Orbit & Osteology

Question 1

What makes up the medial wall of the orbit?

Answer 1

Frontal part of the Maxilla, Lacrimal, Ethmoid and Sphenoid Body

Question 2

What makes up the lateral wall of the orbit?

Answer 2

Zygomatic & Greater Wing of Sphenoid

Question 3

What makes up the floor of the orbit?

Answer 3

Palatine, Zygomatic & Maxilla

Question 4

What makes up the roof of the orbit?

Answer 4

Frontal & Lesser Wing of Sphenoid

Question 5

How is the skull divided into 2 parts?

Answer 5

Cranium or Neurocranium AND facial skeleton and viscerocranium

Question 6

How many bones make up the orbit and what are they?

Answer 6

Seven;
Sphenoid bone (inc. Greater wing & Lesser wing)
Ethmoid bone
Lacrimal bone
Frontal bone
Maxilla
Palatine bone
Zygomatic bone

Question 7

Where is the supraorbital notch/foramen?

Answer 7

Roof of the orbit

Question 8

Where is the zygomatic frontal suture located?

Answer 8

Suture between zygomatic and frontal bones

Question 9

Where of the orbit are the bones the thinnest?

Answer 9

Maxillary bone has the maxillary sinus so the floor of the orbit is quite thin. The ethmoidal bone is where the ethmoid sinus is so it’s thinner.
This means the medial and floor of the orbits are the thinnest compared to frontal and zygomatic due to the positioning of sinuses.

Question 10

What are the 3 posterior orbital foramina?

Answer 10

Superior orbital fissure
Inferior orbital fissure
Optic Canal

Question 11

What are the 4 anterior orbital foramina?

Answer 11

Supraorbital
Infraorbital
Zygomaticofacial
Zygomaticotemporal

Question 12

How many orbital foramina are there?

Answer 12

Seven; 3 posterior and 4 anterior

Question 13

Where is the superior orbital fissure?

Answer 13

Between lesser and greater wings of the sphenoid (where CN III and CN VI exit)

Question 14

What’s in the inferior orbital fissure?

Answer 14

• Zygomatic branch of the maxillary nerve
• Maxillary nerve
• Branches of the pterygopalatine ganglion (sympathetic nerves)
• Inferior ophthalmic vein

Question 15

What is the superior orbital fissure divided into & by what?

Answer 15

Divided into 3 by the Annulus of Zinn (the common tendinous ring)

Question 16

What is the common tendinous ring also known as?

Answer 16

Annulus of Zinn

Question 17

Where is the optic canal in relation to the superior orbital fissure?

Answer 17

Medial

Question 18

What travels through the SOF?

Answer 18

Lacrimal and Frontal branches of the Ophthalmic branch of CN V
Trochlear (CN IV)
Oculomotor (CN III) both superior and inferior divisions
Abducens (CN VI)
Nasociliary Nerve of the Ophthalmic branch of CN V
Superior ophthalmic vein
A branch of the inferior ophthalmic vein

Question 19

What travels through the IOF?

Answer 19

Infraorbital nerve (branch of Maxillary division of CN V)

Zygomatic nerve (branch of Maxillary division of CN V)

Branches of the Pterygopalatine ganglion (sympathetic nerves)

Inferior Ophthalmic vein

Question 20

What are the 4 anterior foramen of the orbit?

Answer 20

Supraorbital
Infraorbital
Zygomaticofacial
Zygomaticotemporal (lies above the zygomaticofacial foramen)

Question 21

What is the supraorbital foramen/notch?

Answer 21

Notch for the supraorbital nerve and vessels to pass (supraorbital artery and supraorbital vein)

Question 22

What are the paranasal sinuses and what are they called?

Answer 22

Paranasal sinuses are air-filled spaces surrounding nasal cavity and are called the frontal, ethmoid, sphenoid and maxillary

Question 23

What is the function of the paranasal sinuses?

Answer 23

No consensus but likely to be a combination:
- They decrease mass while maintaining structure
- Increase voice resonance
- Isolate sensitive structures (roots of teeth, eyeballs, temperature fluctuations during inhalation and exhalation)
- Humidification & warming of inhaled air

Question 24

What sinus does the medial recti touch?

Answer 24

Ethmoidal sinus

Question 25

What do the ethmoidal sinus and the medial recti on the ipsilateral eye touch?

Answer 25

Optic nerve

Question 26

What can a blowout fracture cause?

Answer 26

Double vision, Enophthalmos (sinking of the eyes), reduced sensation to the ipsilateral cheek causing an infraorbital injury

Question 27

What part of the orbit is vulnerable to a blowout fracture?

Answer 27

Medial and inferior walls. Orbital contents can herniate into the ethmoid and maxillary sinuses

Question 28

What symptoms can blowout fractures cause?

Answer 28

Numbness to upper teeth and upper lip = infraorbital foramen (circled) carries infraorbital nerve which provides sensation to upper teeth, upper lip and upper gum

Causes herniation of content or entrapment of muscles

Question 29

What are the 5 cardinal signs of inflammation?

Answer 29

1) Redness
2) Swelling
3) Warmth of that area
4) Pain (such a tender to touch and tender to eye movement)
5) Loss of function

Due to increased blood supply, inflammatory molecules and white blood cells

Question 30

Why can cellulitis easily become orbital cellulitis?

Answer 30

The orbit is surrounded by the paranasal sinuses.

The bony walls that separate the paranasal sinuses from the orbit are thin providing a permeable barrier.

Extension of infection from this sinus is the most common route by which orbital cellulitis develops.

The veins that drain the sinuses (the orbital veins) are valveless, which allows both anterograde and retrograde spread of infections

Question 31

What is infection in front of the septum called?

Answer 31

Area called the Septum which is thick fissure that separates skin and sub-cutaneous skin from the orbit. Infection in front of the septum is a pre-septal/pre-orbital cellulitis and behind is is post-septal cellulitis or orbital cellulitis

Question 32

What infection behind the post-septal called?

Answer 32

Post-septal cellulitis or orbital cellulitis

Question 33

Which form of cellulitis is worse? Pre or post-orbital?

Answer 33

Pre-orbital doesn’t pose a treat to the eye but post-septal/orbital cellulitis does and leads to hospital admission. In children the septum is not fully formed so a pre-septal (as there’s openings in the septum) it can easily lead to a post-septal/orbital cellulitis.

Question 34

What can cellulitis be caused by?

Answer 34

Infection in the sinuses can destroy the integrity of the bone and lead to orbital cellulitis (e.g. if ethmoid sinus it can destroy the medial wall and into the orbit)

Question 35

What are the contents of the orbit?

Answer 35

Periorbita
Fat
Muscles
Tenon’s Capsule
Globe
Lacrimal Gland

Question 36

What is Tenon’s capsule?

Answer 36

Covering around the EOM’s around the orbit (sheaths the muscles). Anteriorly it is close and fused with the conjunctiva. There is a space under the tenon’s for anesthetic (sub-tenon’s block) to immobilize the muscles (in the episcleral space which is between the tenon’s capsule and sclera).

It’s a thin collagen rich membrane surrounding the globe, muscles and optic nerve. This merges with the conjunctiva anteriorly.

Question 37

What is the periorbita?

Answer 37

It’s the orbital periosteum. It’s the layer loosely attached to the bone.

The periorbita is the periosteum of the internal orbit and covers the four bony orbital walls from the anterior aperture of the orbital cavity back to the cone enveloping the optic canal and the superior orbital fissure.

However, it may refer to anything that is around the orbit

Question 38

What is Hutchinson’s Sign also known as?

Answer 38

Herpes Zoster Ophthalmicus

Question 39

What is Hutchinson’s Sign?

Answer 39

Shingles of the ophthalmic branch of the trigeminal nerve. Nasociliary nerve innervates both tip of nose and cornea so:

Vesicle on nose tip therefore off significance in predicting corneal involvement – this is because it supplies the cornea and nose so if there is affected tip of nose (Hutchinson’s Sign) you know there are corneal implications of this.

Shingles can move down any of the nerves!