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Ocular Anatomy - Exam 1 > Exam 1 - 003 The Extraocular Muscles and Tenon's Capsule > Flashcards

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

1
Q

How to define the movements of the eye

A

with respect to the anterior pole of the eye

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

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2
Q

Elevation

A

 Rotation of the eye upward

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3
Q

Depression

A

 Rotation of the eye downward

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4
Q

Abduction

A

 Rotation of the eye laterally

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5
Q

Adduction

A

 Rotation of the eye medially

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6
Q

Intortion

A

 12 o’clock position of the eye rotates medially

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7
Q

Extortion

A

 12 o’clock position of the eye rotates laterally

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8
Q

Fick’s axes

A

Horizontal
Vertical
Sagittal

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9
Q

Horizontal Axis

A

AKA transverse axis

 Allows for elevation and depression

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10
Q

Vertical Axis

A

 Allows for abduction and adduction

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11
Q

Sagittal Axis

A

 Allows for rotation (intorsion and extorsion)

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12
Q

Duction

A

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

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13
Q

Agonist

A

 The muscle that moves an eye in a given direction

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14
Q

Antagonist

A

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

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15
Q

Sherrington’s Law of reciprocal innervation

A

 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)

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16
Q

Hering’s Law

A

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

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17
Q

Version

A

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

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18
Q

Yoked muscles

A

two eyes that are coordinated so that they move together

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19
Q

Levoversion

A

Both eyes look left

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20
Q

Dextroversion

A

Both eyes look right

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21
Q

Infraversion

A

Both eyes look down

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22
Q

Supraversion

A

Both eyes look up

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23
Q

What extraocular muscles originate from the common tendinous ring?

A

Superior Rectus
Inferior Rectus
Lateral Rectus
Medial Rectus

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24
Q

Origins of superior rectus

A

 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

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25
Q

Origins of inferior rectus

A

 Origin: common tendinous ring (annulus of Zinn)

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26
Q

Origin of medial rectus

A

 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

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27
Q

Origin of lateral rectus

A

 Origin: common tendinous ring (annulus of Zinn)

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28
Q

Origin of superior oblique

A

 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

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29
Q

Origin for the inferior oblique

A

 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

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30
Q

Insertions of the rectus muscles

A 
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
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31
Q

Spiral of Tillaux

A
  • A line connecting the rectus muscle insertions

* Starts at the superior rectus and ends at the medial rectus forming an inward spiral

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32
Q

Insertions of the obliques

A

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

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33
Q

Insertion of Superior Oblique

A
  • Inserts onto the upper posterolateral quadrant of the eyeball
  • Action: depresses the eyeball (NOT elevate)
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34
Q

Inferior Oblique

A

• 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

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35
Q

Which EOM attaches closest to the macula?

A

 Inferior oblique – attaches to the sclera overlying the macula

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36
Q

Pathway of the lateral rectus

A

 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

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37
Q

Pathway of the Medial Rectus

A

 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

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38
Q

Pathway of the Superior Rectus

A

 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)

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39
Q

Pathway of the inferior rectus

A

 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

40
Q

Pathway of the superior oblique

A

 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

41
Q

Pathway of the inferior oblique

A

 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

42
Q

Innervation of the lateral rectus

A

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

43
Q

Blood Supply of the lateral rectus

A

 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

44
Q

Action of the lateral rectus

A

 Action

• Abduction – turns the eye laterally (out)

45
Q

Innervation of medial rectus

A

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

46
Q

Blood supply of medial rectus

A

 Blood Supply

• Muscular branch of the ophthalmic artery

47
Q

Action of medial rectus

A

 Action

• Adduction – turns eye medially

48
Q

Innervation of the superior rectus

A

 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

49
Q

Blood Supply of superior rectus

A

 Blood Supply

• Muscular branch of the ophthalmic artery

50
Q

Actions of superior rectus

A

 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

51
Q

Innervation of the inferior rectus

A

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

52
Q

Blood supply of inferior rectus

A

 Blood Supply

• Muscular branch of the ophthalmic artery

53
Q

Actions of inferior rectus

A

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

54
Q

Innervation of superior oblique

A

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

55
Q

Blood supply of superior oblique

A

 Blood Supply

• Muscualr branch of the ophthalmic artery

56
Q

Actions of superior oblique

A

 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

57
Q

Innervation of inferior oblique

A

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

58
Q

Blood supply of inferior oblique

A

 Blood Supply

• Branch of infraorbital artery and muscular branch of ophthalmic artery

59
Q

Actions of inferior oblique

A

 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

60
Q

What muscles elevate the eye?

A

 Superior Rectus (PRIMARY ACTION)

 Inferior Oblique

61
Q

What muscles depress the eye?

A

 Inferior Rectus (PRIMARY ACTION)

 Superior Oblique

62
Q

What muscles abduct the eye?

A

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

63
Q

What muscles adduct the eye

A

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

64
Q

What muscles intort the eye

A

 Superior rectus

 Superior oblique (PRIMARY ACTION)

65
Q

What muscles extort the eye

A

 Inferior rectus

 Inferior Oblique (PRIMARY ACTION)

66
Q

Definition of vision

A

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

67
Q

Yoke muscles

A
  • 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
68
Q

Sherrington’s law of reciprocal innervation

A

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

69
Q

Synergists

A

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

70
Q

Primary gaze

A

 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

71
Q

Physiological H

A

 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

72
Q

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

A
  • 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
73
Q

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

A
  • 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
74
Q

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

A
  • 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
75
Q

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

A
  • 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
76
Q

What happens in extreme abduction?

A
  • The superior rectus becomes the primary elevator of the eye
  • The inferior rectus becomes the primary depressor of the eye
77
Q

What happens in extreme adduction?

A

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

78
Q

Strabismus

A

 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

79
Q

What can cause a decrease in EOM function?

A

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

80
Q

Tenon’s Capsule

A

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

81
Q

Functions of Tenon’s capsule

A

 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

82
Q

Attachments of Tenon’s capsule

A

 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

83
Q

Tenon’s Space

A

 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

84
Q

Structures that pierce Tenon’s capsule and where pierced

A

 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

85
Q

Structures continuous with Tenon’s capsule

A

 Muscle fascia of EOMs

86
Q

Medial Check Ligament

A

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

87
Q

Functions of medial check ligament

A
  • Limits further lateral movement of the eyeball during abduction
  • The medial rectus pulls on the inelastic medial check ligament
88
Q

Lateral check ligament

A

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

89
Q

Functions of lateral check ligament

A
  • Limits further medial movement of the eyeball during adduction
  • The lateral rectus pulls on the inelastic lateral check ligament
90
Q

Suspensory Ligament of Lockwood

A

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

91
Q

Attachments of suspensory ligament of Lockwood

A

 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

92
Q

Functions of suspensory ligament of lockwood

A

 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

93
Q

Expansion between the levator palpebrae superioris and the superior rectus

A

 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

94
Q

Expansion between the inferior rectus and inferior oblique

A

 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

95
Q

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

A

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

96
Q

Reasons to perform enucleation

A

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

Ocular Anatomy - Exam 1 (5 decks)

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