A3 - orbit and eye Flashcards
what is the base of the orbit surrounded by?
the optic margin
describe the medial walls of the orbit
- separated by the ethmoidal sinuses and the upper parts of the nasal cavity
- lie parallel to each other
describe the lateral walls of the orbit
lie approx at a right angle
what 7 bones contribute to the orbit? (A-G)
A = frontal
B = zygomatic
C = maxilla
D = sphenoid
E = ethmoid
F = lacrimal
G = palatine
what bones contribute to the superior wall (roof) of the orbit?
frontal and sphenoid
what bones contribute to the medial wall of the orbit?
- ethmoid
- maxilla
- lacrimal
- sphenoid
what bones contribute to the inferior (floor) of the orbit?
maxilla, palatine and zygomatic
what bones contribute to the lateral wall of the orbit?
sphenoid and zygomatic
what does the superior wall of the orbit separate the orbital cavity from?
the anterior fossa
what does the inferior wall of the orbit separate the orbital cavity from?
maxillary sinus
what does the lateral wall of the orbit separate the orbital cavity from?
middle cranial fossa and the temporal fossa
what makes up the orbital margin (rim) (base)?
- supra-orbital margin : frontal bone
- medial margin : frontal process of the maxilla
- infra-orbital margin : zygomatic process of the maxilla and the zygomatic bone
- lateral margin : zygomatic process of the frontal bone and the zygomatic bone and its frontal process
what is at the apex of the orbit?
optic foramen (canal)
what does the optic canal provide passage for?
the optic nerve (CNII) and opthalmic artery to exit the skull
what is the apex of the orbit bounded by?
medially by the body of the sphenoid bone and laterally by the lesser wing of the sphenoid bone
what is the orbital apex medial to?
the superior orbital fissure
what is the depression in the roof/superior wall of the orbit?
lacrimal fossa — intended for hosting the orbital part of the lacrimal gland
describe features of the medial wall of the orbit
- the lacrimal bone and the frontal process of the maxilla build the lacrimal groove which contains the lacrimal sac
- also contains the anterior and posterior ethmoidal foramina and the trochlea
where are the ethmoidal foramina and what do they do?
- the ethmoidal foramina are found at the junction between the roof and the medial wall as a part of the frontal-ethmoidal suture
- serve as passageways for the anterior and posterior ethmoidal nerves and vessels
what is the trochlea?
- the only cartilage found in the orbit
- it is a pulley-like structure in the orbit through which the tendon of the superior oblique muscle passes
what is the most important landmark of the floor/inferior wall of the orbit?
inferior orbital fissure — separates the floor from the lateral wall, and provides passage for several neurovascular structures
what is the strongest and thickest wall of the orbit?
lateral
what does the lateral wall of the orbit contain?
superior orbital fissure, found between the greater and lesser wing of the sphenoid bone
why is there no suture between the sphenoid bone and maxilla?
they are separated by the inferior orbital fissure
what does the lacrimal fossa hold?
lacrimal gland
what does the lacrimal groove hold?
lacrimal sac
describe the anterior and posterior ethmoidal foramen
- anterior ethmoidal foramen — found at junction between superior and medial orbital walls, transmits anterior ethmoidal vein, artery and nerve
- posterior ethmoidal foramen — found at junction between superior and medial orbital walls, transmits posterior ethmoidal vein, artery and nerve
name the 6 extraocular muscles
- superior/inferior/medial/lateral rectus muscles
- superior/inferior oblique muscles
functions of eyelid
- protect eyeball from injury and excessive light
- keep cornea moist by spreading the lacrimal fluid
what are the 6 layers of the eyelid?
- skin
- subcutaneous tissue
- muscle — orbital part of orbicularis oculi muscle
- orbital septum
- tarsus — plates of the dense connective tissue present in both eyelids. superior tarsus is associated with muscles that raise the upper eyelid
- conjunctiva — thin membrane that covers the posterior surface of the eyelid and reflects onto the anterior surface of the eyeball
what are the 2 different conjunctiva?
- palpebral conjunctiva — transparent mucous membrane reflected onto the eyeball, where it is continuous with the bulbar conjunctiva
- bulbar conjunctiva — thin, transparent and loosely attached to the anterior surface (sclera or ‘white’) of the eyeball where it contains small, visible blood vessels
what do the lines of reflection of the palpebral conjunctiva onto the eyeball form?
form continuous recesses or “pockets” — the superior and inferior conjunctival fornices
label this eyelid
what do tarsal glands do?
produce a lipid secretion to prevent the eyelids from sticking together when closed
what is the medial palpebral?
ligament that connects the tarsi to the medial aspect of the orbit and provides muscle attachment for the orbicularis oculi muscle
what is the levator palpebrae superioris muscle?
- extends from the lesser wing of sphenoid to the superior tarsal plate and the skin of the upper eyelid
- elevates the upper eyelid
what is the superior tarsal?
smooth muscle fibres that are located within the levator palpebrae superioris
what is the periorbita?
the periosteum lining the orbit
what is the periorbita continuous with?
- with periosteal layer of dura mater at superior orbital fissure and optic canal
- with extra cranial periosteum at the orbital margin
- with the fascia covering the extraocular muscles and the fascial sheath of the eyeball
where is the fascial sheath of the eyeball?
extends from the optic nerve to the corneoscleral junction
what does the fascial sheath separate?
the eyeball from the surrounding periorbital fat
what are the medial and lateral check ligaments? what are they attached to and what do they do?
= triangular extensions of the sheaths pf the medial and lateral rectus ligaments
- medial : attached to lacrimal bone. limits abduction
- lateral : attached to zygomatic bone. limits adduction
how do the check ligaments form the suspensory ligament of the eye?
the check ligaments blend with the fascia of the inferior oblique and inferior rectus muscles, forming a sling to suspend the eyeball — suspensory ligament of the eye
where does the inferior check ligament arise from and what does it do?
- arises from the inferior rectus muscle
- when the gaze is directed downwards, the inferior check ligament retracts to the inferior eyelid
- work with the oblique muscles and the retrobulbar fat to prevent the eyeball being pulled backwards by recti muscles
what is enophthalmos sign?
during disease, dehydration and starvation, the eyeballs may be retracted into the orbit
what does the lacrimal gland do?
- secretes LACRIMAL FLUID — contains lysozyme
- the fluid moistens and lubricates the surfaces of the conjucntiva and cornea and provides some nutrients and dissolved O2 to the cornea
- when produced in excess, the overflowing fluid becomes tears
what do the excretory ducts of lacrimal glands do?
convey lacrimal fluid from the lacrimal glands to the conjunctival sac
what do the lacrimal canaliculi do?
commence at lacrimal punctum (opening) on the lacrimal papilla and drain lacrimal fluid from the lacrimal lake (a triangle space at the medial angle of the eye where the tears collects) to the lacrimal sac
what does the nasolacrimal duct do?
conveys the lacrimal fluid to the inferior nasal meatus
describe the flow of lacrimal fluid
- the lacrimal glands secrete lacrimal fluid
- the fluid is passed along the excretory ducts
- the fluid enters the superior conjunctival sac
- blinking pushes a film of fluid over the cornea
- fluid accumulates in the lacrimal lake at the medial aspect of the eye
label this
lacrimal gland innervation (PS + S)
ps = facial nerve
s = opthalmic nerve (CNV1)
what are the 2 groups of eye muscles? what do they do?
- extraocular — move the eyeballs within the orbit
- intrinsic ocular — within the eyeball itself and control how the eyes accommodate
which extraocular muscle opens the eyelid?
levator palpebrae superioris
superior rectus origin, insertion, function
origin: common tendinous ring (annulus of Zinn)
insertion: anterior half of eyeball superiorly
function: elevation, adduction, internal rotation of eyeball
inferior rectus origin, insertion, function
origin: inferior part of common tendinous ring
insertion: anterior half of eyeball inferiorly
function: depression, adduction, external rotation of eyeball
medial rectus origin, insertion, function
origin: medial part of common tendinous ring
insertion: anterior half of eyeball medially
function: adduction of eyeball
lateral rectus origin, insertion, function
origin: lateral part of common tendinous ring
insertion: anterior half of eyeball laterally
function: abduction of eyeball
superior oblique origin, insertion, function
origin: body of sphenoid bone
insertion: superolateral aspect of eyeball (deep to rectus superior, via trochlear orbitae)
function: depression, abduction, internal rotation of eyeball
inferior oblique origin, insertion, function
origin: orbital surface of maxilla
insertion: inferolateral aspect of eyeball (deep to lateral rectus muscle)
function: elevation, abduction, external rotation of eyeball
levator palpebrae superioris origin, insertion, function
origin: lesser wing of sphenoid bone
insertion: anterior surface of tarsus, skin of upper eyelid
function: elevation of upper eyelid
label
label
what is the connective tissue layer of the eyeball composed of posteriorly and anteriorly?
posteriorly = fascial sheath of the eyeball (forms actual socket)
anteriorly = bulbar conjunctiva
what lies between the fascial sheath and the outer layer of the eyeball, facilitating movements of the eyeball within the fascial sheath?
episcleral space (a potential space)
what are the 3 layers of the eyeball?
- fibrous
- vascular
- inner
what does the fibrous layer of the eyeball consist of?
sclera and cornea
describe the sclera
= an opaque layer that surrounds the posterior 5/6th of the eyeball
- provides attachment for extraocular muscles
- thickest posteriorly
what is the posterior pole of the sclera perforated by?
optic nerbe — this site is marked at the posterior sclera foramen — here the outer 2/3rds of the sclera are continuous with the dural sheath of the optic nerve
what is at the posterior junction of the cornoscleral junction?
internal sclera sulcus — contains sclera venous sinus (canal of Schlemm — drains aqueous humor)
describe the cornea
- a transparent layer that is anteriorly continuous with the sclera, occupying the anterior 1/6th of the eyeball
- avascular
- lacrimal fluid provides its external surface with nutrients
and oxygen, and aqueous humor provides the internal surfaces - function is refraction of light
- highly sensitive to touch
what is the innervation of the cornea?
opthalmic nerve (CNVI)
what makes up the vascular layer of the eyeball?
choroid, iris and ciliary body
describe the choroid
- layer of connective tissue and blood vessels
- provides nourishment to the outer layers of the retina
describe the ciliary body
- compromised of the ciliary muscle and ciliary processes
- ciliary muscle : consists of a collection of smooth muscle fibres — these are attached to the lens of the eye by the ciliary process
- the ciliary body controls the shape of the lens, and contributes to formation of aqueous humor
describe the iris
- circular structure, with an aperture in the centre = pupil
- the diameter of the pupil is altered by smooth muscle fibres within the iris, which are innervated by the autonomic nervous system
- situated between the lens and the cornea
what are the 2 layers of the retina?
- pigmented (outer) layer
- neural (inner) layer
describe the pigmented layer of the retina
= outer layer
- formed by a single layer
- it is attached to the choroid and supports the choroid in absorbing light, preventing scattering of light within the eyeball
- it continues around the whole inner surface of the eye
describe the neural layer of the retina
= inner layer
- consists of photoreceptors (light detecting cells)
- it is located posteriorly and laterally in the eye
what is the non-visual retina?
where anteriorly the pigmented layer continues but the neural layer does not
what is at the centre of the optic retina?
macula — yellowish and highly pigmented
what depression does the macula contain?
fovea centralis — has a high conc of light-detecting cells — area responsible for high acuity vision
what is the area called where the optic nerve enters the retina?
optic disc — has no light detecting cells
label
what is the vitreous body? what is it marked by?
- a transparent gel which fills the posterior segment of the eyeball (the area posterior to the lens)
- marked by a narrow canal that runs from the optic disc to the lens = HYALOID CANAL = a foetal remnant
what are 3 main functions of the vitreous body?
- contributes to the magnifying power of the eye
- supports the lens
- holds the layers of the retina in place
what is it called when the lens becomes opaque with age?
cataracts
what is the shape of the lens altered by?
ciliary body (alters its refractive power)
where is the lens located?
between the vitreous humor and the pupil
where are the anterior and posterior chambers of the eye?
- anterior = between the cornea and iris
- posterior = between the iris and ciliary processes
what are the anterior and posterior chambers filled with?
aqueous humor = a clear plasma-like fluid that nourished and protects the eye
what is glaucoma?
a condition when the drainage of aqueous humor is obstructed
what is the eye supplied with blood by branches of?
branches of the opthalmic artery
what does the opthalmic artery arise from?
internal carotid
how does the opthalmic artery enter the orbit?
through the optic canal
venous drainage of eye?
4 vorticose veins that drain into the ophthalmic vein
what do they superior and inferior ophthalmic veins communicate with and where do they pass through? where do they drain?
- superior — with facial vein
- inferior — with pterygoid venous plexus
- both pass through the superior orbital fissure
- drain into the cavernous sinus
what nerve enables sight?
optic nerve (CNII)
what nerves innervate the extra ocular muscles?
> lateral rectus = abducens
superior oblique = trochlear
superior/inferior/medial rectus and inferior oblique = oculomotor
what innervates the intrinsic ocular muscles?
oculomotor
what innervates the upper eyelid?
oculomotor nerve
what innervates the lower eyelid?
infraorbital nerve = a branch of the maximal nerve, that passes through the infraorbital foramen
what are the 3 sensory divisions of the trigeminal nerve?
- ophthalmic (V1)
- maxillary (V2)
- mandibular (V3)
what muscles control what eye movements?
label
label
what does the IOF communicate with?
pterygopalatine fossa
what is the IOF located between?
maxilla and greater wing of sphenoid
what is the SOF located between?
greater and lesser wings of sphenoid
Which part of the vascular coat is pigmented and supplies the retina with oxygen and nutrients?
choroid
Which component of the vascular coat contains smooth muscle and controls the thickness and focus of the lens?
ciliary body
The ciliary processes are folds on the internal surface of the ciliary body, what do they secrete?
aqueous humour
Which part of the retina is the site where the optic nerve enters the eyeball and is insensitive to light?
optic disc
The ciliary ganglion is a parasympathetic ganglion located in the orbit. Post ganglionic fibres run in the short ciliary nerve to supply the sphincter pupillae and ciliary muscles. Which cranial nerve transmits the preganglionic fibres?
oculomotor
