Week 3: Extra-Ocular Muscles Flashcards
Where do EOM originate?
The common tendon of Zinn, at the back of the eye.
- Has close anatomical relationship with superior orbital fissure, lacrimal and frontal nerves = sensory nerves
- Muscles come forward from back of orbit and inset onto eye (first 4 straight muscles- superior lateral medial and inferior, move in direction of name)
Explain the Spiral of Tillaux
- the rectus muscles pass through tenons capsule and insert into the sclera
- the muscles insert at different distances from the cornea
- measured from limbus (edge of cornea+sclera to insertion of muscle)
- the insertion pattern is a spiral with the medial rectus closest to the cornea (5.5mm) and superior rectus the furthest away from the cornea (7.4mm)
- S(8)L(7)I(6)M(5) (check this)
What is Tenon’s Capsule?
- like a big bag that surrounds extra-ocular muscles like a globe.
- is the bulk of the orbital facial system (tough membrane) (lots of fat keeps the eye in place)
- fuses posteriorly with the optic nerve sheath (sealed at back to stop infection getting from the sinuses into the eye but muscles can be susceptible to infection)
- posterior portion is thin and flexible
- posterior to the equator, it is thick and tough, suspending the globe to the periorbital tissues (role in suspensions ligaments that hold the globe in pace because eyeball is only 1/3 of portion).
What are the 6 EOM’s?
- Superior Rectus
- Inferior Rectus
- Medial Rectus
- Lateral Rectus
- Superior Oblique
- Inferior Oblique
What and where is medial rectus?
- originates on both upper and lower limb of common tendons ring and the optic nerve sheath.
- strong and shorter than others, dominant in children
- inserts along a vertical line 5.5mm from the cornea (starts at common tendons ring, runs forward and inserts on the inside of the eye.
- the horizontal plane of eye bisects the insertion
- facial expansion from muscle sheath forms the medial check ligament and attaches to medial wall of orbit.
- the superior oblique, ophthalmic artery and nasociliry nerve all lie above medial rectus
What is the anatomical journey of medial rectus?
Anatomical journey;
-up above = superior oblique
-inside we got medial wall and got nasal sinuses and ophthalmic artery runs quite close to it (gets its blood supply underneath it)
Oblique muscle to the right
Nasociliary nerve comes in through the orbit and down side of nose
What innervates the medial rectus?
Innervation is via cranial nerve III, the oculomotor nerve, and the specific branch runs along the inside of the muscle cone, on the lateral surface. (Cranial nerve is the beast nerve- supplies 4/6 muscles, lid, ciliary body = lots of work to do) - goes though brain and superior orbital fissure and along underside of muscle and inserts inside the muscle cone.
What is the Origin, Insertion, Length, Direction, Innervation, Blood Supply and Action of Medial Rectus?
- Origin: annulus of zinn
- Insertion: medially, in horizontal meridian, 5.5 mm from limbus
- Length: 40mm L, 10mm W, 4mm T
- Direction: 90 degrees
- Innervation: lower CN III
- Blood supply: Inf. Mus. Branch Of Oph. A.
- Action: adduction- inwards to middle (turns eye inwards to middle)
What and where is the Lateral Rectus?
- Originates on (stretches to) both the upper and lower limb of the common tendous ring. . .AND a process of the greater wing of the sphenoid bone (attachment). Makes it vulnerable to severe head trauma because greater wing of sphenoid bone is bat shaped bone at back of the eye and if a lot of trauma then can affect lateral Rectus)
•Inserts parallel to medial rectus 6.9 mm from the cornea. (Tendon 9.2 mm wide, 8.8 long). (Runs similar course to Rectus, run parallel but couple mm back from MR)
•Facial expansion from muscle sheath forms the lateral check ligament and attach to lateral wall of orbit at Whitnalls tubercle. (Lateral check ligament holds it in place)
What innervates the lateral rectus?
> Innervated by the abducens nerve, Cranial n VI which enters the muscle on the medial surface. (It’s nerve)
•The lacrimal artery and nerve run along the superior border. (Lacrimal artery runs in close Association with it)
•The abducens n., ophthalmic artery and ciliary ganglion lie medial to the lateral rectus and between it and the optic nerve.
What’s the Origin, insertion, length, direction, innervation, blood supply and action of the lateral rectus?
Origin: annulus of zinn
•Insertion: laterally, in horizontal meridian, 6.9mm from limbus
•Length: 40 mm L, 9 mm W, 8 mm T
•Direction: 90o
•Innervation: CN VI
•Blood supply: Inf. Mus. Branch Of Oph. A.
•Action: abduction or outwards
What and where is the superior rectus?
Originate on superior limb of the tendonous ring, and optic nerve sheath.
-Tall basketball player
•Muscle passes forward underneath the levator, but the two sheaths are connected resulting in coordinated movements.
- Like a sandwich, top = levator muscle which moves the lid, middle = superior oblique muscle
•Insertion 7.4 mm from limbus, and obliquely.(8mm remember, oblique = horizontal and torsion function)
•The angle from the origin to the insertion is 23° beyond the sagital axis. (see overhead)
What is the superior rectus journey?
Superior Rectus Journey;
- Frontal nerve runs above the s. rectus & levat.
•The nasociliary nerve and ophthalmic artery run below.
•The tendon for insertion of the superior oblique muscle runs below (important for ops) the anterior part of the superior rectus.
What innervates the superior rectus?
-Innervationis via superior division of CN III (cranial nerve 3), from the inferior surface; additional branches make their way to the levator. (To give lid some functions)
What is the action of the superior rectus muscle?
> Eye will sit low if the muscle is not working bc not pulling eye up
Primary action is elevation . . But since the insertion on the globe is lateral as well as superior, contraction will produce rotation about the vertical axis toward midline
•Thus secondary action is adduction (rotates the eye in towards the nose)
•Finally, because the insertion is oblique, contraction produces torsion nasally Intorsion.
-Because muscle runs @ angle to Fick’s axis, contraction not confined to one axis.
