Session 9

Question 1

Describe the structure of the orbital cavity

Answer 1

pyramidal shaped with apex pointing posteriorly
Four bony walls.
Base of pyramid faces anteriorly - tough orbital rip

Question 2

Describe the blood vessels and nerves of the orbit

Answer 2

• Main arterial supply is ophthalmic artery (branch of internal carotid) and its
subsequent branches
• Ophthalmic veins (superior and inferior) drain
venous blood into cavernous sinus, pterygoid plexus and facial vein
• General sensory from the eye (including conjunctiva,
cornea)
– ophthalmic division of trigeminal
• Special sensory vision from retina
– CN2

• Motor nerves to muscles
– CN 3,4,6

Question 3

Describe the anatomical relations of the orbit

Answer 3

• Important anatomical relations include:
– Paranasal air sinuses (maxillary
and ethmoid) 
– Nasal cavity (nasolacrimal duct) 
– Anterior cranial fossa
Implications for:
• Orbital trauma
• Spread of infection

Medial wall and floor of the orbit are the weakest parts of the orbital cavity and tend to fracture most commonly

Insert pic from slide 5

Question 4

What are orbital blow out fractures?

Answer 4

Sudden increase in intra-orbital pressure (e.g. from retropulsion of eye ball [globe] by fist or ball) fractures floor of orbit [maxilla]
• Orbital contents can prolapse and bleed into maxillary sinus,
• Fracture site can ‘trap’ structures e.g. soft tissue, extra ocular muscle located near orbital floor
• Prevents upward gaze on the affected side
• History of trauma to the eye/orbit
• Periorbital swelling, painful
• Double vision (worse on vertical gaze) as eyes are not aligned
• Numbness over cheek, lower eyelid and upper lip ( and upper teeth and
gums) on affected side as infraorbital nerve as part of the maxillary division of trigeminal may be damaged.
Pics from slides 6 and 7

Question 5

What do the eye lids do and how?

Answer 5

Eyelids: protects the front of the eye
• Consist of skin, subcutaneous tissue, tarsal plate (connective tissue structure that gives structure to eyelid), muscles
– Orbicularis oculi (palpebral
part) closes eyelid
– Levator palpebrae retract the eyelid to open eye by pulling on tarsal plate

• And glands
– Meibomian glands
– Sebaceous glands associated
with lash follicle

Insert pic from slide 8 lec 1

Question 6

Glands of the Eyelid and Eyelid Disease

Answer 6

Meibomian glands secrete an oily (lipid-rich) substance onto lid edges; prevents evaporation of tear film and tear spillage: if blocked leads to Meibomian cyst

Eyelash follicle or its associated sebaceous gland can also block (infection-staphylococcus) causing
styes

Blepharitis= inflammation of lids (including skin, lashes and Meibomian glands)

Insert pic from slide 9 lec 1

Question 7

What’s the orbital septum?

Answer 7

Thin sheet of fibrous tissue originating from orbital rim periosteum blends with tarsal plates
• Orbital septum and tarsal plates separate subcutaneous tissue
of eyelid and orbicularis oculi muscle from intra-orbital contents
• Acts as a barrier against superficial infection spreading from the pre-septal to post-septal space (orbital cavity proper)

Question 8

What is periorbital (pre-septal) cellulitis?

Answer 8

Infection occurring within eyelid tissue, superficial to orbital septum
• Secondary to superficial infections e.g. from bites, wounds,
– May be secondary to bacterial sinusitis (fronto-ethmoidal sinuses) in children
• Confined to tissues superficial to orbital septum (and tarsal plates)
• Ocular function (eye movements/vision) remains unaffected
• Can be difficult to differentiate between peri-orbital and the more severe orbital cellulitis
• If any doubt, urgently refer (high dose IV antibiotics + surgical drainage)

Question 9

What is orbital (post-septal) cellulitis?

Answer 9

Infection WITHIN the orbit* posterior or deep to the orbital septum

Orbital veins drain via cavernous sinus, pterygoid venous plexus and facial veins
Potential route for infection to spread intracranially
- cavernous sinus thrombosis
-meningitis

Proptosis/exophthalmos
Reduced +/- painful eye movements
Reduced visual acuity

Question 10

What are the contents of the orbital cavity?

Answer 10

• Eyeball
• Fat helps protect and cushion
• Associated extra-ocular muscles
• Nerves and blood vessels
• Lacrimal apparatus

Question 11

What is the lacrimal apparatus.

Answer 11

Structures involved in tear film production and drainage
• Lacrimal gland (tear production), lacrimal sac
and ducts (tear drainage)
– Ducts = canaliculi and nasolacrimal duct
• Blinking (orbicularis oculi-palpebral part) distributes
tear film across front of eye, rinsing and lubricating conjunctivae and cornea
• Tears are ultimately drained into nasal cavity
• Obstruction to the drainage system leads to
epiphora (overflow of tears over lower eyelid)

Question 12

Describe the anatomy of the eyeball

Answer 12

• Eyeball has three layers
• Outer: sclera (white of eye) continuous
anteriorly as transparent cornea*
• Middle: choroid, ciliary body and iris (vascular)
• Inner: retina (inner photosensitive layer lying
on an outer pigmented layer)
• Eyeball is maintained in position by:
- Suspensory ligament (sits underneath like a
sling)
- Extra-ocular muscles
- Orbital fat ++

Question 13

What lines the anterior surface of the eyeball?

Answer 13

Anterior Surface of Eyeball is Covered with a Conjunctival Membrane (except for cornea)
• Conjunctiva is a transparent mucous membrane
– Produces mucous component of tear film
• Covers white of eye (sclera) and lines inside of eyelids
(forming a conjunctival sac); does not cover over cornea
– Limbus (junction of conjunctivae with cornea; cornea has its
own epithelial covering)
• Highly vascular with small blood vessels within the
membrane A
• Inflammed and injected in infections e.g. conjunctivitis • Haemorrhage from blood vessels readily visible as a
subconjunctival haemorrhage

Question 14

How is light received in the eye?

Answer 14

Light Must Reach and Be Focused onto a Point at the Back of the Eye (Macula)

• Need transparent structures and medium
• Need to refract light* (bending of light) to
bring to a focal point
• Several structures refract light (all transparent)
• Cornea and its associated tear film
• Lens
• Aqueous humour and vitreous humour
• Shape of your eyeball also effects ability to focus light appropriately onto retina
Eye ball too long
• Myopia (short-sighted)
• Hypermetropia (long-sighted)

Question 15

What is the accommodation reflex?

Answer 15

Focusing Near Objects Requires Greater Refraction of Light
• Light rays from near-objects are more divergent
• Greater refraction, beyond capabilities of cornea (which is fixed in shape) to bring into
focus on retina
• Eye accommodates
– Pupil constricts (limits amount of light coming through)
– Eyes converge (to ensure image remains focused on same point of retina in both eyes)
– Lens becomes more biconvex (fatter) by contraction of ciliary muscle
• Note, as we age the lens becomes stiffer and less able to change shape
– Presbyopia (age-related inability to focus near-object)

Question 16

How is light processed by the eye?

Answer 16

• Rods (active at low light levels, do not
mediate colour vision)
• Abundant in peripheral parts of retina

• Cones (high definition, colour vision- active
at high light levels)
• Concentrated within the macula of the retina
• Fovea = only cones

• Action potentials generated in response to
light pass via retinal ganglion cells (RGC)
• RGC axons collect in area of optic disc forming the optic nerve
– Optic disc = blind spot as no photoreceptors present here
• Action potentials propagated along visual
pathway to occipital lobe for interpretation

Question 17

What might cause blurring of vision?

Answer 17

Pathology affecting:
• transparency of structures anterior to retina e.g. opacity in lens such as cataract,
• ability of structures to refract light e.g. irregularity of corneal surface
(astigmatism), ability of lens to change shape (presbyopia), or shape of eyeball
• The retina (including macula) or optic nerve E.g. retinal detachment, age-related macular
degeneration, optic neuritis
- will cause blurring of vision/ decreased acuity

*Age-related macular degeneration is most common cause of adult blindness in UK

Question 18

Is decreased visual acuity alway a refractive error?

Answer 18

Errors of refraction have no effect on light travelling perpendicular to the cornea/ lens (i.e. light does not need to be refracted to be brought into focus on the macula)
• Blurring of vision due to a refractive error, acuity
improves with pin-hole testing

Question 19

What helps eyeball maintain its shape?

Answer 19

Several Chambers Filled with Fluid Help Maintain Shape of Eyeball
Insert slide 26

Question 20

Describe the production and drainage of aqueous humour

Answer 20

• Aqueous humour secreted by ciliary
processes within ciliary body
• Flows from posterior chamber, through
pupil into anterior chamber
• Nourishes lens and cornea
• Drains through iridocorneal angle (between
iris and cornea)
• Via trabecular meshwork into canal of Schlemm (circumferential venous channel draining into venous circulation)
Insert pics from slide 27

Question 21

What is glaucoma?

Answer 21

Optic nerve Damage Secondary to Raised Intraocular Pressure
• Drainage of aqueous humour from anterior chamber blocked causing rise in intra-ocular pressure
– Can develop chronically or acutely
• Chronic=open-angle glaucoma [most common]
– Trabecular meshwork deteriorates as we age
– Many asymptomatic [picked up on routine eye tests]
– Increased IOP ↑ optic disc cupping
– Gradual loss of peripheral vision

Increased optic cup: disc ratio on fundoscopy (increased optic disc cupping)

• Acute-=closed-angle glaucoma [less common]
– Narrowing of iridocorneal angle
– Ophthalmological emergency
• Sight-threatening

Question 22

What type of glaucoma is considered an opthamalogical emergency?

Answer 22

Acute Angle-Closure (Closed Angle) Glaucoma Ophthalmological Emergency
• Older patient 55 years + (most common 70s-80s)
• Acutely painful red eye ++
• Irregular oval-shaped pupil (fixed)
• Blurring of vision
• Halo’s around lights (due to corneal oedema)
• Nausea and vomiting
• Medical (drugs to reduce IOP) then surgical treatment

Question 23

Describe the muscles of the eye and orbit

Answer 23

• Extrinsic muscles - Somatic motor nerves, (some sympathetic innervation too)
– Muscles of the eyelid
– Extra ocular muscles that move the eyeball

• Intrinsic muscles of the eye - Autonomic (visceral) nerves
– Muscles of the iris (dilator and constrictor of
the pupil)
– Ciliary muscle controls thickness of the lens

Supplied by cranial nerves: cranial nerve lesions can cause weakness in certain extraocular muscles

6 extra ocular muscles:

4 recti muscles inferior, lateral, superior, medial
All come from common tendinous ring that encircles apex of the orbit.

2 oblique muscles, superior and inferior

Superior oblique runs through a trochlear to change its direction of pull so instead it runs at 45 degrees to attach at lateral side of eye ball

Slide 3 lec 2

Question 24

What is the primary resting gaze?

Answer 24

Primary Resting Gaze (position of rest)
Equal and opposite pull of all extraocular muscles
• Even ‘at rest’, constancy of activity in all extra ocular muscles on the eyeball
• Each muscle has antagonist of its movement
• During resting gaze their actions are balanced allowing for forward
gaze
• Visual axis of both eyes is aligned
• Two images that reach cortex then ‘fused’, so seen as one
• Binocular vision allows for depth perception enabling ‘3D’ vision

Question 25

How do we change our position of gaze?

Answer 25

• Muscles moving both eyes must be highly co-ordinated and move simultaneously
• Visual axes must remain aligned (conjugate gaze)
• If visual axes maligned
– Diplopia (“double vision”)

• Some extraocular muscles have a single action on the eye
• Some muscles exert several actions on the eye (depending on starting position of eyeball)
• Extraocular muscles run in line with axis of orbit
• Therefore some muscles attach to globe at an oblique angle
– Those attaching to superior and inferior surfaces
• Confers some muscles several ‘actions’ of movement on globe (not just simply ‘up’ and
‘down’)
Images from sled 7 and 8 lec 2

Question 26

Describe the extraocular eye muscles

Answer 26

Action each individual muscle exerts on the eyeball (at resting gaze…and when moving from primary resting gaze)
Superior Rectus Muscle
Elevates Eyeball but has some additional actions
• SR (and IR) arise from apex of the orbit
SR
IR
• SR inserts into superior anterolateral surface of
globe
• Action (if starting from primary resting gaze)
– Elevate
– Slightly adducts (pull eye medially)
– Slightly intorts (internally rotates)
Inferior Rectus Muscle
Depresses Eyeball but has additional actions
• IR inserts into anteroinferior surface of globe
• Action (if starting from primary resting gaze)
– Depress
IR
– Slightly adducts (pull eye medially)
– Slightly extorts (externally rotates)
Superior Oblique Muscle
Intorts the Eyeball but also has depression action
Trochlea*
SO
• Arises from apex of orbit, passes through trochlea, inserts
into superoposterior aspect of globe
IO
– *consider the functional pull of SO being from the area of its
trochlea
• SO action (if starting from primary resting gaze)
– Intort (internally rotate)
– Depress
– Slightly abducts (pull eye laterally)
Inferior Oblique Muscle
Extort the Eyeball but also has elevation action Trochlea
SO
IO
• IO arises from anteromedial surface of floor of orbit;
inserts into inferoposterior aspect of globe • Action of IO (if starting from primary resting gaze)
– Extort (externally rotate)
– Elevate – Slightly abduct (pulls eye laterally)

Question 27

Why do we get abnormalities of gaze

Answer 27

• Constancy of activity in all extra ocular muscles on the
eyeball
– At resting gaze, equal and opposite pull • If a muscle(s) weakened, its ‘influence’ (i.e. exerted by its
anatomical action on the eyeball) is lost (or reduced)
• Other muscle actions no longer antagonised (“balanced”
out)
– Resting position of eyeball may deviate = strabismus (squint)
due to actions of remaining working muscles
• Difficulties with moving eye in certain directions of gaze • Can be congenital or acquired e.g. cranial nerve lesions

Question 28

Describe the clinical examination of the eye muscles

Answer 28

Need to Isolate an Action of Each Muscle to Test Them ..
H
• Some muscles >1 action; some ‘share’ similar movements
• Lateral and medial rectus
– Straight forward as each only performs one action on
the eye – Abduction (LR) and adduction (MR) of the eye
Why the ‘H’?
Why not…
• But, elevation and depression (in midline) involves two
muscles each
+
Starting From Resting Gaze (Midline) Elevation and Depression of the Eye Combine Actions of Two Muscles

Question 29

How might the dominant actions of certain eye muscles change if the starting position of the eye is changed?

Answer 29

Dominant Actions of SR/IR and Oblique Muscles Change if Starting Position of Eye is Changed
• Move starting position of eye
– Medially (adducting) first
– or laterally (abducting) first
• Then test elevation and depression
• This isolates the elevation and depression actions of SR/IO and IR/SO
which cannot be ‘isolated’ when testing from the midline
Recti muscles are main elevator (SR) and depressor (IR) of the eye when the eyeball is starting from the lateral position
Oblique muscles are main elevator (IO) and depressor (SO) of the eye when the eyeball is starting from the medial position

Question 30

How do cranial nerve palsies relate to the eye?

Answer 30

• Abnormalities of eye movements and diplopia
• May be obvious from initial inspection of the eye
– And/or become more apparent on testing eye movements
• Cranial nerves III, IV, VI innervate muscles that move the eyeball
• Can be affected by raised intracranial pressure (e.g. intracranial haemorrhage
or tumour)
• But all can also be affected by vascular disease (microvascular complications) from diabetes and hypertension
• But all can also be affected by vascular disease (microvascular complications)
from diabetes and hypertension

Question 31

How would cranial nerve palsy of CnIII oculomotor nerve affect the eye?

Answer 31

Cranial Nerve Palsies CN III Oculomotor
• Most extra-ocular eye muscles innervated by CN III
(except LR and SO)
• Innervates majority of muscle of eyelid (LPS) and
sphincter pupillae muscle
• Vasculopathic (microvascular) lesions (e.g.
diabetes/hypertension)
– Pupil spared
• Compressive lesions (raised ICP, tumour, posterior
communicating artery aneurysm)
– Parasympathetics run on periphery of CN III – Pupil involved

Question 32

How would cranial never palsy of CNIV trochlear nerve affect the eye?

Answer 32

Cranial Nerve Palsies CN IV Trochlear
• Innervates superior oblique muscle only
• Superior oblique muscle acts to INTORT, and depress and abduct eye
• Lose these actions so eyeball is held EXTORTED, slightly elevated and
adducted
• Compensate for the slight extortion of eyeball by tilting the head
slightly (not seen in image)
• Abnormality in gaze can be very subtle and often missed
• Worsening diplopia (on downward vertical gaze) especially looking
down and medially e.g. walking down stairs, reading
– Remember SO is main depressor of the eyeball when in
adduction

Question 33

How would cranial never palsy of CNVI Abducens nerve affect the eye?

Answer 33

Cranial Nerve Palsies CN VI Abducens
• Innervates lateral rectus
• Unopposed pull of medial rectus
muscle
• Unable to abduct the eye on affected
side
• Report diplopia, made worse on
horizontal gaze

Question 34

Most likely cause of lesions for CN 3, 4 and 6?

Answer 34

• Most likely cause for CN III, ,IV and VI lesions is vasculopathic
– Patients will be otherwise asymptomatic (apart from signs/symptoms directly relating to CN
lesion) – Lesions usually self-resolve within few months
• History will help give a clearer indication for more concerning underlying cause…
– Headache (+/-) vomiting could suggest raised ICP (secondary to tumour or haemorrhage)
– Recent head injury
– Presence of pupil involvement in CN III lesions

Question 35

Summarise extra ocular muscles and their movements

Answer 35

Final slide of lec 2