The Eye Flashcards
What forms the roof of the bony orbit?
Frontal bone and lesser wing of the sphenoid
What separates the orbit from the anterior cranial fossa?
Frontal bone
What forms the floor of the bony orbit?
Maxilla, palatine and zygomatic bones
What forms the medial wall of the bony orbit?
Ethmoid, maxilla, lacrimal and sphenoid bones
What are the three main pathways by which structures can enter and leave the orbit?
1) Optic canal
2) Superior orbital fissure
3) Inferior orbital fissure
What does the optic canal convey?
Optic nerve and opthalmic artery
What does the superior orbital fissure convey?
CN III, CN IV, CN VI and the superior opthalmic vein
What does the inferior orbital fissure convey?
Maxillary nerve (branch of CN V), inferior opthalmic vein and sympathetic nerves
In a blowout fracture, where do orbital contents commonly herniate?
Ethmoid and maxillary sinuses as the medial and inferior walls of the orbit are the weakest
What are the three layers of the eyeball?
Fibrous, vascular and inner layers
What does the fibrous layer of the eyeball consist of?
Sclera and cornea
What does the vascular layer of the eyeball consist of?
1) Choroid (a layer of connective tissue and blood vessels that provides nourishment to the outer layers of the retina)
2) Ciliary body (attached to lens of the eye to control its shape)
3) Iris (has the pupil in the middle - between lens and cornea)
What does the inner layer of the eyeball consist of?
Retina
What does the retina consist of?
Neural layer - consists of photoreceptors
Pigmented layer - supports the neural layer
What marks the centre of the retina?
Macula
What does the macula contain?
Fovea - high concentration of light detecting cells
What is the fovea responsible for?
High acuity vision
What is the area that the optic nerve enters the retina known as?
Optic dic
What are the two fluid filled areas in the eye known as?
Anterior and posterior chambers
Where is the anterior chamber located?
Between cornea and iris
Where is the posterior chamber located?
Between iris and ciliary processes
What are the anterior and posterior chambers filled with?
Aqueous humor
What drains aqueous humor?
Trabecular meshwork - an area of tissue at the base of the cornea
What condition can result if the drainage of aqueous humor is obstructed?
Glaucoma
What is open angle glaucoma?
When the outflow of aqueous humor through the trabecular meshwork is reduced - causing a gradual reduction of the peripheral vision
What is closed angle glaucoma?
Where the iris is forced against the trabecular meshwork, preventing any drainage of aqueous humor (opthalmic emergency - can rapidly cause blindness)
How does the eyeball receive arterial blood?
Opthalmic artery - a branch of the ICA
Occlusion of which artery will quickly result in blindness?
Central artery of the retina (branch of opthalmic artery that supplies the internal surface of the retina)
What do the superior and inferior opthalmic veins drain into?
Cavernous sinus
What is papilloedema?
Swelling of the optic disc - usually occurs secondary to raised ICP
What do important anatomical relations of the orbit include?
Paranasal air sinuses, nasal cavity and anterior cranial fossa
What are some complications of periorbital cellulitis?
Abscess formation and spread of infection intracranially -> cavernous sinus thrombosis
How can periorbital cellulitis spread intracranially?
Opthalmic veins drain into cavernous sinus
What causes a meibomian cyst?
Blockage of meibomian gland
What is a stye?
Blockage of hair follicle glands
What is the conjuctiva?
Transparent mucous membrane that produces mucus and tears - covers sclera and lines inside of eyelides (does not cover cornea)
What nerve is responsible for general sensory from the eye?
Opthalmic division of CN V
What nerve is responsible for special sensory vision from the retina?
Optic nerve (CN II)
What nerves the motor nerves to muscles of the eye?
Oculomotor, trochlea, abducens
CN III, IV, VI
What secretes aqueous humor?
Ciliary processes within ciliar body - flows from posterior chamber through pupil to anterior chamber to nourish lens and cornea
What is the name of the angle that aqueous humor drains through?
Iridocorneal angle (between iris and cornea)
Aqueous humor drains via trabecular meshwork into what?
Canal of Schlemm (venous channel draining into venous circulation)
How many extraocular muscles are there?
Seven
What are the extraocular muscles?
Superior rectus, inferior rectus, medial rectus, lateral rectus
Superior oblique, inferior oblique
Levator palpebrae superioris
How many rectus muscles are there in the eye?
4 - superior, inferior, medial, lateral
How many oblique muscles are there in the eye?
2 - superior and inferior
What is the only muscle involved in raising the superior eyelid?
Levator palpebrae superioris (LPS)
What is the name of the portion of levator palpebrae superioris that is smooth muscle and responds to the sympathetic nervous system?
Superior tarsal muscle
What is the action of levator palpebrae superioris?
Raises the upper eyelid
What innervates levator palpebrae superioris?
Oculomotor nerve (CN III)
Note - superior tarsal muscle which is within LPS is innervated by the SNS
Horner’s syndrome refers to a triad of symptoms produced by damage to the sympathetic trunk in the neck. What are these 3 symptoms?
1) Partial ptosis (due to denervation of the superior tarsal muscle)
2) Miosis (due to denervation of dilator pupillae)
3) Anhydrosis on ipsilateral side of face (due to denervation of the sweat glands)
What could Horner’s syndrome suggest?
Apical lung tumour, aortic aneurysm, thyroid carcinoma
How many muscles control eyeball movements?
6 - rectus muscles and oblique muscles
Where do the rectus muscles originate?
Common tendinous ring - surrounds the optic canal - and attach to the sclera
What are the actions of superior rectus?
Mainly elevation
Also contributes to adduction and medial rotation
What are the actions of inferior rectus?
Mainly depression
Also contributes to adduction and lateral rotation
What are the actions of medial rectus?
Adduction of the eyeball
What are the actions of lateral rectus?
Abduction of the eyeball
What are the actions of superior oblique?
Depression, abduction and medial rotation of the eyeball
What is the only muscle that acts on the eyeball to be innervated by the trochlear nerve?
Superior oblique
What innervates superior oblique?
Trochlear nerve
What is the only muscle that acts on the eyeball to be innervated by the abducens nerve?
Lateral rectus
What innervates lateral rectus?
Abducens nerve
What innervates the extraocular muscles?
Oculomotor nerve (CN III) - mainly Trochlear nerve (CN IV) - superior oblique Abducens nerve (CN VI) - lateral rectus
What position does the eyeball take if a patient has a CN III lesion?
Down and out - pulled laterally by lateral rectus and inferiorly by superior oblique (as they are innervated by other cranial nerves)
What would a CN IV lesion do?
Paralyses superior oblique - diplopia and a head tilt away from the site of lesion
What would a CN VI lesion do?
Paralyses lateral rectus - affected eye will be adducted by the resting tone of the medial rectus
What the mnemonic to remember the innervation of the extraocular muscles?
LR6-SO4
Lateral rectus - CN VI
Superior oblique - CN IV
What muscles are responsible for moving the eyes directly upwards?
Superior rectus and inferior oblique
What muscles are responsible for moving the eyes directly downwards?
Inferior rectus and superior oblique
