Dominic Stone
The human eye is a fascinating organ, and its muscles play a crucial role in vision and eye movement. These muscles, known as extraocular muscles, are responsible for the precise and rapid movements that allow us to see. There are six extraocular muscles that control eye movement, and they work in pairs to ensure our eyes turn in unison. These muscles include four recti muscles (superior, inferior, medial, and lateral rectus) and two oblique muscles (superior and inferior oblique). The recti muscles are straight muscles, while the oblique muscles have an angular approach to the eyeball. The levator palpebrae superioris is another important muscle that controls eyelid elevation. Understanding the intricacies of these external eye muscles is not just fascinating but also plays a vital role in diagnosing and treating various eye conditions and disorders.
| Characteristics | Values |
|---|---|
| Number of external eye muscles | 6 |
| Function | Control eye movement |
| Muscle pairs | Superior and inferior rectus, medial and lateral rectus, superior and inferior oblique |
| Innervation | Oculomotor nerve (CN III), Trochlear nerve (CN IV), Abducens nerve (CN VI) |
| Muscle disorders | Myotonic dystrophy, Oculopharyngeal muscular dystrophy (OPMD), Kearns-Sayre syndrome, Thyroid eye disease or Graves’ disease, Strabismus (eye misalignment), Amblyopia (lazy eye), Certain types of cancers |
| Blood supply | Branches of the ophthalmic artery, including the ciliary arteries and the lacrimal artery |
| Development | Develop along with Tenon's capsule, the fatty tissue of the eye socket (orbit), and three centers of growth associated with nerves |
| Movement | Four muscles control movement in the cardinal directions (up, right, down, left), two muscles counter-move to adjust for head movements |
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What You'll Learn
There are six external eye muscles
The six extraocular muscles are divided into two groups: the four recti (straight) muscles and the two oblique muscles. The four recti muscles are the superior rectus, inferior rectus, medial rectus, and lateral rectus. They originate from the common tendinous ring, a ring of fibrous tissue that surrounds the optic canal at the back of the orbit. From their origin, the muscles pass anteriorly to attach to the sclera of the eyeball. The name recti comes from the Latin word for 'straight', as these muscles have a direct path from origin to attachment.
The two oblique muscles are the superior oblique and inferior oblique. The superior oblique muscle originates at the back of the orbit, closer to the medial rectus, and gets rounder as it courses forward to a rigid, cartilaginous pulley called the trochlea on the upper nasal wall of the orbit. The muscle then turns sharply across the orbit and inserts on the lateral, posterior part of the globe. The inferior oblique muscle, on the other hand, originates at the lower front of the nasal orbital wall, passes inferiorly over the inferior rectus muscle, and inserts under the lateral rectus muscle on the lateral, posterior part of the globe.
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 levator palpebrae superioris is another muscle responsible for raising the upper eyelid, and this can be a voluntary or involuntary action.
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They control eye movement
The human eye has six external muscles, also known as extraocular muscles, which control eye movement. They work in pairs, with one muscle moving and its partner in the same eye helping to control and balance that movement. This is why human eyes can only turn so far. The six muscles are the four recti (straight) muscles and the two oblique muscles.
The four recti muscles are the superior rectus, inferior rectus, medial rectus and lateral rectus. They originate from the common tendinous ring, a ring of fibrous tissue which surrounds the optic canal at the back of the orbit. From their origin, the muscles pass anteriorly to attach to the sclera of the eyeball. The name recti comes from the Latin for 'straight', which represents the fact that the recti muscles have a direct path from origin to attachment.
The two oblique muscles are the superior oblique and inferior oblique. The superior oblique muscle originates at the back of the orbit, getting rounder as it courses forward to a rigid, cartilaginous pulley called the trochlea, on the upper nasal wall of the orbit. The muscle becomes tendinous about 10mm before it passes through the pulley, turning sharply across the orbit, and inserts on the lateral, posterior part of the globe. Thus, the superior oblique travels posteriorly for the last part of its path, going over the top of the eye. The inferior oblique, meanwhile, originates at the lower front of the nasal orbital wall, passes inferiorly over the inferior rectus muscle on its path laterally and posteriorly, and inserts under the lateral rectus muscle on the lateral, posterior part of the globe.
The extraocular muscles are supplied mainly by branches of the ophthalmic artery. 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 take place under the influence of a system of extraocular muscle pulleys, soft tissue pulleys in the orbit. Four of the extraocular muscles have their origin in the back of the orbit in the fibrous ring called the common tendinous ring. The four recti muscles attach directly to the front half of the eye (anterior to the eye's equator). The levator palpebrae superioris is responsible for raising the upper eyelid, and this can be a voluntary or involuntary action.
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They work in pairs
The human eye has six external muscles, also known as extraocular muscles, which work in pairs to control eye movement. When one muscle moves, its partner in the same eye helps to control and balance that movement. This is why human eyes can only turn so far. There is also another type of paired movement that happens involving both eyes, which experts call "yoking" because the eyes turn together like a pair of horses or oxen yoked together.
The six extraocular muscles are the four recti (straight) muscles and the two oblique muscles. The four recti muscles are the superior rectus, inferior rectus, medial rectus, and lateral rectus. The two oblique muscles are the superior oblique and inferior oblique. These muscles are responsible for moving the eyes into different gazes. The recti muscles have a direct path from origin to attachment, while the oblique muscles have an angular approach to the eyeball.
The medial rectus is the muscle closest to the nose. The superior and inferior recti do not pull straight back on the eye, as both muscles also pull slightly medially. This posterior medial angle causes the eye to roll with contraction of either the superior rectus muscle or the inferior rectus muscle. The superior oblique, when activated, pulls the eye downward and laterally. The inferior oblique, which originates at the lower front of the nasal orbital wall, pulls the eye upward and laterally.
The extraocular muscles are supplied mainly by branches of the ophthalmic artery. Each rectus muscle receives blood from two anterior ciliary arteries, except for the lateral rectus muscle, which receives blood from only one. The nuclei or bodies of these nerves are found in the brain stem. The nuclei of the abducens and oculomotor nerves are connected, which is important in coordinating the motion of the lateral rectus in one eye and the medial action on the other.
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They are supplied by the ophthalmic artery
The external eye muscles, or extraocular muscles, are responsible for the movement of the eyes and are supplied with blood by the ophthalmic artery, a crucial vessel that arises from the internal carotid artery. This artery plays a vital role in maintaining the health and function of these muscles, ensuring they receive the necessary oxygen and nutrients.
The ophthalmic artery is a key branch of the internal carotid artery, supplying blood specifically to the structures within the orbit, or eye socket, including the external eye muscles. These muscles, innervated by cranial nerve III (oculomotor nerve), cranial nerve IV (trochlear nerve), and cranial nerve VI (abducens nerve), are responsible for the various movements of the eyes, such as up and down, side to side, and rotational motions.
As the ophthalmic artery travels through the orbit, it gives off several branches, including the muscular branches, which directly supply the extraocular muscles. These muscular branches provide oxygenated blood to the muscles, ensuring their proper function and maintaining the health of the muscle fibers. The blood supply to these muscles is critical for sustaining their constant state of readiness and ability to contract rapidly and precisely.
The superior and inferior muscular branches that arise from the ophthalmic artery supply the respective upper and lower groups of extraocular muscles. Additionally, the ophthalmic artery also provides blood to other important structures in the orbit, such as the eyelids, conjunctiva, lacrimal gland, and the globe of the eye itself, along with its surrounding tissues. This comprehensive blood supply ensures the proper functioning and health of the eye and its associated structures.
Any disruption to the blood supply provided by the ophthalmic artery, whether due to injury, inflammation, or other pathological conditions, can have significant implications for eye health and vision. Thus, the ophthalmic artery serves as a vital lifeline for the external eye muscles, providing nourishment and oxygen to enable the complex and precise movements of the eyes.
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They can be affected by cranial nerve palsies
The extraocular muscles, also known as the external eye muscles, are a group of six muscles that work together to control the movement of the eyes. These muscles are essential for various functions, including eye movement, focus, and maintaining clear vision. As they are under the control of three cranial nerve pairs (III, IV, and VI), cranial nerve palsies can affect the extraocular muscles and their functions.
Cranial nerve palsies refer to a group of disorders characterized by weakness or paralysis of one or more cranial nerves. In the case of the external eye muscles, cranial nerve palsy can cause double vision (diplopia), eye movement restrictions, and even changes in the shape of the cornea, leading to astigmatism. The specific nerve affected will determine the exact symptoms and their severity. For example, damage to the oculomotor nerve (CN III) can result in a droopy eyelid (ptosis) and the pupil becoming smaller (miosis), as well as double vision and an inability to move the eye outward (abduction).
Another example is when the trochlear nerve (CN IV) is damaged, which can lead to a type of diplopia where the patient sees two images vertically displaced, with one image above the other. This is because this nerve specifically controls the superior oblique muscle, which is responsible for depressing, intorting, and abducting the eye. Similarly, damage to the abducens nerve (CN VI) can cause diplopia and eye movement issues, particularly affecting the ability to move the eye outward.
The impact of cranial nerve palsies on the external eye muscles can vary depending on the cause and the individual. In some cases, the effects may be temporary and can be managed with eye patches, prism glasses, or, in more severe cases, surgery. However, if the nerve damage is permanent, it can lead to long-term issues with eye movement and vision, requiring ongoing management and treatment. It is important to seek medical advice if any symptoms of cranial nerve palsy are present, as early diagnosis and treatment can improve outcomes.
In summary, the external eye muscles are vulnerable to the effects of cranial nerve palsies, which can result in a range of symptoms, including diplopia, eye movement restrictions, and changes in eyelid position and pupil size. The specific nerve affected will determine the precise symptoms and their management. Early diagnosis and treatment are crucial for improving long-term outcomes for individuals experiencing these issues.
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Frequently asked questions
External eye muscles, also known as extrinsic or extraocular muscles, are the six muscles that control eye movement.
The six external muscles work in pairs. When one muscle moves, its partner in the same eye helps control and balance that movement. The muscles that control eye movement depend on signals that travel through three cranial nerves.
The four recti muscles (straight) are the superior rectus, inferior rectus, medial rectus and lateral rectus. The two oblique muscles are the superior oblique and inferior oblique.
The external eye muscles are responsible for the movement of the eyes into different gazes. Four of the six muscles control movement in the cardinal directions: north, east, south, west (or up, right, down, left). The other two muscles counteract head movements and adjust eye movement accordingly.
The external eye muscles are supplied mainly by branches of the ophthalmic artery.
