Bony Orbits

• PEG


  Bony orbit
• To introduce you to the anatomy of the bony orbit and some clinical signs
• Objectives

  • Structure
  • Surrounding structures
  • Paranasal sinuses
  • Orbital walls
  • Optic canal
  • Superior orbital fissure
  • Inferior orbital fissure
  • Common tendinous ring
  • Fascia
  • Some clinical signs of orbital disease
• Orbits

  • Pair of bony sockets
  • Orbital axes diverge by about 45º
  • Visual axes parallel
  • Contain eyeballs, extraocular muscles, lacrimal apparatus, nerves, blood vessels, fascia, adipose tissue
• Surrounding structures

  • Anterior cranial fossa
  • Maxillary sinus
  • Nasal cavity
  • Ethmoidal sinus
  • Sphenoidal sinus
  • Middle cranial fossa
  • Temporal fossa
• Paranasal sinuses

  • Frontal
  • Ethmoidal
  • Sphenoidal
  • Maxillary
• Paranasal sinuses


  Mucous membrane lined air-filled cavities that reduce weight of skull and add resonance to voice, communicate with nasal cavity
• Orbital walls


  • Roof
  • Medial
  • Floor
  • Lateral
• Roof


  • Frontal, sphenoid bones
  • Supraorbital notch for blood vessel & nerves
  • Lacrimal, trochlea, anterior & posterior ethmoidal foramina
• Medial


  • Maxilla, lacrimal, ethmoid, sphenoid bones
  • Lacrimal fossa
  • Anterior & posterior lacrimal crests
  • Paper thin ethmoid bone, ethmoiditis commonest cause of orbital cellulitis
• Floor


  • Maxilla, palatine, zygomatic bones
  • Inferior orbital fissure
  • 'Blow out' fracture
• Lateral


  • Zygomatic, sphenoid bones
  • Strongest rim
  • Spina recti lateralis for common tendinous ring
  • Lateral tubercle for attachment of levator palpebrae superioris aponeurosis
  • Zygomatic foramina for blood vessels and nerves
  • Thickest wall, globe protrudes beyond lateral margin, vulnerable to trauma
• Optic canal


  • Formed by sphenoid bone, connects middle cranial fossa with orbit, contains optic nerve and ophthalmic artery, related to sphenoidal & ethmoidal sinuses
• Superior orbital fissure


  • Formed by sphenoid bone, connects middle cranial fossa with orbit, contains oculomotor, trochlear, abducens nerves, prone to pathological lesions
• Inferior orbital fissure


  • Formed by sphenoid & maxilla bones, connects orbit to pterygopalatine & infratemporal fossae, contains nerves leading to face, leads to orbital foramen on maxilla
• Common tendinous ring


  • Origin of recti muscles, attached to spina recti lateralis, forms a muscle cone that encloses optic canal and part of superior orbital fissure, structures entering orbit outside cone include trochlear nerve, structures entering orbit within cone include optic, oculomotor, abducens nerves
• Fascia


  • Consists of periorbita and Tenon's capsule, forms suspensory ligaments, extraocular muscle sheaths, runs continuously with dura mater around optic nerve, orbital septum of eyelids, trochlea pulley, common tendinous ring, orbital adipose tissue, can aid spread of disease
• Exophthalmos (proptosis)


  • Abnormal protrusion of globe, causes include orbital cellulitis, thyroid eye disease, orbital tumour
• Enophthalmus


  • Recession of globe, causes include 'blow-out' fracture
• Dystopia


  • Displacement of globe, causes include lacrimal tumour
• The bony orbit protects the eyes, maintains their position and serves as a rigid base for extraocular muscle actions
• The orbital rim is thick even at birth to prevent injury
• Optometrists need to be aware of

  • The function of features (attachment sites, foramina, fissures etc.) associated with each orbital bone
  • Potential threats to the eye by way of trauma to the orbital bones or spread of infection from closely related sinuses or fasciae
  • Clinical signs of orbital disease (exophthalmos, enophthalmos, dystopia)