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The Orbit: Bone structures. Bones: Those Latin names Protecting the eye while serving its needs. VS112 Sept 5, 2007 Lect 2-3. Reasonable Goals. Overall function is simple, but the details.. Name the bones, Know the construction of the orbit walls, Know the strong and weak points,

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the orbit bone structures

The Orbit: Bone structures

Bones: Those Latin names

Protecting the eye while serving its needs.

VS112

Sept 5, 2007

Lect 2-3

reasonable goals
Reasonable Goals
  • Overall function is simple, but the details..
    • Name the bones,
    • Know the construction of the orbit walls,
    • Know the strong and weak points,
    • What is in the orbit, what holds it there?
    • What comes into, goes out of the orbit?
    • What are holes (fissures, foramina) used for?
skull has 22 bones
Cranium

Parietal (2)

Occipital

Temporal (2)

Sphenoid

Ethmoid

Face

Maxillary (2)

Nasal (2)

Inferior chonchae (2)

Lacrimal (2)

Palatine (2)

Zygomatic (2)

Mandible

Vomer

Skull has 22+ bones

Frontal bone is part of both cranium & face

11 bones make up the orbits
Single Bones

Frontal Bone

Ethmoid Bone

Sphenoid Bone

Paired Bones

Maxillary

Zygomatic

Lacrimal

Palatine

11 bones make up the orbits
lateral view of skull
Lateral View of Skull
  • Frontal
  • Zygomatic
  • Note temoral aspect of Sphenoid
  • Maxillary
  • Lacrimal
  • Ethmoid
sinuses exist in 4 orbital bones
Sinuses exist in 4 Orbital Bones
  • Air filled
  • Mucosa lined
  • Lighten bone
  • Acustic
  • Possible infection site
the basic shape of the orbit is a pyramid
The basic shape of the orbit is a pyramid:

The medial walls are parallel

The depth is 1.5 x base

slide9
The margin of the orbit {VERY STRONG}

4 cm wide

3.5 cm high

3 BONES

Frontal

Zygomatic

Maxillary

4.5 cm deep

terminology
Terminology
  • Fossa: shallow depression in bone
  • Foramen (pl. foramina): hole(s) in bone
  • Fissure: hole between adjacent bones
  • Tubercle: bump attachment site
  • Groove, canal, notch (as they sound)
a key figure of chap 3
A key figure of Chap 3

Let me help you get a 3D understanding of the structures summarized by this figure

reasonable goals15
Reasonable Goals
  • Overall function is simple, but the details..
    • Name the bones,
    • Know the construction of the orbit walls,
    • Know the strong and weak points,
    • What is in the orbit, what holds it there?
    • What comes into, goes out of the orbit?
    • What are holes (fissures, foramina) used for?
the orbital ceiling
The orbital ceiling
  • Frontal
  • Bits of-

Sphenoid

Lacrimal Fossa

Trochlear Fossa

Supraorbital Notch

the lateral wall
The Lateral Wall
  • Not shown are:
    • Zygomatic foramen
    • Whitnalls Tubercle

Zygomatic

Frontal

Sphenoid

the sphenoid bone
The Sphenoid Bone
  • Butterfly
  • (Owl like)
    • Greater Wing
    • Lesser Wing
    • Pterygoid process
  • Many Foramina
    • Optic Foramen
    • Sup. Optic Fissure
lateral view of skull20
Lateral View of Skull
  • Frontal
  • Zygomatic
  • Note temoral aspect ofSphenoid
  • Maxillary
  • Lacrimal
  • Ethmoid
slide21

The Sphenoid Bone &Occipital (at back)Ethmoid (yellow)Palatine (small red)Maxillary(straight on view of structure shown on hand out - page 42)

Now go back to lateral wall slide

the lateral wall22
The Lateral Wall
  • Not shown are:
    • Zygomatic foramen
    • Whitenalls Tubercle

Zygomatic

Frontal

Sphenoid

the medial wall
The Medial Wall
  • Frontal (?)
  • Ethmoid
  • Lacrimal
  • Sphenoid
  • Maxillary
the orbit floor
The Orbit Floor
  • Maxillary

• Sphenoid

  • Zygomatic
  • Palatine
weakest bones are in the floor and medial wall of the orbit
Weakest bones are in the floor and medial wall of the orbit.
  • Transmitted pressure through the tissues(?) or the sturdier bones causes blowout fractures.

Lamina papyracia

blowout fracture of the ethmoid bone ct image
Blowout fracture of the ethmoid bone. CT image.

esfethmoid sinus fracture

mwfmedial wall fracture

connective tissues in the orbit
Connective tissues in the orbit
  • All of the structures within the orbit have a connective tissue sheath
    • Around the Globe & muscles it’s call Tenon’s capsule
      • If the globe is the palm and EOM fingers, then Tenon’s capsule is the glove.
    • Lining the bones, it’s the periosteum
      • periorbita- a special name for orbit bone lining
    • nerves, blood vessels have them too
  • And they are interconnected making for a web of sheaths.
two views
Two Views
  • Tenon’s capsule
  • Periorbita
terminology35
Terminology
  • Fossa: shallow depression in bone
  • Foramen (pl. foramina): hole(s) in bone
  • Fissure: hole between adjacent bones
  • Tubercle: bump attachment site
  • Groove, canal, notch (as they sound)
soft tissue covering
Soft tissue covering
  • Surrounding the sclera is the episclera
    • Connective tissue and blood vessels.
  • Surrounding the episclera is Tenon’s capsule
    • Another layer of connective tissue protecting the globe and making it slippery for movement within the orbit.
soft tissue covering37
Soft tissue covering
  • Check ligaments
    • medial and lateral are most prominent but the inferior rectus and levator have them too.
  • Superior transverse ligament
    • Supports levator muscle (Whitnall’s Ligament)
  • Suspensory ligament (of Lockwood)
    • Connective tissue underneath the globe
orbital infection
Orbital infection
  • Orbital cellulitis: infection of the tissues and fat pads behind/surrounding the eye, but not the eye itself
    • 60% of orbital cellulitus is a secondary infection due to a sinus infection
bone development
Bone development
  • Dermal Bones, most of orbit
    • Foci of osteoblasts differentiated from with the mesoderm
  • Cartilage pre-formed bones: ethmoid and part of sphenoid. (Endochondral bone)
    • Chondrocytes form cartilagenous template of the final bone
    • Osteoblasts invade and differentiate into osteocytes
  • Bone can restructure/repair itself
    • Osteoclast cell can breakdown boney matrix
      • Permits growth of the skull and orbits