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Müller's muscle, also known as the superior tarsal muscle, is a small smooth muscle of the superior orbit that arises from the undersurface of the levator palpebrae superioris muscle. It plays a role in elevating and retracting the upper eyelid, particularly in acute life-threatening situations, triggering a wider field of vision. The muscle is routinely encountered in oculoplastic surgery, and its resection is a treatment for blepharoptosis. While its precise function and purpose are still debated, Müller's muscle is believed to be involved in adjusting the eyelid position in response to changes in pupil size and light intensity.
| Characteristics | Values |
|---|---|
| Other Names | Superior tarsal muscle, cremaster tarsus |
| Location | Upper eyelid |
| Function | Elevates and retracts the upper eyelid |
| Innervation | Sympathetic fibres from the superior cervical ganglion |
| Arterial Supply | Superior branch of the ophthalmic artery |
| Venous Drainage | Not clear from sources |
| Surgical Procedures | Müller muscle-conjunctival resection, levator advancement or resection |
| Length | 10 mm |
| Width | 15 mm |
| Thickness | 0.1-0.5 mm |
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What You'll Learn
The superior tarsal muscle is a synonym for Müller's muscle
The superior tarsal muscle, also known as the Müller muscle, is an accessory smooth muscle that allows for the retraction and elevation of the upper eyelid. The Müller muscle is a small muscle of the superior orbit arising from the undersurface of the levator palpebrae superioris muscle. It is approximately 10 mm long, 15 mm wide, and 0.1–0.5 mm thick. The superior tarsal muscle receives its innervation from the sympathetic nervous system. More specifically, the postganglionic sympathetic fibres stem from the superior cervical ganglion and form the internal carotid plexus around the cervical segment of the internal carotid artery.
The superior tarsal muscle is often encountered in oculoplastic surgery, including ptosis-correcting procedures. Different approaches can be used to correct ptosis, but the Müller muscle-conjunctival resection involves removing a portion of the superior tarsal muscle to remedy the ptosis. Understanding the anatomy and function of the superior tarsal muscle is essential in managing conditions that affect upper eyelid movement. The muscle originates from the inferior aspect of the levator palpebrae superioris and inserts onto the superior tarsal plate of the upper eyelid. The superior tarsal plate is made of dense connective tissue and functions to support the upper eyelid and maintain its shape. The main action of the superior tarsal muscle is to elevate the upper eyelid in a state of sympathetic predominance. This function enables a wider visual field in states of acute life-threatening situations (fight or flight response).
Müller's muscle was first described by Müller in 1858 as a smooth muscle with many features of a striated muscle. It has a sympathetic innervation that is derived from the cervical sympathetic chain via third neuron fibres that pass from the carotid plexus. The precise course of these postganglionic fibres remains unclear. However, it has been suggested to follow the motor nerve fibres of the levator palpebrae superioris muscle and the internal carotid and ophthalmic arteries, or join the ophthalmic division of the trigeminal nerve. The physiologic function and purpose of Müller's muscle have not been clearly defined and remain a source of debate. The most widely accepted theory is that the levator aponeurosis is the main transmitter of movement from the LPS muscle to the tarsus, and that Müller's muscle is a secondary player in maintaining the tone of the eyelids.
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It is a small muscle of the superior orbit
The superior tarsal muscle, also known as Müller's muscle, is a small muscle of the superior orbit. It is a smooth muscle that allows for the retraction and elevation of the upper eyelid. It is approximately 10 mm long, 15 mm wide, and 0.1–0.5 mm thick. The superior tarsal muscle originates from the inferior aspect of the levator palpebrae superioris and inserts onto the superior tarsal plate of the upper eyelid.
The superior tarsal muscle receives its innervation from the sympathetic nervous system. Specifically, the postganglionic sympathetic fibres originate in the superior cervical ganglion and travel via the internal carotid plexus. The precise course of these postganglionic fibres is not entirely clear, but it is hypothesized that they follow the motor nerve fibres of the levator palpebrae superioris muscle and the internal carotid and ophthalmic arteries.
The main action of the superior tarsal muscle is to elevate the upper eyelid, particularly in states of acute life-threatening situations, also known as the fight-or-flight response. This elevation provides a wider visual field, which can be advantageous in such situations. In addition, the muscle has a static tone that contributes to maintaining the eyes open and defining the size of the palpebral fissure.
Müller's muscle is often encountered in oculoplastic surgery, including procedures to correct ptosis, or drooping eyelid. The surgical technique involves the resection of Müller's muscle, sometimes along with the overlying conjunctiva, to remedy ptosis. This procedure has been shown to be safe and effective for patients with good levator function.
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It arises from the undersurface of the levator palpebrae superioris muscle
The superior tarsal muscle, also known as the Müller muscle, is a small muscle of the superior orbit. It arises from the undersurface of the levator palpebrae superioris muscle, near Whitnall's ligament, and extends inferiorly and anteriorly to insert firmly at the superior border of the tarsus. The superior tarsal muscle is composed of thin fibres of smooth muscle tissue and is approximately 15 mm wide, 10 mm long, and 0.1-0.5 mm thick.
The Müller muscle is an accessory smooth muscle that allows for the retraction and elevation of the upper eyelid. It has a static tone, which, in conjunction with the tone of the levator palpebrae superioris muscle, maintains the eyes open and defines the size of the palpebral fissure. The precise function and purpose of the muscle have not been clearly defined, but it is hypothesized that it serves to adjust the upper eyelid's position in response to changes in pupil size and light intensity. This is supported by observations of slight changes in eyelid height in different light conditions.
The superior tarsal muscle receives its innervation from the sympathetic nervous system. More specifically, the postganglionic sympathetic fibres originate in the superior cervical ganglion and travel via the internal carotid plexus, where small branches communicate with the oculomotor nerve as it passes through the cavernous sinus. The ophthalmic artery, a branch of the internal carotid artery, provides the blood supply for the superior tarsal muscle.
Müller's muscle is routinely encountered in oculoplastic surgery, including procedures to correct blepharoptosis (ptosis). Resection of the muscle, with or without the preservation of conjunctival tissue, is a safe and effective technique to treat mild to moderate blepharoptosis in patients with good levator function.
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It elevates and retracts the upper eyelid
The superior tarsal muscle, also known as Müller's muscle, is a small muscle of the superior orbit that arises from the undersurface of the levator palpebrae superioris muscle. It is a smooth muscle that allows for the retraction and elevation of the upper eyelid.
Müller's muscle is innervated by the sympathetic nervous system and receives its blood supply from the ophthalmic artery. The precise course of the postganglionic fibres that innervate the muscle remains unclear, but it is believed that they may follow the motor nerve fibres of the levator palpebrae superioris muscle and the internal carotid and ophthalmic arteries. Alternatively, they may join the ophthalmic division of the trigeminal nerve.
Müller's muscle is thought to play a role in adjusting the upper eyelid's position in response to changes in pupil size and light intensity. This hypothesis is supported by observations of slight changes in eyelid height in different light conditions, which are more noticeable with high magnification and an infrared camera. The muscle may also be involved in the fight-or-flight response, helping to raise the eyelid and widen the visual field in acute life-threatening situations.
Surgical procedures involving Müller's muscle include the treatment of blepharoptosis, or eyelid droop. One such procedure is Müller muscle-conjunctival resection, which involves removing a portion of the superior tarsal muscle, sometimes in conjunction with the conjunctiva and a portion of the tarsal plate. Another procedure is levator advancement or resection, which treats blepharoptosis by advancing or resecting a portion of the levator palpebrae superioris through an external eyelid crease incision.
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It is routinely encountered in oculoplastic surgery
The superior tarsal muscle, also known as Müller's muscle, is a small muscle of the superior orbit that arises from the undersurface of the levator palpebrae superioris muscle. It is responsible for elevating and retracting the upper eyelid, allowing for a wider visual field in acute life-threatening situations, such as the fight-or-flight response.
Müller's muscle is routinely encountered in oculoplastic surgery, particularly in procedures that address eyelid movement disorders, such as ptosis (drooping eyelid) and blepharoptosis. During these surgeries, a portion of the superior tarsal muscle may be removed to correct the condition. Given its proximity to other critical structures, such as the superior tarsal plate and the levator palpebrae superioris, surgeons must exercise caution to avoid damage that could lead to overcorrection or other complications.
Müller's muscle-conjunctival resection is a surgical technique specifically designed to treat blepharoptosis. This procedure involves the resection of Müller's muscle, along with the overlying conjunctiva, while preserving healthy conjunctival tissue. The preservation of the conjunctiva eliminates concerns about dry eye and maintains the full height of the fornix.
Isolated Müller's muscle resection is another surgical approach that has been proven effective in correcting ptosis in patients with moderate to good levator function. This technique is performed under direct visualisation of the relevant eyelid structures, allowing for intraoperative adjustments. Additionally, it has been shown to be successful in both phenylephrine test-negative and test-positive patients.
Understanding the anatomy and function of Müller's muscle is crucial in oculoplastic surgery, particularly when addressing conditions related to upper eyelid movement. While the precise function of Müller's muscle remains a subject of debate, it is believed to play a role in adjusting the upper eyelid's position in response to changes in pupil size and light intensity.
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Frequently asked questions
Müller's muscle is a small smooth muscle of the superior orbit that elevates and retracts the upper eyelid.
The function of Müller's muscle is not yet clearly defined. However, it is believed to be an accessory muscle that helps in raising the upper eyelid and adjusting its position in response to changes in pupil size and light intensity.
The muscle was first described by Müller in 1858, and it is named after him.
Müller's muscle resection is a surgical procedure used to treat blepharoptosis. The procedure involves removing a portion of the superior tarsal muscle or conjunctiva to correct the eyelid droop.
