What bones form the walls of the orbit?
Roof = frontal, lesser wing of sphenoid
Floor = maxilla, palatine, zygomatic
Medial = ethmoid, sphenoid
Lateral = zygomatic, greater wing of sphenoid
Which bones of the orbit are must vulnerable to orbital injuries
Medial wall and floor
Which direction does the apex of the orbit point?
posteriorly
Which direction does the base of the orbit point?
Anteriorly
Name the 3 openings at the orbit apex and what they transmit
Superior orbital fissure = trochlear (CN IV), oculomotor (CN III), abducens (CN VI), superior ophthalmic vein
Inferior orbital fissure = maxillary N (branch of CN V), inferior ophthalmic vein
Optic canal = optic N, ophthalmic artery
What structures are closely related to the orbit?
Ethmoid air cells
Maxillary sinus
Anterior cranial fossa
What is an orbital blow out fracture?
Sudden increased in intra-orbital pressure = fractures floor
Orbital contents can prolapse to maxillary sinus
Fracture site can trap structures (extra orbital muscle located near floor)
Outline the presenting features of an orbital blow out fracture?
Bruising
Eye not moving = anchoring by nipping of the orbital contents
Periorbital swelling = eyelids might be closed
Double vision
Anaesthesia over affected cheek = cutaneous branches of maxillary division of trigeminal N = infra orbital N runs through floor of orbit, out through infraorbital foramen and innervates cheek and lower eye
How does an orbital blow out fracture present on x-ray?
Tear drop sign = prolapse of orbit contents to maxillary sinus through orbital floor
Evidence of fluid in axilla = blood accumulation
What is the role of the eyelids?
Protect eye when palpebral fissure is closed
What is the contents of the eyelid?
Tarsal plates (fibrous skeleton) = tarus superior/inferior
Muscles
Glands at the edges of eyelids
Outline the contents of the orbital cavity
Lacrimal apparatus
Nerves
Blood vessels
Orbital fat
Globe of eye, and its internal structures
Extra-ocular muscles = 6 move the eye
What are the tarsal plates of the eye?
Provide connective tissue skeleton to the eyelid
Firmness and shape
Contain tarsal glands
Describe the orbital septum
Thin sheet of fibrous tissue
Originating from orbital rim
Blends with tendon of LPS and tarsal plate
Separates intra-orbital contents from eyelid fat and orbicularis oculi muscle
What acts as a barrier against infect spreading from the pre-septal space to post-septal space?
Orbital septum
Outline periorbital cellulitis
Can be pre-septal (in front of orbital septum) OR post-septal (behind orbital septum)
Cellulitis of orbital structures
Secondary to = infection from bites, periorbital trauma, sinuses
Complications = abscess, spread of infect intracranially (= cavernous sinus thrombosis)
Treat = IV Abx
What enables infection to spread from the orbit, to intracranially?
Via venous drainage
Name the glands of the eyelid
Meibomian = within tarsal plates, secrete to edge of eyelid
Glands of Zeis = edge of eyelash follicle
Outline the role of glands within the tarsal plate
secrete an oily (lipid-rich) substance onto edges of lid = help prevent evaporation of tear film and tear spillage
Describe a meibomian cyst
Blockage of meibomain glands within the tarsal plate
No pain, red
Describe a stye
Blockage of eyelash follicles – staph infection
Painful, red
What is the lacrimal apparatus?
Secretes tears into conjunctival sac
Made up of =
1) Lacrimal gland
2) Lacrimal sac
3) Nasolacrimal duct
Outline the role of blinking
washes tear film across front of eye
rinsing and lubricating the conjunctivae and cornea
What is the conjunctiva and its role?
Transparent mucous membrane
Produces mucous and tears
Covers sclera and lines inside of eyelids = forming conjunctival sacs
Highly vascular
Describe conjunctivitis (pink eye)
Inflamed conjunctiva
Describe subconjunctival haemorrhage
Haemorrhage in the conjunctiva
Treat = resolves self
Outline the blood vessels of the orbit
Veins = drain to cavernous sinus, pterygoid venous plexus and facial veins
Arteries = ophthalmic A (brach of internal carotid)
Name the nerves of the orbit
Ophthalmic Va of trigeminal = general sensory
Optic N = special sensory
Oculomotor, trochlear, abducens = motor Ns
What maintains the position of the eyeball
Suspensory lig
Rectus muscle
Orbital fat
Name the structures, out to in, of the eye
Cornea = clear
Aqueous humour
Iris = dilate/constrict under autonomic control
Pupil
Lens = inside fibrosis capsule, suspended by ligs attached to ciliary body
Vitreous chamber = vitrous humour
Retina
Macula
Optic disk
Optic N
What is the macula?
Near the centre of the retina in the eye,
Region of keenest vision = high conc of cones
Visible on fundoscopy (slightly darker area of retina)
What is the optic disc?
Raised disc on the retina at the point of entry of the optic nerve
Lacking visual receptors and so creating a blind spot.
What is the retina?
Inner photosensitive layer = nerve impulses that pass to optic N
Outer pigmented layer lying nearest to choroid
What pulls the lens into a flat shape?
Ligs and ciliary body muscle
Naturally = fat shape
What fills the vitreous chamber?
Transparent, jelly-like vitreous humour
Where is the anterior chamber of the eye?
Aqueous humor-filled space
Between cornea and iris
Communicates with posterior chamber via the pupil
Where is the posterior chamber of the eye?
Aqueous humor-filled space
Between iris and suspensory lig of lens/ciliary processes
How is aqueous humour of the eye produced?
Ciliary processes within ciliary body
Flows from posterior chamber, through pupil into anterior chamber
What is the role of aqueous humour?
Nourishment of the lens which is avascular
How is aqueous humour of the eye drained?
Iridocorneal angle = between iris and cornea
Into the canal of Schlemm via trabecular meshwork
What is glaucoma?
Narrowed iridocorneal angle = build up of aqueous humour = rise in intra-ocular pressure = press on optic N
Open-angle glaucoma = blockage within trabecular meshwork
How does the photosensitive layer of the retina generate action potentials in response to light?
Refraction = light (photons) reaches retina = detected by rods/cons = AP generated = pass ganglion of optic disk = optic nerve
Outline refraction in the eye
Bending of light by the cornea
Through the vitreous humour
To the retina
How is light refracted when focusing on near objects?
Light from near-objects – more divergent = requires more refraction
Accommodation reflex =
1) pupil constricts
2) eyes converge = image brought to focus on same point of retina in both eyes
3) lens becomes fatter by suspensory ligs from ciliary body releasing
How does age effects the lens?
Lens becomes stiffer = cant become fatter= cant focus = keep objects at arms length
Presbyopia
Outline cataracts
Effects lens = protein deposits in the lens
Light cant pass through lens to retina
Name the extrinsic muscles of the eye
Inferior oblique (CN III)
Superior oblique (CN IV)
Medial rectus (CN III)
Lateral rectus (CN VI)
Inferior rectus (CN III)
Superior rectus (CN III)
Name the intrinsic muscles of the eye
Ciliary muscle = changes thickness of lens
Iris = constricts/dilates pupil
Which cranial nerves supply the muscles that move the eyeball?
CN III
CN IV
CN VI
Where do most of the muscles that move the eye originate from?
Common tendonas origin – apex of orbital cavity
What is the trochlear?
Pulley in the eye – superior obliques runs through it, being redirected to attach to the eye laterally
Discuss the medial rectus
Adducts
Problem = oculomotor N
Discuss the lateral rectus
Abducts
Problem = abducens N
Discus the superior rectus
Elevate, medial
= up and in
Test = move eye to lateral position (lateral rectus) then move eyeball up
Problem = oculomotor N
Discuss the inferior rectus
Depress, medial
= down and in
Tests = move eye to lateral position (lateral rectus) then move eyeball down
Problem = oculomotor N
Discuss the superior oblique
Depress, lateral, intort
= down and out
Test = move eye into medial position (medial rectus) then move eyeball down
Problem = trochlear N
Discuss the inferior oblique
Elevate, lateral, extort
= up and out
Test = move eye to medial position (medial rectus) then move eyeball up
Problem = oculomotor N
Define intorsion and extorsion
Intort = inward rotation
Extort = outward rotation
Explain how moving the eyeball to an alternative position and then moving it up or down isolates the testing of an individual muscle?
Move eyeball when the direction of gaze is inline with pull of muscle in order to test it
What is a cranial nerve palsy?
Cranial nerve pathology = complete or partial weakness/paralysis
Causes = congenital, trauma, vascular disease (hypertension, DM, strokes, aneurysms, infect, increased ICP
Outline CN III palsy (down and out syndrome)
Innervates muscle of eyelid = loss = ptosis
Parasympathetic to sphincter pupillae = loss = dilation
Differential = vasculopathic, tumour, aneurysm
Outline CN IV palsy
Innervates superior oblique muscle
Lose of normal action = eyeball held extorted, up and in
Compensate by tilting head slightly
Report diff looking down medially (walking down stair, reading)
Differential = vasculopathic, tumour, congenital, trauma
Outline CN VI palsy
Innervated lateral rectus
Unopposed pull of medial rectus muscle
Unable to Abduct eye on affected side
Diplopia
Differential = vasculopathic, tumour, cranial pressure
How is light sensed in the eye?
Neurosensory layer of the retina
Cones = high visual acuity and colour vision
Rods = vision in low light, do not discern colours
Briefly describe retinal detachment
Pigmented layer detaches from neurosensory layer
Can occur spontaneous, or via trauma
Strips photoreceptors of blood supply
What types of cones exist?
Red
Green
Blue
What is colour blindness?
Absence/dysfunction of one of the cone types
What is the optic disk?
Accumulation of retinal axons
No photoreceptors = blind spot
What are photoreceptors?
Rods and cones
Define diplopia
Double vision
Define presbyopia
Hardening of the lens of the eye causing the eye to focus light behind rather than on the retina when looking at close objects
What is a papilloedema?
Optic disk swelling that is caused by increased intracranial pressure
Which structure drains tears from the conjunctival sac directly to the nasal cavity?
nasolacrimal duct
Which two cranial nerves are involved in the corneal reflex?
A reflex response to protect the eye, particularly the cornea, involves first sensing the irritation (via CN Va) which is the afferent (=sensory) arm of this reflex.
The reflex efferent (= motor) response is via the facial nerve, to quickly close our eye (orbicularis oculi).
Which two cranial nerves are responsible for pupillary light reflex?
CN II Optic = afferent
CN III = efferent