The eye and the orbit Flashcards
what bones make up the orbit?
frontal zygomatic maxillary lacrimal ethmoid sphenoid
what do vessels and nerves which supply the orbit enter?
through foramina;
optic foramen
superior orbital fissure
inferior orbital fissure
which structures pass through the optic foramen?
optic nerve
ophthalmic artery
which structures pass through the superior orbital fissure?
ophthalmic vein ophthalmic nerve (V1) occulomotor nerve (III) trochlear nerve (IV) abducent nerve (VI)
which structures pass through the inferior orbital fissure?
maxillary nerve (V2)
what is the depth of the eyeball and the orbit?
eyeball = 24mm orbit = 40mm
apart from the eye, what mainly fills the orbit and why is this of clinical significance?
fat tissue
it is one of the last reserves of fat that we lose if we go into starvation
thats why if someone has sunken in eyeballs it means they have lost a lot of body fat
what muscles control the eyelids and what are their functions?
orbicularis oculi - depresses/closes the eyelid
levator palpebrae superioris - elevates/ opens the eyelid
what is the nerve supply of the levator palpebrae superioris?
CN III - Occulomotor nerve
what helps the orbit eep its shape?
hard palate (tarsal palate)
what is found within the tarsal/hard palate of the orbit and what is its function?
meibomian glands
helps prevent evaporation of the eyes tear film
what type of glands are found are the eyelashes?
sebaceous glands
describe the covering of the conjunctiva.
covers the inside of the eyelids and loops back over the sclera
continues to the fornix (conjunctival fornices)
stops at the corneosclera junction
what part of the eye does the cornea and sclera cover?
cornea covers the anterior 1/6
sclera covers the posterior 5/6
what is the functions of the iris, ciliary body and choroid?
iris controls diameter of the pupil and thus the amount of light that enters
the ciliary body suspends the lens and produces aqueous humour
the choroid supplies blood to the outer layers of the retina
what is the function of the aqueous and venturous humour?
aqueous helps control intraocular pressure
venturous humour cushions the retina
what are the different chambers of the anterior segment of the eye?
anterior chamber infant of the iris
posterior chamber behind the iris
describe the drainage of the aqueous humour.
produced from ciliary body and secreted into posterior chamber
comes through the pupil until it reaches a corner - the angle of the anterior chamber
enters trabecular meshwork at this corneosclero junction
enters the schemms canal this drains into veins in the sclera - episclero veins
wha are the functions of the intrinsic and extrinsic muscles of the eye?
intrinsic controls pupil diameter and helps alter lens curvature to enable us to see near objects
extrinsic muscles move the eye
what are the intrinsic muscles and their nerve supply?
cilliaris muscle - occulomotor nerve III
constrictor pupillae - occulomotor nerve III
dilator pupillae - sympathetic plexus
which muscle helps the us to see near objects and how?
cilliaris muscle
alters lens curvature
what are the extrinsic muscles and their nerve supply?
superior, inferior, medial and lateral rectus superior and inferior oblique superior orbital = trochlear nerve IV superior rectal = abducent nerve VI everything else = Occulomotor nerve III
which muscle originates from the lesser wing of the sphenoid (roof of orbit posteriorly) ?
superior oblique
which muscle originates in the medical part of the orbit floor (anteriorly) ?
inferior oblique
where do the extrinsic muscles attach to the sclera?
rectus muscles anteriorly
oblique muscles posteriorly
what is the nerve innervation of the lacrimal gland?
parasympathetic facial nerve VII
regarding the lacrimal gland, what happens when we close our eye lids?
constriction of the orbiculares oculists muscle creates a negative pressure opening up the lacrimal sac so the fluid is sucked into the punctae for drainage into the lacrimal duct
where is the lacrimal gland situated?
anteriolaterally of the orbit
before tears enter the lacrimal sac, what is it sucked through?
punctae found on the medial side of each eyelid
what supplies motor and sensory innervation to the orbit?
motor ;
- optic (CN II)
- occulomotor (III)
- trochlear (IV)
- abducent (VI)
sensory - ophthalmic V1 and maxillary V2 branches of the trigeminal
what foramen does the sensory innervation of the orbit pass through?
opthalmic nerve V1 - superior orbital fissure
maxillary nerve V2 - inferior orbital fissure
what are the main branches of the ophthalmic nerve?
nasociliary branch
lacrimal branch
frontal branch
what does the maxillary branch V2 supply?
sensory innervation to the lower part / floor of the orbit and eyelids
arterial supply is via what main artery?
opthalmic artery which is a main branch of the internal carotid
the opthalmic artery goes through the orbital cavity via what foramen?
optic foramen
what branches does the ophthalmic artery give off?
central retinal artery
short and long posterior ciliary arteries
which arteries supply the choroid and which parts?
short posterior ciliary artery supplies the posterior part of choroid
long posterior ciliary arteries supply anterior choroid, iris and ciliary body
what is the blood supply of the retina?
the outer layer supplied by the choroid (which is supplied by the short and long posterior ciliary arteries)
the inner layer supplied by the central retinal artery
what does the central retinal artery travel within?
the substance of the optic nerve
how can you view the blood supply of the eye?
through an ophthalmoscope (fund picture)
what is the bright small circle found in the fund picture?
optic disc
what do you find at the optic disc?
the start of the optic nerve
in the centre you find the central retinal artery and vein
what is the name of the venous sinus which drainage of the orbit leads to?
cavernous sinus
where are the venous sinuses situated?
between the layers of the dura matter
what is the epithelium lining of the venous sinus?
squamous epithelium (endothelium)
where do you find the cavernous sinus?
situated on either side of the body of the sphenoid bone where the pituitary fossa is
what structures lie within/near the cavernous sinus?
within the sinus = internal carotid artery
lying superior = optic nerve
lying within the walls of the dura matter are the nerves which enter the orbit through the superior orbital fissure - III, IV, VI, opthalmic and optic nerves
