L2: Orbit

Question 1

Roof of orbit

Answer 1

Frontal bone (small contribution from sphenoid bone)

Question 2

Medial wall of orbit

Answer 2

Maxilla, lacrimal and ethmoid and sphenoid

Question 3

Floor of orbit

Answer 3

Maxilla (small contributions from zygomatic and palatine bones)

Question 4

Lateral wall of orbit

Answer 4

Zygomatic bone and greater wing of sphenoid

Question 5

Clinical: orbital fracture

Answer 5

Fractures within orbit frequently occur within floor and medial wall, however superior and lateral wall fractures also occur
E.g. inferior (floor) fracture - inferior rectus can be dragged leading to patients having upward gaze failure

Question 6

Layers of eyelid (ant to post)

Answer 6

1. Skin
2. Subcutaneous tissue
3. Orbicularis occuli (voluntary muscle)
4. Orbital septum
5. Tarsus
6. Conjuctiva

Upper and lower eyelid similar except for addition of superior tarsal and levator palpbrae superioris muscles in upper eyelid

Question 7

Clinical: Racoon eyes

Answer 7

There is a potential space between skin and subcutaneous tissue/within subcutaneous tissue
Base of skull/skull fracture -> blood accumulates in potential space within eyelids

Question 8

Orbicularis occuli features

Damage

Answer 8

The voluntary muscle of eyelids (palpebrae part) innervated from frontotemporal branch of facial n [VII]
Closes eyelids

Damage to facial n (frontotemporal branch crosses over parotid gland) results in inability to close/blink ipsilateral upper eyelid and lower eyelid droops away
–> assoc w corneal ulcers and spillage of tears

Question 9

Orbital septum

Answer 9

Deep to palpebrae part of o. occuli 
It is an extension of periosteum 
In both upper and lower eyelids
- Protects eye
- Attaches to tendon of LSP in upper eyelid and attaches to tarsus in lower eyelid

Question 10

Tarsus

Answer 10

Major support for each eyelid, plates of dense CT, attached medially to ant lacrimal crest of maxilla and laterally to orbital tubercle on zygomatic bone

• Sup tarsus associated w LPS
• Inf tarsus

Question 11

Muscles associated w raising of eyelid

Answer 11

LPS - somatic muscle of upper eyelid, innervated by [III]

Superior tarsal muscle - collection of smooth muscle fibres (from inf edge of LPS to upper edge of sup tarsus), innervated by post-ganglionic sympathetic fibres from sup cervical ganglion in neck

Question 12

Clinical: Ptosis (partial and complete)

Answer 12

Complete ptosis: damage to nerve innervating LPS causes eyelid to fully drop

Partial: damage to sympathetic fibres to superior tarsal m or damage to muscle itself (e.g. neck trauma damaging sympathetic cervical ganglion)

Question 13

Clinical: Horner’s syndrome

Answer 13

Lesion that leads to loss of sympathetic function in head (e.g. trauma, consequence of surgery)
Miosis (pupillary constriction)
Partial ptosis
Anhidrosis (absence of sweating on ipsilateral side)

Question 14

Conjuctiva

Answer 14

Thin membrane covering post part of eyelid and reflects onto outer surface of eyeball (sclera)
Conjuctiva attaches to eyeball at junction between sclera and cornea
- Membrane forms conjuctival sac when eyelids closed
- Keeps cornea functioning by maintaining moisture
- Highly vascularised

Question 15

Clinical: conjunctivitis

Answer 15

Bacteria can get in and infect conjunctiva - secretion of immunological factors to try and get rid of bacteria (foreign bodies can get stuck in conjunctiva)

Question 16

Tarsus glands

Clinical: blockage of gland

Answer 16

Embedded in tarsus, secrete oily substance that increases viscosity of tears and decreases rate of evaporation from surface of eyeball

Blockage of gland/canal = chalazion (swelling, painless)

Question 17

Sebaceous and sweat glands

Clinical: blockage

Answer 17

Associated with eyelash follicles

Blockage = Hordeolum (stye) - infection

Question 18

Eyelid blood supply and innervation

Answer 18

Arterial:
Ophthalmic a ( + facial a, superficial temporal a)
Venous: ophthalmic veins

Innervation:
Sensory - V1 (upper), V2 (lower)
Motor - VII (palpebrae of o. occuli), III (LPS), sympathetic fibres (sup tarsal m)

Question 19

Periosteal layer

Answer 19

Periorbita= periosteum within orbit (post part forms tendinous ring)
When periosteal layer of dura comes into orbit, foramina it came through is sealed to prevent infection from eye entering
Periosteum thickened at every foramen
Orbital septum = where periorbita and periosteum meet and extend downward to eyeball

Question 20

Structures entering and exiting orbit via optic canal

Answer 20

1. Optic n [II]

2. Ophthalmic a

Question 21

Structures entering and exiting via superior orbital fissure

Answer 21

(Between roof and lateral wall of bony orbit)

1. Sup and inf branches of [III]
2. [IV]
3. [VI]
4. Frontal, nasociliary and lacrimal branches of V1
5. Sup ophthlamic v

Question 22

Structures entering and exiting via inferior orbital fissure

Answer 22

(Separates lateral wall from floor of orbit)

1. Inferior ophthalmic v (may passs through SOF)
2. Infraorbital a and v
3. V3 and its zygomatic branch
4. Vein communicating pterygoid plexus of veins

Question 23

Common tendinous ring

Clinical significance

Answer 23

Zinn ring - thickening of periorbita in post part of orbit around optic canal and central part of SOF
4 rectus muscles originate
Optic canal: [II], ophthalmis a
SOF: nasociliary n, [VI], sup and inf divisions of [III]

Narrowing of ring due to inflammation or recti muscle perforation will put pressure on structures in ring

Question 24

Lacrimal apparatus

Answer 24

Production, movement and drainage of fluid from surface of eyeball
Lacrimal gland, canaliculi, sac, duct
Punta drains tears -> canaliculi -> sac -> nasolacrimal duct

Question 25

Arterial supply to eyeball

Answer 25

Branches of ophthalmic artery (from int carotid, enters through optic canal)
Central retinal artery supplies optic disc and if there is ophthalmic a clot, patient will be blind

Question 26

Clinical: Danger triangle

Answer 26

Opthalmic v communicates with facial veins and cavernous sinus
Provides path for spread of infection from outside to inside (mainly superior)
Infection in eye/nose can spread to brain (meningitis potentially)
Ophthalmic veins do have valves so this is not the reason for spread of infection