Eye and Orbit Flashcards
What are the walls of the orbit?
roof
lateral wall
medial wall
floor
What are the bones of the orbit?
frontal
ethmoid with body of sphenoid posteriorly
lacrimal
maxilla
zygomatic
lesser wing of sphenoid
greater wing of spehnoid
What are the openings into the orbit?
superior orbital fissure
optic canal
nasolacrimal canal
inferior orbital fissure
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What are the contents of the superior orbital fissure?
abducent nerve
lacrimal branch of the ophthalmic nerve (V1)
frontal branch of the ophthalmic nerve (V1)
trochlear (IV)
superior branch of oculomotor nerve (III)
nasociliary branch of opthalmic nerve (V1)
inferior branch of oculomotor nerve (III)
What are the contents of a optic canal?
optic nerve
Where is the superior orbital fissure?
between the lesser and greater wings of sphenoid bone
What CN are in the superior orbital fissure?
CNIII, IV, VI
What are the contents of the orbit?
- optic nerve (CNII) with central retinal artery and vein (end/terminal artery)
- eyelids and lacrimal apparatus
- extraocular muscles
- eyeball
- retrobulbar fat in the orbit supporting the eyeball
What do the optic nerves form and where is it?
As the optic nerves enter the skull they meet & form the optic chiasm that lies just superior & anterior to the pituitary gland (tunnel vision)
What is tunnel vision?
With bitemporal hemianopsia, you lose vision in the temporal visual field of each eye. With one eye closed, the other eye will lose vision in its temporal visual field
What is the structure of optic nerve (CNII)?
dura mater
arachnoid mater
subarachnoid space
pia mater
central retinal vein
central retinal artery
Where do the meninges and subarachnoid space extend?
extend from skull along the optic nerve (CN II) to the sclera
What pathology can occur in the central retinal artery?
can become occluded due to transient causes causing amaurosis fugax that leads to painless temporary loss of vision in the affected eye
What can cause papilloedema?
optic disk swells
Raised intracranial pressure is transmitted to the meninges & subarachnoid space around the optic nerve (CN II) that slows retinal venous drainage via the central retinal vein
What are the layers of eyelids
skin
connective tissue
muscle (orbicularis oculi)
orbital septum
tarsus
conjunctiva
What is the orbital septum?
Anterior border of orbit continuous with periosteum
What is the space between eyelids called?
palpebral fissure
What is the role of the superior/inferior tarsus?
eyelid support
What is preseptal cellulitis?
what is it important to differentiate from?
▪ Infection of the skin/subcutaneous tissue (superficial layers) anterior to the orbital septum
▪ Important to differentiate from orbital cellulitis
What is orbital cellulitis?
what is the threat?
▪ Infection posterior to the orbital septum
▪ Pain on movements of the eye that are restricted along with proptosis (bulging of the eye)
▪ Threatens vision & there is risk of infection spread to cavernous sinus or meninges/brain
What is conjunctivitis?
(pink eye) Inflammation of the membrane covering the posterior surface of the eyelid & eyeball
What is the sensory innervation of the eyelids?
CN V1, V2
What is the arterial supply of the eyelids from?
via the external carotid (facial, transverse facial, superficial temporal) & internal carotid (supratrochlear, supraorbital, lacrimal) arteries
What is venous drainage of the eyelids from?
veins following arteries
What is lymphatic drainage via?
parotid nodes
What are the actions of the orbicularis oculi and what is it innervated by?
Its actions are to close the eyelids gently (involuntary or blinking reflex; palpebral part) or tightly (voluntary; orbital part)
Innervated by the facial nerve (CN VII)
What can malfunction of the orbicularis oculi cause?
may lead to sagging of the lower eyelid, leakage of tears & dry eyes with the potential for corneal ulceration
Where is the lacrimal gland?
upper lateral corner of orbit
Where are tears screted from the lacrimal gland?
Tears are secreted into the conjunctival sac & continually washed across the eye by blinking of the eyelids
How do tears drain?
Tears form a tiny lake at the medial angle of the eye where the lacrimal caruncle lies
Tears drain via punctae to canaliculi, to lacrimal sac, to nasolacrimal duct & to inferior nasal meatus
What is the parasympathetic supply of the lacrimal gland?
path
- Preganglionic parasympathetic fibres from facial nerve (CN VII) nervus intermedius
- Travel in greater petrosal nerve & then nerve of pterygoid canal
- Arrive in the pterygopalatine (‘hay fever’) ganglion
- Postganglionic parasympathetic fibres hitch-hike with zygomatic branch of CN V2 to reach the lacrimal gland
What are the extraocular muscles?
superior oblique
levator palpebrae superioris
superior rectus
medial rectus
lateral rectus
inferior oblique
inferior rectus
from top to bottom
What is the innervation of each extraocular muscle?
superior oblique (IV)
levator palpebrae superioris (III)
superior rectus (III)
medial rectus (III)
lateral rectus (VI)
inferior oblique (III)
infeior rectus (III)
LR6 SO4 R3
What action does each extraocular muscle carry out?
Lateral Rectus: Abduction (moves the eye outward, away from the nose).
Medial Rectus: Adduction (moves the eye inward, toward the nose).
Superior Rectus: Intorsion (twisting of the top of the eye towards the nose)
Inferior Rectus: Extorsion (rotates the top of the eye away from the nose)
Superior Oblique: Intorsion
Inferior Oblique: Extorsion
What is the function of the levator palpebrae superioris?
raising and retracting the upper eyelid
What does the oculmotor nerve supply and carry?
- Supply extraocular muscles as indicated in the previous diagram
- Supply levator palpebrae superioris
- Carry parasympathetics for pupil constriction & accommodation
- Carry sympathetics to supply the smooth muscle component of levator palpebrae superioris (also termed as the superior tarsal muscle)
What can injury of CNIII cause?
remove the parasympathetic pupil constriction leading to a dilated pupil with ptosis (complete loss of levator palpebrae superioris) & the eye is turned downwards & outwards (superior oblique & lateral rectus are intact)
What can CNIII palsy cause?
eaves the superior oblique & lateral rectus unopposed to turn the eye downwards & outwards (divergent squint) along with ptosis (drooping of superior eyelid)
What can compress CNIII?
what does the CNIII lie between?
CN III also passes between the posterior cerebral & superior cerebellar arteries before lying close to the posterior communicating artery
Aneurysms of those vessels may compress CN III
What is ptosis?
drooping of superior eyelid
What muscles are unaffected by CNIII palsy
what actions can they still carry out?
CN IV (trochlear) supplies the superior oblique to turn the eye downwards & laterally
CN VI (abducens) supplies the lateral rectus to abduct the eye outwards
What does CN IV palsy cause?
superior oblique muscle weak, and makes looking down (going downstairs & reading books) difficult
What does CNVI palsy out?
CN VI palsy leaves lateral rectus weak, and therefore the muscles supplied by CN III, CN IV will pull the eye inward causing (convergent squint )
What is the relation of CNIII, IV, VI to the cavernous sinus?
pass anteriorly in the cavernous sinus or its wall to enter the orbit through the superior orbital fissure
What plexus do the CNIII, IV and VI pass close to?
sympathetic fibres forming the plexus on the internal carotid artery & may pick up sympathetic fibres
What is the general structure of the eyeball?
the anterior & posterior chambers are separated by the iris but communicate via the pupil & contain aqueous humour
What are the layers of the eyeball?
The sclera forms the outer fibrous layer (replaced by the cornea anteriorly), then is the vascular choroid layer followed by the retina which is the innermost layer
What is the thicker part of the retina?
the optic part of the retina
What is the choroid and what does it continue as?
The choroid (vascular layer of the eye) continues as the ciliary body, which forms a supportive ring around the lens and iris.
What does the ciliaris muscle in the ciliary body do?
under what nervous control is this?
When the ciliary muscle contracts (under parasympathetic control, Cranial Nerve III), it makes the ring smaller, relaxes the suspensory ligaments, and allows the lens to become rounder. This helps in focusing on close objects (accommodation).
What muscles does the iris contain, what are they innervated by and what is their actions?
Sphincter pupillae (controlled by parasympathetic system, CN III, Edinger-Westphal nucleus): constricts the pupil.
Dilator pupillae (controlled by the sympathetic system): dilates the pupil.
What is the aqueous humour secreted by and what does it reabsorb/drain to?
Produced by the ciliary body.
Drains through the scleral venous sinus (canal of Schlemm).
What is the function of the aqueous humour?
keeps your eye inflated and provides nourishment
What is the cause of glaucoma and how can drugs help?
Caused by increased pressure if drainage is blocked. Drugs that constrict the pupil can help by pulling open the drainage channels
Are the zonular fibres tense or relaxed when the ciliary muscles contact under parasympathetic innervation?
relaxed
Why does the lens become more spherical during parasympathetic stimulation?
This increased curvature/thickness allows the lens to bend light more sharply (refract), focusing it onto the retina for close-up vision.
What is the function of the scleral venous sinus (canal of Schlemm)?
to collect the aqueous humor from the anterior chamber of the eyeball and deliver it to the veins of the eyeball
