Flashcards in Orbit Deck (66)
What is the common fibrous ring?
the common origin of four of the extrinsic eye muscles
What are the four recti orbital muscles?
superior, medial, inferior, and lateral rectus muscles. These are arranged in a cone whose apex is the common tendinous ring
What is the orbit bound by?
the periorbita which is the periostium lining the orbit
What is the periorbita a continuation of?
the periosteum of the surrounding spaces (infratemporal fossa and middle cranial fossa).
The four muscles are invested in their own deep fascia and this forms what structure?
the muscular cone. This is not an official anatomical term but a concept that helps organize our understanding of the orbit.
Both compartments, i.e. the orbit exterior to and interior to the cone of muscles, are filled with what?
What is the function of the fat inside and surrounding the muscular cone?
Fat at body temperature is an incompressible liquid that is responsible for maintaining the position of the eyeball anterior in the orbit against the rearward pull of the extrinsic eye muscles.
What does The suspensory ligament of the orbit do?
it suspends the globe (eyeball) in the orbit against the force of gravity. This and the medial and lateral ligaments are thickened fascia of the muscular cone.
Where is the orbitalis muscles located, what is its purpose, and what is it innervated by?
it plugs the gap left open in the posterior, inferior region of the orbit by the inferior orbital fissure in order to keep the fat of the orbit in place so that the eyes maintain their forward position in the orbit. it is a smooth muscle innervated by sympathetics
What muscles are located in the upper and lower eyelids?
the tarsal muscles which are innervated by sympathetics and contribute to being able to open and close the eyelids
What is the difference between the ptosis associated with the endophthalmia in Horner's Syndrome and the ptosis associated with lesion to the obicularis oculi?
ptosis associated with obicularis coulee is caused by a lesion of CN VII, while Horner's syndrome ptosis/drooping is caused by loss of sympathetic innervation to the superior and inferior palpebral muscles and tarsal plates of the eyelids (and to the head in general).
What are some of the symptoms of Horner's syndrome?
(loss of sympathetic innervation to the head)
causes lack of sweating on the affected side of the head, pupil constriction, superior tarsal muscle and orbitalis are paralyzed, leading to dropping of the eyelids and endophthalmia
How does lack of lacrimal gland secretion cause vision loss?
lack of tears cause the eyes to become more opaque, leading to slow loss of vision
common in older people, bed ridden people
this is why the eyes are closed during surgery
Describe the route of tear drainage.
Tears are produced by the lacrimal gland in the upper lateral aspect of the orbit and drain into the conjunctive sac to the nasolacrimal duct located in the lacrimal bone located on the medial, inferior aspect of the orbit, which then drains to the inferior meatus
Describe the course of the superior and inferior oblique muscles.
The superior oblique m. courses anteriorly and hooks around the trochlea on the medial orbital wall a little anterior to the eyeball, then makes an almost 180 degree turn posteriorly to insert on the medial, superior side of the eyeball just medial or even partially underneath the superior rectus muscle in a slightly posterior position to the midline of the eyeball. Thus, contraction causes the eye to move down and lateral and also to perform intorsion.
The inferior oblique takes a horizontal course under the inferior aspect of the eye, coursing below the inferior rectus to insert on the lateral, slightly posterior aspect of the eyeball just inferior or even partially beneath the lateral rectus. Thus, contraction causes the eyeball to look lateral, up, and also to perform extorsion
What four nerves can be found inside the tendinous ring?
both divisions of CN III, CN VI, and the nasociliary n. of CN V1 all through the superior orbital fissure laterally on the posterior wall of the orbit and
CN II and the ophthalmic artery through the optic canal of the greater wing of the sphenoid bone more medially on the posterior wall
What structures pass through the superior orbital fissure just above, and lateral the tendinous ring?
A. Branches of V1: Frontal (superior to orbit) and lacrimal (lateral to orbit)
B. CN IV, which innervates the SO, which is outside the cone of muscles.
C. Superior ophthalmic vein
Below the tendinous ring through the superior orbital fissure is what structure?
the inferior ophthalmic vein
What bones make up the posterior wall of the orbit?
greater win of the sphenoid, front, ethmoid, lacrimal, palatine, maxilla
What structures do the superior and inferior ophthalmic veins connect?
the angular and facial veins and the cavernous sinus
What muscle does the frontal n. run on top of?
superior levator palpebral m.
What muscle does the lacrimal n. run on top of?
the lateral rectus
Where can the nasociliary n. be found coursing?
inside the muscular cone, so it will be seen underneath the superior rectus posteriorly and then will course medially on top of the medial rectus muscle where it gives off the anterior and posterior ethmoid branches
What artery follows a similar route to the nasociliary n.?
the ophthalmic artery
What does the trochlear n. innervate?
superior oblique. It is found superficial to the muscles of the tendinous ring
How does CN III course in the orbit and what does it innervate?
before entering the tendinous ring, CN III has already split into superior and inferior branches. The superior branch carries fibers to the levator palpebrae superioris and the superior rectus and the inferior branch carries fibers to the medial and inferior rectus and the inferior oblique and to the ciliary ganglion
What innervates the lateral rectus?
How are GSA fibers transmitted to the globe?
Fibers come from the nasociliary nerve and some continue down the long ciliary n. to the globe and others pass through the ciliary ganglion via a connection from the nasociliary n. to the short ciliary n. to the globe. Also contribution from the anterior ciliary nerve fibers from the lacrimal nerve
How are GVE sympathetics transmitted to the globe?
some via the nasociliary and continuing on to to the long ciliary n. and others pass through the ciliary ganglion (via the 'sympathetic root' from their course on the internal carotid plexus and ophthalmic artery) to the short ciliary n. to the globe
How are GVE parasympathetics transmitted to the globe?
preganglionics come from CN III where they cross over to synapse in the ciliary ganglion. Postganglionic fibers then continue via the short ciliary n. to the globe with GVE sympathetics and GSA fibers
What are the GVE parasympathetics in the globe do?
innervate the ciliary muscle which changes the shape of the lens for focusing (accommodation) and the constrictor muscle of the pupil (sphincter pupillae)
What are the GVE sympathetics in the globe do?
dilator pupillae for dilation of the pupil
What is the first branch of the ophthalmic a. once it exits the optic canal?
the central retinal artery
Describe the course of the ophthalmic a.
gives off the central retinal artery (loss of this artery will cause you to go blind!!) that pierces into the optic n. shortly after exiting through the optic canal and a posterior ciliary branch to the posterior eye, then gives off a lacrimal branch which follows the course of the lacrimal n. (which then gives off an anastomosing branch to a branch of the middle meningeal a., a zygomatic branch that follows the course of the zygomatic n. of V2, and continues anteriorly to give off an anterior ciliary branch to the anterior eye), and continues on to follow the course of the nasociliary n, first giving off a supraorbital branch, then giving off anterior and posterior ethmoidal branches, then finally a dorsal branch that courses underneath the sling of the superior orbital m. and a supratrochlear branch at the same time.
What are the main veins of the orbit?
The pterygoid plexus of veins communicates into the orbit via the inferior orbital fissure, where it drains from with the infraorbital v. and the inferior ophthalmic vein coursing posteriorly from the face. The cavernous sinus communicates with the orbit via the superior orbital fissure where it drains the superior ophthalmic v. which runs anterior to posterior from the face from connections with the supraorbital, angular, and facial veins.
The motions of intorsion and extorsion are important in maintaining what?
They serve the physiological function of preserving stereopsis even as the head is tilted.
The upper division of CN III innervates which muscles?
levator palpebrae superioris and superior rectus
Origin of levator palpebrae superioris
lesser wing of sphenoid
Insertion of levator palpebrae superioris
superior tarsal plate and skin of eyelid
Action of evator palpebrae superioris
elevate the upper eyelid. NOT involved with eye movement at all
Origin of superior rectus
common tendinous ring
Insertion of superior rectus
anterior, SUPERIOR hemisphere of the eyeball
Action of superior rectus
elevation, adduction, intorsion (EADI)
The lower division of CN III innervates which muscles?
inferior rectus, medial rectus, and inferior oblique
Origin of inferior rectus, medial, lateral, and superior rectus
common tendinous ring
Insertion of inferior rectus
anterior, INFERIOR hemisphere of the eyeball
Action of inferior rectus
depression, adduction, and extorsion (DADE)
Action of medial rectus
Innervation of lateral rectus
Action of lateral rectus
Innervation of superior oblique
origin of superior oblique
body of sphenoid
Insertion of superior and inferior oblique
lateral posterior quadrant of the eyeball
Action of superior oblique
depression, abduction, and intorsion (DABI)
Innervation of inferior oblique
Action of inferior oblique
elevation, abduction, and extorsion (EABE)
Why do the superior and inferior recti mm. both adduct?
Because they both have origins that are medial to their insertions on the globe, hence they both cause medial movement (adduction) of the globe
The superior and inferior obliques are opposite, so they are ABductors
How do you test the four eye muscles that act on a multi-axis plane?
testing them involves asking the patient to abduct or adduct the eye in the direction opposite of the action of that muscle. For instance, the superior rectus is an adductor, yet it is tested by asking the patient to abduct the eye and then look up. If the patient cannot elevate the abducted eye, then there is a lesion involving that muscle
The superior orbital fissure and optic canal can be found inferior to which bone?
the lesser wing of the sphenoid
What is the most superior nerve to enter the superior orbital fissure?
the trochlear nerve
The frontal n. can be found on top of which muscle?
the levator palpebrae superioris
The lacrimal n. can be found coursing anteriorly on which muscle?
the lateral rectus
How does the nasociliary n. run?
passes superior to the optic nerve, medial across the eyeball underneath the superior rectus to the medial side in between the medial rectus and superior oblique. Gives off the long ciliary and anterior and posterior ethmoid branches
What n. enters the orbit by passing through the superior orbital fissure and through the heads of the lateral rectus?
What travels with the inferior branch of CN III?
preganglionic parasympathetic fibers that synapse at the ciliary ganglion, where its postganaglionics continue to the provide innervation to the sphincter papillae and the ciliary muscles