5) The orbit & the eye Flashcards
What are the boundaries of the orbit?
Roof - Frontal & Sphenoid bones
Floor - Maxilla, Zygomatic (& palatine)
Medial - Ethmoid, Maxilla, Lacrimal
Lateral - Zygomatic, Sphenoid
Where do fractures of the orbit usually occur?
Bony sutures
Medial & inferior walls thin
Medial - Can involve Ethmoidal & Sphenoidal sinus
Inferior - Can involve Maxillary sinus
What is a ‘blow out’ fracture?
Fracture that displaces the orbital walls & contents
Muscle entrapment
Diplopia
Infection
Describe Enopthalmos
Depression of eye
opposite of exophthalmos
Infraorbital bleeding may push eyeball back out (pulsatile)
What are the contents of the Superior Orbital Fissure?
Large French Teenagers…
Large French Teenagers Sit Numb In Anticipation Of Sweets (Lateral to Medial): Lacrimal nerve Frontal nerve Trochlear nerve Superior branch of oculomotor nerve Nasociliary nerve Inferior branch of oculomotor nerve Abducens nerve Ophthalmic veins Sympathetic nerves
Describe the optic nerve
Exits orbit via optic canal
Coverings of pia, arachnoid & dura maters of meninges
(continuous with brain, infection spread)
Central artery & vein
Raised ICP - venous engorgement, papilloedema (optic disc swelling)
Name the 7 extraocular muscles of the orbit
4 Recti: Superior, Inferior, Medial & Lateral 2 Obliques: Superior & Inferior & Levator Palpebrae superioris
What is the innervation of the extraocular muscles of the orbit?
LR6SO4R3
Lateral Rectus - CN VI (Abducens)
Superior Oblique - CN IV (Trochlear)
all the Rest - CN III (oculomotor)
What is an abducent nerve palsy?
Loss of innervation of Lateral Rectus
- Unable to abduct pupil (move laterally)
- Pupil fully adducted (unopposed medial rectus)
Caused by fractures of cavernous sinus/orbit
What is a trochlear nerve palsy?
Loss of innervation to Superior Oblique
- Unable to look down when eye adducted
Caused by orbital fractures/stretching of nerve around brainstem
What is an oculomotor nerve palsy?
Loss of innervation to ‘All the Rest’
- Ptosis (loss of LPS, unopposed orbicularis oculi)
- Fully dilated, non-reactive pupil (loss of sphincter pupillae, unopposed dilator pupillae)
- eye moved DOWN & OUT (unopposed LR & SO)
Caused by fractures involving cavernous sinus or aneurysms
What is the blood supply to the eye?
Ophthalmic artery (branch of ICA) Central artery of Retina (branch of ophthalmic)
End arteries - obstruction, instant & total blindness
Describe the venous drainage of the eye
Superior & Inferior Ophthalmic veins drain into cavernous sinus
Central vein of Retina drain into cavernous sinus
Occlusion - slow, painless loss of vision
Infections may spread via this route from eye to brain
What is the function of the eyelids?
Protect cornea & eyeball
Keep cornea moist - cover with lacrimal fluid via blinking
What strengthens the eyelids?
Tarsal plates, dense bands of connective tissue containing Tarsal glands (lubricate edges of eyelids & prevent sticking)
What 4 main things make up the lacrimal apparatus?
Lacrimal gland (secretes lacrimal fluid - tears)
Lacrimal ducts
Lacrimal canaliculi
Nasolacrimal duct
Which muscles open the eyelids?
Levator palpebrae superioris (CN III)
+ Superior Tarsal muscles
(Horner’s Syndrome)
Which muscles close the eyelid?
Orbicularis Oculi (CN VII)
Bell’s Palsy
What happens if the eyelids are prevented from closing properly?
Protective blinking lost
Cornea becomes dry, unprotected from dust etc
Irritation of eyeball - excessive tear formation
What are the 3 layers of the eyeball?
Outer protective layer
Middle vascular layer
Inner retina layer
What makes up the outer protective layer of the eyeball?
Sclera
Cornea
What makes up the middle vascular layer of the eyeball?
Choroid
Ciliary body
Iris
What makes up the inner retina layer of the eyeball?
Optic part - photosensitive
Non-visual part
What 3 things is the retina made up of?
Fundus
Macula
Optic Disc
What is myopia?
Short or near-sight, “short-sightedness”
Image focussed in front of retina
(Long distance objects are out of focus)
What is hyeropia/hypermetropia?
Long or far-sight, “long-sightedness”
Image focussed behind the retina
(Short distance objects are out of focus)
What is presbyopia?
Far sight “long-sightedness”
Due to age-related changes of lens
What is the purpose of aqueous humor?
Responsible for intraocular pressure
Produced by ciliary process
Drains into scleral venous sinus
How is glaucoma caused?
Raised intraocular pressure
Outflow of aqueous humor blocked
Pressure builds up in anterior & posterior chambers of eye
How does short-sightedness (myopia) occur?
Parasympathetic activity of CN III
Sphincter like contraction of ciliary muscle
Lens more globe like/fatter
How does long-sightedness (hyeropia) occur?
No parasympathetic activity to ciliary muscles
Lens stretched
Flatter lens
Becomes thicker with age (presbyopia)
What are cataracts?
Clouding of the lens
Decreases vision
Reduced focusing power of lens
Name some of the causes of cataracts
Age Trauma Radiation Genetics Skin diseases Drug use
What is the purpose of vitreous humor?
Holds retina in place
Retina:
Rods - low light black & white
Cones - Bright light, colour vision
What is the corneal reflex testing?
Contraction of the orbicularis oculi causing the eye to blink
Afferent fibres - Ophthalmic nerve (Vi)
Efferent fibres - Temporal & zygomatic branches of facial nerve
Loss of reflex - corneal ulceration
What is mydriasis?
Dilation of the pupil
- under activity of PSNS, lack of innervation to sphincter pupillae
- over activity of SNS, increase innervation to dilator pupillae
May be caused by raised ICP
How is blindness related to glaucoma?
Compression of inner layer of eyeball (retina) & central artery of retina
How may retinal detachment be caused?
Blow to eye (detachment may occur days or weeks after trauma)
Pigment cell layer not firmly attached to neural layer
Flashes of light or specks seen
What is coloboma?
Absence of a section of the iris
Birth defect, penetrating or non-penetrating injuries to eyeball, surgical iridectomy
What is hyphema?
Haemorrhage within the anterior chamber of the eyeball
Usually blunt force trauma to eyeball
Haemorrhages usually stops within few days
What is exopthalmos?
Protrusion of the eye
whites of sclera visible all around cornea & iris
What are the causes of exopthalmos?
Bilateral: Grave’s disease (Hyperthyroidism)
Unilateral: Aneurysm, haematoma
What may be the consequences of raised intracranial pressure?
Compression of optic nerve & blood vessel supplying retina
Blindness
Vein occluded before artery, oedema of retina (papilloedema)
What is a meibomian cyst?
Blocked tarsal gland
Lies behind eyelash within eyelid
What is a stye?
Infection of the sebaceous gland at the base of the eyelash
