Exam 1 - 003 The Extraocular Muscles and Tenon's Capsule

Question 1

How to define the movements of the eye

Answer 1

with respect to the anterior pole of the eye

use the center of the cornea/pupil as the anterior pole

Question 2

Elevation

Answer 2

 Rotation of the eye upward

Question 3

Depression

Answer 3

 Rotation of the eye downward

Question 4

Abduction

Answer 4

 Rotation of the eye laterally

Question 5

Adduction

Answer 5

 Rotation of the eye medially

Question 6

Intortion

Answer 6

 12 o’clock position of the eye rotates medially

Question 7

Extortion

Answer 7

 12 o’clock position of the eye rotates laterally

Question 8

Fick’s axes

Answer 8

Horizontal
Vertical
Sagittal

Question 9

Horizontal Axis

Answer 9

AKA transverse axis

 Allows for elevation and depression

Question 10

Vertical Axis

Answer 10

 Allows for abduction and adduction

Question 11

Sagittal Axis

Answer 11

 Allows for rotation (intorsion and extorsion)

Question 12

Duction

Answer 12

 Refers to the movement of one eyeball (monocular eye movements)
 Movements that each eye can do alone

Question 13

Agonist

Answer 13

 The muscle that moves an eye in a given direction

Question 14

Antagonist

Answer 14

 The muscle in the same eye as the agonist that moves the eye in the opposite direction of the agonist

Question 15

Sherrington’s Law of reciprocal innervation

Answer 15

 Increased innervation to an agonist muscle is accompanied by a simultaneous proportional decrease in innervation to its antagonist muscle
 Basically the pairing of muscles against the muscles whose actions do the opposite movements
 ABduction
 ADduction
 Supra-duction (Elevation)
 Infra-duction (Depression)

Question 16

Hering’s Law

Answer 16

both muscles moving the eyes into a particular direction will simultaneously receive equal innervation from the CNS.

Question 17

Version

Answer 17

 Simultaneous movement of both eyes in the same direction to keep the two eyes fixated on an object (yoke)

Question 18

Yoked muscles

Answer 18

two eyes that are coordinated so that they move together

Question 19

Levoversion

Answer 19

Both eyes look left

Question 20

Dextroversion

Answer 20

Both eyes look right

Question 21

Infraversion

Answer 21

Both eyes look down

Question 22

Supraversion

Answer 22

Both eyes look up

Question 23

What extraocular muscles originate from the common tendinous ring?

Answer 23

Superior Rectus
Inferior Rectus
Lateral Rectus
Medial Rectus

Question 24

Origins of superior rectus

Answer 24

 Origin: common tendinous ring (annulus of Zinn)
• ALSO from the dural sheath surrounding the optic nerve, so this muscle can be affected by optic neuritis, resulting in pain during eye movement caused by the stretching of the dura

Question 25

Origins of inferior rectus

Answer 25

 Origin: common tendinous ring (annulus of Zinn)

Question 26

Origin of medial rectus

Answer 26

 Origin: common tendinous ring (annulus of Zinn) • ALSO from the dural sheath surrounding the optic nerve, so this muscle can be affected by optic neuritis, resulting in pain during eye movement, caused by the stretching of the dura

Question 27

Origin of lateral rectus

Answer 27

 Origin: common tendinous ring (annulus of Zinn)

Question 28

Origin of superior oblique

Answer 28

 Anatomical Origin: Lesser wing of sphenoid superior and medial to the optic canal • Outside of the annulus of Zinn  Functional Origin: the pulley for the superior oblique muscle’s tendon

Question 29

Origin for the inferior oblique

Answer 29

 Origin: maxilla on the orbital floor • posterior to the orbital margin • lateral to the nasolacrimal canal opening  ***The only EOM that does not originate from the orbital apex***

Question 30

Insertions of the rectus muscles

Answer 30

``` Remember: (farthest) SLIM (closest to limbus) Superior Rectus - 7.7 mm Lateral Rectus - 6.9 mm Inferior Rectus - 6.5 mm Medial Rectus - 5.5 mm • ***the closer to the limbus a muscle attaches, the stronger its pull o Medial rectus is closest to make them more effective for close work ```

Question 31

Spiral of Tillaux

Answer 31

* A line connecting the rectus muscle insertions | * Starts at the superior rectus and ends at the medial rectus forming an inward spiral

Question 32

Insertions of the obliques

Answer 32

Insert furthest from the limbus becuase they attach to the posterior aspect of the eyeball  Insert posterior to the equator of the eyeball and posterior to the vertical axis of the eyeball

Question 33

Insertion of Superior Oblique

Answer 33

* Inserts onto the upper posterolateral quadrant of the eyeball * Action: depresses the eyeball (NOT elevate)

Question 34

Inferior Oblique

Answer 34

• Inserts into the lower posterolateral quadrant of the eyeball attaching to the sclera overlying the macula of the retina • Action: elevates the eyeball (NOT depresses) - attaches to the sclera overlying the macula

Question 35

Which EOM attaches closest to the macula?

Answer 35

 Inferior oblique – attaches to the sclera overlying the macula

Question 36

Pathway of the lateral rectus

Answer 36

 Origin: common tendinous ring  Pathway • Pierces Tenon’s capsule • Inserts into the sclera about 6.9 mm from the limbus o Often visible through the conjunctiva and Tenon’s capsule if the patient looks very far medially

Question 37

Pathway of the Medial Rectus

Answer 37

 Origin (2) • Common tendinous ring • Dural sheath of the optic nerve (CN II)  Pathway • Passes along the medial wall of the orbit, below the belly of the superior oblique • Pierces Tenon’s capsule and inserts into the sclera, about 5.5 mm from the limbus

Question 38

Pathway of the Superior Rectus

Answer 38

 Origin (2) • Common tendinous ring • Dural sheath of the optic nerve  Pathway • Passes anterolaterally at an angle of 23 degrees to the globe’s anterior-posterior axis (when looking straight ahead • Pierces Tenon’s capsule • Inserts into the sclera about 7.7 mm from the limbus (furthest from limbus)

Question 39

Pathway of the inferior rectus

Answer 39

 Origin • Common tendinous ring  Pathway • Parallel with the superior rectus • Passes anterolaterally at an angle of 23 degrees to the globe’s anterior-posterior axis (when looking straight ahead • Pierces Tenon’s capsule • Inserts into the sclera about 6.5 mm from the limbus

Question 40

Pathway of the superior oblique

Answer 40

 Longest muscle due to its long tendon  Origin • Antomical – lesser wing of sphenoid (superior and medial to the optic canal • Functional – pulley of the trochlea  Pathway • Passes forward between the roof and medial wall on the way to the trochlea • Becomes a tendon 10 mm posterior to the trochlea • After passing through the pulley (its functional origin) the tendon turns posterolaterally and pierces Tenon’s capsule • Then passes under the superior rectus muscle tendon • Spreads in a fan like manner • Inserts into the sclera posterior to the equator of the eyeball and posterior to the vertical axis of the eyeball o So inserts into the posterior-lateral quadrant of the eyeball to allow for abduction • In primary gaze, the SO’s tendon forms angle of 54 degrees with the A-P axis of the eyeball o The eye is pulled from the functional origin

Question 41

Pathway of the inferior oblique

Answer 41

 Origin • Floor of the orbit at a small depression on the orbital plate of the maxilla o Just posterior to the orbital margin and lateral to the nasolacrimal canal opening  Pathway • Passes posterior and lateral, following the curve of the inferior surface of the eyeball • Runs inferior to the inferior rectus muscle • Reaches the posterolateral surface of the eyeball • **path is almost parallel to SO’s tendon o The tendon of IO forms an angle of 51 degrees with A-P axis of the eyeball • Pierces Tenon’s capsule • Inserts into the sclera posterior to the equator and vertical axis of the eyeball

Question 42

Innervation of the lateral rectus

Answer 42

 Innervation • Abducens muscle (CN VI) o Enters the medial surface of the muscle posterior to its midpoint

Question 43

Blood Supply of the lateral rectus

Answer 43

 Blood supply • Muscular Branch of the lacrimal artery (branch of ophthalmic artery • Enters on the medial surface • All other EOMs receive muscular branch from the ophthalmic artery

Question 44

Action of the lateral rectus

Answer 44

 Action | • Abduction – turns the eye laterally (out)

Question 45

Innervation of medial rectus

Answer 45

 Innervation • Branch of the inferior division of CN III o entering on the inner surface of the muscle

Question 46

Blood supply of medial rectus

Answer 46

 Blood Supply | • Muscular branch of the ophthalmic artery

Question 47

Action of medial rectus

Answer 47

 Action | • Adduction – turns eye medially

Question 48

Innervation of the superior rectus

Answer 48

 Innervation • Superior division of CN III o Enters on the inferior surface of the muscle at the junction of its middle and posterior thirds o Then pierces SR and continues to the levator palpebrae superioris

Question 49

Blood Supply of superior rectus

Answer 49

 Blood Supply | • Muscular branch of the ophthalmic artery

Question 50

Actions of superior rectus

Answer 50

 Actions • Elevation • Intorsion – moves 12 o’clock position on the eye medially o Allowed because the muscle passes medial to the vertical the muscle passes medial to the vertical axis of the eyeball • Adduction o Because the muscle passes medial to the vertical axis of the eyeball

Question 51

Innervation of the inferior rectus

Answer 51

 Innervation • Branch of inferior division of CN III • Enters the ocular (medial) surface at the junction of its middle and posterior thirds

Question 52

Blood supply of inferior rectus

Answer 52

 Blood Supply | • Muscular branch of the ophthalmic artery

Question 53

Actions of inferior rectus

Answer 53

 Actions • Depression • Extorsion • Adduction  SR lies below levator palpebrae superioris  SR lies above superior oblique’s tendon and inferior oblique

Question 54

Innervation of superior oblique

Answer 54

 Innervation • CN IV • Enters the muscle superiorly and near its lateral border

Question 55

Blood supply of superior oblique

Answer 55

 Blood Supply | • Muscualr branch of the ophthalmic artery

Question 56

Actions of superior oblique

Answer 56

 Actions • Intorsion • Depression o Because it inserts on the posterior aspect of the eyeball • Abduction o Because its tendon passes medial to the vertical axis

Question 57

Innervation of inferior oblique

Answer 57

 Innervation • Inferior division of CN III • Enters muscle on the superior surface

Question 58

Blood supply of inferior oblique

Answer 58

 Blood Supply | • Branch of infraorbital artery and muscular branch of ophthalmic artery

Question 59

Actions of inferior oblique

Answer 59

 Actions • Extortion • Elevation o Because of insertion on the posterior aspect of the eyeball • Abduction o Because its tendon passes medial to the vertical axis

Question 60

What muscles elevate the eye?

Answer 60

 Superior Rectus (PRIMARY ACTION) |  Inferior Oblique

Question 61

What muscles depress the eye?

Answer 61

 Inferior Rectus (PRIMARY ACTION) |  Superior Oblique

Question 62

What muscles abduct the eye?

Answer 62

 Superior Oblique  Inferior Oblique  Lateral Rectus (PRIMARY ACTION)

Question 63

What muscles adduct the eye

Answer 63

 Superior rectus  Inferior rectus  Medial rectus (PRIMARY ACTION)

Question 64

What muscles intort the eye

Answer 64

 Superior rectus |  Superior oblique (PRIMARY ACTION)

Question 65

What muscles extort the eye

Answer 65

 Inferior rectus |  Inferior Oblique (PRIMARY ACTION)

Question 66

Definition of vision

Answer 66

 Refers to simulataneous movement of both eyes in the same direction to keep the two eyes fixated on an object

Question 67

Yoke muscles

Answer 67

* Muscles in each eye that work at the same time and in the same direction to accomplish aversion * If the muscles aren’t yoked, the patient gets diplopia

Question 68

Sherrington's law of reciprocal innervation

Answer 68

 Contraction of a muscle is accompanied by a simultaneous proportional relaxation of the antagonist muscles

Question 69

Synergists

Answer 69

 Two or more muscles that move the eye in the same direction

Question 70

Primary gaze

Answer 70

 All six EOMs are exerting contraction sufficient to keep the eye centered in the palpebral fissure  EOMs are constantly active with low levels of tonic innervation  No single EOM acts alone

Question 71

Physiological H

Answer 71

 Clinical test used to evaluate EOMs clinically  Start with transilluminator directly in front of patient (primary position)  Then move the light in the shape of an H  Serves to move the eyes to a position where the optic axis (anterior-posterior axis) of the eyeball is aligned with the muscle you want to test • At this point the muscle becomes a pure elevator or a pure depressor if discussing SR, SO, IR or IO  ***Make sure to see the light reflex at all times***

Question 72

What angle must the superior rectus turn in order to line up the muscle plane with the A-P axis of the eyeball

Answer 72

* Abducted 23 degrees * Up and to the right or left * At this point the muscle’s axis is lined up with the A-P axis of the eyeball, so its action of adduction is cancelled and its action of elevation increases * When the eye is abducted, the superior rectus becomes the only evevator of the eye

Question 73

What angle must the inferior rectus turn in order to line up the muscle plane with the A-P axis of the eyeball

Answer 73

* Abducted 23 degrees * At this point the muscle’s axis is lined up with the A-P axis of the eyeball, so its action of adduction is cancelled and its action of depression increases

Question 74

What angle must the superior oblique turn in order to line up the muscle plane with the A-P axis of the eyeball

Answer 74

* Adducted about 54 degrees * At this point the muscle’s axis is lined up with the A-P axis of the eyeball, so its action of abduction is cancelled and its action of depression increases * When the eye is adducted the superior oblique becomes the only depressor of the eye

Question 75

What angle must the inferior oblique turn in order to line up the muscle plane with the A-P axis of the eyeball

Answer 75

* Adducted about 51 degrees * At this point the muscle’s axis is lined up with the A-P axis of the eyeball, so its action of abduction is cancelled and its action of elevation increases * When the eye is adducted the inferior oblique becomes the only elevator of the eye

Question 76

What happens in extreme abduction?

Answer 76

* The superior rectus becomes the primary elevator of the eye * The inferior rectus becomes the primary depressor of the eye

Question 77

What happens in extreme adduction?

Answer 77

eye in extreme adduction • The superior oblique becomes the primary depressor of the eye • The inferior oblique becomes the primary elevator of the eye

Question 78

Strabismus

Answer 78

 A manifest misalignment of the eyes so the point in different directions  Results in diplopia  Esotropia • One or both eyes turn in towards the nose  Exotropia • One or both eyes deviate away from the nose

Question 79

What can cause a decrease in EOM function?

Answer 79

o Damage to the muscle’s nerve (LR6 SO4)3 o Restriction of the agonist due to fibrosis or fluid accumulating by the muscle or entrapment of the muscle or muscle fascia o Restriction of the antagonist due to entrapment of the muscle or muscle fascia o To check muscle restriction  Anesthetize the eye  Use a Q-tip to try physically moving the eye • If it will not move then muscle restriction should be suspected

Question 80

Tenon's Capsule

Answer 80

o AKA fascia bulbi o A dense sheet of connective tissue that surrounds the eyeball from near the corneoscleral junction (limbus) to the optic nerve o Separates the eueball from the orbital fat o Forms a socket for the eyeball to sit in o Lies between the bulbar conjunctiva and the sclera  Bulbar conj lies external to Tenon’s capsule

Question 81

Functions of Tenon's capsule

Answer 81

 Acts as a barrier to prevent the spread of orbital infections to the globe  Positions and supports the eyeball in the orbit  Permits the extraocular muscles to smoothly move the eyeball • Very little movement occurs between Tenon’s capsule and the eyeball • The eyeball and capsule move together on the bed of orbital fat

Question 82

Attachments of Tenon's capsule

Answer 82

 Anteriorly • Firmly attached to the sclera about 1.5 mm behind the limbus  Posteriorly • Fuses with o Sclera around the exit of the optic nerve o Dura mater of the meninges around the optic nerve

Question 83

Tenon's Space

Answer 83

 Potential space between the episclera (outermost layer of the sclera) of the eyeball and Tenon’s capsule  Potential space in which fluids due to trauma or inflammation can accumulate

Question 84

Structures that pierce Tenon's capsule and where pierced

Answer 84

 Tendons of the extraocular muscles • Tenon’s capsule forms a tubular sleeve that covers the tendons of the EOMs and reflects back onto the muscles to be continuous with the muscle’s fascia  Long and Short Posterior Ciliary Nerves and Arteries • LPCN, SPCN, LPCA, SPCA • Pierce the posterior part  Vortex veins • Pierce the posterior part of the capsule as they leave the eyeball to enter the ophthalmic veins • Drain the choroid layer of the eyeball • Medial and lateral superior vortex veins drain into superior ophthalmic vein • Medial and lateral inferior vortex veins drain into inferior ophthalmic vein  Optic Nerve • Pierces the posterior part of the capsule

Question 85

Structures continuous with Tenon's capsule

Answer 85

 Muscle fascia of EOMs

Question 86

Medial Check Ligament

Answer 86

 Formed by the muscle fascia of the medial rectus  Attachments • Lacrimal bone behind the posterior lacrimal crest

Question 87

Functions of medial check ligament

Answer 87

* Limits further lateral movement of the eyeball during abduction * The medial rectus pulls on the inelastic medial check ligament

Question 88

Lateral check ligament

Answer 88

 Formed by the muscle fascia of the lateral rectus  Attachments • Lateral orbital tubercle on the zygomatic bone

Question 89

Functions of lateral check ligament

Answer 89

* Limits further medial movement of the eyeball during adduction * The lateral rectus pulls on the inelastic lateral check ligament

Question 90

Suspensory Ligament of Lockwood

Answer 90

o Formed by Tenon’s capsule and the thickened muscle fascia of the inferior rectus and inferior oblique o Hammock-like dense connective tissue sheet o Extends from the zygomatic bone at the lateral orbital tubercle to the lacrimal bone

Question 91

Attachments of suspensory ligament of Lockwood

Answer 91

 Suspensory ligament of Lockwood, along with an anterior extension from the muscle fascia of the inferior rectus, attaches to the inferior edge of the tarsal plate

Question 92

Functions of suspensory ligament of lockwood

Answer 92

 When a person looks down it helps with pulling down the lower eyelid  Maintains appropriate alignment of the lid with the eyeball  Supports the eyeball  Maintain the eyeball’s position in the orbit, especially if the bones of the orbital floor are damaged or removed • Acts like a sling to prevent the eyeball from dropping into the maxillary sinus

Question 93

Expansion between the levator palpebrae superioris and the superior rectus

Answer 93

 Thinner than check ligaments • Extends between the fascia of LPS (just posterior to its aponeurosis) and SR  Attachments • Superior conjunctiva’s fornix  Function • Allows the two muscles to work together o If the eyeball is elevated then the upper eyelid is also raised

Question 94

Expansion between the inferior rectus and inferior oblique

Answer 94

 Muscle fascia of the inferior rectus is thickened on the underside and blends with the muscle fascia of the inferior oblique  The muscle fascias help form the suspensory ligament of Lockwood

Question 95

Role of Tenon's capsule during enucleation of the eyeball and placement of a prosthetic eye

Answer 95

o Enucleation of the eyeball  Removal of the eyeball • Cut the optic nerve and detach EOMs o Tenon’s capsule should be preserved to serve as a socket for the prosthetic eye  Medpore Sphere Implant • Placed in Tenon’s capsule and EOMs are attached to the medpore sphere implant • Made of hydroxyapatite, a bone like material that EOMs can be sewn into o This is done because Tenon’s capsule is continuous with the EOM muscle fascia, so when the EOMs contract, Tenon’s capsule will move  About 6 months later the prosthetic eye is attached onto the medpore sphere with a pin • The prosthetic eye will move like a normal eye  Based on Herring’s law of equal innervation, the EOMs of the prosthetic eye will get the same innervation of the normal eye

Question 96

Reasons to perform enucleation

Answer 96

 Blind, painful eye  Intraocular malignant tumors  Intraocular tumors  Blind, deformed eye