Is weakness of both the superior rectus and inferior oblique. A worsening in upgaze also occurs in inferior oblique overaction, since the affected eye will elevate more than normal in upgaze. A worsening of horizontal diplopia in lateral gaze in one direction implicates either the ipsilateral lateral rectus or contralateral medial rectus. To test the inferior rectus from the superior oblique, the clinician asks the patient to first look out (or lateral) to orient the visual gaze axis perpendicular to the superior oblique muscle fiber direction, then down. After the superior oblique is trapped, the only muscle that can mediate depression is the inferior rectus.

The superior oblique muscle, or obliquus oculi superior, is a fusiform muscle originating in the upper, medial side of the orbit (i.e. from beside the nose) which abducts, depresses and internally rotates the eye. It is the only extraocular muscle innervated by the trochlear nerve (the fourth cranial nerve).

Structure[edit]

The superior oblique muscle loops through a pulley-like structure (the trochlea of superior oblique) 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.

The superior oblique arises immediately above the margin of the optic foramen, superior and medial to the origin of the superior rectus, 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 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, laterally, and inferiorly beneath the superior rectus to the lateral part of the bulb of the eye, and is inserted onto the scleral surface, behind the equator of the eyeball, the insertion of the muscle lying between the superior rectus and lateral rectus.

Function[edit]

The primary (main) action of the superior oblique muscle is intorsion (internal rotation),^[1] 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 and lateral rectus 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.^{[citation needed]}

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.^[2]

Clinical significance[edit]

Superior oblique palsy is a common complication of closed head trauma. 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 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[edit]

• Eye movement of lateral rectus muscle, superior view

• Eye movement of medial rectus muscle, superior view

• Eye movement of inferior rectus muscle, superior view

• Eye movement of superior rectus muscle, superior view

• Eye movement of superior oblique muscle, superior view

• Eye movement of inferior oblique muscle, superior view

• Anterior view

• Nerves of the orbit. Seen from above.

• Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.

References[edit]

This article incorporates text in the public domain from page 1022 of the 20th edition ofGray's Anatomy(1918)

1. ^https://emedicine.medscape.com/article/1189759-overview#a3
2. ^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.

External links[edit]

• Anatomy figure: 29:01-03 at Human Anatomy Online, SUNY Downstate Medical Center

Case

Medial Rectus Muscle Function

A 47-year-old patient presented to the hospital following an alleged assault involving multiple kicks to his face. He was found to have considerable ecchymosis around the right orbit, a right eye subconjunctival haemorrhage, and paraesthesia of the right side of his face. Visual acuity was better than 0.0 LogMAR in both eyes.

At his initial assessment he reported mild horizontal and vertical diplopia in upgaze and downgaze only. His examination demonstrated generalised mild restriction in all positions of gaze in the right eye, maximal in upgaze. In primary position only an exophoria was present. This corresponded with the Hess chart findings which consisted of a compressed pattern in the right eye and an expanded pattern in the left eye (Figure 1). On the basis of these findings there was concern about muscle or orbital fat entrapment. A CT performed at this time demonstrated a right orbital floor fracture with orbital fat herniating into the maxillary sinus (Figure 2). An orbital floor reconstruction was performed 10 days later without complication. After the orbital plate was inserted a forced duction test confirmed the globe was freely mobile.

Preoperative clinical findings following initial injury. 1a. Ocular motility, 1b. Hess chart shows compression in the right eye.

CT scan of orbit using soft tissue windows. 2a Orbital floor fracture following initial injury. 2b. Coronal section following orbital floor repair. The bodies of the left and right medial recti have been highlighted to demonstrate their asymmetric positioning. The right medial rectus is clearly elevated in comparison to the contralateral side. 2c. Coronal section of the orbit shows the medial rectus tendon in close proximity to and distorted by the orbital plate. Anatomical structures are labelled, * indicates the globe. 2d. Sagittal section shows posterior extension of orbital plate. 2e. Coronal section following orbital plate exchange shows right medial rectus now symmetrical with left. 2f. Sagittal section following orbital plate exchange shows less posterior extension of orbital plate.

Immediately after surgery the patient complained of significantly increased vertical diplopia with new symptoms of torsion in all positions of gaze. He was found to have a right hypotropia and excyclotorsion maximal on levoversion of up to 10 degrees on synoptophore (Figure 3). There was also some limitation in upgaze that appeared to be due to mechanical restriction, particularly in dextroelevation.

Postoperative clinical findings following orbital floor repair. 3a. Ocular motility, 3b. Synoptophore performed postoperatively with left eye fixating. Esotropia, excyclotorsion and mild left hypertropia noted in primary position. Left hypertropia maximal in dextroelevation. Esotropia was present in all positions of gaze and maximal in dextrodepression. Excyclotorsion was maximal in levoversion. 3c. Hess chart showing a compressed appearance in the right eye. Note restriction of upgaze in the right eye with associated overaction of the left superior rectus and underaction of right inferior oblique, medial rectus and inferior oblique.

A CT was performed, which showed changes in the position of medial rectus and inferior rectus following orbital plate insertion (Figure 2). The orbital plate elevated the right medial rectus and distorted the natural course of the muscle. When compared to the contralateral medial rectus, it was clear that the right medial rectus was elevated. Figure 2c demonstrates the medial rectus tendon appearing to ride on the border of the orbital plate. The inferior rectus is also seen in close apposition to the orbital plate. Based on imaging alone, entrapment or scarring between the muscle and plate could not be excluded. The superior rectus, lateral rectus, superior oblique and inferior oblique showed no abnormality on CT imaging.

Based on these clinical findings, combined with the CT, a diagnosis of medial rectus pulley distortion and possible inferior rectus mechanical restriction was made. The patient was offered a revision of the orbital plate to attempt to resolve the double vision. He elected to go ahead and 6 weeks after the injury the original plate was replaced with a smaller plate that extended less posteriorly and medially. No additional scarring or entrapment was found during the operation. After the plate was inserted the globe was freely mobile on forced duction testing.

Following his second operation the patient reported a total resolution of his symptoms. Examination revealed return of normal ocular motility and no significant torsion (Figure 4). The repeated CT scan showed return of the medial rectus to a normal position (Figure 2). He was able to resume all of his premorbid daily activities without any orthoptic aids.

Medial Rectus And Inferior Oblique Dmg Muscle

Medial Rectus Function

Postoperative clinical findings following orbital plate exchange. 4a. Ocular motility, 4b. Synoptophore, left eye fixation, no torsion in any position of gaze, 4c. Hess chart.