Session 9 - Workbook Notes Flashcards
Briefly explain what the orbit is.
The Orbit: a bony pyramid housing the eyeball and many other structures
Describe the orbit’s shape, location and function.
The ORBIT is a PYRAMIDAL SHAPED bony cavity within the facial skeleton which contains (and protects) the eyeball, its muscles, nerves, vessels and most of the lacrimal apparatus.
What surrounds the orbit?
A number of different bones make up its FOUR WALLS, many of which you met when we explored the skull osteology.
Fig. 1
Label the image.
You can review these bones on the plastic skulls during the group work (and personal study) but it is worth familiarising yourself with these now, by looking at the image above.
- Frontal bone
- Supraorbital margin
- Sphenoid bone
- Optic canal
- Superior orbital fissure
- Zygomatic bone
- Maxilla
- Supraorbital foramen
- Nasal bone
- Lacrimal bone
- Ethmoid bone
- Lacrimal fossa
- Palatine bone
- Infraorbital foramen
Which part of the orbit is the weakest and how is it likely to be damaged?
The INFERIOR (I.E. FLOOR) and MEDIAL WALLS OF THE ORBIT are THE WEAKEST and thus most vulnerable to FRACTURE when there is direct impact to the front of the eye e.g. by a ball or fist.
What does direct impact to the front of the eye lead to?
This impact leads to a SUDDEN INCREASE IN INTRAORBITAL PRESSURE; it is often the floor (not the medial wall) that fractures in such injuries.
What can occur if someone is punched in the eye?
The resulting fracture from such an injury is called an ORBITAL BLOW-OUT FRACTURE.
Why is the floor of the orbit more likely to fracture than the medial wall in an orbital blow-out fracture?
Although the MEDIAL WALL, formed by the ETHMOID BONE is very thin (the part of the ethmoid forming the medial wall of the orbit is known as the lamina papyracea- which translates to ‘paper thin’), and is actually thinner than the floor, the presence of the walled air cells (anterior, middle, posterior ethmoidal air cells) act as buttresses and convey an added strength to the medial wall.
Other than the additional strength to the medial wall (ethmoid bone) of the orbit, give one other clinical significance of the walled air cells.
These air cells can also become infected (acute sinusitis), and given their proximity to the orbit, this infection can sometimes break through the thin lamina papyracea and track into the orbit, causing ORBITAL CELLULITIS.
Fig. 2
Label the image.
- Periorbital fat
- Fractured orbital floor
What is the function of the openings at the orbital apex?
Series of Openings at the Orbital Apex: Transmit Nerves & Blood Vessels
What enables structures to enter into and out of the orbit?
A series of HOLES AT THE APEX OF THE ORBIT allow for a number of structures to enter into and out of the orbit.
What are the three holes around the orbit?
These include:
[optic canal
superior orbital fissure
inferior orbital fissure]
What travels through the optic canal?
• The OPTIC CANAL, transmitting the OPTIC NERVE and OPHTHALMIC ARTERY
