Logan Steele
The superior rectus muscle is one of the extraocular muscles that control eye movements. It is located outside the eyeball but within the orbit. The superior rectus muscle originates from the annulus of Zinn and inserts into the anterosuperior surface of the eye. Its primary function is to elevate the eye, but it also contributes to intorsion and adduction. The superior rectus muscle is innervated by the superior branch of the oculomotor nerve (CN III). Variations of this muscle are rare, but it may be congenitally absent in some cases.
| Characteristics | Values |
|---|---|
| Type | Muscle |
| Location | Orbit, outside the eyeball |
| Group | Extraocular muscles |
| Function | Elevation, adduction, internal rotation of the eyeball |
| Innervation | Superior branch of the oculomotor nerve (CN III) |
| Blood supply | Ophthalmic artery, supraorbital branch, two anterior ciliary arteries |
| Associated conditions | Weakness, paralysis, overreactivity, congenital absence |
| Treatment for weakness | Eye surgery to weaken or reposition the muscle |
| Congenital absence causes | Apert syndrome |
| Congenital absence treatment | Surgery using parts of medial rectus and lateral rectus muscles |
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What You'll Learn
Superior rectus muscle and eye elevation
The superior rectus muscle is one of the extraocular muscles, which are responsible for eye movement. There are six extraocular muscles, which can be divided into two groups: recti and oblique muscles. The four recti muscles are the superior rectus, inferior rectus, medial rectus, and lateral rectus. The two oblique muscles are the superior and inferior obliques.
The superior rectus muscle is located outside the eyeball but within the orbit. It originates from the annulus of Zinn, a common tendinous ring at the apex of the orbit that surrounds the optic canal. It inserts into the anterosuperior surface of the eye, with an insertion width of around 11 mm. The superior rectus muscle is innervated by the superior branch of the oculomotor nerve (CN III). It is vascularized by the ophthalmic artery and its supraorbital branch.
The primary function of the superior rectus muscle is to elevate the eye, causing the cornea to move superiorly. It is the only muscle capable of elevating the eye when it is in a fully abducted position. It also contributes to adduction and intorsion (internal rotation). When the eye is abducted by the lateral rectus, the superior rectus produces ocular elevation, and is solely responsible for this movement. However, when the eye is adducted by the medial rectus, the superior rectus no longer produces effective ocular elevation, and instead produces internal rotation and adduction.
The superior rectus muscle is associated with several medical conditions and may be weak, paralysed, overreactive, or congenitally absent in some people. Weakness of the inferior rectus muscle, which may occur as a result of local anaesthetics used in cataract surgery, can lead to a strengthening of the superior rectus muscle, causing it to be overreactive and elevating the eye. Treatment for this condition may involve eye surgery to weaken or reposition the superior rectus muscle. In rare cases, the superior rectus muscle may be congenitally absent due to conditions such as Apert syndrome, resulting in a reduced ability to elevate the eye.
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Congenital absence of the superior rectus muscle
The superior rectus muscle is one of the extraocular muscles responsible for eye movements, specifically elevating, adducting, and intorting the eyeball. Congenital absence of the superior rectus muscle is a rare condition where this muscle is missing from birth. It is a type of congenital cranial dysinnervation disorder (CCDD) and can lead to significant challenges with eye movement and alignment. This condition is often inherited in an autosomal dominant manner, meaning that if one parent carries the responsible mutated gene, there is a 50% chance that their child will inherit the condition.
The absence of the superior rectus muscle can result in a range of ocular motility issues. The most common finding is a restrictive type of strabismus, where the eye movement is limited, leading to misalignment. Typically, the affected individual will present with a large-angle hypertropia, where one eye deviates upward, and an esotropia, where one eye turns inward. This misalignment can cause significant visual impairment, including a reduction in binocular vision and the potential development of amblyopia, commonly known as lazy eye.
In addition to the strabismus, patients with congenital absence of the superior rectus muscle may also experience other eye movement abnormalities. They may have a reduced ability to elevate their eyes, particularly when looking toward the side of the affected muscle. This limitation in upward gaze can lead to a head tilt, as individuals compensate by positioning their heads to help align their eyes correctly. Some patients may also experience nystagmus, which is an involuntary rhythmic movement of the eyes, typically from side to side but sometimes also up and down.
The diagnosis of congenital absence of the superior rectus muscle is primarily based on clinical examination and the identification of characteristic eye movement abnormalities. A detailed family history is also important, as the presence of similar eye movement disorders in family members can support the diagnosis. While not always necessary, advanced imaging techniques such as magnetic resonance imaging (MRI) can be useful in confirming the absence of the muscle or identifying associated abnormalities. Electrophysiological tests, such as electromyography (EMG), can also be employed to assess the function of the extraocular muscles and the integrity of the neural pathways that control them.
Management of this condition aims to improve eye alignment and restore binocular vision. In some cases, prism glasses may be prescribed to help bend light entering the eyes and thus improve alignment. However, surgery is often the primary treatment option. Surgical intervention typically involves weakening or recessing the antagonist muscle, the inferior rectus, to improve eye alignment. Sometimes, a muscle transposition procedure may be considered, where another muscle is repositioned to partially take over the function of the missing superior rectus.
Ultimately, the management approach is tailored to each patient, considering the severity of their eye movement abnormalities and the impact on their vision and quality of life. Early diagnosis and intervention are crucial to achieving optimal outcomes. While there is currently no cure for congenital absence of the superior rectus muscle, ongoing research in the field of CCDDs aims to improve understanding, diagnosis, and management of these rare conditions. Genetic counseling may also be beneficial for affected individuals and their families to understand the inheritance patterns and risks associated with this rare disorder.
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Superior rectus muscle and the oculomotor nerve
The superior rectus muscle is an extrinsic muscle of the eye, located outside the eyeball but within the orbit. It is one of the extraocular muscles, which serve to move the eyes within the orbit. The superior rectus muscle originates from the annulus of Zinn, a connective tissue ring located at the apex of the orbit, surrounding the optic canal. It inserts into the anterosuperior surface of the eye, with a width of around 11 mm and approximately 8 mm from the corneal limbus.
The superior rectus muscle is innervated by the superior branch of the oculomotor nerve (CN III). The oculomotor nerve is a somatic motor nerve, providing voluntary control over the superior rectus muscle. It originates from the nucleus of the oculomotor nerve, which is located in the mesencephalon. The superior rectus muscle is supplied by the superior division of the ipsilateral oculomotor nerve. Each superior rectus muscle is innervated by the contralateral oculomotor nucleus.
Contraction of the superior rectus muscle causes the eye to move in multiple planes simultaneously. It produces elevation in the transverse plane, adduction in the vertical plane, and internal rotation (intorsion) in the anteroposterior plane. The superior rectus muscle is the only muscle capable of elevating the eye when it is in a fully abducted position. It is also associated with the levator palpebrae superioris muscle, which controls the elevation of the upper eyelid.
The superior rectus muscle can be weakened or paralysed due to issues with nerve conduction of the oculomotor nerve. This may be congenital, often with a familial genetic link, or acquired, commonly resulting from head injuries. Local anaesthetics used during cataract surgery can also weaken the inferior rectus muscle, leading to a strengthening of the superior rectus muscle and potential elevation of the eye. Treatment for such conditions may involve eye surgery to weaken or reposition the superior rectus muscle.
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Superior rectus muscle and venous drainage
The superior rectus muscle is an extraocular muscle located outside the eyeball but within the orbit. It is innervated by the superior branch of the oculomotor nerve (CN III). Its primary function is to elevate the eye, but it also contributes to intorsion and adduction.
The superior rectus muscle is associated with several medical conditions and may be weak, paralysed, overreactive, or congenitally absent in some individuals. Weakness of the inferior rectus muscle, which may be caused by local anaesthetics during cataract surgery, can lead to a strengthening of the superior rectus muscle, resulting in potential overreactivity and elevation of the eye. This can be treated with eye surgery to weaken or reposition the superior rectus muscle.
The superior rectus muscle is also associated with the levator palpebrae superioris muscle, which is responsible for eyelid elevation. The two muscles are connected by the check ligament, which ensures they act simultaneously. The superior oblique tendon, which is located underneath the superior rectus muscle, can be inadvertently hooked during surgical procedures, potentially leading to a significant iatrogenic motility disturbance.
Much of the venous drainage of the orbit and the extraocular muscles occurs near the superior rectus muscle. Obstruction of this venous drainage can lead to venous congestion in the eye, causing a condition known as exophthalmos, or bulging of the eyeball. This condition can be detected through CT scans.
The superior rectus muscle receives its blood supply from two anterior ciliary arteries, which communicate with the anterior circle of the ciliary body. This blood supply is crucial for the proper functioning of the muscle and the overall health of the eye.
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Superior rectus muscle and eye surgery
The superior rectus muscle is one of the four rectus muscles, which also include the inferior rectus, medial rectus, and lateral rectus. The superior rectus muscle is located outside the eyeball but within the orbit. It is responsible for elevating the eye, causing the cornea to move superiorly. This muscle also contributes to adduction and intorsion.
In some cases, the superior rectus muscle may be weakened or paralysed due to problems with nerve conduction of the oculomotor nerve (CN III). This can be congenital, often with a familial genetic link, or acquired, most frequently due to head injuries. Local anaesthetics used in cataract surgery can also inadvertently weaken the inferior rectus muscle, which may subsequently strengthen the superior rectus muscle and lead to an elevated eye position that interferes with normal vision.
Eye surgery can be employed to address issues with the superior rectus muscle. This may involve weakening or repositioning the muscle to restore normal eye function. During surgery, care must be taken to avoid disrupting the blood supply to the extraocular muscles, as these blood vessels also supply a significant portion of the anterior segment of the eye. Unsatisfactory alignment is the most common complication of superior rectus surgery, and other potential complications include diplopia, scleral perforation, and postoperative infections.
When performing surgery on the superior rectus muscle, it is important to isolate it and ensure that the superior oblique tendon is not inadvertently hooked. A small muscle hook is typically used to retract the conjunctiva and Tenon's fascia posteriorly along the lateral border of the superior rectus muscle. A Desmarres retractor can also be placed in the posterior aspect of the incision to improve exposure of the temporal border of the muscle and the superior oblique tendon.
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Frequently asked questions
The superior rectus muscle is one of the extraocular muscles. It is located outside the eyeball but within the orbit.
The primary function of the superior rectus muscle is elevation, although it also contributes to intorsion and adduction. It is the only muscle that can elevate the eye when it is in a fully abducted position.
The superior rectus originates from the annulus of Zinn, a common tendinous ring at the apex of the orbit that surrounds the optic canal. It inserts into the anterosuperior surface of the eye, with an insertion width of around 11 mm.
