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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. 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

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  1. The Orbit: Bone structures Bones: Those Latin names Protecting the eye while serving its needs. VS112 Sept 5, 2007 Lect 2-3

  2. 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?

  3. 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

  4. Single Bones Frontal Bone Ethmoid Bone Sphenoid Bone Paired Bones Maxillary Zygomatic Lacrimal Palatine 11 bones make up the orbits

  5. Bones of the skull

  6. Lateral View of Skull • Frontal • Zygomatic • Note temoral aspect of Sphenoid • Maxillary • Lacrimal • Ethmoid

  7. Sinuses exist in 4 Orbital Bones • Air filled • Mucosa lined • Lighten bone • Acustic • Possible infection site

  8. The basic shape of the orbit is a pyramid: The medial walls are parallel The depth is 1.5 x base

  9. The margin of the orbit {VERY STRONG} 4 cm wide 3.5 cm high 3 BONES Frontal Zygomatic Maxillary 4.5 cm deep

  10. 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)

  11. A key figure of Chap 3 Let me help you get a 3D understanding of the structures summarized by this figure

  12. 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?

  13. The orbital ceiling • Frontal • Bits of- Sphenoid Lacrimal Fossa Trochlear Fossa Supraorbital Notch

  14. The Lateral Wall • Not shown are: • Zygomatic foramen • Whitnalls Tubercle Zygomatic Frontal Sphenoid

  15. Bones of the skullNow look at the Sphenoid

  16. The Sphenoid Bone • Butterfly • (Owl like) • Greater Wing • Lesser Wing • Pterygoid process • Many Foramina • Optic Foramen • Sup. Optic Fissure

  17. Lateral View of Skull • Frontal • Zygomatic • Note temoral aspect ofSphenoid • Maxillary • Lacrimal • Ethmoid

  18. 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

  19. The Lateral Wall • Not shown are: • Zygomatic foramen • Whitenalls Tubercle Zygomatic Frontal Sphenoid

  20. The Medial Wall • Frontal (?) • Ethmoid • Lacrimal • Sphenoid • Maxillary

  21. The Orbit Floor • Maxillary • Sphenoid • Zygomatic • Palatine

  22. Main components of fissures

  23. Let me help you get a 3D understanding of the structures summarized by this figure Fig 3.2

  24. 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

  25. Blowout fracture of the floor of maxillary bone.

  26. Blowout fracture of the floor of maxillary bone. CT image

  27. Blowout fracture of the ethmoid bone. CT image. esfethmoid sinus fracture mwfmedial wall fracture

  28. 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.

  29. Two Views • Tenon’s capsule • Periorbita

  30. A better view

  31. 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)

  32. 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.

  33. 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

  34. 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

  35. 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

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