The superior oblique muscle, or obliquus oculi superior, is a
fusiform muscle
Anatomical terminology is used to uniquely describe aspects of skeletal muscle, cardiac muscle, and smooth muscle such as their actions, structure, size, and location.
Types
There are three types of muscle tissue in the body: skeletal, smooth, a ...
originating in the upper, medial side of the
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
(i.e. from beside the nose) which abducts, depresses and internally rotates the eye. It is the only
extraocular muscle
The extraocular muscles (extrinsic ocular muscles), are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the oth ...
innervated by the
trochlear nerve
The trochlear nerve (), ( lit. ''pulley-like'' nerve) also known as the fourth cranial nerve, cranial nerve IV, or CN IV, is a cranial nerve that innervates just one muscle: the superior oblique muscle of the eye, which operates through the pu ...
(the fourth cranial nerve).
Structure
The superior oblique muscle loops through a pulley-like structure (the
trochlea of superior oblique
The trochlea of superior oblique is a pulley-like structure in the eye. The tendon of the superior oblique muscle passes through it. Situated on the superior nasal aspect of the frontal bone, it is the only cartilage found in the normal orbit. Th ...
) and inserts into the sclera on the posterotemporal surface of the eyeball. It is the pulley system that gives superior oblique its actions, causing depression of the eyeball despite being inserted on the superior surface.
![Trochlear and frontal nerves](https://upload.wikimedia.org/wikipedia/commons/1/18/Trochlear_and_frontal_nerves.jpg)
The superior oblique arises immediately above the margin of the optic foramen, superior and medial to the origin of the
superior rectus
The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles. It is innervated by the superior division of the oculomotor nerve (III). In the primary position (looking straight ahead), its primary function is elevation ...
, and, passing forward, ends in a rounded tendon, which plays in a fibrocartilaginous ring or pulley attached to the trochlear fossa of the
frontal bone
The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, pa ...
.
The contiguous surfaces of the tendon and ring are lined by a delicate mucous sheath, and enclosed in a thin fibrous investment.
The tendon is reflected
caudally
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
,
laterally, and
inferiorly beneath the
superior rectus
The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles. It is innervated by the superior division of the oculomotor nerve (III). In the primary position (looking straight ahead), its primary function is elevation ...
to the lateral part of the bulb of the eye, and is inserted onto the
scleral surface, behind the equator of the
eyeball
Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and con ...
, the insertion of the muscle lying between the
superior rectus
The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles. It is innervated by the superior division of the oculomotor nerve (III). In the primary position (looking straight ahead), its primary function is elevation ...
and
lateral rectus
Lateral is a geometric term of location which may refer to:
Healthcare
* Lateral (anatomy), an anatomical direction
*Lateral cricoarytenoid muscle
*Lateral release (surgery), a surgical procedure on the side of a kneecap
Phonetics
*Lateral co ...
.
Function
The primary (main) action of the superior oblique muscle is intorsion (internal rotation), the secondary action is depression (primarily in the adducted position) and the tertiary action is abduction (lateral rotation).
The extraocular muscles rotate the eyeball around vertical, horizontal and antero-posterior axes. Extraocular muscles other than the
medial rectus
The medial rectus muscle is a muscle in the orbit near the eye. It is one of the extraocular muscles. It originates from the common tendinous ring, and inserts into the anteromedial surface of the eye. It is supplied by the inferior division of ...
and
lateral rectus
Lateral is a geometric term of location which may refer to:
Healthcare
* Lateral (anatomy), an anatomical direction
*Lateral cricoarytenoid muscle
*Lateral release (surgery), a surgical procedure on the side of a kneecap
Phonetics
*Lateral co ...
have more than one action due to the angle they make with the optical axis of the eye while inserting into the eyeball. The superior and inferior oblique muscles make an angle of 51 degrees with the optical axis.
The depressing action of superior oblique (making the eye look down towards the mouth) is most effective when the eye is in an adducted position. This is because as the eye is abducted (looks laterally), the contribution made by superior oblique to depression of the eye decreases, as the inferior rectus muscle causes this movement more directly and powerfully. The main muscle for abduction is the lateral rectus, so although superior oblique contributes to a downwards and lateral eye movement, testing this motion would not be specific enough as inferior and lateral recti muscles would also be tested. Therefore, during neurological examinations, the superior oblique is tested by having the patient look inwards and downwards, testing only the depressing action of the muscle. This is a source of confusion on the subject as although clinical testing asks the patient to adduct and depress the eye, anatomically the muscle depresses and abducts it.
The great importance of intorsion and extorsion produced by the two oblique muscles can only be understood when it is considered with regards to the other muscle actions present. The two obliques prevent the eye from rotating about its long axis (retina to pupil) when the superior and inferior rectus muscles contract. This is because the orbit does not face directly forwards- the centre-line of the orbit is a little over 20 degrees out from the mid-line. But because the eyes do face forwards, when acting alone, as well as making the eye look up, superior rectus causes it to rotate slightly about the long axis, so the top of the eye moves medially (intorsion). Similarly, in addition to making the eye look down, inferior rectus would cause the eye to rotate about the long axis so the top of the eye moves slightly laterally (extorsion), if acting alone. Clearly this is undesirable as our vision would rotate when we looked up and down. For this reason, these two rectus muscles work in conjunction with the two obliques. When acting alone, superior oblique causes intorsion, inferior oblique, extorsion. Hence, when inferior rectus contracts so we look down, superior oblique also contracts to prevent extorsion of the eye, and when superior rectus contracts so we look up, inferior oblique contracts to prevent intorsion, thus the undesired rotatory actions of the inferior and superior recti about the long axis of the eye are cancelled out. This keeps our vision horizontally level, irrespective of eye position in the orbit.
[Dr. Robert Acland's Atlas of Human Anatomy, University of Louisville. Volume 5: Head and Neck Part 2, Section 5: The Eye and its Surroundings.]
Clinical significance
Superior oblique palsy is a common complication of closed
head trauma
A head injury is any injury that results in trauma to the skull or brain. The terms ''traumatic brain injury'' and ''head injury'' are often used interchangeably in the medical literature. Because head injuries cover such a broad scope of inju ...
. Restriction of superior oblique movement due to an inelastic tendon is found in
Brown syndrome, leading to difficulty elevating the eye in the adducted position.
Superior oblique myokymia is an uncommon neurological condition caused by vascular compression of the
trochlear nerve
The trochlear nerve (), ( lit. ''pulley-like'' nerve) also known as the fourth cranial nerve, cranial nerve IV, or CN IV, is a cranial nerve that innervates just one muscle: the superior oblique muscle of the eye, which operates through the pu ...
resulting in repeated, brief, involuntary episodes of movement of the eye.
Surgical operations of the superior oblique include tenotomy, recession, silicone expander lengthening, split tendon lengthening, tucking, and the
Harada-Ito procedure.
Additional images
File:Gray776.png, Nerves of the orbit. Seen from above.
File:Gray890.png, Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.
References
External links
*
{{Authority control
Muscles of the head and neck
Human eye anatomy
de:Augenmuskeln#Musculus obliquus superior