Orbit Flashcards
Describe the shape of the orbit, the bones that form each of its walls and the openings associated with each wall
roof is orbital plate of frontal bone and some of lesser wing of sphenoid
lateral wall is zygomatic bone and greater wing of sphenoid
floor is zygomatic, orbital floor of maxilla, and palatine bone
medial wall is frontal process of maxilla, ethmoid bone, lacrimal bone, and some body of sphenoid
optic canal between roof and lateral wall between roots of lesser wing of sphenoid
superior orbital fissure between roof and lateral wall, between greater and lesser wing
inferior orbital fissure between orbital maxilla and greater wing
List the fascias of the orbit and describe their anatomical extent and function
periorbita is the periosteum of the orbit and is continuous through the optic canal with periosteum of cranial fossa
bulbar sheath is a thin membrane which covers all of eyeball except the cornea, smooth inner surface helps lubes eye movement, perforated by tendons, ciliary vessels, and nerves
muscular fasciae surrounds all the extraocular muscles, but that around the lateral and medial recti also give off the lateral and medial check ligaments respectively, safety check for eye movement
Explain the position and significance of the common tendinous ring and list the structures that enter or leave the orbit, the openings they pass though and their anatomical course in relationship to the common tendinous ring
tendinous ring is aka annulus tendineus, surrounds the optic canal, four recti mm originate from it, optic, occulomotor, abducens, and ciliary nerves enclosed by it
see other notecards for entrances and exits
Describe the motor nerves within the orbit including their course and functions
occulomotor n does medial, sup, and inf recti mm, inferior oblique m, and levator palpebrae m, from interpeduncular fossa of midbrain, makes a sup and inf divisions in orbit, contains preganglionic parasympathetic fibers that synapse in ciliary ganglion
trochlear n arises from dorsal brainstem, sup oblique
abducens emerges at pontomedullary junction, lateral rectus
parasymp from CN3 does ciliary mm and sphincterpupillae
parasymp from facial n do lacrimation
symp fibers from sup cerv ganglion do dilator pupillae
Describe the course and functions of the sensory nerves within the orbit
optic nerve does special visceral afferent
opthalmic n provides sensory of the corneal epithelium
maxillary n and facial nerve are also somehow involved
List the origin, insertion, function and innervation of the seven ocular muscles
all but levator palpebrae insert on sclera
motor movements are easily self explanatory
recti originate on tendinous ring, sup oblique on sphenoid bone body, inf oblique on maxilla, levator palpebrae on lesser wing of sphenoid
Define the accommodation reflex and describe the anatomical and functional basis of the three distinct actions involved in the reflex.
it’s when the pupil constricts when suddenly focusing from a distant object to a near one, reason is that a more narrow aperture is needed for macro vision to block diverging angles of light, involves CN3
three actins are eye at rest, near vision increases lens convexity, and constriction of pupil
Describe the vasculature of the orbit and its clinical significance.
opthalmic artery arises from internal carotid, supplies orbital structures, gives off many branches to include the central artery of the retina (blocking this leads to blindness)
the sup and inf opthalmic veins drain to cavernous sinus and infraorbital vein, these viens connect the cavernous sinus with the facial veins and also lack valves so they allow intracranial spread of infection
what enters orbit through optic canal?
optic nerve and opthalmic artery
what enters orbit through sup orbital fissure and through tendinous ring?
occulomotor, abducens, nasociliary nn
what enters or exits orbit through sup orbital fissure and above tendinous ring?
trochlear n, frontal n (branch of opthalmic, gives off supraorbital and supratrochlear nn), lacrimal n, superior opthalmic vein
what enters or exits the orbit through the inferior orbital fissure?
inferior opthalmic vein, infraorbital and zygomatic branches of v2
oculomotor nerve damage causes?
downward and laterally oriented eyeballm diplopia, ptosis (levator palpebrae), pupillary dilation and loss of accomodation reflex (pupil contracts for near objects)
trochlear n damage causes?
extorsion of eye, maximum diplopia when looking downward and to side of head with affected trochlear n
patients tilt their heads to the side to accomodate for extorsion
abducens n damage?
horizontal diploplia, medial strabismus (inability to move eye past a point), patients compensate by rotating head
