EXTRAOCULAR MUSCLES AND TENON'S CAPSULE

Question 1

State the origin of the following muscles. Be specific and complete.

• superior oblique
• inferior rectus
• inferior oblique
• medial rectus
• superior rectus
• lateral rectus

Answer 1

> Superior oblique’s anatomical origin is on the lesser wing of the sphenoid bone superior & medial to the optic canal and outside the annulus of Zinn. Superior oblique’s functional origin is the pulley for the superior oblique muscle’s tendon).

> Inferior rectus (along with superior rectus, medial rectus, lateral rectus) originate from common tendinous ring (annulus of Zinn) , an oval, connective tissue ring made of thickened periorbita located at the apex of the orbit. It surrounds the optic canal and the central portion of the superior orbital fissure

> Additionally, superior rectus and medial rectus also originate from dural sheath surrounding optic nerve

> Inferior oblique originates from the maxilla on the orbital floor just posterior to orbital margin & just lateral to nasolacrimal canal opening
**inferior oblique is the only extraocular muscle that does NOT originate from the orbital apex

Question 2

Which muscle inserts into the eyeball closest to the limbus?

Answer 2

The medial rectus inserts closest to the limbus

Question 3

Which muscle inserts into the eyeball furthest from the limbus?

Answer 3

The superior rectus inserts farthest from limbus (SLIM = mnemonic for the attachments of the four rectus muscles to the eyeball starting with the one furthest away from the limbus).

Question 4

Which EOM’s have the action of adducting the eyeball?

Answer 4

Medial rectus

Adduction is also the tertiary action of the superior and inferior rectus

Question 5

What are the actions of the inferior oblique? State them all.

Answer 5

Primary: Extorsion
Secondary: Elevation
Tertiary: Abduction

Question 6

Tenon’s capsule lies _______ to the bulbar conjunctiva

Answer 6

Internal to

Question 7

Anteriorly Tenon’s capsule attaches to _____ while posteriorly it fuses with ______ and _______

Answer 7

Anteriorly, Tenon’s capsule is firmly attached to the sclera behind the limbus (corneoscleral junction).

Posteriorly, Tenon’s capsule fuses with both the sclera around the exit of the optic nerve and the dura mater of meninges around the optic nerve

Question 8

What forms the lateral check ligament?

Answer 8

The muscle fascia of the medial rectus & lateral rectus muscles are expanded to form strong “check ligaments” that limit how far these muscles pull on the eyeball, and thus keep their movements “in check”)

The lateral check ligament attaches to the lateral orbital tubercle on the zygomatic bone. If the eye is adducted, the lateral check ligament limits further medial movement of the eyeball when the lateral rectus starts to pull on the inelastic lateral check ligament

Question 9

What are the bony attachments of the suspensory ligament of Lockwood? What structures contribute to its formation?

Answer 9

Ligament of Lockwood = A “hammock like” dense connective tissue sheet that extends from the zygomatic
bone (lateral orbital tubercle) to the lacrimal bone, formed by contributions of Tenon’s capsule and muscle fascias of inferior rectus/inferior oblique

Purpose= acts like a sling or hammock to support the eyeball & prevent the eyeball from falling into maxillary sinus if the orbital floor is damaged

Question 10

Name the 2 structures that you have learned so far that attach to the lateral orbital tubercle

Answer 10

Suspensory Ligament of Lockwood

Lateral check ligament

Question 11

What are all the actions of the superior rectus muscle?

Answer 11

Primary: elevation
Secondary: intorsion
Tertiary: adduction

Question 12

What is the function of the expansion between the levator palpebrae superioris and superior rectus muscle?

Answer 12

A thinner expansion extends from the fascia of levator palpebrae superioris (just posterior to its aponeurosis) to the muscle fascia of superior rectus. It extends between the 2 muscles and attaches to the superior conjunctiva’s fornix.
– It allows the two muscles to work together so that, as the eyeball is elevated (with the assistance of superior rectus) the upper eyelid is likewise raised!

Question 13

At the eyeball the _______ muscle lies closest to the eyeball’s inferior surface

Answer 13

Inferior rectus (The inferior oblique runs inferior to inferior rectus muscle and reaches posterolateral surface of the eyeball. Its path is almost parallel to superior oblique tendon).

Question 14

At the eyeball, the superior rectus tendon lies ________ to the superior oblique muscle tendon

Answer 14

over

“After passing through the pulley (its functional origin) the tendon turns posterolaterally and pierces Tenon’s capsule and then passes under the superior rectus muscle tendon & spreads out in a fan-like manner and inserts into the sclera
• it inserts into the sclera posterior to the equator of the eyeball & posterior to the vertical axis of the eyeball”

Question 15

Name all the muscles that act to intort the eyeball

Answer 15

Superior rectus (secondary action) and superior oblique

Question 16

What muscles would be used to look:

• up and to the right (right _____ and left ____)
• down and to the left
• straight up

Answer 16

UP AND TO THE RIGHT: right superior rectus and left inferior oblique
DOWN AND TO THE LEFT: right superior oblique and left inferior rectus
STRAIGHT UP: right superior rectus + inferior oblique; left superior rectus and inferior oblique

Question 17

If a person cannot look up and to the left with their left eye, what muscle is not working?

Answer 17

Left Superior rectus

Question 18

If a person cannot look down and to the right with their left eye, what muscle is not working?

Answer 18

Left Superior Oblique

Question 19

Which muscle attaches to the eyeball closest to the limbus? Why is it the ideal position for it? (i.e. Does the position make it stronger or weaker? What is the muscle used for?

Answer 19

Medial rectus

The closer to the limbus a muscle attaches, the stronger is its pull on the eyeball. The medial rectus muscles are used to bring the eyes inward towards the nose during near work so they lie closest to the limbus to be most effective!

Question 20

The medial rectus muscle lies _____ to the superior oblique muscle belly.

Answer 20

It passes along the medial wall of the orbit (below the superior oblique’s muscle belly). It pierces Tenon’s capsule and inserts into the sclera

Question 21

(CO) 1. Describe Fick’s axes and types of eye movements about the axes

Answer 21

Fick’s axes describe the planes of movement the eye is capable of:
Horizontal (transverse) axis: allows elevation and depression
Vertical axis: allows abduction and adduction

Sagittal axis: allows rotation (intorsion & extorsion)
axis passes through the pupil and the reference point is the 12 o’clock position of the cornea
Intorsion = if 12 o’clock rotates medially (towards the nose)
Extorsion = if 12 o’clock rotates laterally (towards the ear)

Question 22

(CO) 2. Describe Hering’s law and Sherrington’s law concerning eye movements and all the general comments about eye movements accompanying them. Be sure to include definitions of ductions, versions, synergist, antagonist, and different types of versions and ductions, etc. and examples.

Answer 22

According to Hering’s law, both muscles moving the eyes in a particular direction will simultaneously receive equal innervation from the CNS.

According to Sherrington’s law of reciprocal innervation, increased innervation to an agonist muscle is accompanied by simultaneous proportional decrease in innervation of its antagonist muscle.

Duction = movement of one eyeball and all the movements each eye can do alone 
Version = simultaneous movement of both eyes in the same direction to keep the two eyes fixated on an object
Synergist = two or more muscles that move one eye in the same direction 
Antagonist = a muscle in the same eye that moves the eye in the opposite direction of a given muscle

Question 23

(CO) 3. Describe the origins and insertions of the extra-ocular muscles. Be specific.

• relate the four rectus muscle attachments to the limbus; which attaches closest to the limbus vs. farthest away
• describe which muscles attach farthest from the limbus because they attach to the posterior aspect of the eyeball
• describe the EOM which attaches closest to the macula

Answer 23

Inferior oblique inserts into the lower posterolateral quadrant of the eyeball; attaching to the sclera overlying the macula of the retina ▪ inferior oblique will elevate the eyeball (not depress it)

Question 24

(CO) 4. Describe the path of each extra-ocular muscle through the orbit including:

• anatomical relationships to other muscles in the orbit and at their insertions into the eyeball (i.e. SR tendon lies above SO tendon insertion, IO tendon lies below IR tendon insertion)
• specific innervations
• actions

Answer 24

SUPERIOR OBLIQUE
Anatomical relations: longest muscle
after passing through pulley, it turns posterolaterally and pierces Tenon’s capsule then under superior rectus muscle tendon
Origin: from lesser wing of sphenoid bone superior and medial to optic canal, passes between roof and medial wall on way to trochlea
Insertion: into sclera posterior to equator of eyeball and vertical axis of eyeball
Innervations: CN4 (trochlear); enters muscle superiorly by orbit roof
Actions: tendon passes posterior to vertical axis thus allowing action of abduction; main action is intorsion. Secondary action is depression since it insets on posterior aspect of eyeball.

INFERIOR RECTUS
Anatomical relations: Parallels superior rectus
Origin: from common tendinous ring
Insertion: Inserts into sclera obliquely from limbus
Innervations: Inferior division CN3
Actions: Depression, extorsion, adduction (because the muscle passes medial to the vertical axis of the eyeball)

INFERIOR OBLIQUE
Anatomical relations: Inferior to inferior rectus
Origin: floor of orbit as small depression on orbital plate of maxilla posterior to orbital margin and lateral to nasolacrimal canal (EOM doesn’t originate from orbit)
Insertion: into the sclera posterior to equator and to vertical axis of eyeball; overlying macula of retina
Innervations: Inferior division of CN3
Actions: Extorsion, elevation (because it insets posterior aspect of eyeball), abduction (because tendon passes posterior to vertical axis

MEDIAL RECTUS
Anatomical relations: passes along medial wall of orbit (below superior oblique muscle belly); strongest EOM
Origin: common tendinous ring + dural sheath of optic nerve
Insertion: into sclera 5.5mm from limbus (closest)
Innervations: branch of inferior division CN3 entering inner surface of muscle
Actions: Adducts

SUPERIOR RECTUS
Anatomical relations:
Origin: common tendinous ring and dural sheath of optic nerve
Insertion: sclera obliquely (farthest)
Innervations: superior division of CN3
Actions: Elevation, Intorsion, Adduction (as the muscle passes medial to the vertical axis of the eyeball)

LATERAL RECTUS
Anatomical relations: Often visible through the conjunctiva and Tenon’s capsule if patient looks very far
medially
Origin: common tendinous ring and passes along lateral wall
Insertion: sclera
Innervations: cranial nerve 6 (abducens), entering on medial surface of the muscle, posterior to the midpoint
Actions: abduction

Question 25

(CO) 5. State all the muscles that do each of the following actions: elevate, depress, abduct, adduct, intort, and extort the eyeball.

Answer 25

see table on page 16

Question 26

(CO) 6. Describe how to clinically assess each of the extra-ocular muscles using the Physiological H
-For SR, SO, IR, IO muscles be sure to know the angle that the eye must turn in order to line up the muscle plane with the A-P axis of the eyeball

Answer 26

“Physiological H” is the clinical test used to evaluate the EOMs clinically
▪ Start with your transilluminator light directly in front of the patient. This is called the “primary position” (1). Then move the light into the additional positions.
In this way you are tracing out a large letter H.

With the physiological H you are moving the eyes to a position where the optic
axis (anterior – posterior axis of the eyeball is aligned with the axis of the muscle you want to test at which point the muscle becomes a pure elevator or a pure depressor, if you are discussing SR, SO, IR, IO.

The appropriate angle is 51 degrees, but anything between 40-50 degrees is acceptable.

Question 27

(CO) 7. Describe/recognize which extra-ocular muscle is not functioning properly given a clinical case and the results of clinical EOM testing.

Answer 27

see previous question

Question 28

(CO) 8. Describe Tenon’s capsule including:

• what it is, its location on the eyeball and attachment sites on the eyeball
• function(s)
• Tenon’s space (location, clinical significance)
• structures that pierce it (and where pierced)
• the structures it is continuous with or attaches to
• relationship to the EOM tendons and muscle

Answer 28

Also known as fascia bulbi, it is a dense sheet of connective tissue that surrounds the eyeball near the corneoscleral junction to the optic nerve. It separates the eyeball from surrounding orbital fat by forming a socket for the eyeball between the bulbar conjunctiva and sclera.

Tenon’s space is an episcleral space between the episclera of the eyeball and Tenon’s capsule where fluids due to trauma/inflammation can accumulate.

Structures that pierce Tenon’s capsule: tendons of EOMS (forming tube around tendons), long and short posterior ciliary nerves/arteries, vortex veins + optic nerve (posterior part of capsule)

Functions include acting as a barrier to prevent spread of orbital infections into the globe, allowing smooth movement of the eyeball, and supporting it in the orbit

Anteriorly Tenon’s capsule is firmly attached to the sclera. Posteriorly, it fuses with both the sclera around the exit of the optic nerve and dura mater of the meninges around the optic nerve.

As the tendons of the extraocular muscles pierce Tenon’s capsule to insert into the sclera, Tenon’s capsule forms a tubular sleeve that covers the tendons of the extraocular muscles and reflects back onto the muscles to be continuous with the muscles’ fascia (epimysium).

Question 29

(CO) 9. Describe the medial and lateral check ligaments including what they are formed by, attachment sites, and what their function is

Answer 29

The muscle fascia of the medial rectus & lateral rectus muscles are expanded to form strong “check ligaments” that limit how far these muscles pull on the eyeball, and thus keep their movements “in check”)

MEDIAL CHECK LIGAMENT
Attachment site: lacrimal bone behind posterior lacrimal crest
Function: If the eye is abducted, the medial check ligament limits further lateral movement of the eyeball when the medial rectus starts to pull on the inelastic medial check ligament

LATERAL CHECK LIGAMENT
Attachment site: lateral orbital tubercle on the zygomatic bone
Function: If the eye is adducted, the lateral check ligament limits further medial movement of the eyeball when the lateral rectus starts to pull on the inelastic lateral check ligament

Question 30

(CO) 10. Describe the suspensory ligament of Lockwood including what contributes to its formation, attachment sites (be specific), functions

Answer 30

It is formed by contributions from Tenon’s capsule and the muscle fascias of the inferior rectus (IR) & inferior oblique (IO)

Extends from the zygomatic bone (lateral orbital tubercle) to the lacrimal bone

Support the eyeball and maintain the eyeball’s position in the orbit, especially if the bones of the orbital floor are damaged or removed. Acts like a sling or hammock to support the eyeball & prevent the eyeball from
falling into maxillary sinus if the orbital floor is damaged.

Question 31

(CO) 11. Describe the expansion between the levator palpebrae superioris and superior rectus muscle fascias and the expansion of the inferior rectus/inferior oblique muscle fascias including:

• what they are formed by
• attachment sites (be specific)
• function

Answer 31

The muscle fascias of the other extraocular muscles have less well developed “expansions”:
• A thinner expansion extends from the fascia of levator palpebrae superioris (just posterior to its aponeurosis) to the muscle fascia of superior rectus. It extends between the 2 muscles and attaches to the superior conjunctiva’s fornix.
– It allows the two muscles to work together so that, as the eyeball is elevated (with the assistance of superior rectus) the upper eyelid is likewise raised!

• The muscle fascia of the inferior rectus is thickened on its underside & blends with the muscle fascia of the inferior oblique and together they help form the suspensory ligament of Lockwood. An anterior extension from the muscle fascia of the inferior rectus & suspensory ligament of Lockwood attaches to the inferior edge of the inferior tarsal plate
– When a person look down, it assists in pulling down the lower eyelid and helps maintain an appropriate alignment of the lid with the eyeball