Flashcards in H&N 6.1 the orbit Deck (59):
What bones make up the orbit?
What bones make up the lateral orbit?
What bones make up the roof of the orbit?
What bones make up the medial border of the orbit?
What bones make up the floor of the orbit?
Which wall of the orbit is the weakest?
The floor of the orbit.
What openings are there into the orbit?
-superior orbital fissure
-inferior orbital fissure
What runs through the optic canal?
-optic nerve (CN II)
-central retinal artery,
-central retinal vein.
What structures run through the superior orbital fissure?
-occulomotor nerve (CN III) (sup and inf. branches)
-trochlea nerve (CN IV)
-abducens nerve (CN VI)
-opthalmic branches of the trigeminal nerve (lacrimal, frontal, nasocilliary)
-superior opthalmic vein.
What structures run through the inferior orbital fissure?
-inferior opthalmic vein.
What main structures make up the eyeball?
What is the function of the lens?
-it focus' light into the eye and onto the retina.
How is the lens held in place?
By suspensory ligaments, the cilliary bodies.
What is the coloured part of the eye known as?
Why is the pupil black?
Because it is emitting no light, and absorbing lots of light, hense we see it as black.
What is the function of the cilliary bodies?
They alter the thickness of the lens, allowing us to focus our eyes, eg on close or distant objects.
What is the function of the retina?
It's there the cone cells are found, which allow us to see.
You get conversion of light energy into chemical impulses which travel to the brain via the optic nerve, allowing us to build a picture.
What is the blind spot?
Where the optic nerve enters the orbit there are no cone cells, so you cannot see.
its found where the optic disc is.
Everyone has one on each eye.
What are the 3 layers of the coverrings of the eyeball?
-outer fibrous= sclera/cornea
-middle vascular= choroid.
-inner layer- retina.
Why is the outer fibrous layer split into sclera and cornea?
Theyre the same except the cornea is transparent, allowing light to pass into the lens.
If it wasnt transparent, and what the same colour as the fibrous sclera we wouldnt be able to see.
What is the function of the outer fibrous layer of the eyeball?
It maintains the shape of the eye.
How do we examine the eye?
-fundoscope (allows visual)
What structures do you see using a fundoscope?
-optic disc (always medial)
-macula + fovea (area of highest visual acuity)
-arteries and veins of the eye
What is retinal detachment and what is the cause?
Commonly caused by trauma, there is detachment of the retina from the underlying layers of the orbit (the choroid).
If you used a fundoscope, the image would be occluded because of the detached retina.
There will be interrupted supply od blood and nutrients to the retina, as this is supplied by the vascular layer so this needs correcting quickly, otherwise partial blindness can occur,
What are the coverrings of the optic nerve, and how is this clinically relevant?
continuation of the brain so coverred in meninges, can become inflamed in meningitis, which is what causes the associated photobia.
How can the eye be compartmentalised?
-into anterior and posterior segment.
Anterior can be further divided into anterior and posterior chambers.
Where is the anterior chamber of the eye found and what does it contain?
-found between the cornea and the lens,
contains aqueous humour.
What is the function of aqueous humour?
To supply nutrients to the cornea and lens, which are both avascular (allowing them to be transparent).
Where does the anterior chamber of the eye drain?
Aqueous humour drains via the trabecular meshwork.
What happens when there is blockage of the trabecular meshwork of the eye?
What is this more commonly known as?
You get a build up of aqueous humour which can lead to oedema of the eye and also begin to compress the posteiror segment, causing compression of the blood supply and optic nerve, which can lead to vision loss.
Open angle glaucoma.
How do you treat open angle glaucoma?
By giving medications which unblock the trabecular meshwork, allowing drainage.
This is not classed as an emergency.
Why is it known as 'open angle' glaucoma?
The angle between the cornea and the iris increases, due to the build up in pressure.
What are cateracts?
Where there is increased opacity of the lens, eg due to protein deposits.
Leads to increasingly worse vision.
How are cateracts treated?
Simply by removing the old lens and inserting a new artificial one.
A simple, cheap and quick surgery which can dramatically increase someones QoL.
How many muscles are there of the eye?
What are the muscles of the eye and their innervation?
-levator palpabrae superioris
ALL INNERVATED BY THE OCCULOMOTOR NERVE.
-lateral rectus (Abducens nerve)
-superior oblique (trochlea nerve)
What is the function of the superior oblique muscle of the eye?
rotates the eye medially and inferiorly.
What is the function of the inferior oblique muscle?
rotates the eye medially and superiorly.
Why is it rare to damage the inferior oblique on its own?
It's innervated by the occulomotor nerve, so if the nerve is damaged all the muscles it innervates (most of the muscles of the eye) will also become paralysed.
What happens in a trochlea nerve lesion, with regards to the eye?
You lose the ability to rotate the eye medially and inferiorly.
Activities such as walking downstairs and reading become difficult and cause diplopia.
looking at someone you may not know, can be compensated by a slight tilt of the head.
What happens in an occulomotor lesion?
Eye loses all motor innervation except superior oblique and lateral rectus, so sits in the DOWN AND OUT position.
full ptosis of the eyelid due to loss of levator palpabrae superioris.
What happens in an abducens nerve lesion?
eyes look cross eyed, unable to move eye laterally.
What further branches does the occulomotor nerve split into?
superior and inferior branches.
What is a common fracture associated with the orbit?
A blow out fracture.
Inferior border of the orbit is weak, and breaks when there is trauma.
This can allow contents of the orbit to move down into the space below- the maxillary sinus.
Why might someone who has had a blow out fracture find it difficult to look up with the affected eye?
The inferior rectus muscle can become trapped, causing it to be 'constantly contracted'. This means looking up cannot happen because there is constant opposition from the inferior rectus.
What is the arterial blood supply to the orbit?
Via the opthalmic artery, a branch of the internal carotid artery.
This further splits, the central retinal artery runs within the optic nerve.
Many end arteries.
What happens if there is damage to the central retinal artery?
Damage to the central retinal artery leads to a 'cherry spot' being seen on fundoscopy.
What is the venous drainage of the orbit?
via the central retinal vein which drains into the superior opthalmic vein, which along with the inferior opthalmic vein drains into the cavernous sinus.
What happens if there is central retinal vein occlusion?
You can drain the eye of blood, leads to oedema, visual changes etc.
This may resolve by itself, or may progress leading to ischaemia, which will result in vision loss.
There is no known treatment, but things like antithrombotics such as aspirin are used to try and resolve to clot.
What is papilloedema?
oedema of the optic disc following rasied intracranial pressure.
What are the conjunctiva?
a thin clear film over the rest of the eye and eyelids, which stops at the sclerocorneal junction.
What happens in conjunctivitis?
Red inflammaed conjunctiva.
Does affect vision because there is no conjunctival coverring of the cornea.
How can the conjunctiva be subdivided?
Into the palpebral conjunctiva (coverring the eyelid)
and the bulabar conjunctiva (coverring the sclera)
What's the functions of the eyelids?
to protect against:
-injury including forreign objects
What structures does the eyelid contain?
-eye lashes (help keep out forreign objects).
-tarsal glands/meibomian glands.
-muscle fibres, eg of LPS.
What's the function of the meibomian/tarsal glands?
To secrete meibium, which prevents evapration of the tear coverring of the eye, maintaining protection.
What happens when there is blockage of the meibomium glands?
What is a stye?
What's a common cause?
When there is infection of the cilliary glands, causes small painful bumps, which often resolve on their own.
Common cause: Staph. Aureus.