Session 8 - functional anatomy and disorders of the eye Flashcards
what are the borders of the orbital cavity
Roof (superior wall) – Formed by the frontal bone and the lesser wing of the sphenoid. The frontal bone separates the orbit from the anterior cranial fossa.
Floor (inferior wall) – Formed by the maxilla, palatine and zygomatic bones. The maxilla separates the orbit from the underlying maxillary sinus.
Medial wall – Formed by the ethmoid, maxilla, lacrimal and sphenoid bones. The ethmoid bone separates the orbit from the ethmoid sinus.
Lateral wall – Formed by the zygomatic bone and greater wing of the sphenoid.
Apex – Located at the opening to the optic canal, the optic foramen.
Base – Opens out into the face, and is bounded by the eyelids. It is also known as the orbital rim
what are the three openings at the apex of the orbital cavity transmitting blood vessels and nerves into and out of the orbit
superior orbital fissure
inferior orbital fissure
optic canal
what feature of the orbit conveys some protection to the structure
the tough orbital rim
what is the weakest part of the orbit
the medial wall and the floor of the orbit
this is because of the paranasal air cavities (maxillary and ethmoid)
what are the paranasal sinues
air-filled extensions of the respiratory part of the nasal cavity. There are four paired sinuses, named according to the bone in which they are located; maxillary, frontal, sphenoid and ethmoid.
they may contribute to the humidifying of the inspired air. They also reduce the weight of the skull.
As the paranasal sinuses are continuous with the nasal cavity, an upper respiratory tract infection can spread to the sinuses. Infection of the sinuses causes inflammation (particularly pain and swelling) of the mucosa, and is known as sinusitis. If more than one sinus is affected, it is called pansinusitis.
The maxillary nerve supplies both the maxillary sinus and maxillary teeth, and so inflammation of that sinus can present with toothache.
what are the symptoms of an orbital blow out fracture
• Periorbital swelling, painful
• Double vision (especially on vertical
gaze)
• Impaired vision
• Anaesthesia over affected cheek (upper teeth and gums) on affected
side
• limited movement of eyeball- eye can’t look up as muscle is nicked
symptoms occur because the infraorbital nerve which is a branch of the trigeminal nerve runs along the floor of the orbit and provides sensory innervation to the cheek
what happens in an orbital blow out fracture
Sudden increase in intra-orbital pressure (e.g. from retropulsion of eye ball [globe] by fist or ball) fractures floor of orbit (weakest part)
Orbital contents and blood can prolapse into maxillary sinus; the fracture site can ‘trap’ structures e.g. soft tissue, extra orbital muscle located near floor or orbit
what features on an x-ray may indicate an orbital blow out fracture
tear drop sign- fracture of the floor of the orbit -shadow of tissue prolapsing down from orbital floow
fluid level - as blood accumulates
black maxillary paranasal air sinus- as it is full of air
what are the contents of the eyelids (palpebrae)
– Protect the eye when palpebral fissure is closed
– Tarsal plates and muscles
– Glands at the edges of the eyelids
what are the contents of the orbital cavity
– Lacrimal apparatus
– Nerves and blood vessels
– Orbital fat (lots!)
– Globe of the eye (eyeball) and its internal structures
– Extrinsic ocular muscles (extra-ocular)
• Muscles that move the
eyeball
what is the orbital septum
is a thin sheet of fibrous tissue originating from orbital rim
– Blends with tendon of LPS and tarsal plates
• Orbital septum separates intra-orbital contents from eyelid fat and orbicularis oculi muscle
• Acts as a barrier against infection spreading from the pre-septal space
to post-septal (orbital cavity proper)
what is the function of the tarsal plate
provides a connective tissue skeleton to the eyelid
– Firmness and shape
what is pre-septal orbital cellulitis
Infection in front of membrane Orbital septum prevents it going into orbital cavity
Localised to eyelids
what is post-septal orbital cellulitis
Deep inside orbital cavity If infection spreads behind orbital septum most concerning Redness and swelling much more diffused Deeper inside the eye
what are the potential complications of periorbital cellulitis
Complications include abscesses formation and spread of infection
intracranially- cavernous sinus thrombosis
Veins of orbit drain to cavernous sinus,
pterygoid venous plexus and facial veins
what are meibomian glands
and what happens when they get blocked
a special kind of sebaceous gland at the rim of the eyelids inside the tarsal plate, responsible for the supply of meibum, an oily substance that prevents evaporation of the eye’s tear film and tear spillage
what happens if a meibomian gland gets blocked up
you get a meibomian cyst
why do you get a stye
when eyelash follicles block they can get infected with staph
how do you treat meibomian cysts and styes
Treat conservatively
Give hot compresses to unblock glands to release contents
Watch and wait
Surgical incise if had for very long time
what is the conjunctivae of the eye
Conjunctivae (transparent mucous membrane) that produces mucous and tears to lubricate the conjunctival and corneal surfaces
Covers white of eye (sclera) and lines inside of eyelids
(forming a conjunctival sac); does not cover over cornea
Highly vascular with small blood vessels within the
membrane
what is the lacrimal apparatus
involved in secretion of tears into conjunctival sac – Lacrimal gland (arranged around edge of levator palpebrae superioris) – Lacrimal sac – Nasolacrimal duct
why do we blink
Blinking washes tear film across front of eye, rinsing and lubricating the conjunctivae and cornea
what is conjunctivitis
inflammation of the conjunctiva of the eye (pink eye) can be caused by infection or allergies
what is the main arterial supply to the orbit
opthalmic artery which is branch of the ICA
what is the venous drainage of the orbit
Ophthalmic veins which drain venous blood into cavernous sinus, pterygoid plexus and facial vein
which nerve provides general sensory to the eye (including conjunctiva and cornea)
opthalmic division of trigeminal Va
which nerve provides special sensory vision from retina
optic nerve
which motor nerves supply the muscles of the orbit
occulomotor
trochlea
abducens
what maintains the position of the eyeball (the eyeball does not sit on the orbital floor)
– Suspensory ligament (sits underneath like a sling)
– Rectus muscles
– Orbital fat
what are the three layers of the eyeball
– Outer: fibrous, tough sclera (white of eye) continuous
anteriorly as transparent cornea*
– Middle: vascular consisting of choroid, ciliary body and
iris
– Inner: retina (inner photosensitive layer lying on an outer pigmented layer- prevents scattering of light)
where is the anterior chamber found and what is found within the anterior chamber
it is found between the cornea and the iris
aqueous humour
where is the posterior chamber found and what is found within the anterior chamber
it is found between the iris and the lens
aqueous humour
how does the pupil adjust its size
muscles of iris constrict and dilate under autonomic control to adjust the size of the pupil
why is the cornea avasular
must be transparent for light to get through
what is found within the vitreous chamber
vitrous humour
what happens when the ciliary body receives PS innervation
causes them to contract and move inward - muscles move in
so tension in the ligaments suspending the lens to the ciliary body decreases
and the lens gets fatter
what is your blind spot also know as
optic disc
what is the most common cause of blindness
Age-related macular degeneration
what produces aqueous humour
by ciliary processes within ciliary body in the posterior chamber
it flows from the posterior chamber to the anterior chamber
to nourish the lens and cornea
how does aqueous humour drain
and in what condition can it get blocked
it drains through the iridocorneal angle (between iris and cornea) in the anterior chamber via trabecular meshwork into canal of Schlemm
you get gluacoma
what are the common causes of glaucoma
Trabecular meshwork deteriorates (age: chronic): open angle glaucoma
Narrowing of iridocorneal angle (acute): closed angle glaucoma - is an anthropological emergency
both cause a rise in intra-ocular pressure and damage to the optic nerve (optic disc cupping)
what is open angle glaucoma
what happens if it is left untreated
how do you treat it
blockage within the trabecular mesh network
leads to a rise in intraoccular pressure
develops painlessly over time
opticians screen for it
cupping of optic disc and visual field loss
if untreated can lead to damage of optic nerve
causing impaired vision and blindness
give topical beta blockers to reduce the production of aqueous humour and increase its drainage
failing that a trabeculectomy may be required
what is closed glaucoma
how do they present
what happens if untreated
how do you treat it
narrowing of the irido-corneal angle (angle between cornea and iris) by the peripheral edge of the iris
less common
access to trabecular meshwork is blocked off
rapid rise in intraoccular pressure
present with sudden onset of a painful red eye, blurred vision or halos around objects (corneal odema)
nausea and vomitting
eye feels hard and tender to palpate through upper eyelid
irreversible sight loss
muscarinic eye drops (analgesia)
drugs tor educes IOP
how do we see
Light (photons) must reach the photosensitive retina to be detected by
photoreceptors (rods/cones)
– Action potentials generated in response to light
– Pass via ganglion cells whose axons collect in area of optic disc- optic nerve
• Light must reach and be focused on retina
– Transparent medium
– Refraction (bending of light)
• Pathology affecting the retina, the transparency of structures anterior to retina or
ability to refract light will cause visual disturbance
why do we get refraction of light as light enters the eye
Light will be refracted as it passes through a number of structures and ‘fluids’
from outside eye towards retina
– From air into liquid tear film-refract
– Through cornea- refract (most refraction of light occurs at the air-cornea
interface)
– Through lens and vitreous humour before reaches retina
what is the accommodation reflex
Light rays from near-objects are more divergent and require greater refraction to bring them into focus on retina
the cornea alone cannot bend light enough so we need the lens to adjust
• Eye can accommodate to do this
– Pupil constricts
– Eyes converge (image is brought to focus on same point of retina in both eyes)
– Lens becomes more biconcave (fatter)- ciliary bodies contract and move in to release the tension
Focusing Near Objects Requires Greater Refraction of Light
what happens to your lens as you get older
As you get older the lens becomes stiffer
The lens is less able to change shape
Presbyopia- age related inability to focus near objects
Have to hold things at arms length
which cranial nerves supply the muscles that move the eyeball
CNIII
CNIV
CNVI
occulomotor nerve innervaes most of them
what is the control of the extrinsic (etraoccular) muscles of the eye
e.g. muscles of the eyelid and muscles that move the eye ball (globe)
somatic motor nerves- conscious control
some sympathetic innervation too
what is the control of the intrinsic muscles of the eye
e.g. Muscles of the iris (dilator and constrictor of
the pupil)
and Ciliary muscle controls thickness of the
autonomic visceral nerves
how many muscles move the eyeball
what is their attachment
where do they originate from
six
sclera of eyeball
most muscles originate from a fibrous ring at the back of the orbit (SR, IR, MR, LR)
What are the two muscles not innervated by the occulomotor nerve
lateral rectus innervated by abducens
superior obliqe innervated by trochlear
what muscles enables the eyes to look directly upwwards
Superior rectus pulls the eye up and pull the eyeball in slightly medially(inwards)
Inferior oblique also helps to pull the eye up and slightly out
The slightly medial action of the superior rectus is cancelled out by the slight lateral action of the inferior obliques so we can look directly up in the midline
which muscles are moving the eyes downwards
Inferior rectus - depresses eyeball and brings it in slightly medially (inwards)
Superior oblique also helps move the eye down, slightly moves the eye laterally (down and out)
Intorts the eyeball- turns clockwise (when
we rotate head)
Secondary action of inferior rectus and superior oblique cancel out so we have a
direct downward gaze so eye is directly in
the midline
what is the secondary action of superior oblique
roll the eye out and down
intort the eyeball- roll it clockwise
what is the secondary action of inferior oblique
Roll the eye up and out
Extort the eyeball (roll it anticlockwise)
what is the secondary action of superior and inferior rectus
roll the eye inwards medially
what is the main action of superior oblique
depresses the eyeball
what is the main action of inferior oblique
elevates the eyeball
how do we test the lateral and medial rectus muscles
get the patient to look straight forwards and abduct and adduct the eye (look from side to side)
how do we test the action of superior oblique
Move eye into medial position (looking towards nose) then move eyeball down
how do we test the action of inferior rectus
Move eye into lateral position then move eyeball down
how do we test the action of inferior oblique
Move eye into medial position then move eyeball up
how do we test the action of superior rectus
Move eye into lateral position then move eyeball up
what muscles is the main depressor of the eye when the eyeball is starting from the medial position
superior oblique
why might you get a crainal nerve palsy
raised intracranial pressure
(e.g. intracranial haemorrhage or tumour)
But can also be affected by vascular disease (microvascular complications)
from diabetes and hypertension
how does the eye look if we get a CNIII palsy and why
the eye looks down and out
this is because the only two extra occular muscles not innervated by thecocculomotor nerve are lateral rectus and superior oblique
eye struggles to open as LPS is paralysed- complete ptosis
dilated pupil as CNIII also carries parasympathetics to the sphincter pupillae muscle causing constriction
how does the eye look if we get a CNIV palsy and why
what do patients do to compensate
eyeball is held extorted- up and in
trochlear nerve innervates the superior oblique muscle
which acts to intort and move eyeball down and out
they tilt their heads slightly
report difficulty when looking down and medial- walking down stairs and reading
how does the eye look if we get a CNVI palsy and why
symptoms
eye inwards abducens nerves innervates lateral rectus so get unopposed pull of medial rectus unable to abduct eye on affected side diplopia made worose on horizontal gaze
why might you get a CNIII palsy
vasculopathic
tumour
anneurysm
why might you get a CNIV palsy
vasculopathic
tumour
congenital
trauma
why might you get a CNVI palsy
vasculopathic
tumour
cranial pressure
