9 Flashcards
1
Q
Describe the orbital cavity
A
- pyramid shaped with apex pointing posteriorly
- four bony walls: frontal bone, sphenoid bone, zygomatic bone, thmoid bone, lacrimal bone, palatine bone
See S9 anatomy slide 3
2
Q
What is the weakest part of the orbit, and what happens if it is fractured?
A
- inferior (floor) and medial walls
- vulnerable to fracture
- leads to sudden increase in intraorbital pressure
- often the floor that fractures (orbital blow-out fracture)
- orbital contents can bleed into maxillary sinus and prevent upward gaze on the affect side
- pt. Will have history of trauma to eye, periorbital swelling, painful, double vision, numbness over cheek, lower eyelid and upper lip (b/c infraorbital nerve is affected)
- usually not medial wall because ethmoid air cells act as buttresses and give extra strength to the medial wall but the air cells are prone to infection which can cause orbital cellulitis
See S9 anatomy slide 6-7
3
Q
What are the blood vessels and nerves of the orbit and what openings do they go through?
A
- main arterial supply is ophthalmic artery (from internal carotid) and its subsequent branches and it goes through optic canal
- opthalmic veins (superior (superior orbital fissure) and inferior (inferior orbital fissure)) drain venous blood into cavernous sinus, pterygoid plexus and facial vein
- general sensory from the eye (including conjunctiva, cornea): trigeminal ophthalmic division which goes through superior orbital fissure
- special sensory vision from retina: optic nerve which goes through optic canal
- motor nerve to muscles: oculomotor, trochlear, abducens which all go through superior orbital fissure
See S9 anatomy slide 4
4
Q
What are the anatomical relation for the orbit and their implications?
A
- paranasal air sinuses (maxillary and ethmoid)
- nasal cavity (nasolacrimal duct, connects it to orbital fossa)
- anterior cranial fossa
Implications for
- orbital trauma
- spread of infection
See S9 anatomy slide 5
5
Q
Describe the eyelid
A
- consists of skin, subcutaneous tissue, tarsal plate, muscles
- tarsal plates: dense CT which strengthens the eyelid and gives their shape, contains tarsal glands
- contains lacrimal glands which protect eye and prevent it from drying out
- muscles: orbicularis oculi (palpebral part) which closes eyelid and levator palpebrae superioris which retracts eyelid
- contains glands: meibomian glands which secrete oily substance that lubricate the eyelid and prevent tears evaportating too quickly and sebaceous glands associated with lash follicle
See S9 anatomy slide 8
6
Q
What pathologies can occur in the eyelid?
A
Stye
- if the glands or hair follicles are blocked then a stye is produced
- they are a self-limiting so can use a warm compress to resolve it
- more superficial and close to edge
- painful
Meibomian cyst
- occurs when meibomian gland is blocked
- oily secretions are built up into a lump
- deeper within eyelid
Blepharitis
- inflammation of edges of the lid
- pt. Will experience crusting
- includes skin, lashes and meibomian glands
See S9 anatomy slide 9
7
Q
Describe the orbital septum
A
- thin sheet of fibrous tissue originating from orbital rim periosteum bleeds with tarsal plates
- directly underneath the orbicularis oculi
- orbital septum and tarsal plates separate subcutaneous tissue or eyelid and orbicularis oculi form intra-orbital contents
- acts as a barrier against superficial infection spreading from the pre-septal to post-septal space (orbital cavity proper)
See S9 anatomy slide 10
8
Q
What is periorbital (pre-septal) cellulitis?
A
- infection occuring WITHIN eyelid tissue, SUPERFICAL to orbital septum
- secondary to superficial infections (ex. Bites, wounds)
- may be secondary to bacterial sinusitis in kids
- confined to tissues superficial to orbital septum (and tarsal plates) so deeper structures are unaffected
- ocular function is unaffected
- can be difficult to differentiate between peri-orbital and the more severe orbital cellulitis
- if any doubt, urgently refer IV and surgical drainage
See S9 anatomy slide 11
9
Q
What is orbital (post-septal) cellulitis?
A
- infection WITHIN the orbit (not globe of eye) posterior or deep to the orbital septum
- will push the eye forward
- painful eye movements and they may be reduced
- as pressure increases, optic nerve may be involved which will affect vision (reduced visual acuity)
- proptosis/exopthalmous
- orbital veins drain to cavernous sinus, pterygoid venous plexus and facial veins
- potential route for infection to spread intracranially (ex. Cavernous sinus thrombosis, meningitis)
See S9 anatomy slides 12-13
10
Q
List the contents of the orbital cavity
A
- eyeball
- fat
- associated extra-ocular muscles
- nerves and blood vessels
- lacrimal apparatus
11
Q
Describe the lacrimal apparatus
A
- structures involved in tear film production and drainage
- consists of lacrimal gland, lacrimal ducts and lacrimal canaliculi
- lacrimal gland secretes tears and is under parasympathetic control via facial nerve
- tears enter conjunctival sac through lacrimal ducts and pass into the lacrimal lake
- from here the fluid drains into lacrimal sac before going to nasal cavity via the nasolacrimal duct
- Blinking (caused by palpebral orbicularis oculi) distributes tear film across front of eye, rinsing and lubricating conjunctivae and cornea
See S9 anatomy slide 15
12
Q
What is epiphora?
A
- obstruction to the drainage system in lacrimal apparatus
- overflow of tears over lower eyelid
13
Q
How is the eye protected from corneal abrasions and ulcerations?
A
- outer epithelial layer of cornea is constantly undergoing mitosis
- so easily regenerates if damaged
- injuries that penetrate deeper into cornea can lead to permanent scarring and possible visual impairment
14
Q
Describe the anatomy of the eyeball
A
- globe with 3 layers
- Outer: sclera (white of eye), tough outer layer that is a continuation of dura around optic nerve and is continuous anteriorly as transparent CORNEA; provides attachment for extra-ocular muscles and gives shape to the eyeball
- Middle: choroid, ciliary body and iris (vascular)
- Inner: retina which has an inner photosensitive layer (neurosensory cell layer) lying on an outer pigmented epithelial cell layer
Eyeball is maintained in position by
- suspensions ligament (sits underneath like a sling)
- extra-ocular muscles
- supported by lots of bridal fat
See S9 anatomy slide 16
15
Q
Describe the two layers of the retina
A
Pigmented epithelial cell layer
- contains melanin which helps to absorb scattered light passing into the eye
- reduced reflection and allows us to focus images appropriately on to the retina
Neurosensory layer
- area of retina that senses light
- where photoreceptors (rods and cones) are found
16
Q
What is the conjunctival membrane (aka conjunctivae) and what happens when it is damaged?
A
- thin transparent layer of cells covering the sclera except the cornea
- is highly vascular with blood vessels within membrane
- produced mucous component of tear film
Inflammation
- known as conjunctivitis
- highly contagious
- eye appears red
- often viral aetiology
- eye feels uncomfortable and “gritty” with tearing
- treatment: good hygiene and eye drops
Haemorrhage
- known as subconjunctival haemorrhage
- causes “red eye”
- when one of the vessels ruptures
- common, not painful
- slowly resolves, like a bruise
See S9 anatomy slide 17
17
Q
What is the limbus?
A
-junction between conjunctivae and cornea
18
Q
Describe how light is used by the eye
A
- need transparent structures and medium
- need to refract light to bring to a focal point
- most of refraction occurs between air and cornea
- several structures refract light (all transparent): cornea and it’s associated tear film, Lens, aqueous humour and vitreous Humour
Cones
- located in the macula (slightly darker than rest of retina, lies lateral to optic disc) of the retina
- fovea: very centre of macula which contains only cones
- responsible for high visual acuity and colour viscous
Rods
- active at low light levels, do not mediate colour vision
- abundant in peripheral parts of retina
- photoreceptors convert the light energy into electric impulses
- action potentionasl generated in response to light via retinal ganglion cells (RGC)
- RGC axons collect in area of optic disc forming the optic nerve
- optic disc= blind spot since no photoreceptors are present
- action potentials propagated along visual pathway to occipital lobe for interpretation
See S9 anatomy slide 19, 22-23
19
Q
How does the shape of your eyeball affect your ability to focus light appropriately onto retina?
A
- Myopia: short-sighted, eyeball too long so point of focus is too far in front of retina
- Hypermetriopia: long-sighted, eyeball too short so point fo focus
20
Q
What is the accommodation reflex?
A
- focussing NEAR objects requires greater refraction of light
- with very near objects, light rays are more divergent and greater refraction beyond the capabilities of the cornea is needed
- so we must increase the refractive power of the eye through the accommodation reflex
- consists of 3 components: automatic contraction of pupil, convergence of eyes, thickening of lens
- pupillary constriction ensures light from the near object passes through centre of lens
- convergence ensures that both retinae focus on the one object
- contraction of ciliary muscles moves ciliar body closer to the lens and so the pull of the circular suspensory ligament loosens the lens which allows the lens to be more biconvex (rounder)
- as we age, lens becomes stiffer and less able to change shape
- known as PRESBYOPIA
See S9 anatomy slide 20-21
