL Medical School in London. He scored in the top 10% of candidates who sat the Duke Elder examination and runs ophthalmology and Duke Elder revision sessions aimed at medical students. He also runs a YouTube channel aimed at medical students, covering topics ranging from study tips, productivity and vlogs of his journey through medical school.

Published: 20/12/21

Last updated: 23/1/25