Bones - Bony Orbit

Question 1

Superior border of the bony orbit?

Answer 1

Superior (roof) - Frontal bone and lesser wing of sphenoid.

The frontal bone also separates the the orbit from the anterior cranial fossa.

Question 2

Inferior border of bony orbit?

Answer 2

Inferior (floor) - Maxilla, palatine and zygomatic bones.

The maxilla separates the bony orbit from the maxilla sinus.

Question 3

Medial wall of the bony orbit?

Answer 3

Medial - ethmoid, lacrimal, maxilla and sphenoid bones.

The ethmoid bone separates the bony orbit from the ethmoid sinus.

Question 4

Lateral wall of the bony orbit?

Answer 4

Lateral - zygomatic and greater wing of sphenoid.

Question 5

Apex of the bony orbit?

Answer 5

Located at the opening of the optic canal, the optic foramen.

Question 6

Base of the bony orbit?

Answer 6

Opens out into the face and is bounded by the eyelids. It is also known as the orbital rim.

Question 7

Contents of the bony orbit?

Answer 7

1) Eyeball
2) Extraocular muscles
3) Eyelids
4) Nerves
5) Blood vessels
6) Orbital fat

Question 8

Pathways into the orbit?

What do they transmit?

Answer 8

1) Optic canal - ophthalmic artery (a branch of the internal carotid, distal to the cavernous sinus) and the opthalmic nerve.
2) Superior orbital fissure - transmits several structures:
i) lacrimal nerve
ii) frontal nerve
iii) trochlear nerve (CN IV) - innervates the superior oblique muscle (extraocular)
iv) oculomotor nerve (CN III) - innervates the LVP, medial rectus, inferior rectus, superior rectus, inferior oblique.
v) nasaciliary nerve
vi) abducens nerve (CN VI) - innervates the lateral rectus
vii) superior ophthalmic vein
3) Inferior orbital fissure - transmits a few structures:
i) zygomatic branch of the maxillary nerve
ii) inferior ophthalmic vein
iii) sympathetic nerves
4) Other minor openings:
i) nasalacrimal canal - drains lacrimal fluid
ii) supraorbital foramen - supraorbital nerve that provides sensory information to the ipsilateral forehead.
iii) infraorbital canal - opens into the the infraorbital foramen. Transmits the infraorbital nerve that provides sensory information to the lower eyelid, part of the nose, anterior cheek and upper lip.

Question 9

Clinical relevance: fractures of the bony orbit

Aetiology?

Types of orbital fractures?

Points of weakness?

Answer 9

There are two types of major bony orbit fractures:

1) Orbital rim fracture - usually occurs at the fissure joining the maxilla, zygomatic and frontal bones.
2) ‘Blowout’ fracture - this refers to the partial herniation of orbital contents through one of its walls.

This is usually due to blunt force trauma to the eye.

The medial and inferior walls are the weakest, with the contents herniating into the ethmoid and maxillary sinuses.