orbit Flashcards
what are the bones of the orbit *
roof - orbital plate of the frontal bone
floor - orbital plate of the maxilla (thin) (cheek bone)
lateral wall - zygoma and greater wing of sphenoid (posterior to the zygoma)
medial wall - frontal process of maxilla, lacrimal bone (small), orbital plate of ethmoid (lamina papyracea), lesser wing of sphenoid
what is a blowout injury
when there is driect trauma to the eye
blow put floor of orbit
eye drops into cheek cavity = double vision etc
what are the orbital formina *
optic canal - optic nerve (CN2), opthalamic artery
inferior orbital fissure - maxillary division of trigeminal V2, infraorbital vessels
superior orbital fissure - CN involved in extrinxic muscle function (CN3 4 6), opthalmic division of trigeminal V1, opthalmic vessels, sympathetic fibres run with vessels
what is the opthamlic artery *
the main blood supply to the eye
where are the orbital foramina *
optic canal - in the lesser wing of the spenoid bone
superior orbital fissure - in lesser wing of sphenoid
inferior orbital fissure - lesser wing of the sphenoid (nerves run along maxilla and exit via the infraorbital fissure)
what are the 2 categories of the extrinsic muscles of the orbit *
recti
obliques
describe the recti muscles *
inferior, superior, medial and lateral
origin - at back of orbit in common tendinous ring
insertion - into the sclera, 5mm behind the corneal margin (anterior to the equator)
nerve supply - inferior superior and medial are innervated by oculomotor CN3, lateral abducens CN6
describe the oblique muscles (extrinsic muscles of the orbit) *
inferior and superior
origin - inferior: in orbital surface of maxilla
Superior: from the body of the sphenoid
insertion - inferior: into the posterior/inferior quadrant of thee globe
superior: posterior/superior quadrant via the trochlea (bony spur in medial aspect of orbit)
nerve supply - inferior: CN3, superior: trochear nerve CN4
what is the muscle of the upper eyelid *
levator palpebrae superioris
describe the levator palpebrae superioris *
origen - lesser wing of sphenoid
insertion - into the superior tarsal plate and skin of the eyelid
nerve supply - CN3, and sympathetic supply to sm (important clincially)
why is it important clinically that the levator palpebrae superioris has sympathetic innervation *
horner’s syndrome (loss os SNS to head and neck)
symptom is ptosis (drooping of upper eyelid)
describe the path of the optic nerve and its insertion into the globe *
through the optic canal to the back of the globe
large nerve
retinal ganglion cells axons going back via optic chiasm to the occipital lobe
what is the common tendinous ring, where is it *
origin for all the muscles in the orbit
back of the orbit
describe the muscles and their location in the orbit *
levator palpebrae superioris - at the top of orbit, muscle to the upper eyelid
superior oblique - origin in c tendinous ring, up passes through pully system with trochlear, pass back to lateral superior quadrant of the globe, inserts into the posterior globe of the eye
superior rectus muscle - origin in common tendinous ring at back of orbit - insert into globe of eye anterior to equator
inferior oblique - originates in orbital plate of the maxilla (in the lower orbital nasal wall), inserts into the posterior globe of the eye
inferior rectus - origin in common tendinous ring at back of orbit - insert into globe of eye anterior to equator
lateral rectus - origin in common tendinous ring at back of orbit - insert into globe of eye anterior to equator
medial rectus - origin in common tendinous ring at back of orbit - insert into globe of eye anterior to equator
describe the function of the superior oblique muscle *
contraction = move pupil down and out
function of the superior rectus *
straight forward contraction pulls pupil up
describe the function of the inferior oblique muscle *
moves the pupil up and ou t
describe the function of the inferior rectus *
depresser muscle - move pupil down
describe the function of the lateral rectus *
abduct the eye - pull the pupil away from the midline
describe the function of the medial rectus *
adduct the eye - move pupil to the middle
describe ISOLATED muscle actions - ie not what would happen in real life *
LR - abduction
MR - adduction
SO - depressor and abductor
IO - elevator and abductor
SR - adduction and elevation
IR - adduction and depression
describe how you test the muscle action of the orbit clinically *
you need to get eye so that it is line with the muscle that you are testing
LR and MR - see whether eye follows finger - adduction/abduction (remember 1 eye will adduct and one will abduct in persuit so different muscles are being used in each eye)
to check depression - adduct/abduct first so you can isolate the muscle that is causing the depression. when adducted - SO, abducter - IR
elevation - also need to adduct/abduct first - adduct - IO, abducted - SR
what are the nerves of the orbit superficially
optic - made of axons of ganglion cells in retina
oculomotor - has 2 rami, motor fibres to MR, SR, IF, IO, LPS (eyelid), PNS fibres
trochear - motor to SO
abducens - motor fibres to LR
what are the branches of the opthalmic division of the trigeminal nerve
lacrimal
frontal branches into supratrochlear and supraorbital,
nasocilary branches to ciliary ganglion PNS, ethmoidal and infratrochlear
describe the location of the nerves of the orbit and how they reach the orbit
oculomotor goes through superorbital fissure
trigeminal ganglion sits in Meckel’s cave, opthalmic division enters orbit through superorbital fisure
branches of the opthalmic division of the trigeminal nerve - frontal nerve, lacrimal nerve (going to lacrimal gland on lateral orbit)
describe the location of the CN in the cavernous sinus and relevance of this
in the lateral wall
except abducens CN6, runs with the internal carotid
infection/thhrombosis here can affect all these nerves
describe the ciliary ganglion
PNS innervation
sits behind globe of eye
preganglionic fibres are in the inferior ramus of oculomotor nerve
postganglionic fibres are in the short ciliary nerves
they innervate the sphincter pupillae and ciliary muscle
describe the blood vessels of the orbit
opthalmic artery supplies blood to central artery of retina, muscular branches, ciliary, lacrimal, supratrochlear and supraorbital branches
opthalmic veins - superior (drain into cavernous sinus - potential route of infection back into cranial cavity) inferior (drain into the pterycoid plexus - no passage into the cranial cavity)
why is it important to look at arteries in eye clinically
check that they are ok
also check systemic disease
in diabetics - can see diabetic retinopathies
in people with trauma see papilloedema indicate raised intracranial pressure
summarise the lacrimal system
lacrimal gland in the anterolateral superior orbit
PNS secretomotor fibres are from facial nerve CN 7 - they come from the pterygopalatine ganglion, pass through zygomaticotemporal branch and then join lacrimal nerves. (ganglion is behind the cheek) lacrimal nerves are sensory branches of trigeminal
lacrimal sac in medial canthus of eye - drains into inferior meatus of the nose via the nasolacrimal duct
describe tears
they wash across the cornea
have a protective function
keep eye moist
collect in lacrimal sac and drain through nasolacrimal duct into nose
what could be the problem if someone presents with a dry eye
a PNS problem - no production of tears
what are the afferent and efferent arms of the corneal reflex *
afferent - CN5
efferent - CN7
what are the afferent and efferent arms of the pupillary light reflex *
afferent - CN2
efferent - CN 3
What are the afferenet and efferent nerves of the accommodation reflex *
Afferent CN2
efferent CN 3
Describe the optic nerve *
Extension of brain from retina to visual centers of the brain
leaves the orbit through the optic canal
Describe the oculomotor nerve *
Leaves the brain stem between meidbrain and pons
passes through the cavernous sinus
branches into superior and inferior divisions just before orbit
they enter the orbit through superior orbital fissure lying in the common tendinous ring
superior branches passes up over CN2 innervatibg the superior recurs an elevator palpebrae superioris
inferior branch has 3 branches innervatibg medial, inferior rectud and inferior oblique
3rd branch of inferior gives rise to the ciliary ganglion - this is the pns root to ganglion
What is the edinger Westphalia nucleus *
The pns pregnaglionic nucleus - pns outflow to the ciliary ganglion
Describe the pretectum *
Group of 7 nuclei
most known function is the pupillary light reflex controlled by the olivary pretectal nucleus
What is horners syndrome *
Loss of sons function in head
because of a lesion
What are the 3 typical features of horners syndrome *
Pupillary constriction because of paralysis of the dilator pupillary muscle
partial ptosis- dropping of upper eyelid due to paralysis of superior tarsal muscle
absence of sweating on the ipsilateral side of face and neck due to absence of innervatibg of the sweat glands,
Describe the tarsal muscle *
Superior tarsus in upper eyelid - part of the levator palpebrae superioris
inferior in lower eyelid
they are plates of dense connective tissue
Describe the path of the sympathetic fibers of the orbit *
Arise from t1
enter sympathetic chain through the white rami communicants - ascend to superior cervical ganglion - synapse with post ganglion fibers
post gang fibres travel with internal carotid artery and branches (ophthalmic artery)
then either go through the ciliary ganglion and join with short ciliary nerves, or pass through long ciliary nerves - both reach eye
innervate the dilator pupillary muscle
Describe the superior cervical ganglion *
Area of c1-2
What is the effect of loss of CN3
Complete ptosis - loss of supply to legatos palpebrae superiosis
describe the action of the ciliary muscle *
it is controlled by parasympathetics from the oculomotor nerve
contraction of the ciliary muscle decreases the size of the ring formed from the ciliary body - reducing tension on the suspensory ligament of the lens
therefore the lens is more relaxed so rounded causing accomodation for near vision
that is why eyes get tired looking at near objects becasue of contraction of the ciliary muscle
describe the action of the sphincter pupillae *
muscle fibres in the iris
innervated by parasympathetics from oculomotor nerve
when contract they constrict pupil
describe the action of the dilator pupillae *
fibres in the iris
innervated by sympathetics from the superior cervical ganglion T1
contraction dilates the pupil
how do you test if someone has a squint*
shine light 40cm away from eye straight on
the light should be reflected symaettrically from the cornea on both eyes - if unsymetrical - show have a squint which is ocular misalignment - used to test the muscle function of the eye
when pt looks at light, reflection should be nasal to the centre of both pupils
describe opthalamoscopy
you vcan see the vitreous chamber of the eye using an opthalmoscope - small battery operated light with tiny lens so yoiu can see the vitreous chamber and the posterior wall of the eye
you can see the optic nerve, the typical 4 branches of the central retinal artery and the fovea
shine the light in the eye and look for the red reflex - then get closer until you can see the arteries of the eye
describe 6th nerve palsy *
affect to lateral rectus muscle
unable to abduct so eye deviates in
souble vision bad when looking to side of effected eye because eye cant move in that direction
describe 4th nerve palsy *
superior oblique muscle is affected
eye looks medial and is raised
describe the conjunctiva *
it is a thin membrane covering the posterior surface of the eyelid
it covers the full extent of teh posterior surface of the eyelid and reflects onto the sclera
it attaches to the membrane at the junction between the sclera and conjunctiva
a conjuctival sac is formed when eyes are closed and upper and lower extensions of these sacs are the superior and inferior conjunctival fornices
importance of the conjunctiva *
keep the eye and inside surface of eyelid lubricated and moist so eye can open without friction which would cause eye irritation
describe the eyelid anatomy *
space between eyelids when open is the palpebral fissure
the layers of the eyelids are; skin, subcutaneous tissue, vol muscle, orbital septum, tarsus, conjunctiva
the superior eyelid has 2 more muscles than the lower eyelid
describe the innervation of eyelid *
sensory is from trigeminal branches - opthalmic and maxillary nerve
motor is from - facial, oculomotor and sympathetic fibres
function of the eyelid *
spread tears across the eye
protect the eye from foreign bodies
