Exam 1 - 003 The Extraocular Muscles and Tenon's Capsule Flashcards
How to define the movements of the eye
with respect to the anterior pole of the eye
use the center of the cornea/pupil as the anterior pole
Elevation
Rotation of the eye upward
Depression
Rotation of the eye downward
Abduction
Rotation of the eye laterally
Adduction
Rotation of the eye medially
Intortion
12 o’clock position of the eye rotates medially
Extortion
12 o’clock position of the eye rotates laterally
Fick’s axes
Horizontal
Vertical
Sagittal
Horizontal Axis
AKA transverse axis
Allows for elevation and depression
Vertical Axis
Allows for abduction and adduction
Sagittal Axis
Allows for rotation (intorsion and extorsion)
Duction
Refers to the movement of one eyeball (monocular eye movements)
Movements that each eye can do alone
Agonist
The muscle that moves an eye in a given direction
Antagonist
The muscle in the same eye as the agonist that moves the eye in the opposite direction of the agonist
Sherrington’s Law of reciprocal innervation
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)
Hering’s Law
both muscles moving the eyes into a particular direction will simultaneously receive equal innervation from the CNS.
Version
Simultaneous movement of both eyes in the same direction to keep the two eyes fixated on an object (yoke)
Yoked muscles
two eyes that are coordinated so that they move together
Levoversion
Both eyes look left
Dextroversion
Both eyes look right
Infraversion
Both eyes look down
Supraversion
Both eyes look up
What extraocular muscles originate from the common tendinous ring?
Superior Rectus
Inferior Rectus
Lateral Rectus
Medial Rectus
Origins of superior rectus
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
Origins of inferior rectus
Origin: common tendinous ring (annulus of Zinn)
Origin of medial rectus
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
Origin of lateral rectus
Origin: common tendinous ring (annulus of Zinn)
Origin of superior oblique
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
Origin for the inferior oblique
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
Insertions of the rectus muscles
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
Spiral of Tillaux
- A line connecting the rectus muscle insertions
* Starts at the superior rectus and ends at the medial rectus forming an inward spiral
Insertions of the obliques
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
Insertion of Superior Oblique
- Inserts onto the upper posterolateral quadrant of the eyeball
- Action: depresses the eyeball (NOT elevate)
Inferior Oblique
• 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
Which EOM attaches closest to the macula?
Inferior oblique – attaches to the sclera overlying the macula
Pathway of the lateral rectus
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
Pathway of the Medial Rectus
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
Pathway of the Superior Rectus
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)
Pathway of the inferior rectus
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
Pathway of the superior oblique
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
Pathway of the inferior oblique
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
Innervation of the lateral rectus
Innervation
• Abducens muscle (CN VI)
o Enters the medial surface of the muscle posterior to its midpoint
Blood Supply of the lateral rectus
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
Action of the lateral rectus
Action
• Abduction – turns the eye laterally (out)
Innervation of medial rectus
Innervation
• Branch of the inferior division of CN III
o entering on the inner surface of the muscle
Blood supply of medial rectus
Blood Supply
• Muscular branch of the ophthalmic artery
Action of medial rectus
Action
• Adduction – turns eye medially
Innervation of the superior rectus
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
Blood Supply of superior rectus
Blood Supply
• Muscular branch of the ophthalmic artery
Actions of superior rectus
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
Innervation of the inferior rectus
Innervation
• Branch of inferior division of CN III
• Enters the ocular (medial) surface at the junction of its middle and posterior thirds
Blood supply of inferior rectus
Blood Supply
• Muscular branch of the ophthalmic artery
Actions of inferior rectus
Actions
• Depression
• Extorsion
• Adduction
SR lies below levator palpebrae superioris
SR lies above superior oblique’s tendon and inferior oblique
Innervation of superior oblique
Innervation
• CN IV
• Enters the muscle superiorly and near its lateral border
Blood supply of superior oblique
Blood Supply
• Muscualr branch of the ophthalmic artery
Actions of superior oblique
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
Innervation of inferior oblique
Innervation
• Inferior division of CN III
• Enters muscle on the superior surface
Blood supply of inferior oblique
Blood Supply
• Branch of infraorbital artery and muscular branch of ophthalmic artery
Actions of inferior oblique
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
What muscles elevate the eye?
Superior Rectus (PRIMARY ACTION)
Inferior Oblique
What muscles depress the eye?
Inferior Rectus (PRIMARY ACTION)
Superior Oblique
What muscles abduct the eye?
Superior Oblique
Inferior Oblique
Lateral Rectus (PRIMARY ACTION)
What muscles adduct the eye
Superior rectus
Inferior rectus
Medial rectus (PRIMARY ACTION)
What muscles intort the eye
Superior rectus
Superior oblique (PRIMARY ACTION)
What muscles extort the eye
Inferior rectus
Inferior Oblique (PRIMARY ACTION)
Definition of vision
Refers to simulataneous movement of both eyes in the same direction to keep the two eyes fixated on an object
Yoke muscles
- 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
Sherrington’s law of reciprocal innervation
Contraction of a muscle is accompanied by a simultaneous proportional relaxation of the antagonist muscles
Synergists
Two or more muscles that move the eye in the same direction
Primary gaze
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
Physiological H
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
What angle must the superior rectus turn in order to line up the muscle plane with the A-P axis of the eyeball
- 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
What angle must the inferior rectus turn in order to line up the muscle plane with the A-P axis of the eyeball
- 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
What angle must the superior oblique turn in order to line up the muscle plane with the A-P axis of the eyeball
- 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
What angle must the inferior oblique turn in order to line up the muscle plane with the A-P axis of the eyeball
- 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
What happens in extreme abduction?
- The superior rectus becomes the primary elevator of the eye
- The inferior rectus becomes the primary depressor of the eye
What happens in extreme adduction?
eye in extreme adduction
• The superior oblique becomes the primary depressor of the eye
• The inferior oblique becomes the primary elevator of the eye
Strabismus
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
What can cause a decrease in EOM function?
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
Tenon’s Capsule
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
Functions of Tenon’s capsule
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
Attachments of Tenon’s capsule
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
Tenon’s Space
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
Structures that pierce Tenon’s capsule and where pierced
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
Structures continuous with Tenon’s capsule
Muscle fascia of EOMs
Medial Check Ligament
Formed by the muscle fascia of the medial rectus
Attachments
• Lacrimal bone behind the posterior lacrimal crest
Functions of medial check ligament
- Limits further lateral movement of the eyeball during abduction
- The medial rectus pulls on the inelastic medial check ligament
Lateral check ligament
Formed by the muscle fascia of the lateral rectus
Attachments
• Lateral orbital tubercle on the zygomatic bone
Functions of lateral check ligament
- Limits further medial movement of the eyeball during adduction
- The lateral rectus pulls on the inelastic lateral check ligament
Suspensory Ligament of Lockwood
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
Attachments of suspensory ligament of Lockwood
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
Functions of suspensory ligament of lockwood
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
Expansion between the levator palpebrae superioris and the superior rectus
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
Expansion between the inferior rectus and inferior oblique
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
Role of Tenon’s capsule during enucleation of the eyeball and placement of a prosthetic eye
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
Reasons to perform enucleation
Blind, painful eye
Intraocular malignant tumors
Intraocular tumors
Blind, deformed eye
