Dominic Stone
The human eye is a fascinating organ that allows us to see the world around us. Our vision depends on the proper functioning of ocular motor systems, which control the position and movement of the eyes. These systems include the extraocular muscles, which are responsible for executing precise and fast eye movements. While most of these muscles develop throughout our lives, it is important to understand which ocular muscle develops last and how this impacts our visual perception. This knowledge can help us protect our eye health and address any potential issues that may arise, such as double vision or eye misalignment.
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What You'll Learn
- The extraocular muscles develop along with Tenon's capsule and the fatty tissue of the eye socket
- There are seven extraocular muscles, six of which control eye movement
- The seventh extraocular muscle, the levator palpebrae superioris, controls eyelid elevation
- The four recti muscles are named according to their relative positions of attachment
- The two oblique muscles are the inferior oblique muscle and the superior oblique muscle
The extraocular muscles develop along with Tenon's capsule and the fatty tissue of the eye socket
The extraocular muscles are the seven extrinsic muscles of the eye in humans and other animals. Six of these muscles control the movement of the eye, while the levator palpebrae superioris controls eyelid elevation. The four recti muscles, the superior rectus, inferior rectus, medial rectus, and lateral rectus, originate from the common tendinous ring, a fibrous ring at the back of the orbit. From their origin, they pass anteriorly to attach to the sclera of the eyeball. The two oblique muscles are the inferior oblique muscle and the superior oblique muscle.
The extraocular muscles develop alongside Tenon's capsule and the fatty tissue of the eye socket. Tenon's capsule is a dense, elastic, and vascular connective tissue layer that surrounds the globe, except over the cornea. It acts as a barrier to orbital fat, separating it from the globe. Anterior Tenon's capsule extends from the penetration sites of the rectus muscles to the limbus, while posterior Tenon's capsule extends to the optic nerve. The extraocular muscles must penetrate Tenon's capsule to enter the episcleral space, where the majority of extraocular muscle surgery is performed.
The recti muscles, or straight muscles, have a direct path from origin to attachment, while the oblique muscles take an angular approach to the eyeball. The recti muscles are all of almost equal length, around 40 mm, but their tendons differ in length. The superior oblique muscle is controlled by the trochlear nerve (CN IV), and a lesion of this nerve will paralyse the muscle, resulting in double vision (diplopia) and a head tilt away from the lesion site. The lateral rectus muscle is controlled by the abducens nerve (CN VI), and a lesion will result in paralysis of the muscle and the affected eye being adducted by the resting tone of the medial rectus.
The extraocular muscles are supplied mainly by branches of the ophthalmic artery, either directly or indirectly. Each rectus muscle receives blood from two anterior ciliary arteries, except for the lateral rectus muscle, which receives blood from only one. The exact number and arrangement of these ciliary arteries may vary. The movements of the extraocular muscles are influenced by a system of extraocular muscle pulleys, soft tissue pulleys in the orbit, which are fundamental to eye movement.
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There are seven extraocular muscles, six of which control eye movement
The human eye is a fascinating organ, with its movements controlled by a group of highly specialised muscles known as extraocular muscles. These muscles are located within the orbit but are extrinsic to the eyeball, allowing them to direct the movements of the eyeball and the superior eyelid. There are seven extraocular muscles, six of which are directly responsible for eye movement, while the seventh controls eyelid elevation.
The six muscles that govern eye movement are further categorised into two groups: the recti muscles and the oblique muscles. The four recti muscles include the superior rectus, inferior rectus, medial rectus, and lateral rectus. As their name suggests, derived from the Latin word for "straight," these muscles follow a direct path from their origin to attachment. They originate from the common tendinous ring, a fibrous ring surrounding the optic canal at the back of the orbit, and attach to the sclera of the eyeball.
On the other hand, the two oblique muscles are the superior oblique and inferior oblique. Unlike the recti muscles, the oblique muscles take an angular approach to the eyeball. They originate from the body of the sphenoid bone and attach to the posterior surface of the sclera. This unique structure enables them to perform specific functions, such as depressing, abducting, and medially rotating the eyeball.
The seventh extraocular muscle, the levator palpebrae superioris (LPS), is responsible for raising the upper eyelid. This muscle can be voluntarily or involuntarily activated, allowing for the elevation of the eyelid. The LPS is innervated by the oculomotor nerve (CN III), while the superior tarsal muscle within it is influenced by the sympathetic nervous system.
The intricate coordination of these seven extraocular muscles enables the eye to move in various directions, ensuring precise and rapid movements. This complex system is vital for tasks such as reading, where constant shifts in gaze are necessary. By understanding the anatomy and functions of these muscles, we can better comprehend the remarkable ability of the human eye to capture and follow visual targets.
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The seventh extraocular muscle, the levator palpebrae superioris, controls eyelid elevation
The levator palpebrae superioris is the seventh extraocular muscle. It is responsible for raising the upper eyelid, and this can be a voluntary or involuntary action. The levator palpebrae superioris is also known as LPS and is the only muscle involved in raising the superior eyelid.
The levator palpebrae superioris is a skeletal muscle. It originates from the inferior surface of the lesser wing of the sphenoid bone, just above the optic foramen. It extends along the roof of the orbit, from the apex of the orbit to the superior eyelid. The muscle fibres penetrate the upper eyelid, inserting into its parts via two aponeurotic fascicles. The deep fibres attach to the anterior surface of the superior tarsus. The most lateral fibres of the muscle's aponeurosis attach to the orbital tubercle of the zygomatic bone, while the most medial fibres attach to the medial palpebral ligament.
The levator palpebrae superioris receives its blood supply from branches of the ophthalmic artery, specifically the muscular branches and the supraorbital artery. Blood is drained into the superior ophthalmic vein. The levator palpebrae superioris is innervated by the oculomotor nerve (CN III). The superior tarsal muscle, located within the LPS, is innervated by the sympathetic nervous system.
Damage to the levator palpebrae superioris or its innervation can cause ptosis, or drooping of the eyelid. Lesions in CN III can cause ptosis because without stimulation from the oculomotor nerve, the levator palpebrae cannot oppose the force of gravity, and the eyelid droops. Ptosis can also result from damage to the adjoining superior tarsal muscle or its sympathetic innervation. This damage to the sympathetic supply occurs in Horner's syndrome and presents as partial ptosis.
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The four recti muscles are named according to their relative positions of attachment
The human eye has seven extrinsic muscles, known as extraocular muscles. Six of these muscles are responsible for eye movement, while the seventh, the levator palpebrae superioris, controls eyelid elevation. The four recti muscles are part of the six muscles that control eye movement.
The four recti muscles originate from the common tendinous ring, a fibrous ring at the back of the orbit. From their origin, the muscles pass anteriorly to attach to the sclera of the eyeball. The recti muscles are all of almost equal length, measuring around 40 mm, but the lengths of their associated tendons differ.
The superior rectus muscle and the inferior rectus muscle do not pull straight back on the eye. Instead, they pull slightly medially, causing the eye to roll with contraction. The medial rectus muscle is responsible for adduction, while the lateral rectus muscle is responsible for abduction.
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The two oblique muscles are the inferior oblique muscle and the superior oblique muscle
The extraocular muscles are the seven extrinsic muscles of the eye in humans and other animals. Six of these muscles control the movement of the eye, while the seventh, the levator palpebrae superioris, controls eyelid elevation. The six muscles responsible for eye movement are the four recti muscles and the two oblique muscles. The two oblique muscles are the inferior oblique muscle and the superior oblique muscle.
The inferior oblique muscle is an extraocular muscle that primarily rotates the eyeball externally. It is almost entirely muscular, unlike the superior oblique, which is both muscular and tendinous. The inferior oblique is shorter than the other extraocular muscles, and its tendon is also shorter than those of its counterparts. The muscle has two surfaces: the superior ocular and the inferior orbital surfaces. It is defined by its anterior and posterior borders at the orbital groove. The inferior oblique tendon inserts in the sclera under the lateral rectus. The anterior border is about 10 mm from the lateral rectus insertion point, while the posterior border is 1 to 2 mm in front of the macula.
The inferior oblique muscle works in synergy with the superior rectus muscle to elevate the pupil. However, their rotatory actions oppose and neutralize each other. This complementary action ensures that no rotation of the eyeball occurs during its elevation. In addition, the inferior oblique muscle also acts with the check ligaments and the retrobulbar fat to prevent retraction of the eyeball by the rectus muscles. These structures provide support for the eyeball and help retain its position.
The superior oblique muscle is controlled by the trochlear nerve (CN IV). A lesion of CN IV will paralyse the superior oblique muscle, resulting in double vision (diplopia) and possibly a head tilt away from the site of the lesion.
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