Session 8 Flashcards
1
Q
Describe the orbital cavity
A
- 4 bony walls
- Pyramid shaped
- Base of pyramid faces outwards; apex deep inside orbital cavity
- Tough orbital rim
2
Q
Which are 2 important bones involved in the orbital cavity?
A
- Ethmoid bone contributes to medial wall
- Maxillary bone contributes to floor
- Contain lots of air cavities
- More susceptible to fracture
- Weakest parts of orbital cavity
3
Q
Outline some key anatomical relations of the orbit
A
- Anterior cranial fossa sits just superior
- Contains frontal lobe - can be damaged in penetrating eye trauma
- Ethmoid air sinuses near medial wall
- Maxillary air sinus forms part of floor
- Connected to nasal cavity via nasolacrimal duct
4
Q
What are the implications for the anatomical relations of the orbit?
A
- Orbital surgery
- Spread of infection into or out of orbit e.g. acute sinusitis affecting ethmoid sinus can spread to orbit
- Orbital trauma
5
Q
How does orbital blowout fracture occur?
A
- Trauma to eye/orbit e.g. eye is hit by fist or ball
- Eyeball propelled back into orbit
- Pressure in orbital cavity suddenly increases
- Pushes against walls of cavity
- Weakest wall (floor of orbit) fractures
6
Q
What does orbital blowout fracture result in?
A
- Orbital contents prolapse
- Bleeding into maxillary sinus
- Soft tissue, blood and muscles near orbital floor can trap in fracture site
- Entrapment prevents upwards gaze (other eye movements may also be restricted)
7
Q
What might be seen on an X-ray/CT scan in someone who has suffered an orbital blowout fracture?
A
- Opacity filling the maxillary sinus beneath the affected eye
8
Q
What is classic presentation of an orbital blowout fracture?
A
- Painful eye
- Periorbital swelling and bruising
- Double vision, worse in vertical gaze
- Numbness over cheek, lower eyelid and upper lip on affected side
9
Q
How do we manage orbital blowout fracture?
A
- CT Orbit and refer to ophthalmology
- Prophylactic antibiotics
- Avoid nose blowing, Valsalva manoeuvres and driving (until diplopia resolves)
- 1 week follow up - symptoms may resolve on their own
- Surgical repair 1-2 weeks post injury if symptoms persisit
10
Q
What does the optic canal transmit?
A
- Optic nerve
- Ophthalmic artery (has several branches including central retinal artery)
11
Q
What does the superior orbital fissure transmit?
A
- Branches of ophthalmic nerve (Va)
- Oculomotor nerve
- Trochlear nerve
- Abducens nerve
- Superior ophthalmic vein (communicates with cavernous sinus)
12
Q
What does the inferior orbital fissure transmit?
A
- Infraorbital nerve (branch Vb)
- Inferior ophthalmic vein (communicates with pterygoid venous plexus
13
Q
Which nerve is responsible for carrying sensation to the eye?
A
- Ophthalmic division of trigeminal nerve
14
Q
What provides the main arterial supply to the orbit and the eye?
A
- Ophthalmic artery (branch of ICA) and its branches
- Incl central retinal artery
15
Q
Outline the pathway taken by the central retinal artery
A
- Runs inside optic nerve
- This allows artery to get inside eyeball and give branches that supply retina
16
Q
What provides the main venous drainage of the orbit and eye?
A
- Ophthalmic veins (superior and inferior)
- Provide connections with cavernous sinus, pterygoid plexus and facial vein
17
Q
Outline the blood supply to the retina
A
- Supplied by central retinal vein
- Also draws supply from underlying choroid layer
- Ciliary arteries feed extensive capillary bed within choroid layer (choriocapillaris)
- Retina requires both circulations to function properly
18
Q
What do the eyelids consist of?
A
- Skin
- Subcutaneous tissue
- Muscles
- Tarsal plate
19
Q
What is the function of the tarsal plates?
A
- Connective tissue
- Give eyelid firmness and shape
20
Q
What are the key muscles that run within the eyelid?
A
- Orbicularis oculi (palpebral part)
- Levator palpebrae superioris
21
Q
What is the action of orbicularis oculi (palpebral part)?
A
- Runs through eyelid itself
- Closes eyelid
- Supplied by facial nerve
22
Q
What is the action of levator palpebrae superioris?
A
- Retracts eye lid
- 2 components
1. Skeletal muscle supplied by oculomotor nerve
2. Superior tarsal muscle (smooth muscle) innervated by sympathetics
23
Q
Which glands are found within the eyelids?
A
1.Meibomian glands
- found within tarsal plate
- modified sebaceous
- provide lipid layer of tear film
- prevent tear evaporation and spillage over lid
2. Glands associated with lash follicle
- oily substance
24
Q
What is a stye?
A
- Due to blockage in gland associated with a hair follicle
- Outer part of lid affected
- Painful
- Red with a white punctum
- Infected (staphylococcus)
- Treat with warm compresses and may need abx
25
What is a Meibomian cyst?
- Due to blockage in Meibomian glands
- Deeper within lid
- Painless
- Firm lump palpable
- Enlarges gradually
- Blocked duct - non-infective
- 1/3 resolve spontaneously
- Surgical incision if persists
26
What is blepharitis?
- Inflammation of eyelid margin
- Multifactorial causes e.g. staphylococcus, Meibomian gland dysfunction
- Crusting, dry eyelids, swollen, red
- Not serious
- Treat with warm compress and lid hygiene
27
What is the orbital septum?
- Thin fibrous sheet originating from orbital rim
- Separates intra-orbital contents from muscle and subcutaneous tissue of eyelid
- Blends with tarsal plates
28
What is the role of the orbital septum?
- Barrier against infection spreading from superficial eyelid region (pre-septal) into the orbital cavity (post-septal)
29
What is infection involving the superficial tissues of the eye called?
- Pre-septal (periorbital) cellulitis
30
What is infection involving tissues within the orbit of the eye called?
- Post-septal cellulitis
- Very concerning
31
What causes pre-septal cellulitis?
- Secondary to superficial infections e.g. from bites, wounds
32
Where does periorbital cellulitis affect the eye?
- Confined to tissues superficial to orbital septum and tarsal plates
- Painful
- Eye movements and vision remain unaffected
33
What should you do if a patient comes in with pre-septal cellulitis?
- If you can't tell whether it's peri-orbital or orbital cellulitis, urgently refer
34
What is orbital (post-septal) cellulitis?
- Infection within the orbit
- Spread of infection from paranasal air sinus
- Proptosis/exophthalmos
- Reduced and painful eye movements
- Reduced visual acuity
35
Why is orbital cellulitis so concerning?
- Orbital veins drain to cavernous sinus and pterygoid venous plexus
- Potential route for infection to spread intracranially
- Can lead to cavernous sinus thrombosis and meningitis
- Damage to optic nerve can cause permanent blindness
36
What are the contents of the orbital cavity?
- Nerves
- Blood vessels
- Lots of fat
- Lacrimal apparatus
- Eyeball (globe)
- Extra-ocular muscles
37
What does tear film consist of?
- Three layers
1. Oily (Meibomian glands)
2. Water (lacrimal gland)
3. Mucus (goblet cells in conjunctiva)
38
What is the function of blinking?
- Distributes tear film across surface of eye
- Rinses and lubricates conjunctiva and cornea
39
How do we drain our tears?
- Lacrimal gland produces tears
- Blinking sweeps tears across surface of eye to medial corner of eye
- Lacrimal punctum
- Lacrimal canaliculus
- Lacrimal sac
- Nasolacrimal duct
- Drains to inferior meatus of nasal cavity
40
What happens if drainage of tears becomes obstructed?
- Epiphora (overflow of tears over lower eyelid)
41
What can block the drainage of tears?
- Infection
- Injury
- Stenosis
42
What maintains the eyeball in position?
- Suspensory ligament (sits underneath it like a sling)
- Extra-ocular muscles
- Lots of orbital fat
43
Describe the conjunctival membrane
- Transparent
- Mucous membrane
- Reflects onto inner surface of upper and lower lid
- Does not run over cornea
- Vascular
44
Outline conjunctivitis
- Uncomfortable, gritty
- Watery +/- discharge
- Infectious (typically viral)
- Very contagious
- Self-limiting
45
Outline sub-conjunctival haemorrhages
- Burst blood vessel in conjunctiva
- Painless
- No other symptoms
- Often spontaneous (without cause)
46
What are the 3 layers of the eye from outermost to innermost?
- Sclera (continues as cornea anteriorly)
- Choroid (vascular; continuous with ciliary body and iris)
- Retina (photosensitive layer
47
Where does the optic nerve start?
- At the optic disc of the retina
- Might lead to a blind spot because there are no photoreceptors at this site
48
What are the points of highest acuity vision?
- Macula
- Fovea
- Thinnest points of retina so light doesn't have to travel through so many cell layers to reach photoreceptors
- Contain lots of cones
- Known as central vision
49
What are the symptoms of a central retinal artery occlusion?
- Sudden painless loss of sight in one eye, developing over seconds
50
What is a central retinal artery occlusion?
- Blockage stopping blood getting to vessels supplying front of retina
- E.g. due to an embolus
- Choroidal layer remains perfused with blood
51
What is seen on examination of an eye with central retinal artery occlusion?
- Pale, ischaemic retina
- Cherry red spot = macula
- Macula is thinnest part of retina so underlying choroid is accentuated in this area
- Appears red due to pallor of ischaemic retina
52
What is the globe of the eye filled with?
- Aqueous humour (water) that bathes lens and cornea to provide them with energy
- Vitreous humour (firm and jelly-like)
53
What are the chambers of the eye?
- Anterior chamber between cornea and iris
- Posterior chamber between iris and lens/ciliary body
54
What is the ciliary body of the eye?
- Contains ciliary muscle and ciliary processes that secrete aqueous humour
55
Outline the production and drainage of aqueous humour
- Secreted by ciliary processes in ciliary body
- Flows from posterior chamber to anterior chamber via pupil
- Nourishes lens and cornea
- Drains through iridocorneal angle
- Via trabecular meshwork into canal of Schlemm
- Ends up in venous circulation
56
What is glaucoma?
- Optic nerve damage secondary to raised intraocular pressure
- Sight threatening
57
What can cause a rise in intra-ocular pressure?
- Blockage in drainage of aqueous humour from anterior chamber
58
Outline open-angle glaucoma
- Chronic
- Most common type
- Many asymptomatic
- Increased intra-ocular pressure leads to increased optic disc cupping
- Gradual loss of peripheral vision
59
Outline closed-angle glaucoma
- Acute
- Less common
- Narrowing of iridocorneal angle so aqueous humour cannot drain
- Ophthalmological emergency
60
What is a typical presentation of acute closed-angle glaucoma?
- Older patients aged 55+ (most common 70s-80s)
- Acutely painful red eye
- Irregular oval-shaped pupil
- Pupil is fixed (doesn't constrict or dilate)
- Blurring of vision
- Halos around light
- Nausea and vomiting
61
How is acute closed-angle glaucoma treated?
- Drugs to reduce IOP
- Surgical treatment
62
How does light enter the eyes so that we can see?
- Light needs to reach and be focused onto macula
- Pupil regulates light entry via action of muscles in iris
- Tear film, cornea and lens refract light to bring it into focus
- Shape of eyeball also important
63
What happens if the eyeball isn't the correct length?
- Too long = myopic/short-sighted
- Too short = hypermetropic/long-sighted
64
What is the accommodation reflex?
- Focusing near objects requires greater refraction of light to focus onto retina
- This is beyond capability of cornea (fixed shape)
65
Outline the accommodation reflex
1. Pupil constricts to limit light coming through
2. Eyes converge to ensure image remains focused on same point of retina in both eyes
3. Lens becomes more biconvex (fatter) by contraction of ciliary muscle
66
What is presbyopia?
- Age-related inability to focus near objects
- Lens becomes stiffer with age and less able to change shape
67
What is the function of the cones?
- Colour vision
- High definition
- Active at high light levels
- Lots found in macula and fovea
68
What is the function of the rods?
- Non-colour vision
- Low acuity
- Active at low light levels
- Lots found in peripheral retina
69
What do the photoreceptors do?
- Convert light signals into action potentials
- These are then propagated via retinal ganglion cells
70
Outline the process of phototransduction
- Action potentials propagated via retinal ganglion cells
- These collect at optic disc to form optic nerve
- Action potentials propagated along visual pathway
- Reach occipital lobe for interpretation
71
What is visual acuity?
- Ability of eye to discern shapes and details of what we see
72
How is visual acuity measured?
- Snellen chart
- Read set of letters of increasingly smaller size
- One eye at a time
- 6m distance
- Normal vision = 6/6
-Top number = 6m distance (constant)
- Bottom number = pt's score
73
What can cause decreased visual acuity?
- Lack of transparency of structures anterior to retina e.g. cataracts
- Changed refractive ability of structures anterior to retina e.g. astigmatism, presbyopia, change in eyeball shape
- Problems with retina or optic nerve e.g. retinal detachment, age-related macular degeneration, optic neuritis
74
How do we discern the cause of decreased visual acuity?
- Check for red reflex using ophthalmoscope
- Absence suggests light prevented from reaching retina and reflecting back
- Red colour is due to colour of retina
75
What are cataracts?
- Clouding of lens due to protein degradation
- Light scatters so isn't focused onto retina
76
What are the different reasons for decreased visual acuity?
- Refractive - due to changes in cornea, lens or eyeball size
- Non-refractive due to retina or optic nerve problem
77
How do we determine whether decreased visual acuity is refractive or non-refractive?
- Repeat Snellen chart with pinhole
- This allows light to enter directly perpendicular to cornea and lens
- Light does not need to be refracted to focus on macula
- If acuity improves with pinhole = refractive
- If acuity does not improve with pinhole = non-refractive
78
Why do we have binocular vision?
- Allows for wider field of vision and depth perception
- Enables 3D vision
-Visual axis of both eyes needs to be aligned so that light hits retina in same spot in each eye
- Also need conjugate eye movement
- Allows brain to fuse information from each eye and create a single image
79
What causes diplopia?
- Misalignment of two visual axes
- Image focuses on different areas of each retina
- Brain unable to fuse information
- 2 images seen, can be displaced horizontally, vertically and/or diagonally
80
What are the extra-ocular muscles?
1. Superior rectus
2. Inferior rectus
3. Medial rectus
4. Lateral rectus
5. Superior oblique
6. Inferior oblique
81
What is the attachment of the extra- ocular muscles?
- Sclera
82
What is the origin of the extra-ocular muscles?
- Apex of orbit
- Except inferior oblique - this originates from floor of orbital cavity anteriorly
- 4 recti arise from a common tendinous ring
83
What is the innervation of the extra-ocular muscles?
- Most are innervated by oculomotor nerve (CN III)
- Lateral rectus innervated by abducens nerve (CN VI)
- Superior oblique innervated by trochlear nerve (CN IV)
84
What direction do the extra-ocular muscles travel in?
- Run in line with axis of orbit
- Therefore some muscles attach at an oblique angle
- Confers several actions of movement on globe
85
Describe the action of the extra-ocular muscles when our gaze is resting
- Even at rest, constancy of activity in all extra-ocular muscles on eyeball
- During resting gaze their actions are balanced allowing for forward gaze
- Each muscle has antagonist of its movement
86
How do the extra-ocular muscles work to allow us to change the position of our gaze?
- Antagonists relax while certain extraocular muscles exert greater pull
- Muscles moving both eyes must be highly coordinated and move simultaneously
- Visual axes must remain aligned for conjugate gaze
87
What are the different directions the eyeball can move in?
- Elevation/depression
- Abduction/adduction (towards nose)
- Intorsion/extorsion
88
What is the action of medial rectus?
- Adduction of eyeball
- Inserts into medial aspect sclera
89
What is the action of lateral rectus?
- Abduction of eyeball
- Inserts into lateral aspect of sclera
90
Where do superior and inferior recti arise from?
- Apex of orbit
91
Where does superior rectus insert?
- Obliquely into superior anterolateral surface of globe
92
What is the action of superior rectus?
- Elevates eyeball
- Slightly adducts
- Slightly intorts
- More powerful elevator when eye is positioned laterally
93
Where does inferior rectus insert?
- Obliquely into anteroinferior surface of globe
94
What is the action of inferior rectus?
- Depresses eyeball
- Slightly adducts
- Slightly extorts
- More powerful depressor when eye is positioned laterally
95
What is the origin of the superior oblique muscle?
- Arises from apex of orbit
- Passes through trochlea
96
Where does superior oblique muscle insert?
- Superior-posterior aspect of globe
97
What is the action of superior oblique?
- Intorts eyeball
- Depresses
- Slightly abducts
- More powerful depressor when eye is positioned medially
98
Where does inferior oblique arise?
- Anteromedial surface of floor of orbit
99
Where does inferior oblique insert?
- Infero-posterior surface of globe
100
What is the action of inferior oblique?
- Extorts eyeball
- Elevates
- Slightly abduct (pulls eye laterally)
- More powerful elevator when eye is positioned medially
101
Which extraocular muscles are stronger elevators and depressors of the eyeball when the eye is in the adducted position?
- Obliques
102
Which extraocular muscles are stronger elevators and depressors of the eyeball when the eye is in the abducted position?
- Recti
103
Outline how the anatomical actions of the extraocular muscles help make sense of abnormalities of gaze
- If a muscle/muscles is weakened, its influence is lost
- Other muscle actions are no longer antagonised (balanced out)
- Resting position of eyeball may deviate (strabismus) due to actions of remaining working muscles
- Difficulties with moving eye in certain directions of gaze
104
If the eye is in an adducted position, which muscle may be damaged?
- Lateral rectus
- Abduction is no longer occurring
- Could be due to CN VI lesion
105
If eye is in an elevated, adducted position, which muscle may be damaged?
- Superior oblique
- Depression and abduction no longer occurring
- Could also be due to CN IV lesion
106
How do we clinically examine eye movements?
- Pt needs to keep head still and follow finger movement
- Draw an H shape with finger
- Test abduction and adduction of eyes (LR and MR)
- When eye position starts abducted, up and down movements is mostly controlled by rectus muscles
- When eye position starts adducted, dominant muscles are obliques for up and down movements
107
What does CN III innervate?
- Superior rectus, inferior rectus, medial rectus, inferior oblique
- Levator palpebrae superioris
- Sphincter pupillae
108
What are the acquired causes of CN III cranial nerve palsies?
- Vasculopathic (microvascular) lesions e.g. due to diabtes/hypertension
- Pupil is spared
- Compressive lesions e.g. due to raised ICP, tumour, posterior communicating artery aneurysm
- Pupil is involved
109
What is ocular misalignment (strabismus)?
- Common in children (congenital or develops in infancy)
- Exact cause not always known
- Treat by cover 1 eye, specific lens prescription, surgery
- In adults it is acquired due to pathology or disease involving neuromuscular junctions or nerves supplying extraocular muscles
110
What kind of damage to nerves can lead to strabismus?
- Vasculopathic - microvascular ischaemia secindary to diabetes or hypertension
- Physical compression e.g. from tumour or aneurysm
- Raised ICP
111
What happens to the eye when CN IV is affected by palsies?
- Loss of intorsion, depression and abduction of eyeball
- Because superior oblique muscle is no longer innervated
- Eye is extorted, slightly elevated and adducted
- Extorsion of eyeball compensated by head tilt
- Worsening diplopia on downward/medial gaze
112
What happens to the eye when CN VI is affected by palsies?
- Innervates lateral rectus
- Unopposed pull of medial rectus muscle
- Unable to abduct eye on affected side
- Diplopia that worsens on horizontal gaze
113
What is the most likely cause for CN III, IV and VI lesions?
- Vasculopathic
- Patients will be otherwise asymptomatic
- Lesions usually self-resolve within a few months
114
In the case of a CN III, IV or VI lesion, what history is concerning?
- Headache +/- vomiting could suggest raised ICP (secondary to tumour or haemorrhage)
- Recent head injury
- Presence of pupil involvement in CN III lesions and eye pain/headache
