Dominic Stone
The human eye is a fascinating organ, with several muscles working together to enable vision. The eye muscles are a crucial part of our vision, controlling the movement of our eyes and contributing to their overall function. There are six external muscles that control the movement of our eyes, allowing us to direct our gaze in different directions. These muscles work in pairs, with each muscle having a partner that helps control and balance the movement. In addition to these muscles, the orbicularis oculi muscle, located just beneath the skin, is responsible for eyelid movement and plays a role in facial expressions. This muscle assists in closing the eyelids and facilitating tear drainage. Furthermore, the levator palpebrae superioris and superior tarsal muscles act together to open the eyelid, specifically the upper eyelid. These muscles receive innervation from the oculomotor nerve (CN III) and work in tandem to enable us to see the world around us.
| Characteristics | Values |
|---|---|
| Name of the muscle that opens the eye | Levator palpebrae superioris |
| Other names | Levator palpebrae, levator muscle |
| Location | Just beneath the skin of the eyelids; runs along the superior orbit |
| Innervation | Innervated by the oculomotor nerve (CN III) |
| Blood supply | Ophthalmic artery, specifically its lacrimal, supratrochlear, supraorbital, and muscular branches |
| Lymphatic drainage | Upper eyelid lymphatics drain to the preauricular/parotid lymph nodes and the deep cervical lymph nodes |
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What You'll Learn
- The levator palpebrae superioris muscle is a skeletal muscle that opens the eyelid
- The superior tarsal muscle (Müller muscle) is a smooth muscle that attaches to the superior tarsal plate
- The orbicularis oculi muscle is a sphincter-like muscle that closes the eyelids
- The oculomotor nerve (CN III) controls the movements of the superior, inferior and medial rectus muscles
- The trochlear nerve (CN IV) controls the superior oblique muscle
The levator palpebrae superioris muscle is a skeletal muscle that opens the eyelid
The oculomotor nerve plays a crucial role in synchronising the movement of the upper eyelid during upward gaze, ensuring that the levator palpebrae superioris and superior rectus muscles work together seamlessly. The levator palpebrae superioris is also associated with the Whitnall ligament and levator aponeurosis, a tendon sheath that expands from the distal end of the muscle.
The blood supply to the levator palpebrae superioris is directed by four arterial systems, namely the lacrimal, supratrochlear, supraorbital, and muscular branches, which originate from the ophthalmic artery. These vessels connect to the superior peripheral arcade, providing essential circulation to the upper eyelid. The superior ophthalmic vein is responsible for draining blood from the orbital muscles, including the levator palpebrae superioris.
It is important to note that the orbicularis oculi muscle, situated just beneath the eyelid skin, also plays a role in eyelid movement. While the main function of this muscle is to close the eyelids, it assists in opening the eyes as well. The orbicularis oculi is subdivided into different sections, including the orbital and palpebral, each contributing to the overall functionality and structural integrity of the eyelid.
In summary, the levator palpebrae superioris muscle is a skeletal muscle that opens the eyelid, working in conjunction with other muscles and neural systems to facilitate the complex movements of the human eye.
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The superior tarsal muscle (Müller muscle) is a smooth muscle that attaches to the superior tarsal plate
The superior tarsal muscle, also known as the Müller muscle, is a thin, smooth muscle that is approximately 15 mm wide and 10 mm long. It originates from the inferior aspect of the levator palpebrae superioris muscle 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 superior tarsal muscle is an accessory muscle that allows for the retraction and elevation of the upper eyelid. It works in conjunction with the levator palpebrae superioris muscle to raise the upper eyelid. Specifically, it assists the levator palpebrae superioris by maintaining upper eyelid elevation after being raised by the latter. The superior tarsal muscle also lifts the upper eyelid an additional 2 mm beyond the range of the levator palpebrae superioris, following a sympathetic nervous system response.
The superior tarsal muscle has specific physiologic variants that differ based on their attachment to the superior tarsal plate. Four variations have been identified: Pattern 1, where the muscle attaches to the upper border of the superior tarsal plate; Pattern 2M (medial), where it attaches to the medial aspect of the plate; Pattern 3, where it attaches along the whole extent of the superior tarsal plate; and Pattern 4, which has not been fully described. Pattern 3 is the most frequently observed variant.
The superior tarsal muscle is often involved in oculoplastic surgery, particularly in procedures that correct elevation dysfunctions of the upper eyelid, such as ptosis-correcting procedures. For example, the Müller muscle-conjunctival resection involves removing a portion of the superior tarsal muscle to treat ptosis. Given the proximity of the superior tarsal muscle to other structures, care must be taken during surgery to avoid damage that could lead to overcorrection of conditions like blepharoptosis.
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The orbicularis oculi muscle is a sphincter-like muscle that closes the eyelids
The orbicularis oculi muscle is a critical muscle in eyelid movement. Situated just beneath the skin of the eyelid, it extends from the medial to the lateral canthal region, enhancing the eyelid's structural integrity and functionality. The main function of this muscle is to close the eyelids, but it also assists with tear drainage. The orbicularis oculi is a sphincter-like muscle arranged concentrically around the upper and lower eyelids. It is divided into orbital and palpebral sections, each further subdivided based on function. The orbital portion of the orbicularis oculi facilitates the forceful closure of the eyelids. This muscle is also integral to facial expressions and is affected by conditions such as Bell Palsy and blepharospasm.
The orbicularis oculi originates from the 2nd pharyngeal arch's local mesenchymal tissue and develops similarly to the extraocular muscles. Initially forming as a sheet covering the lid's anterior surface, it later differentiates into pretarsal, preseptal, and orbital parts as the upper and lower lids separate. The eyelids receive arterial inflow from the distal branches of the internal and external carotid arteries. The orbicularis oculi has three distinct parts: palpebral, lacrimal, and orbital. The palpebral portion, also known as the muscle of Riolan or pars ciliaris, is adjacent to the eyelid margin and appears as a distinct coloured line along the length of the upper and lower eyelid margins.
The levator palpebrae superioris and superior tarsal muscles, on the other hand, are responsible for opening the eyelid. These muscles are only present in the upper eyelid. The levator palpebrae superioris is a skeletal muscle that courses anteriorly along the superior orbit, running superiorly to the superior rectus muscle. The supraorbital artery and the frontal and lacrimal nerves are situated superior to this muscle within the orbit. Distally, the levator palpebrae superioris expands to form a tendon sheath known as the levator aponeurosis, which lies near the Whitnall ligament. The levator aponeurosis inserts onto the upper eyelid skin anteriorly and the upper tarsal plate's anterior surface inferiorly.
The superior ophthalmic vein empties into the cavernous sinus, while the inferior ophthalmic vein drains into the pterygoid venous plexus. The medial upper eyelid's lymphatic vessels were previously thought to drain medially along the angular artery, but recent findings suggest that the upper eyelid lymphatics, including the levator palpebrae superioris muscles, drain solely laterally to the preauricular/parotid lymph nodes and the deep cervical lymph nodes. The levator palpebrae superioris is innervated by the oculomotor nerve (CN III), which also controls the movements of the superior, inferior, and medial rectus muscles, as well as the inferior oblique muscle.
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The oculomotor nerve (CN III) controls the movements of the superior, inferior and medial rectus muscles
The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, plays a crucial role in controlling eye movements. It is responsible for the movement of the superior, inferior, and medial rectus muscles, as well as the inferior oblique muscle. These muscles work together to enable the eyes to move in different directions, up and down, or at diagonal angles.
The oculomotor nerve is a cranial nerve that enters the eye socket through the superior orbital fissure. It innervates the extraocular muscles, which are the muscles responsible for eye movements and raising the eyelid. These extraocular muscles include the superior rectus, which elevates the eye when looking straight ahead, the medial rectus, which adducts the eye from a primary position, and the inferior rectus, which moves the eye down. The inferior oblique muscle, another extraocular muscle innervated by CN III, elevates the eye when it is adducted from its primary position.
The superior branch of the oculomotor nerve provides motor innervation to the superior rectus and levator palpabrae superioris muscles. The levator palpabrae superioris muscle is responsible for raising the upper eyelid. Additionally, sympathetic fibres accompany the superior branch to innervate the superior tarsal muscle, which helps maintain the eyelid's elevated position.
The inferior branch of CN III provides motor innervation to the inferior rectus, medial rectus, and inferior oblique muscles. It also supplies pre-ganglionic parasympathetic fibres to the ciliary ganglion, which ultimately innervates the sphincter pupillae and ciliary muscles. The ciliary muscles play a role in adjusting the shape of the lens, enhancing short-range vision.
The oculomotor nerve has both somatic (voluntary) and autonomic (involuntary) functions. Somatic functions include the elevation of the upper eyelid and the coordination of eye muscles for visual tracking and gaze fixation. Autonomic functions include pupillary constriction and accommodation, which is the ability to focus on nearby objects, such as during reading.
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The trochlear nerve (CN IV) controls the superior oblique muscle
The trochlear nerve, also known as cranial nerve IV or CN IV, is responsible for controlling the superior oblique muscle. This nerve is one of 12 sets of cranial nerves and plays a crucial role in enabling movement in the eye. It allows us to look down and move our eyes towards or away from our nose.
The superior oblique muscle, which the trochlear nerve controls, works like a pulley. It starts at the upper back of the eye and extends forward, threading through a small bony opening called the trochlea on the upper-inner side of the eye socket. After passing through the trochlea, it attaches to the top of the eyeball, just behind the superior rectus.
The trochlear nerve originates in the midbrain, specifically from the posterior part, and follows a long and complex path to reach the superior oblique muscle. It passes through several areas, including the trochlear nucleus near the top of the brainstem, the ambient cistern near the brain's outer protective tissue, the cavernous sinus (a hollow space in the middle of the skull), and finally, the orbit (the bony socket of the skull housing the eyeball).
The trochlear nerve is unique among the cranial nerves as it is the only one that exits dorsally from the brainstem. This long intracranial course makes it vulnerable to various conditions and injuries that can affect its function. Damage to the trochlear nerve can lead to issues with eye movement and vision, with common signs including double vision (diplopia) and blurry vision, especially when looking down.
The trochlear nerve is examined clinically by testing eye movements. Patients are typically asked to follow a point, such as the tip of a pen, with their eyes without moving their head. This helps assess the nerve's function and identify any potential issues.
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Frequently asked questions
The levator palpebrae superioris and superior tarsal muscles act to open the eyelid.
The levator palpebrae superioris muscle courses anteriorly along the superior orbit, running superiorly to the superior rectus muscle.
The orbicularis oculi muscle is critical in eyelid movement and is responsible for the forceful closure of the eyelids.
The superior tarsal muscle (Müller muscle) is a smooth muscle that attaches to the superior tarsal plate and lies posterior to the levator aponeurosis.
