orbit

• Orbit

  Two bony sockets that hold and protect the eyeballs and their associated structures
• Structures in the orbit

  • Optic nerve
  • Extraocular muscles
  • Lacrimal apparatus
  • Fascia
  • Neurovasculature
  • Orbital fat
• Bones of the orbit

  • Maxilla
  • Frontal
  • Zygomatic
  • Ethmoid
  • Lacrimal
  • Sphenoid
  • Palatine
• Walls of the orbit

  • Roof (superior): Orbital surface of frontal bone, lesser wing of sphenoid bone
  • Medial: Orbital plate of ethmoid bone, frontal process of maxilla, lacrimal bone, lesser wing of sphenoid bone
  • Floor (inferior): Orbital surface of maxilla, orbital process of palatine bone, zygomatic bone
  • Lateral: Frontal process of zygomatic bone, greater wing of sphenoid bone
• Fissures and foramina of the orbit

  • Supraorbital foramen
  • Infraorbital groove
  • Infraorbital foramen
  • Anterior and posterior ethmoidal foramina
  • Optic canal
  • Superior orbital fissure
  • Inferior orbital fissure
• Extraocular muscles

  Seven skeletal muscles located within the orbital cavity, external to the eyeball
• Extraocular muscles

  • Levator palpebrae superioris
  • Superior rectus
  • Inferior rectus
  • Medial rectus
  • Lateral rectus
  • Superior oblique
  • Inferior oblique
• Functions of extraocular muscles

  1. Elevate upper eyelid

  2. Move eyeball in various directions
• Ophthalmic artery

  Provides the main arterial supply to the orbit with minor contributions from the external carotid artery
• Ophthalmic veins

  Principal drainage system of the orbit
• Nerves of the orbit

  • Optic nerve (CN II)
  • Oculomotor nerve (CN III)
  • Trochlear nerve (CN IV)
  • Abducens nerve (CN VI)
  • Ophthalmic (V1) and maxillary (V2) branches of trigeminal nerve (CN V)
  • Autonomic nerves
• Nerves of the orbit facilitate vision, movements of the eye, tear production and general sensation
• Inferior ophthalmic vein

  Drains into superior ophthalmic vein/cavernous sinus/pterygoid plexus of veins
• Central retinal vein

  Drains into cavernous sinus but may join superior ophthalmic vein
• Vorticose veins

  Drain into ophthalmic veins
• Infraorbital vein

  Drains into pterygoid venous plexus
• Nerves of the orbit

  • Zygomatic nerve
  • Trigeminal nerve
  • Supratrochlear nerve
  • Supraorbital nerve
  • Superior branch of oculomotor nerve
  • Short ciliary nerves
  • Ophthalmic nerve
  • Oculomotor nerve
  • Maxillary nerve
  • Lacrimal nerve
  • Infratrochlear nerve
  • Infraorbital nerve
  • Inferior branch of oculomotor nerve
  • Frontal nerve
  • Communicating branch of zygomatic nerve to lacrimal nerve
  • Ciliary ganglion
  • Branch of nasociliary nerve to ciliary ganglion
• Nasociliary nerve

  Arises from the ophthalmic branch (CN V1) of the trigeminal nerve and runs obliquely forward through the orbit, giving off the long ciliary, posterior and anterior ethmoidal and infratrochlear nerves
• Nasociliary nerve


  Conveys sensation from the skin of the dorsum of the nose, eyelids, medial conjunctiva, membranes of the ethmoidal air cell, sphenoid sinus and portions of the nasal cavity
• Nasociliary nerve


  Transmits sympathetic fibers which supply sensory fibers to the sclera, cornea, iris and ciliary body through the ciliary ganglion
• Key points about the nerves of the orbit


  • Oculomotor nerve (CN III)
  • Ophthalmic nerve (V1)
  • Maxillary nerve (V2)
  • Ciliary ganglion
  • Trochlear nerve
  • Short ciliary nerves
  • Optic nerve
  • Nasociliary nerve
  • Lacrimal nerve
  • Frontal nerve
  • Abducens nerve
• Ciliary ganglion


  Parasympathetic ganglion in the orbit; receives preganglionic fibers from the oculomotor nerve, gives off postganglionic branches (short ciliary nerves) to ciliary muscle and sphincter pupillae
• Ciliary ganglion


  Also passes postganglionic sympathetic fibers from internal carotid plexus as well as sensory/afferent fibers
• Contents of the superior orbital fissure


  • Lacrimal and frontal nerve (branches of CN V1)
  • Trochlear nerve
  • Superior ophthalmic vein
  • Inferior and superior branches of oculomotor nerve
  • Nasociliary nerve (branch of CN V1)
  • Abducens nerve
  • Superior branch of inferior ophthalmic vein
• Contents of the inferior orbital fissure


  • Inferior branch of inferior ophthalmic vein
  • Orbital branches of pterygopalatine ganglion
  • Infraorbital nerve (branch of CN V2)
  • Infraorbital artery and vein
  • Zygomatic nerve (branch of CN V2)
• Common tendinous ring (of Zinn)


  Fibrous tissue that serves as a common origin for the four rectus muscles, encircling the inferolateral part of the superior orbital fissure and surrounding the superior branch of the oculomotor nerve, nasociliary nerve, abducens nerve and the inferior branch of the oculomotor nerve as they pass through
• Eyeball


  • Globe shaped, sits within the anterior aspect of the orbit of the skull, contains the optical structures responsible for vision
• Layers of the eyeball


  • Outer fibrous layer (sclera and cornea)
  • Middle vascular layer (choroid, ciliary body, iris)
  • Inner layer (retina)
• Anterior and posterior chambers


  Located between the cornea and lens, separated by the iris, filled with aqueous humor
• Postremal chamber


  Located posterior to the lens, houses the vitreous body
• Vitreous body
• Vitreous humor
• c part


  • Part of retina
• Iris


  • Part of eyeball
• The choroid of the eye is located between the sclera and retina and is filled with numerous vascular bundles which supply the outer portion of the retina
• Ciliary body


  • Thickening of muscular and connective tissue posterior to the iris and anterior portion of the sclera
• Iris


  • Pigmented, contains a central aperture known as the pupil
• Retina


  • Forms the inner layer of the eye, composed of non-visual and optic parts
• Postremal/vitreous chamber


  • Compartment located posterior to the lens and enveloped by the retina, occupied by a semi-solid/jelly-like structure known as the vitreous body
• Vitreous body


  • Semi-solid/jelly-like structure, contains a fluid-like substance known as vitreous humor