HS2-9 Eye Flashcards
Describe the volume composition of the orbit. (3)
eyeball (globe) = 20%
fat = 50-60%
remainder = muscles, nerves, vessels
Where is the diameter of the orbit greatest?
behind rim
What separates the two orbits? (2)
ethmoidal sinuses
upper part of nasal cavity
The superior orbital fissure leads to
the middle cranial fossa
What structures pass through the superior orbital fissure? (5)
CN III
CN IV
CN V1
CN VI
ophthalmic vein
The optic canal leads to
the middle cranial fossa
What structures pass through the optic canal? (2)
optic nerve
ophthalmic artery (a branch of internal carotid)
The inferior orbital fissure leads to (2)
infratemporal fossa
pterygopalatine fossa
What structures pass through the inferior orbital fissure? (3)
zygomatic nerve (branch of V2)
infraorbital nerve (branch of V2)
maxillary vessels
Describe the pathway of structures that leads to the infraorbital foramen.
infraorbital groove → infraorbital canal → infraorbital foramen
What structures pass through the infraorbital foramen?
infraorbital neurovascular bundle
The nasolacrimal canal leads to
the nasal cavity
What structures pass through the nasolacrimal canal?
nasolacrimal duct
The ethmoidal foramina lead to
the nasal cavity
What structures pass through the ethmoidal foramina? (2)
branches of V1
ophthalmic vessels
Describe the outer layer of the eyelid.
thin skin
Describe the inner layer of the eyelid.
lined with transparent inner mucous membrane = conjunctiva
The conjunctiva of the eyelid is continuous with
the epithelium of the cornea
The inner and outer layers of the eyelids enclose what space?
conjunctival sac
What is the functional advantage of the conjunctiva?
conjunctiva allows eyelid to move more easily over globe
What two structures comprise the skeleton of the eyelid?
orbital septum
tarsal plates
What is the orbital septum?
fibrous membrane continuous with orbital periosteum
What are tarsal plates?
dense bands of fibrocartilage that give eyelids their rounded shape
What structure is responsible for giving eyelids their rounded shape?
tarsal plates
What are the three primary muscles associated with the eyelids?
levator palpebrae superioris
superior tarsal muscle
orbicularis oculi
What two muscles are responsible for opening the eyelids?
levator palpebrae superioris (stronger)
superior tarsal muscle
Where does the levator palpebrae superioris insert?
inserts onto skin of eyelid
What innervates the levator palpebrae superioris?
oculomotor nerve (CN III)
What is the origin and insertion of the superior tarsal muscle?
origin = underside of levator palpebrae superioris
insertion = tarsal plate
What innervates the superior tarsal muscle?
sympathetic fibers from the superior cervical ganglion
What muscle is responsible for closing the eyelids?
orbicularis oculi
What innervates the orbicularis oculi?
facial nerve (CN VII)
What are the major functions of eye moisture? (2)
keep cornea and conjunctiva moist
remove irritants
Describe the significance of the lacrimal gland in tear production.
lacrimal gland secretes lacrimal fuid, the primary aqueous component of the tear film
Describe the nutrient-providing function of lacrimal fluid in tears.
provides nutrients and dissolved O2 for avascular cornea
What are tarsal glands?
modified sebaceous glands embedded in tarsal plates
What do tarsal glands produce? (2)
oily secretion that:
contributes to tear film
lubricates edges of eyelids
Describe the drainage pathway associated with the lacrimal gland of orbit. (7)
lacrimal gland → superior/inferior puncta → canaliculi → lacrimal sac → nasolacrimal duct → inferior nasal meatus → nasal cavity
Describe the pathway of innervation to the lacrimal gland. (5)
preganglionic secretomotor fibers conveyed by greater petrosal nerve (branch of CN VII)
then conveyed by nerve of pterygoid canal
synapse and pterygopalatine ganglion
postganglionic fibers travel with zygomatic nerve (branch of CN V2)
then travel with lacrimal nerve (branch of CN V1) to lacrimal gland
What is Tenon’s capsule/bulbar fascia?
thin fascial sheath enveloping globe, from optic nerve to corneoscleral junction
What is the function of Tenon’s capsule/bulbar fascia?
forms socket (support) for globe
separates globe from orbital fat
checks and coordinates movements of ocular muscles
What are the three axes of global movement? List the movements associated with each axis.
transverse axis = elevation, depression
vertical axis = medial/adduction, lateral/abduction
longitudinal axis =
What are the six extrinsic extraocular muscles?
in pairs of antagonists:
superior and inferior rectus
medial and lateral rectus
superior and inferior oblique
What is the annulus of Zinn?
fibrous ring surrounding optic canal that is part of superior orbital fissure
What is the origin of all the extraocular rectus (superior/inferior/medial/lateral) muscles?
annulus of Zinn
What is the origin of the levator palpebrae superioris?
bone near optic canal
What is the origin of the superior oblique (an extraocular muscle)?
bone near optic canal
What is the origin of the inferior oblique?
antero-medial aspect of orbital floor
Describe the movements/actions associated with the superior and inferior rectus, which are EOMs.
elevation (superior rectus)
depression (inferior rectus)
Describe the movements/actions associated with the medial and lateral rectus, which are EOMs.
adduction (medial rectus)
abduction (lateral rectus)
Describe the movements/actions associated with the superior and inferior obliques, which are EOMs.
depression (superior oblique - moves pupil down and out)
elevation (inferior oblique - moves pupil up and out)
When do the superior and inferior obliques (EOMs) function more efficiently?
when the globe has already been adducted by the medial rectus
When do the superior and inferior rectus (EOMs) function more efficiently?
when the globe has already been abducted by the lateral rectus
Sketch a diagram of the six tests of extraoecular eye movements. List the associated muscle for each movement.
List the sources of innervation for the six extraocular muscles.
superior rectus = superior ramus of CN III
inferior rectus = inferior ramus of CN III
lateral rectus = CN VI (think LR6)
medial rectus = inferior ramus of CN III
superior oblique = CN IV (think SO4)
inferior oblique = inferior ramus of CN III
What muscles of the orbit does CN III innervate?
superior ramus of CN III:
levator palpebrae superioris
superior rectus
inferior ramus of CN III:
inferior rectus
medial rectus
inferior oblique
The levator palpebrae superioris is innervated by
the superior ramus of CN III
What divisions of the trigeminal nerve are relevant to the orbit? (1 +3, 1 +2)
opthalmic division of trigeminal nerve (CN V1), which further branches into:
frontal nerve
lacrimal nerve
nasociliary nerve
maxillary division of trigeminal nerve (CN V2), which further branches into:
infraorbital nerve
zygomatic nerve
How does the frontal nerve further subdivide in the context of the orbit?
frontal nerve → supratrochlear + supraorbital nerve
Describe the function of the two branches of the frontal nerve in the context of the orbit.
supratrocheal nerve (more medial) = sensory supply to upper eyelid and forehead
supraorbital nerve (more lateral) = sensory supply to upper eyelid, forehead, and scalp
What is the function of the lacrimal nerve in the context of the orbit? (2)
sensory supply to upper eyelid
carries postganglionic parasympathetic fibers to lacrimal gland
What is the function of the nasociliary nerve in the context of the orbit? (2)
sensory to eyeball (especially cornea) via long ciliary branches
sensory to anterosuperior part of nasal cavity
Arrange the subdivisions of the opthalmic division of the trigeminal nerve (CN V1) in terms of position.
frontal = largest and most superior
lacrimal = most lateral
nasociliary = most inferior and medial
What is the function of the infraorbital nerve in the context of the orbit?
sensory supply to:
upper lip
lower eyelid
upper dentition
What is the function of the zygomatic nerve in the context of the orbit?
sensory to skin of cheekbone
carries postganglionic parasympathetic fibers to lacrimal gland
What is the ciliary ganglion?
parasympathetic ganglion for smooth muscle of eyelid
What are the three concentric layers of the globe?
outer fibrous layer = sclera + cornea
middle vascular layer = choroid + ciliary body + iris
inner sensory layer = retina
What are the three chambers of the globe?
anterior chamber (anterior to iris)
posterior chamber (posterior to iris)
vitreous chamber (behind lens)
What structure demarcates the boundaries of the anterior and posterior chambers of the globe?
iris
What is the major refractory element of the eye?
lens
What is the function of aqueous humor? (3)
provides nutrients for avascular cornea + lens
removes metabolic waste products
generates intraocular pressure to maintain shape of globe
What is the function of the vitreous chamber?
holds retina in place
supports lens
transmits light
What is the limbus (of the eye)?
transition zone between sclera and cornea
What is the sclera? (2)
whites of the eye
provides attachment for extraocular and intrinsic muscles of the eye
What is the choroid?
pigmented and highly vascular structure that lines sclera
What is the function of the ciliary body?
anchors lens and controls its shape
thus controls focus of the lens
The ciliary processes attach to
the suspensory ligament of the lens (after crossing through the posterior chamber)
The ciliary processes secrete
aqueous humor
What structure holds the lens in the pathway of light?
suspensory ligaments
What is the function of ciliary muscle?
moves ciliary body forward and inward → decreases tension on zonular fibers → lens more spherical → better focus on retina
Is the ciliary muscle innervated via a sympathetic or parasympathetic pathway?
parasympathetic
What is the function of the iris?
regulates the size of the pupil and therefore controls amount of light reaching the retina
What are the two muscles associated with the iris?
sphincter (constrictor) pupillae muscle
dilator pupillae muscle
Differentiate between the sphincter pupillae and dilator pupillae muscles in terms of structure and innervation.
sphincter pupillae muscle = circular fibers + parasympathetic innervation
dilator pupillae = radial fibers + sympathetic innervation
The retina belongs to what nervous system?
the retina is part of the CNS
What is the optic disc?
“blind spot”
site where the optic nerve joins the retina
What vessel supplies blood to most of the retina?
central artery of retina
What is the ora serrata?
anterior termination of neural part of retina
In the context of the eye, what is accommodation?
process by which eye changes focus from distant to near objects by changing shape of lens
What muscle actions are associated with accommodation of the lens?
contraction of medial rectus muscles
constriction of pupil by sphincter pupillae muscle
What is the “near triad?”
accommodation
contraction of rectus muscles
miosis
What is miosis?
constriction of pupils
Describe the innervation pathway of the “near triad” of the eye.
under parasympathetic control:
preganglionic = oculomotor nerve
ganglion = ciliary ganglion
postganglionic = short ciliary nerves that travel to ciliary and sphincter pupillae muscles
How does a sympathetic response affect the eye? (2)
upper eyelids retract by superior tarsal muscles
pupils open widely by dilator pupillae muscle
Horner’s syndrome is caused by
loss of sympathetic innervation to the face
What are the three classic symptoms of Horner’s syndrome?
right eyelid ptosis = eyelid drooping
anhidrosis = absence of sweating
right eyelid miosis = constriction of pupil
What can cause the loss of sympathetic innervation to the face that results in Horner’s syndrome? (3)
secondary brain injury
damage to cervical sympathetic trunk
Pancost tumor
If you have partial ptosis, which muscle is nonfunctional? Which muscle is dominating?
nonfunctional = levator palepbrae superioris
dominating = superior tarsal
If a pupil is dilated but won’t constrict, which muscle is nonfunctional? Which is dominating?
nonfunctional = sphincter pupillae out
dominating = dilator pupillae
If the pupil is held down and out, which muscles are not working? Which are working?
not working = superior rectus, inferior rectus, medial rectus, inferior oblique
working = lateral rectus, superior oblique
